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Scientific research is a process concerned with the creation, collective accumulation, contextualization, updating and maintenance of knowledge. Wikis provide an environment that allows to collectively accumulate, contextualize, update and maintain knowledge in a coherent and transparent fashion. Here, we examine the potential of wikis as platforms for scholarly publishing. In the hope to stimulate further discussion, the article itself was drafted on Species-ID – a wiki that hosts a prototype for wiki-based scholarly publishing – where it can be updated, expanded or otherwise improved.
Background:
During the last years, (19)F-MRI and perfluorocarbon nanoemulsion (PFC) emerged as a powerful contrast agent methodology to track cells and to visualize inflammation. We applied this new modality to visualize deep tissue abscesses during acute and chronic phase of inflammation caused by Staphylococcus aureus infection.
Methodology and Principal Findings:
In this study, a murine thigh infection model was used to induce abscess formation and PFC or CLIO (cross linked ironoxides) was administered during acute or chronic phase of inflammation. 24 h after inoculation, the contrast agent accumulation was imaged at the site of infection by MRI. Measurements revealed a strong accumulation of PFC at the abscess rim at acute and chronic phase of infection. The pattern was similar to CLIO accumulation at chronic phase and formed a hollow sphere around the edema area. Histology revealed strong influx of neutrophils at the site of infection and to a smaller extend macrophages during acute phase and strong influx of macrophages at chronic phase of inflammation.
Conclusion and Significance:
We introduce (19)F-MRI in combination with PFC nanoemulsions as a new platform to visualize abscess formation in a murine thigh infection model of S. aureus. The possibility to track immune cells in vivo by this modality offers new opportunities to investigate host immune response, the efficacy of antibacterial therapies and the influence of virulence factors for pathogenesis.
A total of 127 extraintestinal Escherichia coli strains of the capsule serotypes Kl, KS, and KlOO from human and animal sources were analyzed for DNA sequences specific for the genes for various adhesins (P fimbriae fpap] and P-related sequences fprs], S fimbriae [s/a)/FlC fimbriae [foc], and type I fimbriae lfim]), aerobactin (aer), and hemolysin (hly). The expression of corresponding virulence factors was also tested. Twenty-four selected strains were analyzed by long-range DNA mapping to evaluate their genetic relationships. DNA sequences for the adhesins were often found in strains not expressing them, while strains with hemolysin and aerobactin genes usually did express them. Different isolates of the same serotype orten expressed different virulence patterns. The use of virulence-associated gene probes for Southern hybridization with genomic DNA fragments separated by pulsed-field gel electrophoresis revealed that a highly heterogeneous restriction fragment length and hybridization pattern existed even within strains of the same serotype. Long-range DNA mapping is therefore useful for the evaluation of genetic relatedness among individual isolates and facilitates the performance of .precise molecular epidemiology.
A total of 16 Escherichia coli 06 strains isolated from cases of extraintestinal infections were analysed for the genetic presence and phenotypic expression of fimbrial adhesins ( P, S/FIC, type I), aerobactin and hemolysin. ln addition restriction fragment length polymorphisms (RFLPs) of Xbal-cleaved genomic DNA of seven selected strains, separated by orthogonal field alternation gel electrophoresis {OFAGE) were determined and virulence-associated DNA probes were used for Southern hybridization studies of the Xbal-cleaved genomic DNAs. The virulence characteristics and hybridization patterns obtained differed between the various isolates. ln three isolates hemolysin genes and P fimbrial determinants were located on the same Xbal fragments. Furthermore, multiple copies of FIC determinants (foc) could be detected in two strains. Our data show that the new technique of pulse field electrophoresis tagether with Southern hybridization represents a powerful tool for the genetic analysis of pathogenic bacteria.
Background: In principle, the elimination of malignancies by oncolytic virotherapy could proceed by different mechanisms - e.g. tumor cell specific oncolysis, destruction of the tumor vasculature or an anti-tumoral immunological response. In this study, we analyzed the contribution of these factors to elucidate the responsible mechanism for regression of human breast tumor xenografts upon colonization with an attenuated vaccinia virus (VACV). Methods: Breast tumor xenografts were analyzed 6 weeks post VACV infection (p.i.; regression phase) by immunohistochemistry and mouse-specific expression arrays. Viral-mediated oncolysis was determined by tumor growth analysis combined with microscopic studies of intratumoral virus distribution. The tumor vasculature was morphologically characterized by diameter and density measurements and vessel functionality was analyzed by lectin perfusion and extravasation studies. Immunological aspects of viral-mediated tumor regression were studied in either immune-deficient mouse strains (T-, B-, NK-cell-deficient) or upon cyclophosphamide-induced immunosuppression (MHCII+-cell depletion) in nude mice. Results: Late stage VACV-infected breast tumors showed extensive necrosis, which was highly specific to cancer cells. The tumor vasculature in infected tumor areas remained functional and the endothelial cells were not infected. However, viral colonization triggers hyperpermeability and dilatation of the tumor vessels, which resembled the activated endothelium in wounded tissue. Moreover, we demonstrated an increased expression of genes involved in leukocyte-endothelial cell interaction in VACV-infected tumors, which orchestrate perivascular inflammatory cell infiltration. The immunohistochemical analysis of infected tumors displayed intense infiltration of MHCII-positive cells and colocalization of tumor vessels with MHCII+/CD31+ vascular leukocytes. However, GI-101A tumor growth analysis upon VACV-infection in either immunosuppressed nude mice (MHCII+-cell depleted) or in immune-deficient mouse strains (T-, B-, NK-cell-deficient) revealed that neither MHCII-positive immune cells nor T-, B-, or NK cells contributed significantly to VACV-mediated tumor regression. In contrast, tumors of immunosuppressed mice showed enhanced viral spreading and tumor necrosis. Conclusions: Taken together, these results indicate that VACV-mediated oncolysis is the primary mechanism of tumor shrinkage in the late regression phase. Neither the destruction of the tumor vasculature nor the massive VACV-mediated intratumoral inflammation was a prerequisite for tumor regression. We propose that approaches to enhance viral replication and spread within the tumor microenvironment should improve therapeutical outcome.
Bacteriosponges contain large amounts of morphologically and phylogenetically diverse microorganisms in their mesohyl. The association is permanent, stable and highly specific, however, little is known about the establishment and maintenance of this association. The first aim of this Ph.D. thesis was to examine cospeciation between eight Aplysina species from the Mediterranean and Caribbean and their cyanobacterial associates. Host phylogeny was constructed with 18S rDNA and ITS-2 sequences using an alignment based on the secondary structure of the molecular markers and five different algorithms each. The genus Aplysina appeared as monophyletic. Aplysina sponges could be distinguished into a Caribbean and a Mediterranean cluster and a possible Tethyan origin is suggested. Comparison of the host phylogeny to the 16S rDNA phylogeny of the cyanobacterial strains revealed the lack of a congruent pattern. Therefore it is proposed that Aplysina sponges have not cospeciated with their cyanobacterial phylotypes and probably also not with other sponge specific microbes. The second aim of this Ph.D. thesis was to examine vertical transmission of microorganisms through reproductive stages of sponges. A general transmission electron microscopy (TEM) suvey revealed a clear correlation in that bacteriosponges always contained many microorganisms in their reproductive stages whereas non-bacteriosponges were always devoid of microbes in their reproductive stages. The transmission of the microbial community via sponge reproductive stages is concluded. Based on the previous results Ircinia felix was chosen for a detailed documentation of vertical transmission. I. felix larvae contained large amounts of microorganisms extracellularly in the central region whereas the outer region was almost free of microbes as shown by TEM. In I. felix juveniles microorganisms were located between densely packed sponge cells. The microbial profiles of I. felix adult, larvae, and juveniles were compared using denaturing gradient gel electrophoresis (DGGE). Similar microbial community patterns were found in adult and the respective larvae indicating that a large subset of the adult microbial community was vertically transmitted. In contrast, microbial communities of larvae pools released by different adult individuals seemed to be more variable. Juvenile banding patterns were a mixture of sponge specific and seawater microbes due to DNA extraction artefacts but demonstrated that at least half of the adult microbial community is present in the next generation. Finally, a comprehensive phylogenetic analysis was conducted by sequencing excised DGGE bands from adult and offspring of the bacteriosponges Agelas wiedenmayeri, I. felix, and Smenospongia aurea and by taking additional 16S rDNA sequences of Ectyoplasia ferox and Xestospongia muta (unpublished data of the laboratory). The identification of 24 vertical transmission clusters in at least 8 eubacterial phyla demonstrates that a complex and uniform microbial community is transferred via sponge reproductive stages. Vertical transmission is specific in that the microorganisms of bacteriosponges, but not those from seawater, are passed on, but unselective in that there appears to be no differentiation between individual sponge-specific lineages. In conclusion, vertical transmission points to a mutualistic and long-term association of bacteriosponges and complex microbial consortia.
Multidrug-resistant bacteria represent one of the most important health care problems worldwide. While there are numerous drugs available for standard therapy, there are only a few compounds capable of serving as a last resort for severe infections. Therefore, approaches to control multidrug-resistant bacteria must be implemented. Here, a strategy of reactivating the established glycopeptide antibiotic vancomycin by structural modification with polycationic peptides and subsequent fatty acid conjugation to overcome the resistance of multidrug-resistant bacteria was followed. This study especially focuses on the structure–activity relationship, depending on the modification site and fatty acid chain length. The synthesized conjugates showed high antimicrobial potential on vancomycin-resistant enterococci. We were able to demonstrate that the antimicrobial activity of the vancomycin-lipopeptide conjugates depends on the chain length of the attached fatty acid. All conjugates showed good cytocompatibility in vitro and in vivo. Radiolabeling enabled the in vivo determination of pharmacokinetics in Wistar rats by molecular imaging and biodistribution studies. An improved biodistribution profile in comparison to unmodified vancomycin was observed. While vancomycin is rapidly excreted by the kidneys, the most potent conjugate shows a hepatobiliary excretion profile. In conclusion, these results demonstrate the potential of the structural modification of already established antibiotics to provide highly active compounds for tackling multidrug-resistant bacteria.
