Olga Soutourina - Academia.edu (original) (raw)

Papers by Olga Soutourina

Research paper thumbnail of MvaT proteins in Pseudomonas spp.: a novel class of H-NS-like proteins

Research paper thumbnail of Formation of D-tyrosyl-tRNATyr accounts for the toxicity of D-tyrosine toward Escherichia coli

The Journal of biological chemistry, Jan 8, 2004

D-Tyr-tRNATyr deacylase cleaves the ester bond between a tRNA molecule and a D-amino acid. In Esc... more D-Tyr-tRNATyr deacylase cleaves the ester bond between a tRNA molecule and a D-amino acid. In Escherichia coli, inactivation of the gene (dtd) encoding this deacylase increases the toxicity of several D-amino acids including D-tyrosine, D-tryptophan, and D-aspartic acid. Here, we demonstrate that, in a Deltadtd cell grown in the presence of 2.4 mm D-tyrosine, approximately 40% of the total tRNATyr pool is converted into D-Tyr-tRNATyr. No D-Tyr-tRNATyr is observed in dtd+ cells. In addition, we observe that overproduction of tRNATyr, tRNATrp, or tRNAAsp protects a Deltadtd mutant strain against the toxic effect of D-tyrosine, D-tryptophan, or D-aspartic acid, respectively. In the case of D-tyrosine, we show that the protection is accounted for by an increase in the concentration of L-Tyr-tRNATyr proportional to that of overproduced tRNATyr. Altogether, these results indicate that, by accumulating in vivo, high amounts of D-Tyr-tRNATyr cause a starvation for L-Tyr-tRNATyr. The deacyla...

Research paper thumbnail of Global analysis of gene expression in mammalian kidney

Pfl�gers Archiv - European Journal of Physiology, 2005

The past decade has seen the achievement of sequencing of human, rat and mouse genomes and the de... more The past decade has seen the achievement of sequencing of human, rat and mouse genomes and the development of high-throughput methods for quantitative monitoring of gene expression. The aim of the beginning post-genomic era is to determine the function of all these genes, a challenge in which the community of physiologists should have a leading role. In this short review, we discuss the relevance, feasibility and impact of transcriptome analysis in renal physiology. Comparison of transcriptomes demonstrates that cell lines are poor physiological models, making it necessary to work on native kidney tissue. Palliating kidney heterogeneity therefore requires the development of methods for transcriptome analysis sensitive enough to be compatible with microdissected nephron segments. Axial comparison of transcriptomes along the human nephron unexpectedly points out that the segmentation of nephrons concerns not only genes involved in solute and water transport functions and their regulation, but also genes related to the control of cell division, differentiation and apoptosis. Comparison of transcriptome of a same nephron segment from mice under different pathophysiological conditions outlines the wide pleiotropy of kidney function regulations. Both types of comparative studies also identify yet unknown transcripts specifically expressed along the nephron or under pathophysiological conditions.

Research paper thumbnail of A Novel H-NS-like Protein from an Antarctic Psychrophilic Bacterium Reveals a Crucial Role for the N-terminal Domain in Thermal Stability

Journal of Biological Chemistry, 2003

We describe here new members of the H-NS protein family identified in a psychrotrophic Acinetobac... more We describe here new members of the H-NS protein family identified in a psychrotrophic Acinetobacter spp. bacterium collected in Siberia and in a psychrophilic Psychrobacter spp. bacterium collected in Antarctica. Both are phylogenetically closely related to the HvrA and SPB Rhodobacter transcriptional regulators. Their amino acid sequence shares 40% identity, and their pre- dicted secondary structure displays a structural and

Research paper thumbnail of Environmental control of flagellar motility in prokaryotes: implication of DNA topology and nucleoid-associated proteins

Research paper thumbnail of Global Control of Cysteine Metabolism by CymR in Bacillus subtilis