Multidrug‐resistant bacteria represent one of the biggest challenges facing modern medicine. The increasing prevalence of glycopeptide resistance compromises the efficacy of vancomycin, for a long time considered as the last resort for the treatment of resistant bacteria. To reestablish its activity, polycationic peptides were conjugated to vancomycin. By site‐specific conjugation, derivatives that bear the peptide moiety at four different sites of the antibiotic were synthesized. The most potent compounds exhibited an approximately 1000‐fold increased antimicrobial activity and were able to overcome the most important types of vancomycin resistance. Additional blocking experiments using d‐Ala‐d‐Ala revealed a mode of action beyond inhibition of cell‐wall formation. The antimicrobial potential of the lead candidate FU002 for bacterial infection treatments could be demonstrated in an in vivo study. Molecular imaging and biodistribution studies revealed that conjugation engenders superior pharmacokinetics.
Introduction: Surgery is currently the definitive treatment for early-stage breast cancer. However, the rate of positive surgical margins remains unacceptably high. The human sodium iodide symporter (hNIS) is a naturally occurring protein in human thyroid tissue, which enables cells to concentrate radionuclides. The hNIS has been exploited to image and treat thyroid cancer. We therefore investigated the potential of a novel oncolytic vaccinia virus GLV1h-153 engineered to express the hNIS gene for identifying positive surgical margins after tumor resection via positron emission tomography (PET). Furthermore, we studied its role as an adjuvant therapeutic agent in achieving local control of remaining tumors in an orthotopic breast cancer model.
Methods: GLV-1h153, a replication-competent vaccinia virus, was tested against breast cancer cell lines at various multiplicities of infection (MOIs). Cytotoxicity and viral replication were determined. Mammary fat pad tumors were generated in athymic nude mice. To determine the utility of GLV-1h153 in identifying positive surgical margins, 90% of the mammary fat pad tumors were surgically resected and subsequently injected with GLV-1h153 or phosphate buffered saline (PBS) in the surgical wound. Serial Focus 120 microPET images were obtained six hours post-tail vein injection of approximately 600 mu Ci of I-124-iodide.
Results: Viral infectivity, measured by green fluorescent protein (GFP) expression, was time-and concentrationdependent. All cell lines showed less than 10% of cell survival five days after treatment at an MOI of 5. GLV-1h153 replicated efficiently in all cell lines with a peak titer of 27 million viral plaque forming units (PFU) ( < 10,000-fold increase from the initial viral dose) by Day 4. Administration of GLV-1h153 into the surgical wound allowed positive surgical margins to be identified via PET scanning. In vivo, mean volume of infected surgically resected residual tumors four weeks after treatment was 14 mm(3) versus 168 mm(3) in untreated controls (P < 0.05).
Conclusions: This is the first study to our knowledge to demonstrate a novel vaccinia virus carrying hNIS as an imaging tool in identifying positive surgical margins of breast cancers in an orthotopic murine model. Moreover, our results suggest that GLV-1h153 is a promising therapeutic agent in achieving local control for positive surgical margins in resected breast tumors.
Transcriptome analysis of individual cells by single-cell RNA-seq (scRNA-seq) has become routine for eukaryotic tissues, even being applied to whole multicellular organisms. In contrast, developing methods to read the transcriptome of single bacterial cells has proven more challenging, despite a general perception of bacteria as much simpler than eukaryotes. Bacterial cells are harder to lyse, their RNA content is about two orders of magnitude lower than that of eukaryotic cells, and bacterial mRNAs are less stable than their eukaryotic counterparts. Most importantly, bacterial transcripts lack functional poly(A) tails, precluding simple adaptation of popular standard eukaryotic scRNA-seq protocols that come with the double advantage of specific mRNA amplification and concomitant depletion of rRNA. However, thanks to very recent breakthroughs in methodology, bacterial scRNA-seq is now feasible. This short review will discuss recently published bacterial scRNA-seq approaches (MATQ-seq, microSPLiT, and PETRI-seq) and a spatial transcriptomics approach based on multiplexed in situ hybridization (par-seqFISH). Together, these novel approaches will not only enable a new understanding of cell-to-cell variation in bacterial gene expression, they also promise a new microbiology by enabling high-resolution profiling of gene activity in complex microbial consortia such as the microbiome or pathogens as they invade, replicate, and persist in host tissue.
S fimbrial adhesins (Sfa) enable pathogenic Escherichia coli strains to bind to sialic acid-containing eucaryotic receptor molecules. In order to determine the inftuence of culture conditions on the expression of the sfa determinant in a wild-type strain, we fused the gene lacZ, coding for the enzyme ß-galactosidase, to the sfaA gene, responsible for the major protein subunit of S fimbriae. By using a plasmid which carries an R6K origin, the sfaA-Iac hybrid construct was site-specifically integrated into the chromosome of the uropathogenic E. coli strain S36WT. The expression of lacZ, which was under the control of the sfa wild-type promoters, was now equivalent to the sfa expression of strain S36WT. With the help of this particular wild-type construct, it was demonstrated that the sfa determinant is better expressed on solid media than in liquid broth. The growth rate bad a strong inftuence on Sfa expression under aerobic but not under anaerobic conditions. Production of Sfa was further regulated by catabolite repression, osmolarity, and temperature.
We have previously shown that during an infection with Leishmania major, susceptible BALB/c mice, as opposed to mice of a resistant strain (C57BLl6), are primed by lipopolysaccharide for the production of high levels of tumor necrosis factor-\(\alpha\) (TNF-\(\alpha\)) which is known to be a potent maerophage M\(\Phi\) stimulator in other parasitic diseases. In the present study we investigated whether TNF-\(\alpha\) activates M\(\Phi\) for killing of L. major parasites. In the absence of interferon-y (IFN-\(\gamma\)) or lipopolysaccharide, TNF-\(\alpha\) (0.025-25000 U/ml) failed to activate peritoneal exudate M\(\Phi\) from BALB/c mice for killling of L. major amastigotes. In the presence of suboptimal doses of IFN-\(\gamma\) (5 or 10 Vlml), however, TNF-\(\alpha\) mediated a rapid elimination of intracellular parasites, which was highly significant compared to IFN-\(\gamma\) alone. Tbe combination of TNF with interleukin 4, in contrast, was inactive in this respect and allowed survival of intracellular parasites. From these data we conelude that the presence of IFN-\(\gamma\) is crucial for TNF-\(\alpha\)-mediated killing of L. major parasites by M\(\Phi\). Disease progression in susceptible mice therefore seems to be a consequence of a deficiency of IFN-\(\gamma\) and a predominance of interleukin 4 rather than the result of an excess amount of TNF-\(\alpha\).
Background
Malignant pleural effusion (MPE) is associated with advanced stages of lung cancer and is mainly dependent on invasion of the pleura and expression of vascular endothelial growth factor (VEGF) by cancer cells. As MPE indicates an incurable disease with limited palliative treatment options and poor outcome, there is an urgent need for new and efficient treatment options.
Methods
In this study, we used subcutaneously generated PC14PE6 lung adenocarcinoma xenografts in athymic mice that developed subcutaneous malignant effusions (ME) which mimic pleural effusions of the orthotopic model. Using this approach monitoring of therapeutic intervention was facilitated by direct observation of subcutaneous ME formation without the need of sacrificing mice or special imaging equipment as in case of MPE. Further, we tested oncolytic virotherapy using Vaccinia virus as a novel treatment modality against ME in this subcutaneous PC14PE6 xenograft model of advanced lung adenocarcinoma.
Results
We demonstrated significant therapeutic efficacy of Vaccinia virus treatment of both advanced lung adenocarcinoma and tumor-associated ME. We attribute the efficacy to the virus-mediated reduction of tumor cell-derived VEGF levels in tumors, decreased invasion of tumor cells into the peritumoral tissue, and to viral infection of the blood vessel-invading tumor cells. Moreover, we showed that the use of oncolytic Vaccinia virus encoding for a single-chain antibody (scAb) against VEGF (GLAF-1) significantly enhanced mono-therapy of oncolytic treatment.
Conclusions
Here, we demonstrate for the first time that oncolytic virotherapy using tumor-specific Vaccinia virus represents a novel and promising treatment modality for therapy of ME associated with advanced lung cancer.
Oligopeptides incorporating \(N3\)-(4-methoxyfumaroyl)-L-2,3-diaminopropanoic acid (FMDP), an inhibitor of glucosamine-6-phosphate synthase, exhibited growth inhibitory activity against \(Candida\) \(albicans\), with minimal inhibitory concentration values in the 0.05–50 μg mL\(^{-1}\) range. Uptake by the peptide permeases was found to be the main factor limiting an anticandidal activity of these compounds. Di- and tripeptide containing FMDP (F2 and F3) were transported by Ptr2p/Ptr22p peptide transporters (PTR) and FMDP-containing hexa-, hepta-, and undecapeptide (F6, F7, and F11) were taken up by the oligopeptide transporters (OPT) oligopeptide permeases, preferably by Opt2p/Opt3p. A phenotypic, apparent resistance of \(C. albicans\) to FMDP-oligopeptides transported by OPT permeases was triggered by the environmental factors, whereas resistance to those taken up by the PTR system had a genetic basis. Anticandidal activity of longer FMDP-oligopeptides was strongly diminished in minimal media containing easily assimilated ammonium sulfate or L-glutamine as the nitrogen source, both known to downregulate expression of the OPT genes. All FMDP-oligopeptides tested were more active at lower pH and this effect was slightly more remarkable for peptides F6, F7, and F11, compared to F2 and F3. Formation of isolated colonies was observed inside the growth inhibitory zones induced by F2 and F3 but not inside those induced by F6, F7, and F11. The vast majority (98%) of those colonies did not originate from truly resistant cells. The true resistance of 2% of isolates was due to the impaired transport of di- and to a lower extent, tripeptides. The resistant cells did not exhibit a lower expression of \(PTR2\), \(PTR22\), or \(OPT1–3\) genes, but mutations in the \(PTR2\) gene resulting in T422H, A320S, D119V, and A320S substitutions in the amino acid sequence of Ptr2p were found.
Compared to transcriptional activation, other mechanisms of gene regulation have not been widely exploited for the control of transgenes. One barrier to the general use and application of alternative splicing is that splicing-regulated transgenes have not been shown to be reliably and simply designed. Here, we demonstrate that a cassette bearing a suicide exon can be inserted into a variety of open reading frames (ORFs), generating transgenes whose expression is activated by exon skipping in response to a specific protein inducer. The surprisingly minimal sequence requirements for the maintenance of splicing fidelity and regulation indicate that this splicing cassette can be used to regulate any ORF containing one of the amino acids Glu, Gln or Lys. Furthermore, a single copy of the splicing cassette was optimized by rational design to confer robust gene activation with no background expression in plants. Thus, conditional splicing has the potential to be generally useful for transgene regulation.
The sfa determinant codes for S fimbrial adhesins which constitute adherence factors of pathogenic Escherichia coli strains. Wehave recently shown that the sfa determinant is transcribed from three prömoters, pA, pB, and pC. In comparison with the promoters pB and pC, promoter pA, which is located in front of the structural gene sfaA, showed very weak activity. Herewe have determined the exact positions ofthe mRNA start points by primer extension studies. We have also shown that mRNAs of 500, 700 and 1400 bases can be detected using oligonucleotide probes specific for the genes sfaB, sfaC and sfaA. SfaB and SfaC arepositive regulators infiuencing fimbriation and the production of the S-specific adhesin which is encoded by the gene sfaS Iocated in the distal half of the determinant. In addition, it is demonstrated that SfaB and SfaC interfere with the regulatory effect of the histone-like protein H-NS, encoded by a locus termed drdX or osmZ. In a drdx+ strain the regulators are necessary for transcription of the sfa determinant. In contrast, sfa expression is activator-independent in a drdx- strain. In this latter genetic background, a substantial fraction of the sfa transcripts is initiated from promoter pA. On the basis of these data we discuss a model for the regulation of this adhesin-specific determinant.
Bacteriophage AR9 is a recently sequenced jumbo phage that encodes two multisubunit RNA polymerases. Here we investigated the AR9 transcription strategy and the effect of AR9 infection on the transcription of its host, Bacillus subtilis. Analysis of whole-genome transcription revealed early, late, and continuously expressed AR9 genes. Alignment of sequences upstream of the 5′ ends of AR9 transcripts revealed consensus sequences that define early and late phage promoters. Continuously expressed AR9 genes have both early and late promoters in front of them. Early AR9 transcription is independent of protein synthesis and must be determined by virion RNA polymerase injected together with viral DNA. During infection, the overall amount of host mRNAs is significantly decreased. Analysis of relative amounts of host transcripts revealed notable differences in the levels of some mRNAs. The physiological significance of up- or downregulation of host genes for AR9 phage infection remains to be established. AR9 infection is significantly affected by rifampin, an inhibitor of host RNA polymerase transcription. The effect is likely caused by the antibiotic-induced killing of host cells, while phage genome transcription is solely performed by viral RNA polymerases.
Background: RNA-seq and its variant differential RNA-seq (dRNA-seq) are today routine methods for transcriptome analysis in bacteria. While expression profiling and transcriptional start site prediction are standard tasks today, the problem of identifying transcriptional units in a genome-wide fashion is still not solved for prokaryotic systems.
Results: We present RNASEG, an algorithm for the prediction of transcriptional units based on dRNA-seq data. A key feature of the algorithm is that, based on the data, it distinguishes between transcribed and un-transcribed genomic segments. Furthermore, the program provides many different predictions in a single run, which can be used to infer the significance of transcriptional units in a consensus procedure. We show the performance of our method based on a well-studied dRNA-seq data set for Helicobacter pylori.
Conclusions: With our algorithm it is possible to identify operons and 5'- and 3'-UTRs in an automated fashion. This alleviates the need for labour intensive manual inspection and enables large-scale studies in the area of comparative transcriptomics.
Malaria and HIV are among the most important global health problems of our time and together are responsible for approximately 3 million deaths annually. These two diseases overlap in many regions of the world including sub-Saharan Africa, Southeast Asia and South America, leading to a higher risk of co-infection. In this study, we generated and characterized hybrid molecules to target P. falciparum and HIV simultaneously for a potential HIV/malaria combination therapy. Hybrid molecules were synthesized by covalent fusion between azidothymidine (AZT) and dihydroartemisinin (DHA), tetraoxane or chloroquine (CQ); and a small library was generated and tested for antiviral and antimalarial activity. Our data suggest that dihyate is the most potent molecule in vitro, with antiplasmodial activity comparable to that of DHA (IC50 = 26 nM, SI > 3000), a moderate activity against HIV (IC50 = 2.9 µM; SI > 35) and safe to HeLa cells at concentrations used in the assay (CC50 > 100 µM). Pharmacokinetic studies further revealed that dihyate is metabolically unstable and is cleaved following an O-dealkylation once in contact with cytochrome P450 enzymes. The later further explains the uneffectiveness of dihyate against the CQ-sensitive P. berghei N strain in mice when administered by oral route at 20 mg/kg. Here, we report on a first approach to develop antimalarial/anti-HIV hybrid molecules and future optimization efforts will aim at producing second generation hybrid molecules to improve activity against HIV as well as compound bioavailability. With the emergence of resistant parasites against all the counterpart drugs of artemisinin derivatives used in artemisinin based combination therapies (ACTs), the introduction of antibiotics in the treatment of malaria has renewed interest on the identification of antibiotics with potent antimalarial properties. In this study we also investigated the antiplasmodial potential of thiostrepton and derivatives, synthesized using combinations of tail truncation, oxidation, and addition of lipophilic thiols to the terminal dehydroamino acid. We showed that derivatives SS231 and SS234 exhibit a better antiplasmodial activity (IC50 = 1 µM SI > 59 and SI > 77 respectively) than thiostrepton (IC50 = 8.95 µM, SI = 1.7). The antiplasmodial activity of these derivatives was observed at concentrations which are not hemolytic and non-toxic to human cell lines. Thiostrepton and derivatives appeared to exhibit transmission blocking properties when administered at their IC50 or IC90 concentrations and our data also showed that they attenuate proteasome activity of Plasmodium, which resulted in an accumulation of ubiquitinated proteins after incubation with their IC80 concentrations. Our results indicate that the parasite’s proteasome could be an attractive target for therapeutic intervention. In this regard, thiostrepton derivatives are promising candidates by dually acting on two independent targets, the proteasome and the apicoplast, with the capacity to eliminate both intraerythrocytic asexual and transmission stages of the parasite. To further support our findings, we evaluated the activity of a new class of antimalarial and proteasome inhibitors namely peptidyl sulfonyl fluorides on gametocyte maturation and analogues AJ34 and AJ38 were able to completely suppress gametocytogenesis at IC50 concentrations (0.23 µM and 0.17 µM respectively) suggesting a strong transmission blocking potential. The proteasome, a major proteolytic complex, responsible for the degradation and re-cycling of non-functional proteins has been studied only indirectly in P. falciparum. In addition, an apparent proteasome-like protein with similarity to bacterial ClpQ/hslV threonine-peptidases was predicted in the parasite. Antibodies were generated against the proteasome subunits alpha type 5 (α5-SU), beta type 5 (β5-SU) and pfhslV in mice and we showed that the proteasome is expressed in both sexual and asexual blood stages of P. falciparum, where they localize in the nucleus and in the cytoplasm. However, expression of PfhslV was only observed in trophozoites and shizonts. The trafficking of the studied proteasome subunits was further investigated by generating parasites expressing GFP tagged proteins. The expression of α5-SU-GFP in transgenic parasite appeared to localize abundantly in the cytoplasm of all blood stages, and no additional information was obtained from this parasite line. In conclusion, our data highlight two new tools towards combination therapy. Hybrid molecules represent promising tools for the cure of co-infected individuals, while very potent antibiotics with a wide scope of activities could be useful in ACTs by eliminating resistant parasites and limiting transmission of both, resistances and disease.
Sepsis caused by Gram-positive bacterial pathogens is a major fatal disease but its molecular basis remains elusive. Toll-like receptor 2 (TLR2) has been implicated in the orchestration of inflammation and sepsis but its role appears to vary for different pathogen species and clones. Accordingly, Staphylococcus aureus clinical isolates differ substantially in their capacity to activate TLR2. Here we show that strong TLR2 stimulation depends on high-level production of phenol-soluble modulin (PSM) peptides in response to the global virulence activator Agr. PSMs are required for mobilizing lipoproteins, the TLR2 agonists, from the staphylococcal cytoplasmic membrane. Notably, the course of sepsis caused by PSM-deficient S. aureus is similar in wild-type and TLR2-deficient mice, but TLR2 is required for protection of mice against PSM-producing S. aureus. Thus, a crucial role of TLR2 depends on agonist release by bacterial surfactants. Modulation of this process may lead to new therapeutic strategies against Gram-positive infections.
The fungal cell wall is essential for the maintenance of cellular integrity and mediates interactions of the cells with the environment. It is a highly flexible organelle whose composition and organization is modulated in response to changing growth conditions. In the pathogenic yeast Candida albicans, a network of signaling pathways regulates the structure of the cell wall, and mutants with defects in these pathways are hypersensitive to cell wall stress. By harnessing a library of genetically activated forms of all C. albicans zinc cluster transcription factors, we found that a hyperactive Czf1 rescued the hypersensitivity to cell wall stress of different protein kinase deletion mutants. The hyperactive Czf1 induced the expression of many genes with cell wall-related functions and caused visible changes in the cell wall structure. C. albicans czf1Δ mutants were hypersensitive to the antifungal drug caspofungin, which inhibits cell wall biosynthesis. The changes in cell wall architecture caused by hyperactivity or absence of Czf1 resulted in an increased recognition of C. albicans by human neutrophils. Our results show that Czf1, which is known as a regulator of filamentous growth and white-opaque switching, controls the expression of cell wall genes and modulates the architecture of the cell wall.