Journal of Bacteriology, 2006

YrzC has previously been identified as a repressor controlling ytmI expression via its regulation... more YrzC has previously been identified as a repressor controlling ytmI expression via its regulation of YtlI activator synthesis in Bacillus subtilis. We identified YrzC as a master regulator of sulfur metabolism. Gene expression profiles of B. subtilis yrzC mutant and wild-type strains grown in minimal medium with sulfate as the sole sulfur source were compared. In the mutant, increased expression

Research paper thumbnail of Regulation of bacterial motility in response to low pH in Escherichia coli: the role of H-NS protein

Microbiology (Reading, England), 2002

The effect of detrimental conditions on bacterial motility in Escherichia coli was investigated. ... more The effect of detrimental conditions on bacterial motility in Escherichia coli was investigated. Expression profiling of mutant E. coli strains by DNA arrays and analysis of phenotypic traits demonstrated that motility and low-pH resistance are coordinately regulated. Analysis of transcriptional fusions suggests that bacterial motility in response to an acidic environment is mediated via the control by H-NS of flhDC expression. Moreover, the results suggested that the presence of an extended mRNA 5' end and DNA topology are required in this process. Finally, the presence of a similar regulatory region in several Gram-negative bacteria implies that this mechanism is largely conserved.

Research paper thumbnail of Riboswitch Discovery by Combining RNA-Seq and Genome-Wide Identification of Transcriptional Start Sites

Methods in Enzymology, 2014

Deep-sequencing technologies applied to RNA have tremendous potential to identify novel transcrip... more Deep-sequencing technologies applied to RNA have tremendous potential to identify novel transcripts with single-nucleotide resolution. By combining whole-transcript cDNA sequencing (RNA-seq) and genome-wide identification of transcription start sites (dRNA-seq), it is possible to characterize long 5'-untranslated regions potentially endowed with regulatory capacities and to detect premature termination of transcription. This can be used to identify new potential riboswitches. In this chapter, we provide a detailed protocol of the dRNA-seq method based on differential pretreatment of RNAs with tobacco acid pyrophosphatase to differentiate between 5'-ends of primary and processed RNAs. We also give a briefer protocol of the preparation of RNA-seq libraries and of how to go through data bioinformatics analysis and data visualization using genome browsers. This approach is powerful to identify novel riboswitches and to demonstrate the functionality of riboswitches predicted in silico.

Research paper thumbnail of Pleiotropic Role of the RNA Chaperone Protein Hfq in the Human Pathogen Clostridium difficile

Journal of Bacteriology, 2014

Clostridium difficile is an emergent human pathogen and the most common cause of nosocomial diarr... more Clostridium difficile is an emergent human pathogen and the most common cause of nosocomial diarrhea. Our recent data strongly suggest the importance of RNA-based mechanisms for the control of gene expression in C. difficile. In an effort to understand the function of the RNA chaperone protein Hfq, we constructed and characterized an Hfq-depleted strain in C. difficile. Hfq depletion led to a growth defect, morphological changes, an increased sensitivity to stresses, and a better ability to sporulate and to form biofilms. The transcriptome analysis revealed pleiotropic effects of Hfq depletion on gene expression in C. difficile, including genes encoding proteins involved in sporulation, stress response, metabolic pathways, cell wall-associated proteins, transporters, and transcriptional regulators and genes of unknown function. Remarkably, a great number of genes of the regulon dependent on sporulation-specific sigma factor, SigK, were upregulated in the Hfq-depleted strain. The altered accumulation of several sRNAs and interaction of Hfq with selected sRNAs suggest potential involvement of Hfq in these regulatory RNA functions. Altogether, these results suggest the pleiotropic role of Hfq protein in C. difficile physiology, including processes important for the C. difficile infection cycle, and expand our knowledge of Hfq-dependent regulation in Gram-positive bacteria.