Abstract
Protein kinases are central components of almost all signaling pathways that control cellular activities. In the model organism Saccharomyces cerevisiae, the paralogous protein kinases Ypk1 and Ypk2, which control membrane lipid homeostasis, are essential for viability, and previous studies strongly indicated that this is also the case for their single ortholog Ypk1 in the pathogenic yeast Candida albicans. Here, using FLP-mediated inducible gene deletion, we reveal that C. albicans ypk1Δ mutants are viable but slow-growing, explaining prior failures to obtain null mutants. Phenotypic analyses of the mutants showed that the functions of Ypk1 in regulating sphingolipid biosynthesis and cell membrane lipid asymmetry are conserved, but the consequences of YPK1 deletion are milder than in S. cerevisiae. Mutational studies demonstrated that the highly conserved PDK1 phosphorylation site T548 in its activation loop is essential for Ypk1 function, whereas the TORC2 phosphorylation sites S687 and T705 at the C-terminus are important for Ypk1-dependent resistance to membrane stress. Unexpectedly, Pkh1, the single C. albicans orthologue of Pkh1/Pkh2, which mediate Ypk1 phosphorylation at the PDK1 site in S. cerevisiae, was not required for normal growth of C. albicans under nonstressed conditions, and Ypk1 phosphorylation at T548 was only slightly reduced in pkh1Δ mutants. We found that another protein kinase, Pkh3, whose ortholog in S. cerevisiae cannot substitute Pkh1/2, acts redundantly with Pkh1 to activate Ypk1 in C. albicans. No phenotypic effects were observed in cells lacking Pkh3 alone, but pkh1Δ pkh3Δ double mutants had a severe growth defect and Ypk1 phosphorylation at T548 was completely abolished. These results establish that Ypk1 is not essential for viability in C. albicans and that, despite its generally conserved function, the Ypk1 signaling pathway is rewired in this pathogenic yeast and includes a novel upstream kinase to activate Ypk1 by phosphorylation at the PDK1 site.
Author summary
Protein kinases are key components of cellular signaling pathways, and elucidating the specific roles of individual kinases is important to understand how organisms adapt to changes in their environment. The protein kinase Ypk1 is highly conserved in eukaryotic organisms and crucial for the maintenance of cell membrane homeostasis. It was previously thought that Ypk1 is essential for viability in the pathogenic yeast Candida albicans, as in the model organism Saccharomyces cerevisiae. Here, by using forced, inducible gene deletion, we reveal that C. albicans mutants lacking Ypk1 are viable but have a strong growth defect. The phenotypes of the mutants indicate that the known functions of Ypk1 are conserved in C. albicans, but loss of this kinase has less severe consequences than in S. cerevisiae. We also unravel the puzzling previous observation that C. albicans mutants lacking the Ypk1-activating kinase Pkh1, which is essential in S. cerevisiae, have no obvious growth defects. We show that the protein kinase Pkh3, which has not previously been implicated in the Ypk1 signaling pathway, can substitute Pkh1 and activate Ypk1 in C. albicans. These findings provide novel insights into this conserved signaling pathway and how it is rewired in a human-pathogenic fungus.
The yeast form of the fungus Candida albicans promotes persistence in the gut of gnotobiotic mice
(2017)
Many microorganisms that cause systemic, life-threatening infections in humans reside as harmless commensals in our digestive tract. Yet little is known about the biology of these microbes in the gut. Here, we visualize the interface between the human commensal and pathogenic fungus Candida albicans and the intestine of mice, a surrogate host. Because the indigenous mouse microbiota restricts C. albicans settlement, we compared the patterns of colonization in the gut of germ free and antibiotic-treated conventionally raised mice. In contrast to the heterogeneous morphologies found in the latter, we establish that in germ free animals the fungus almost uniformly adopts the yeast cell form, a proxy of its commensal state. By screening a collection of C. albicans transcription regulator deletion mutants in gnotobiotic mice, we identify several genes previously unknown to contribute to in vivo fitness. We investigate three of these regulators—ZCF8, ZFU2 and TRY4—and show that indeed they favor the yeast form over other morphologies. Consistent with this finding, we demonstrate that genetically inducing non-yeast cell morphologies is detrimental to the fitness of C. albicans in the gut. Furthermore, the identified regulators promote adherence of the fungus to a surface covered with mucin and to mucus-producing intestinal epithelial cells. In agreement with this result, histology sections indicate that C. albicans dwells in the murine gut in close proximity to the mucus layer. Thus, our findings reveal a set of regulators that endows C. albicans with the ability to endure in the intestine through multiple mechanisms.
All Staphylococcus aureus genomes contain a genomic island, which is termed vSa\(\alpha\) and characterized by two clusters of tandem repeat sequences, i.e. the exotoxin (set) and 'lipoprotein-like' genes (lpl). Based on their structural similarities the vSa\(\alpha\) islands have been classified as type I to IV. The genomes of highly pathogenic and particularly epidemic S. aureus strains (USA300, N315, Mu50, NCTC8325, Newman, COL, JH1 or JH9) belonging to the clonal complexes CC5 and CC8 bear a type I vSa\(\alpha\) island. Since the contribution of the lpl gene cluster encoded in the vSa\(\alpha\) island to virulence is unclear to date, we deleted the entire lpl gene cluster in S. aureus USA300. The results showed that the mutant was deficient in the stimulation of pro-inflammatory cytokines in human monocytes, macrophages and keratinocytes. Purified lipoprotein Lpl1 was further shown to elicit a TLR2-dependent response. Furthermore, heterologous expression of the USA300 lpl cluster in other S. aureus strains enhanced their immune stimulatory activity. Most importantly, the lpl cluster contributed to invasion of S. aureus into human keratinocytes and mouse skin and the non-invasive S. carnosus expressing the lpl gene cluster became invasive. Additionally, in a murine kidney abscess model the bacterial burden in the kidneys was higher in wild type than in mutant mice. In this infection model the lpl cluster, thus, contributes to virulence. The present report is one of the first studies addressing the role of the vSa\(\alpha\) encoded lpl gene cluster in staphylococcal virulence. The finding that the lpl gene cluster contributes to internalization into non-professional antigen presenting cells such as keratinocytes high-lights the lpl as a new cell surface component that triggers host cell invasion by S. aureus. Increased invasion in murine skin and an increased bacterial burden in a murine kidney abscess model suggest that the lpl gene cluster serves as an important virulence factor.
Two-component systems (TCSs) are the most important sensing mechanisms in bacteria. In Streptomyces, TCSs-mediated responses to environmental stimuli are involved in the regulation of antibiotic production. This study examines the individual role of two histidine kinases (HKs), AbrC1 and AbrC2, which form part of an atypical TCS in Streptomyces coelicolor. gRT-PCR analysis of the expression of both kinases demonstrated that both are expressed at similar levels in NB and NMMP media. Single deletion of abrC1 elicited a significant increase in antibiotic production, while deletion of abrC2 did not have any clear effect. The origin of this phenotype, probably related to the differential phosphorylation ability of the two kinases, was also explored indirectly, analyzing the toxic phenotypes associated with high levels of phosphorylated RR. The higher the AbrC3 regulator phosphorylation rate, the greater the cell toxicity. For the first time, the present work shows in Streptomyces the combined involvement of two different HKs in the response of a regulator to environmental signals. Regarding the possible applications of this research, the fact that an abrC1 deletion mutant overproduces three of the S. coelicolor antibiotics makes this strain an excellent candidate as a host for the heterologous production of secondary metabolites.
The pathogenic yeast Candida albicans can develop resistance to the widely used antifungal agent fluconazole, which inhibits ergosterol biosynthesis, by the overexpression of genes encoding multidrug efflux pumps or ergosterol biosynthesis enzymes. Zinc cluster transcription factors play a central role in the transcriptional regulation of drug resistance. Mrr1 regulates the expression of the major facilitator MDR1, Tac1 controls the expression of the ABC transporters CDR1 and CDR2, and Upc2 regulates ergosterol biosynthesis (ERG) genes. Gain-of-function mutations in these transcription factors result in constitutive overexpression of their target genes and are responsible for fluconazole resistance in many clinical C. albicans isolates. The transcription factor Ndt80 contributes to the drug-induced upregulation of CDR1 and ERG genes and also binds to the MDR1 and CDR2 promoters, suggesting that it is an important component of all major transcriptional mechanisms of fluconazole resistance. However, we found that Ndt80 is not required for the induction of MDR1 and CDR2 expression by inducing chemicals. CDR2 was even partially derepressed in ndt80D mutants, indicating that Ndt80 is a repressor of CDR2 expression. Hyperactive forms of Mrr1, Tac1, and Upc2 promoted overexpression of MDR1, CDR1/CDR2, and ERG11, respectively, with the same efficiency in the presence and absence of Ndt80. Mrr1- and Tac1-mediated fluconazole resistance was even slightly enhanced in ndt80D mutants compared to wild-type cells. These results demonstrate that Ndt80 is dispensable for the constitutive overexpression of Mrr1, Tac1, and Upc2 target genes and the increased fluconazole resistance of strains that have acquired activating mutations in these transcription factors.
Transposon insertion sequencing is a high-throughput technique for assaying large libraries of otherwise isogenic transposon mutants providing insight into gene essentiality, gene function and genetic interactions. We previously developed the Transposon Directed Insertion Sequencing (TraDIS) protocol for this purpose, which utilizes shearing of genomic DNA followed by specific PCR amplification of transposon-containing fragments and Illumina sequencing. Here we describe an optimized high-yield library preparation and sequencing protocol for TraDIS experiments and a novel software pipeline for analysis of the resulting data. The Bio-Tradis analysis pipeline is implemented as an extensible Perl library which can either be used as is, or as a basis for the development of more advanced analysis tools. This article can serve as a general reference for the application of the TraDIS methodology.
Model enteric bacteria such as Escherichia coli and Salmonella enterica express hundreds of small non-coding RNAs (sRNAs), targets for most of which are yet unknown. Some sRNAs are remarkably well conserved, indicating that they serve cellular functions that go beyond the necessities of a single species. One of these ‘core sRNAs’ of largely unknown function is the abundant ∼100-nucleotide SdsR sRNA which is transcribed by the general stress σ-factor, σ\(^{S}\) and accumulates in stationary phase. In Salmonella, SdsR was known to inhibit the synthesis of the species-specific porin, OmpD. However, sdsR genes are present in almost all enterobacterial genomes, suggesting that additional, conserved targets of this sRNA must exist. Here, we have combined SdsR pulse-expression with whole genome transcriptomics to discover 20 previously unknown candidate targets of SdsR which include mRNAs coding for physiologically important regulators such as the carbon utilization regulator, CRP, the nucleoid-associated chaperone, StpA and the antibiotic resistance transporter, TolC. Processing of SdsR by RNase E results in two cellular SdsR variants with distinct target spectra. While the overall physiological role of this orphan core sRNA remains to be fully understood, the new SdsR targets present valuable leads to determine sRNA functions in resting bacteria.
The cell wall synthesis pathway producing peptidoglycan is a highly coordinated and tightly regulated process. Although the major components of bacterial cell walls have been known for decades, the complex regulatory network controlling peptidoglycan synthesis and many details of the cell division machinery are not well understood. The eukaryotic-like serine/threonine kinase Stk and the cognate phosphatase Stp play an important role in cell wall biosynthesis and drug resistance in S. aureus. We show that stp deletion has a pronounced impact on cell wall synthesis. Deletion of stp leads to a thicker cell wall and decreases susceptibility to lysostaphin. Stationary phase Δstp cells accumulate peptidoglycan precursors and incorporate higher amounts of incomplete muropeptides with non-glycine, monoglycine and monoalanine interpeptide bridges into the cell wall. In line with this cell wall phenotype, we demonstrate that the lipid II:glycine glycyltransferase FemX can be phosphorylated by the Ser/Thr kinase Stk in vitro. Mass spectrometric analyses identify Thr32, Thr36 and Ser415 as phosphoacceptors. The cognate phosphatase Stp dephosphorylates these phosphorylation sites. Moreover, Stk interacts with FemA and FemB, but is unable to phosphorylate them. Our data indicate that Stk and Stp modulate cell wall synthesis and cell division at several levels.
Numerous small non-coding RNAs (sRNAs) in bacteria modulate rates of translation initiation and degradation of target mRNAs, which they recognize through base-pairing facilitated by the RNA chaperone Hfq. Recent evidence indicates that the ternary complex of Hfq, sRNA and mRNA guides endoribonuclease RNase E to initiate turnover of both the RNAs. We show that a sRNA not only guides RNase E to a defined site in a target RNA, but also allosterically activates the enzyme by presenting a monophosphate group at the 5′-end of the cognate-pairing “seed.” Moreover, in the absence of the target the 5′-monophosphate makes the sRNA seed region vulnerable to an attack by RNase E against which Hfq confers no protection. These results suggest that the chemical signature and pairing status of the sRNA seed region may help to both ‘proofread’ recognition and activate mRNA cleavage, as part of a dynamic process involving cooperation of RNA, Hfq and RNase E.
This thesis aimed at searching for new effective agents against Multidrug-Resistant Enterobacteriaceae. This is necessitated by the urgent need for new and innovative antibacterial agents addressing the critical priority pathogens prescribed by the World Health Organization (WHO). Among the available means for antibiotics discovery and development, nature has long remained a proven, innovative, and highly reliable gateway to successful antibacterial agents. Nevertheless, numerous challenges surrounding this valuable source of antibiotics among other drugs are limiting the complete realization of its potential. These include the availability of good quality data on the highly potential natural sources, limitations in methods to prepare and screen crude extracts, bottlenecks in reproducing biological potentials observed in natural sources, as well as hurdles in isolation, purification, and characterization of natural compounds with diverse structural complexities.
Through an extensive review of the literature, it was possible to prepare libraries of plant species and phytochemicals with reported high potentials against Escherichia coli and Klebsiella pneumnoniae. The libraries were profiled to highlight the existing patterns and relationships between the reported antibacterial activities and studied plants’ families and parts, the type of the extracting solvent, as well as phytochemicals’ classes, drug-likeness and selected parameters for enhanced accumulation within the Gram-negative bacteria. In addition, motivations, objectives, the role of traditional practices and other crucial experimental aspects in the screening of plant extracts for antibacterial activities were identified and discussed.
Based on the implemented strict inclusion criteria, the created libraries grant speedy access to well-evaluated plant species and phytochemicals with potential antibacterial activities. This way, further studies in yet unexplored directions can be pursued from the indicated or related species and compounds. Moreover, the availability of compound libraries focusing on related bacterial species serves a great role in the ongoing efforts to develop the rules of antibiotics penetrability and accumulation, particularly among Gram-negative bacteria. Here, in addition to hunting for potential scaffolds from such libraries, detailed evaluations of large pool compounds with related antibacterial potential can grant a better understanding of structural features crucial for their penetration and accumulation. Based on the scarcity of compounds with broad structural diversity and activity against Gram-negative bacteria, the creation and updating of such libraries remain a laborious but important undertaking.
A Pressurized Microwave Assisted Extraction (PMAE) method over a short duration and low-temperature conditions was developed and compared to the conventional cold maceration over a prolonged duration. This method aimed at addressing the key challenges associated with conventional extraction methods which require long extraction durations, and use more energy and solvents, in addition to larger quantities of plant materials. Furthermore, the method was intended to replace the common use of high temperatures in most of the current MAE applications. Interestingly, the yields of 16 of 18 plant samples under PMAE over 30 minutes were found to be within 91–139% of those obtained from the 24h extraction by maceration. Additionally, different levels of selectivity were observed upon an analytical comparison of the extracts obtained from the two methods. Although each method indicated selective extraction of higher quantities or additional types of certain phytochemicals, a slightly larger number of additional compounds were observed under maceration. The use of this method allows efficient extraction of a large number of samples while sparing heat-sensitive compounds and minimizing chances for cross-reactions between phytochemicals.
Moreover, findings from another investigation highlighted the low likelihood of reproducing antibacterial activities previously reported among various plant species, identified the key drivers of poor reproducibility, and proposed possible measures to mitigate the challenge. The majority of extracts showed no activities up to the highest tested concentration of 1024 µg/mL. In the case of identical plant species, some activities were observed only in 15% of the extracts, in which the Minimum Inhibitory Concentrations (MICs) were 4 – 16-fold higher than those in previous reports. Evaluation of related plant species indicated better outcomes, whereby about 18% of the extracts showed activities in a range of 128–512 μg/mL, some of the activities being superior to those previously reported in related species.
Furthermore, solubilizing plant crude extracts during the preparation of test solutions for Antibacterial Susceptibility Testing (AST) assays was outlined as a key challenge. In trying to address this challenge, some studies have used bacteria-toxic solvents or generally unacceptable concentrations of common solubilizing agents. Both approaches are liable to give false positive results. In line with this challenge, this study has underscored the suitability of acetone in the solubilization of crude plant extracts. Using acetone, better solubility profiles of crude plant extracts were observed compared to dimethyl sulfoxide (DMSO) at up to 10 %v/v. Based on lacking toxicity against many bacteria species at up to 25 %v/v, its use in the solubilization of poorly water-soluble extracts, particularly those from less polar solvents is advocated.
In a subsequent study, four galloylglucoses were isolated from the leaves of Paeonia officinalis L., whereby the isolation of three of them from this source was reported for the first time. The isolation and characterization of these compounds were driven by the crucial need to continually fill the pre-clinical antibiotics pipeline using all available means. Application of the bioautography-guided isolation and a matrix of extractive, chromatographic, spectroscopic, and spectrometric techniques enabled the isolation of the compounds at high purity levels and the ascertainment of their chemical structures.
Further, the compounds exhibited the Minimum Inhibitory Concentrations (MIC) in a range of 2–256 µg/mL against Multidrug-Resistant (MDR) strains of E. coli and K. pneumonia exhibiting diverse MDR phenotypes. In that, the antibacterial activities of three of the isolated compounds were reported for the first time. The observed in vitro activities of the compounds resonated with their in vivo potentials as determined using the Galleria mellonella larvae model. Additionally, the susceptibility of the MDR bacteria to the galloylglucoses was noted to vary depending on the nature of the resistance enzymes expressed by the MDR bacteria. In that, the bacteria expressing enzymes with higher content of aromatic amino acids and zero or positive net charges were generally more susceptible. Following these findings, a plausible hypothesis for the observed patterns was put forward.
The generally challenging pharmacokinetic properties of galloylglucoses limit their further development into therapeutic agents. However, the compounds can replace or reduce the use of antibiotics in livestock keeping as well as in the treatment of septic wounds and topical or oral cavity infections, among other potential uses.
Using nature-inspired approaches, a series of glucovanillin derivatives were prepared following feasible synthetic pathways which in most cases ensured good yields and high purity levels. Some of the prepared compounds showed MIC values in a range of 128 – 512 μg/mL against susceptible and MDR strains of Klebsiella pneumoniae, Methicillin-Resistant Staphylococcus aureus (MRSA) and Vancomycin-Resistant Enterococcus faecium (VRE). These findings emphasize the previously reported essence of small molecular size, the presence of protonatable amino groups and halogen atoms, as well as an amphiphilic character, as crucial features for potential antibacterial agents.
Due to the experienced limited success in the search for new antibacterial agents using purely synthetic means, pursuing semi-synthetic approaches as employed in this study are highly encouraged. This way, it is possible to explore broader chemical spaces around natural scaffolds while addressing their inherent limitations such as solubility, toxicity, and poor pharmacokinetic profiles.