Research paper thumbnail of Genome-Wide Identification of Regulatory RNAs in the Human Pathogen Clostridium difficile

PLoS Genetics, 2013

Clostridium difficile is an emergent pathogen, and the most common cause of nosocomial diarrhea. ... more Clostridium difficile is an emergent pathogen, and the most common cause of nosocomial diarrhea. In an effort to understand the role of small noncoding RNAs (sRNAs) in C. difficile physiology and pathogenesis, we used an in silico approach to identify 511 sRNA candidates in both intergenic and coding regions. In parallel, RNA-seq and differential 59-end RNA-seq were used for global identification of C. difficile sRNAs and their transcriptional start sites at three different growth conditions (exponential growth phase, stationary phase, and starvation). This global experimental approach identified 251 putative regulatory sRNAs including 94 potential trans riboregulators located in intergenic regions, 91 cis-antisense RNAs, and 66 riboswitches. Expression of 35 sRNAs was confirmed by gene-specific experimental approaches. Some sRNAs, including an antisense RNA that may be involved in control of C. difficile autolytic activity, showed growth phase-dependent expression profiles. Expression of each of 16 predicted c-di-GMP-responsive riboswitches was observed, and experimental evidence for their regulatory role in coordinated control of motility and biofilm formation was obtained. Finally, we detected abundant sRNAs encoded by multiple C. difficile CRISPR loci. These RNAs may be important for C. difficile survival in bacteriophage-rich gut communities. Altogether, this first experimental genome-wide identification of C. difficile sRNAs provides a firm basis for future RNome characterization and identification of molecular mechanisms of sRNA-based regulation of gene expression in this emergent enteropathogen.

Research paper thumbnail of Genome-Wide Analysis of Cell Type-Specific Gene Transcription during Spore Formation in Clostridium difficile

PLoS Genetics, 2013

Clostridium difficile, a Gram positive, anaerobic, spore-forming bacterium is an emergent pathoge... more Clostridium difficile, a Gram positive, anaerobic, spore-forming bacterium is an emergent pathogen and the most common cause of nosocomial diarrhea. Although transmission of C. difficile is mediated by contamination of the gut by spores, the regulatory cascade controlling spore formation remains poorly characterized. During Bacillus subtilis sporulation, a cascade of four sigma factors, s F and s G in the forespore and s E and s K in the mother cell governs compartment-specific gene expression. In this work, we combined genome wide transcriptional analyses and promoter mapping to define the C. difficile s F , s E , s G and s K regulons. We identified about 225 genes under the control of these sigma factors: 25 in the s F regulon, 97 s E -dependent genes, 50 s G -governed genes and 56 genes under s K control. A significant fraction of genes in each regulon is of unknown function but new candidates for spore coat proteins could be proposed as being synthesized under s E or s K control and detected in a previously published spore proteome. SpoIIID of C. difficile also plays a pivotal role in the mother cell line of expression repressing the transcription of many members of the s E regulon and activating sigK expression. Global analysis of developmental gene expression under the control of these sigma factors revealed deviations from the B. subtilis model regarding the communication between mother cell and forespore in C. difficile. We showed that the expression of the s E regulon in the mother cell was not strictly under the control of s F despite the fact that the forespore product SpoIIR was required for the processing of pro-s E . In addition, the s K regulon was not controlled by s G in C. difficile in agreement with the lack of pro-s K processing. This work is one key step to obtain new insights about the diversity and evolution of the sporulation process among Firmicutes.

Research paper thumbnail of Characterization of the SigD Regulon of C. difficile and Its Positive Control of Toxin Production through the Regulation of tcdR

Research paper thumbnail of Insights into the Rrf2 repressor family - the structure of CymR, the global cysteine regulator of Bacillus subtilis

Research paper thumbnail of RcsB plays a central role in H-NS-dependent regulation of motility and acid stress resistance in Escherichia coli

Research in Microbiology, 2010

In Escherichia coli, hns mutants lack flagellar motility and display an increase in acid stress r... more In Escherichia coli, hns mutants lack flagellar motility and display an increase in acid stress resistance. Spontaneous phenotypic revertants showed reversion of both H-NS-controlled phenotypes. In the present study, suppressor mutations were identified in the rcsB gene. In addition to RcsA, our experiments establish that H-NS indirectly controlled the RcsB regulator via repression of RcsD. We also show that RcsB D56E , mimicking phosphorylated RcsB, interacts with GadE to form a RcsB-P/GadE complex, a general direct regulator of glutamate-, arginine-and lysine-dependent acid resistance pathways. In addition, we showed that H-NS positively affects motility via the flhDC master operon repression by RcsB. This substantiates the central role of RcsB in H-NS-mediated control of motility and acid stress resistance.