The role of macrophages in primary and secondary infection of mice with Salmonella typhimurium
(1982)
Elimination of macrophages with high-molecular dextran sulphate (OS) markedly impairs resistance of mice to primary infection with smooth, virulent strains of Salmonella typhimurium, whereas stimulation of this system by killed Bordetella pertussis organisms increases resistance. In infection with rough, avirulent strains of S. iyphimurium the elimination of macro phages was not followed by an essential loss of resistance, and it appears that other non-specific defence mechanisms, for example the complement system, may have compensated for the lack of macrophages. Macrophages, therefore, play an important role in defence during primary infection with virulent strains. In immunity to challenge infection with S. typhimurium, macrophages play an even more significant role. Treatment with OS completely removes immunity, and both humoral and cell-mediated immune mechanisms seem to require the participation of macrophages.
Cutaneous leishmaniasis is an infectious disease that is endemic especially in tropical and desert regions with an incidence of 1.5 million cases per year and a prevalence of 12 million people infected worldwide. The infection can be caused by the intracellular parasite Leishmania major. The disease has been studied extensively in the murine model. It has become apparent that the induction of a class of interferon (IFN)--producing CD4+ T helper cells (TH1 cells) that activate macrophages to kill the parasites they harbor is desicive for the establishment of immunity. The redirection of the host’s immune response towards a protective TH1 phenotype will also be the key to an effective vaccine. Dendritic cells (DC) loaded with leishmanial antigens ex vivo were lately described as vaccines against L. major infections. One single recombinant Leishmania antigen, LeIF (Leishmania homologue of eukaryotic ribosomal initiation factor 4a), which was identified as a protein that stimulates DC to secrete interleukin (IL)-12 and discussed as a pattern-associated molecular pattern (PAMP), was found to mediate a protective TH1-dependent effect when used for pulsing of DC. The application of recombinant proteins is tied to many disadvantages, which is why other methods of antigen administration have been developed. RNA electroporation of DC has recently emerged from tumor research as a safe and versatile method of antigen delivery, by which a large number of RNA molecules encoding a specific antigen gains access to the cytosol of DC by an electrical impulse. The present study describes, for the first time, transfection of DC with RNA encoding a molecularly defined parasite antigen. Initially, a standardized protocol for RNA transfection was established, using the enhanced green fluorescent protein (EGFP) as reporter antigen. EGFP-RNA was well translatable in an in vitro translation system, and both a DC cell line (fetal skin-derived DC; FSDC) and murine primary bone marrow-derived DC (BMDC) could be transfected efficiently, with a yield of up to 90% and 75%, respectively. In both cell types, maximal transfection efficiency was attained with 20 µg RNA and could not be further increased with larger amounts of RNA. The level of antigen expression, measured as the mean fluorescence intensity (MFI) by flow cytometry, was directly proportional to the amount of RNA used for transfection. In FSDC, transfection efficiency and MFI were generally higher than in BMDC when the same amounts of RNA were used. Furthermore, the kinetics was shown to be sensitive to treatment with lipopolysaccharide (LPS): the expression peak was higher and was reached sooner, followed by a more rapid decline. In transfection experiments with LeIF, two variants of LeIF-RNA were used: LeIF(fl)-RNA, encoding the complete LeIF sequence, and LeIF(226)-RNA, encoding only the aminoterminal half of the LeIF sequence (226 amino acids), the immunogenic part of LeIF. Only LeIF(fl) was detectable by Western Blot in whole cell lysates of BMDC after LeIF(fl)-RNA transfection, whereas LeIF(226) could never be detected in LeIF(226)-transfected BMDC. However, as both constructs were well translatable in a cell-free system, the failure to detect LeIF(226) in BMDC lysates did not represent a failure in RNA translation, but rather a rapid antigen degradation. It was therefore expected that LeIF(226)-transfected BMDC should nevertheless be able to present LeIF(226)-derived antigenic peptides to T cells from BALB/c mice primed with recombinant LeIF (rLeIF). This hypothesis was confirmed by measuring IFN- production in BMDC-T cell co-incubation assays, showing that rLeIF-pulsed, LeIF(226)- and LeIF(fl)-transfected day 7 BMDC did indeed activate T cells from LeIF-immunized mice in an antigen-specific manner. In contrast, IL-4 was not produced, which was consistent with the fact that T cells found in lymph nodes from LeIF-primed mice are primarily of the TH1 type. In the supernatants of LeIF-transfected BMDC cultures, in contrast to rLeIF-pulsed BMDC, the proinflammatory cytokines IL-1β, IL-6, IL-10 and IL-12 were not detected. This effect was not due to the electroporation procedure, as cytokine production by BMDC electroporated with rLeIF was only partially impaired. Also, the expression levels of CD86 were lower upon LeIF transfection than after pulsing with rLeIF. Thus, LeIF transfection did not induce maturation of DC. In conclusion, LeIF-transfected BMDC may have acted as semi-mature antigen-specific tolerance inducers, with regulatory T cells as responders. The effect of LeIF transfection on the immunostimulatory capacity of BMDC was not significantly increased when day 8 or 9 BMDC were used. However, day 8, and even more day 9 BMDC pulsed with rLeIF mounted a vigorous T cell response. Day 9 BMDC were able to activate naïve T cells. In conclusion, before a strong T cell response against LeIF can be induced, DC need to – besides presenting antigen and expressing co-stimulatory molecules – exhibit a susceptibility to the innate signaling molecule LeIF which is linked to their maturation age. This third signal is provided by extracellular rLeIF, but it is not conveyed – or is suppressed – by intracellular LeIF after LeIF-RNA transfection. Furthermore, electroporation of rLeIF abrogated IL-12 production by BMDC completely, the production of IL-1 was reduced with higher antigen doses, and the production of IL-10 was partially increased. The IL-6 production was unaffected. This altered cytokine profile suggests that LeIF as a PAMP might have a bipartite nature: besides exhibiting the capacity to stimulate IL-12 production upon extracellular presence, thereby enhancing host resistance against L. major, LeIF could also contribute to parasitic host evasion mechanisms from intracellular compartments of DC, possibly by interfering with mitogen-activated protein (MAP) kinase signaling pathways. Thus, the adjuvant properties of LeIF depend both on its mode of delivery (transfection with RNA vs. pulsing with the recombinant protein) and the targeted compartment (extra- vs. intracellular). From this work, it can be summarized that BMDC are well transfectable with a parasite antigen. The antigen is processed and presented, but it is not recognized as a PAMP by DC. Hence, transfection with antigen-encoding mRNA by itself does not convey all necessary signals for the elicitation of a potent immune response.
Microorganisms that colonize the human body face large fluctuations in their surroundings. Therefore, those microbes developed sophisticated mechanisms that allow them to adapt their cell biology and maintain cellular homeostasis. One organelle vital to preserve cell physiology is the vacuole. The vacuole exhibits a wide range of functions and is able to adjust itself in response to both external and internal stimuli. Moreover, it plays an important role in host interaction and virulence in fungi such as Candida albicans. Despite this connection, only a few regulatory proteins have been described to modulate vacuolar biology in fungal pathogens. Furthermore, whether such regulation alters fungus-host interplay remains largely unknown.
This thesis focuses on the characterization of ZCF8, a fungus-specific transcription regulator in the human-associated yeast C. albicans. To this end, I combined genome-wide protein-DNA interaction assays and gene expression analysis that identified genes regulated by Zcf8p. Fluorescence microscopy uncovered that several top targets of Zcf8p localize to the fungal vacuole. Moreover, deletion and overexpression of ZCF8 resulted in alterations in vacuolar morphology and in luminal pH and rendered the fungus resistant or susceptible to a vacuole-disturbing drug. Finally, in vitro adherence assays showed that Zcf8p modulates the attachment of C. albicans to human epithelial cells in a vacuole-dependent manner.
Given those findings, I posit that the previously uncharacterized transcription regulator Zcf8p modulates fungal attachment to epithelial cells in a manner that depends on the status of the fungal vacuole. Furthermore, the results highlight that vacuolar physiology is a substantial factor influencing the physical interaction between Candida cells and mammalian mucosal surfaces.
Protein kinases play central roles in virtually all signaling pathways that enable organisms to adapt to their environment. Microbial pathogens must cope with severely restricted iron availability in mammalian hosts to invade and establish themselves within infected tissues. To uncover protein kinase signaling pathways that are involved in the adaptation of the pathogenic yeast Candida albicans to iron limitation, we generated a comprehensive protein kinase deletion mutant library of a wild-type strain. Screening of this library revealed that the protein kinase Ire1, which has a conserved role in the response of eukaryotic cells to endoplasmic reticulum stress, is essential for growth of C. albicans under iron-limiting conditions. Ire1 was not necessary for the activity of the transcription factor Sef1, which regulates the response of the fungus to iron limitation, and Sef1 target genes that are induced by iron depletion were normally upregulated in ire1Δ mutants. Instead, Ire1 was required for proper localization of the high-affinity iron permease Ftr1 to the cell membrane. Intriguingly, iron limitation did not cause increased endoplasmic reticulum stress, and the transcription factor Hac1, which is activated by Ire1-mediated removal of the non-canonical intron in the HAC1 mRNA, was dispensable for Ftr1 localization to the cell membrane and growth under iron-limiting conditions. Nevertheless, expression of a pre-spliced HAC1 copy in ire1Δ mutants restored Ftr1 localization and rescued the growth defects of the mutants. Both ire1Δ and hac1Δ mutants were avirulent in a mouse model of systemic candidiasis, indicating that an appropriate response to endoplasmic reticulum stress is important for the virulence of C. albicans. However, the specific requirement of Ire1 for the functionality of the high-affinity iron permease Ftr1, a well-established virulence factor, even in the absence of endoplasmic reticulum stress uncovers a novel Hac1-independent essential role of Ire1 in iron acquisition and virulence of C. albicans.
The proteasome of malaria parasites: A multi-stage drug target for chemotherapeutic intervention?
(2012)
The ubiquitin/proteasome system serves as a regulated protein degradation pathway in eukaryotes, and is involved in many cellular processes featuring high protein turnover rates, such as cell cycle control, stress response and signal transduction. In malaria parasites, protein quality control is potentially important because of the high replication rate and the rapid transformations of the parasite during life cycle progression. The proteasome is the core of the degradation pathway, and is a major proteolytic complex responsible for the degradation and recycling of non-functional ubiquitinated proteins. Annotation of the genome for Plasmodium falciparum, the causative agent of malaria tropica, revealed proteins with similarity to human 26S proteasome subunits. In addition, a bacterial ClpQ/hslV threonine peptidase-like protein was identified. In recent years several independent studies indicated an essential function of the parasite proteasome for the liver, blood and transmission stages. In this review, we compile evidence for protein recycling in Plasmodium parasites and discuss the role of the 26S proteasome as a prospective multi-stage target for antimalarial drug discovery programs.
The primary transcriptome of Neisseria meningitidis and its interaction with the RNA chaperone Hfq
(2017)
Neisseria meningitidis is a human commensal that can also cause life-threatening meningitis and septicemia. Despite growing evidence for RNA-based regulation in meningococci, their transcriptome structure and output of regulatory small RNAs (sRNAs) are incompletely understood. Using dRNA-seq, we have mapped at single-nucleotide resolution the primary transcriptome of N. meningitidis strain 8013. Annotation of 1625 transcriptional start sites defines transcription units for most protein-coding genes but also reveals a paucity of classical σ70-type promoters, suggesting the existence of activators that compensate for the lack of −35 consensus sequences in N. meningitidis. The transcriptome maps also reveal 65 candidate sRNAs, a third of which were validated by northern blot analysis. Immunoprecipitation with the RNA chaperone Hfq drafts an unexpectedly large post-transcriptional regulatory network in this organism, comprising 23 sRNAs and hundreds of potential mRNA targets. Based on this data, using a newly developed gfp reporter system we validate an Hfq-dependent mRNA repression of the putative colonization factor PrpB by the two trans-acting sRNAs RcoF1/2. Our genome-wide RNA compendium will allow for a better understanding of meningococcal transcriptome organization and riboregulation with implications for colonization of the human nasopharynx.
Old yellow enzymes (OYEs) are widely found in the bacterial, fungal, and plant kingdoms but absent in humans and have been used as biocatalysts for decades. However, OYEs’ physiological function in bacterial stress response and infection situations remained enigmatic. As a pathogen, the Gram-positive bacterium Staphylococcus aureus adapts to numerous stress conditions during pathogenesis. Here, we show that in S. aureus genome, two paralogous genes (ofrA and ofrB) encode for two OYEs. We conducted a bioinformatic analysis and found that ofrA is conserved among all publicly available representative staphylococcal genomes and some Firmicutes. Expression of ofrA is induced by electrophilic, oxidative, and hypochlorite stress in S. aureus. Furthermore, ofrA contributes to S. aureus survival against reactive electrophilic, oxygen, and chlorine species (RES, ROS, and RCS) via thiol-dependent redox homeostasis. At the host–pathogen interface, S. aureusΔofrA has defective survival in macrophages and whole human blood and decreased staphyloxanthin production. Overall, our results shed the light onto a novel stress response strategy in the important human pathogen S. aureus.
Human herpesvirus 6A (HHV-6A) replicates in peripheral blood mononuclear cells (PBMCs) and various T-cell lines in vitro. Intriguingly, the virus can also establish latency in these cells, but it remains unknown what influences the decision between lytic replication and the latency of the virus. Incoming virus genomes are confronted with the nuclear domain 10 (ND10) complex as part of an intrinsic antiviral response. Most herpesviruses can efficiently subvert ND10, but its role in HHV-6A infection remains poorly understood. In this study, we investigated if the ND10 complex affects HHV-6A replication and contributes to the silencing of the virus genome during latency. We could demonstrate that ND10 complex was not dissociated upon infection, while the number of ND10 bodies was reduced in lytically infected cells. Virus replication was significantly enhanced upon knock down of the ND10 complex using shRNAs against its major constituents promyelocytic leukemia protein (PML), hDaxx, and Sp100. In addition, we could demonstrate that viral genes are more efficiently silenced in the presence of a functional ND10 complex. Our data thereby provides the first evidence that the cellular ND10 complex plays an important role in suppressing HHV-6A lytic replication and the silencing of the virus genome in latently infected cells.
Malaria is a vector-borne disease caused by the protozoan parasite of the genus Plasmodium and it is transmitted from human to human by female Anopheles mosquitoes during a blood meal. For malaria transmission to occur, the malaria parasite must undergo a crucial developmental sexual phase inside the mosquito midgut. In this study, we sought to investigate the interplay of the malaria parasite in the mosquito midgut with regard to the identification of novel types of transmission blocking intervention strategies. These strategies are aimed at reducing the spread of malaria by blocking the development of the mosquito midgut-specific stages of Plasmodium. We focused on three aspects. The first aspect was to investigate the interplay between mosquito midgut bacteria and malaria parasites in order to determine the potential influence of malaria parasites on the composition of the mosquito gut microbiota and also determine midgut bacteria which could be exploited as vehicles for the generation of paratransgenic Anopheles mosquitoes. We analyzed the microbial diversity of gut bacteria of the Asian malaria vector Anopheles stephensi during development and under different feeding regimes, including feeds on malaria parasite-infected blood, using the human pathogenic P. falciparum as well as the rodent malaria model P. berghei. 16S rRNA and DGGE analyses demonstrated a reduction in the microbial diversity during mosquito development from egg to adult and identified the gram-negative bacterium Elizabethkingia meningoseptica as the dominant species in the midgut of laboratory-reared male and female mosquitoes. E. meningoseptica is transmitted between generations and its predominance in the mosquito midgut was not altered by diet, when the gut microbiota was compared between sugar-fed and blood-fed female mosquitoes. Furthermore, feeds on blood infected with malaria parasites did not impact the presence of E. men-ingoseptica in the gut. Interestingly, extracts from E. meningoseptica exhibited antibacterial, antifungal and antiplasmodial activities, which may account for its dominance in the midgut of the malaria vector. Isolates of E. meningoseptica were cultivable, making the bacterium a potential candidate vehicle for the generation of paratransgenic Anopheles mosquitoes. The second aspect of this thesis was to determine transcriptome changes that occur during the first half hour following transmission of P. falciparum to the mosquito vector in order to better understand gene regulation mechanisms important for the change of hosts and determine novel proteins which could be exploited in malaria transmission blocking interventions. We initially used suppression subtractive hybridization (SSH) to compare mRNA levels of P. falciparum gametocytes before and 30 min fol-lowing activation. We identified a total of 126 genes for which transcript expression changed during gametogenesis. Among these, 17.5% had putative functions in signaling, 14.3% were assigned to cell cycle and gene expression, 8.7% were linked to the cytoskeleton or motor complex, 7.9% were involved in proteostasis and 6.4% in metabolism, 12.7% were genes encoding for cell surface associated proteins, 11.9% were assigned to other functions, and 20.6% represented genes of unknown function. For 40% of the identified genes there has as yet not been any protein evidence. We further selected a subset of 34 genes from all the above ontology groups and analyzed the transcript changes during gametogenesis in detail by quantitative realtime RT-PCR. Of these, 29 genes were expressed in gametocytes, and for 20 genes transcript expres-sion in gametocytes was increased compared to asexual blood stage parasites. Transcript levels of eight genes were particularly high in activated gametocytes, pointing at functions downstream of gametocyte transmission to the mosquito which could be exploited in malaria transmission blocking strategies. The last aspect of this thesis was to determine the transmission blocking effect of a range of antimicrobial molecules as transmission blocking agents. The molecules were either isolated from insect hemolymph or recombinantly expressed in tobacco and designed to act either directly on the mosquito midgut stages or cover receptors on mosquito tissues like the midgut epithelium which the parasite would need for transit. We were able to show an antiplasmodial and transmission blocking effect of the anti-microbial molecule harmonine, a defense compound isolated from the hemolymph of the Asian ladybug Harmonia axyridis. Harmonine thus represents a potential lead structure for the development of novel antimalarials.
FinO-domain proteins are a widespread family of bacterial RNA-binding proteins with regulatory functions. Their target spectrum ranges from a single RNA pair, in the case of plasmid-encoded FinO, to global RNA regulons, as with enterobacterial ProQ. To assess whether the FinO domain itself is intrinsically selective or promiscuous, we determine in vivo targets of Neisseria meningitidis, which consists of solely a FinO domain. UV-CLIP-seq identifies associations with 16 small non-coding sRNAs and 166 mRNAs. Meningococcal ProQ predominantly binds to highly structured regions and generally acts to stabilize its RNA targets. Loss of ProQ alters transcript levels of >250 genes, demonstrating that this minimal ProQ protein impacts gene expression globally. Phenotypic analyses indicate that ProQ promotes oxidative stress resistance and DNA damage repair. We conclude that FinO domain proteins recognize some abundant type of RNA shape and evolve RNA binding selectivity through acquisition of additional regions that constrain target recognition. FinO-domain proteins are bacterial RNA-binding proteins with a wide range of target specificities. Here, the authors employ UV CLIP-seq and show that minimal ProQ protein of Neisseria meningitidis binds to various small non-coding RNAs and mRNAs involved in virulence.
Methionine is the first amino acid of every newly synthesised protein. In combination with its role as precursor for the vital methyl-group donor S-adenosylmethionine, methionine is essential for every living cell. The opportunistic human pathogen Staphylococcus aureus is capable of synthesising methionine de novo, when it becomes scarce in the environment. All genes required for the de novo biosynthesis are encoded by the metICFE-mdh operon, except for metX. Expression is controlled by a hierarchical network with a methionyl-tRNA-specific T-box riboswitch (MET-TBRS) as centrepiece, that is also referred to as met leader (RNA). T-box riboswitches (TBRS) are regulatory RNA elements located in the 5’-untranslated region (5’-UTR) of genes. The effector molecule of T-box riboswitches is uncharged cognate tRNA. The prevailing mechanism of action is premature termination of transcription of the nascent RNA in the absence of the effector (i.e. uncharged cognate tRNA) due to formation of a hairpin structure, the Terminator stem. In presence of the effector, a transient stabilisation of the alternative structure, the Antiterminator, enables transcription of the downstream genes (‘read-through’). Albeit, after the read-through the thermodynamically more stable Terminator eventually forms. The Terminator and the Antiterminator are two mutually exclusive structures. Previous work of the research group showed that in staphylococci the MET-TBRS ensures strictly methionine-dependent control of met operon expression. Uncharged methionyl-tRNA that activates the system is only present in sufficient amounts under methionine-deprived conditions. In contrast to other bacterial TBRS, the staphylococcal MET-TBRS has some characteristic features regarding its length and predicted secondary structure whose relevance for the function are yet unkown.
Aim of the present thesis was to experimentally determine the structure of the met leader RNA and to investigate the stability of the met operon-specific transcripts in the context of methionine biosynthesis control. Furthermore, the yet unknown function of the mdh gene within the met operon was to be determined.
In the context of this thesis, the secondary structure of the met leader was determined employing in-line probing. The structural analysis revealed the presence of almost all highly conserved T-box riboswitch structural characteristics. Furthermore, three additional stems, absent in all T-box riboswitches analysed to date, could be identified. Particularly remarkable is the above average length of the Terminator stem which renders it a potential target of the double-strand-specific endoribonuclease III (RNase III). The RNase III-dependent cleavage of the met leader could be experimentally verified by the use of suitable mutants. Moreover, the exact cleavage site within the Terminator was determined.
The unusual immediate separation of the met leader from the met operon mRNA via the RNase III cleavage within the Terminator stem induces the rapid degradation of the met leader RNA and, most likely, that of the 5’-region of the met mRNA. The met mRNA is degraded from its 5’-end by the exoribonuclease RNase J. The stability of the met mRNA was found to vary over the length of the transcript with an instable 5’-end (metI and metC) and a longer half-life towards the 3’-end (metE and mdh). The varying transcript stability is reflected by differences in the available cellular protein levels. The obtained data suggest that programmed mRNA degradation is another level of regulation in the complex network of staphylococcal de novo methionine biosynthesis control.
In addition, the MET-TBRS was studied with regard to a future use as a drug target for novel antimicrobial agents. To this end, effects of a dysregulated methionine biosynthesis on bacterial growth and survival were investigated in met leader mutants that either caused permanent transcription of the met operon (‘ON’) or prevented operon transcription (‘OFF’), irrespective of the methionine status in the cell. Methionine deprivation turned out to be a strong selection pressure, as ‘OFF’ mutants acquired adaptive mutations within the met leader to restore met operon expression that subsequently re-enabled growth.
The second part of the thesis was dedicated to the characterisation of the Mdh protein that is encoded by the last gene of the met operon and whose function is unknown yet. At first, co-transcription and -expression with the met operon could be demonstrated. Next, the Mdh protein was overexpressed and purified and the crystal structure of Mdh was solved to high resolution by the Kisker research group (Rudolf-Virchow-Zentrum Würzburg). Analysis of the structure revealed the amino acid residues crucial for catalytic activity, and zinc was identified as a co-factor of Mdh. Also, Mdh was shown to exist as a dimer. However, identification of the Mdh substrate was, in the context of this thesis, (still) unsuccessful. Nevertheless, interactions of Mdh with enzymes of the met operon could be demonstrated by employing the bacterial two-hybrid system. This fact and the high conservation of mdh/Mdh on nucleotide and amino acid level among numerous staphylococcal species suggests an important role of Mdh within the methionine metabolism that should be a worthwhile subject of future research.
FinO domain proteins such as ProQ of the model pathogen Salmonella enterica have emerged as a new class of major RNA-binding proteins in bacteria. ProQ has been shown to target hundreds of transcripts, including mRNAs from many virulence regions, but its role, if any, in bacterial pathogenesis has not been studied. Here, using a Dual RNA-seq approach to profile ProQ-dependent gene expression changes as Salmonella infects human cells, we reveal dysregulation of bacterial motility, chemotaxis, and virulence genes which is accompanied by altered MAPK (mitogen-activated protein kinase) signaling in the host. Comparison with the other major RNA chaperone in Salmonella, Hfq, reinforces the notion that these two global RNA-binding proteins work in parallel to ensure full virulence. Of newly discovered infection-associated ProQ-bound small noncoding RNAs (sRNAs), we show that the 3′UTR-derived sRNA STnc540 is capable of repressing an infection-induced magnesium transporter mRNA in a ProQ-dependent manner. Together, this comprehensive study uncovers the relevance of ProQ for Salmonella pathogenesis and highlights the importance of RNA-binding proteins in regulating bacterial virulence programs.
IMPORTANCE
The protein ProQ has recently been discovered as the centerpiece of a previously overlooked “third domain” of small RNA-mediated control of gene expression in bacteria. As in vitro work continues to reveal molecular mechanisms, it is also important to understand how ProQ affects the life cycle of bacterial pathogens as these pathogens infect eukaryotic cells. Here, we have determined how ProQ shapes Salmonella virulence and how the activities of this RNA-binding protein compare with those of Hfq, another central protein in RNA-based gene regulation in this and other bacteria. To this end, we apply global transcriptomics of pathogen and host cells during infection. In doing so, we reveal ProQ-dependent transcript changes in key virulence and host immune pathways. Moreover, we differentiate the roles of ProQ from those of Hfq during infection, for both coding and noncoding transcripts, and provide an important resource for those interested in ProQ-dependent small RNAs in enteric bacteria.
Bioluminescent reporter genes, such as those from fireflies and bacteria, let researchers use light production as a non-invasive and non-destructive surrogate measure of microbial numbers in a wide variety of environments. As bioluminescence needs microbial metabolites, tagging microorganisms with luciferases means only live metabolically active cells are detected. Despite the wide use of bioluminescent reporter genes, very little is known about the impact of continuous (also called constitutive) light expression on tagged bacteria. We have previously made a bioluminescent strain of Citrobacter rodentium, a bacterium which infects laboratory mice in a similar way to how enteropathogenic Escherichia coli (EPEC) and enterohaemorrhagic E. coli (EHEC) infect humans. In this study, we compared the growth of the bioluminescent C. rodentium strain ICC180 with its non-bioluminescent parent (strain ICC169) in a wide variety of environments. To understand more about the metabolic burden of expressing light, we also compared the growth profiles of the two strains under approximately 2,000 different conditions. We found that constitutive light expression in ICC180 was near-neutral in almost every non-toxic environment tested. However, we also found that the non-bioluminescent parent strain has a competitive advantage over ICC180 during infection of adult mice, although this was not enough for ICC180 to be completely outcompeted. In conclusion, our data suggest that constitutive light expression is not metabolically costly to C. rodentium and supports the view that bioluminescent versions of microbes can be used as a substitute for their non-bioluminescent parents to study bacterial behaviour in a wide variety of environments.
Staphylococcus aureus is a commensal of the human nose and skin. Human skin fatty acids, in particular cis-6-hexadecenoic acid (C-6-H), have high antistaphylococcal activity and can inhibit virulence determinant production. Here, we show that sub-MIC levels of C-6-H result in induction of increased resistance. The mechanism(s) of C-6-H activity was investigated by combined transcriptome and proteome analyses. Proteome analysis demonstrated a pleiotropic effect of C-6-H on virulence determinant production. In response to C-6-H, transcriptomics revealed altered expression of over 500 genes, involved in many aspects of virulence and cellular physiology. The expression of toxins (hla, hlb, hlgBC) was reduced, whereas that of host defence evasion components (cap, sspAB, katA) was increased. In particular, members of the SaeRS regulon had highly reduced expression, and the use of specific mutants revealed that the effect on toxin production is likely mediated via SaeRS
The widespread CsrA/RsmA protein regulators repress translation by binding GGA motifs in bacterial mRNAs. CsrA activity is primarily controlled through sequestration by multiple small regulatory RNAs. Here we investigate CsrA activity control in the absence of antagonizing small RNAs by examining the CsrA regulon in the human pathogen Campylobacter jejuni. We use genome-wide co-immunoprecipitation combined with RNA sequencing to show that CsrA primarily binds flagellar mRNAs and identify the major flagellin mRNA (flaA) as the main CsrA target. The flaA mRNA is translationally repressed by CsrA, but it can also titrate CsrA activity. Together with the main C. jejuni CsrA antagonist, the FliW protein, flaA mRNA controls CsrA-mediated post-transcriptional regulation of other flagellar genes. RNA-FISH reveals that flaA mRNA is expressed and localized at the poles of elongating cells. Polar flaA mRNA localization is translation dependent and is post-transcriptionally regulated by the CsrA-FliW network. Overall, our results suggest a role for CsrA-FliW in spatiotemporal control of flagella assembly and localization of a dual-function mRNA.
The tropical disease malaria, which results in more than one million deaths annually, is caused by protozoan parasites of the genus Plasmodium and transmitted by blood-feeding Anopheline mosquitoes. Parasite transition from the human host to the mosquito vector is mediated by gametocytes, sexual stages that are formed in human erythrocytes, which therefore play a crucial part in the spread of the tropical disease. The uptake by the blood-feeding mosquito triggers important molecular and cellular changes in the gametocytes, thus mediating the rapid adjustment of the parasite from the warm-blooded host to the insect host and subsequently initiating reproduction. The contact with midgut factors triggers gametocyte activation and results in their egress from the enveloping erythrocyte, which then leads to gamete formation and fertilization. This review summarizes recent findings on the role of gametocytes during transmission to themosquito and particularly focuses on the molecular mechanisms underlying gametocyte activation and emergence from the host erythrocyte during gametogenesis.