Research paper thumbnail of Effect of mild acid pH on the functioning of bacterial membranes in Vibrio cholerae

PROTEOMICS, 2002

In this paper, we initiated the first two-dimensional electrophoresis map of Vibrio cholerae, the... more In this paper, we initiated the first two-dimensional electrophoresis map of Vibrio cholerae, the aetiological agent of cholera disease. In this pathogen the efficient adaptation to detrimental conditions plays an important role in its survival in both the aquatic reservoir and human intestine. By proteome analysis we investigated the effect of mild acid treatment on the physiology of V. cholerae. More than 50 proteins were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry and database searching. Amongst them, pH regulated proteins belong to various functional classes such as intermediary metabolism and bacterial envelope. Several proteins whose accumulation level was decreased in response to acidic pH are known to be involved in the organization and the functioning of membranes, including lipopolysaccharide. Consistent with this, we observed an increased susceptibility to hydrophobic drugs, a loss of motility and a reduction in the ability to form a biofilm in cells grown at pH 6. Our results suggest that V. cholerae is able to sense a moderate decrease in pH and to modify accordingly its structure and physiology.

Research paper thumbnail of Tissue Compartment Analysis for Biomarker Discovery by Gene Expression Profiling

PLoS ONE, 2009

Background: Although high throughput technologies for gene profiling are reliable tools, sample/t... more Background: Although high throughput technologies for gene profiling are reliable tools, sample/tissue heterogeneity limits their outcomes when applied to identify molecular markers. Indeed, inter-sample differences in cell composition contribute to scatter the data, preventing detection of small but relevant changes in gene expression level. To date, attempts to circumvent this difficulty were based on isolation of the different cell structures constituting biological samples. As an alternate approach, we developed a tissue compartment analysis (TCA) method to assess the cell composition of tissue samples, and applied it to standardize data and to identify biomarkers.

Research paper thumbnail of S-box and T-box riboswitches and antisense RNA control a sulfur metabolic operon of Clostridium acetobutylicum

Nucleic Acids Research, 2008

The ubiGmccBA operon of Clostridium acetobutylicum is involved in methionine to cysteine conversi... more The ubiGmccBA operon of Clostridium acetobutylicum is involved in methionine to cysteine conversion. We showed that its expression is controlled by a complex regulatory system combining several RNA-based mechanisms. Two functional convergent promoters associated with transcriptional antitermination systems, a cysteine-specific T-box and an S-box riboswitch, are located upstream of and downstream from the ubiG operon, respectively. Several antisense RNAs were synthesized from the downstream S-box-dependent promoter, resulting in modulation of the level of ubiG transcript and of MccB activity. In contrast, the upstream T-box system did not appear to play a major role in regulation, leaving antisense transcription as the major regulatory mechanism for the ubiG operon. The abundance of sense and antisense transcripts was inversely correlated with the sulfur source availability. Deletion of the downstream promoter region completely abolished the sulfur-dependent control of the ubiG operon, and the expression of antisense transcripts in trans did not restore the regulation of the operon. Our data revealed important insights into the molecular mechanism of cis-antisensemediated regulation, a control system only rarely observed in prokaryotes. We proposed a regulatory model in which the antisense RNA controlled the expression of the ubiG operon in cis via transcriptional interference at the ubiG locus.

Research paper thumbnail of Large-scale monitoring of pleiotropic regulation of gene expression by the prokaryotic nucleoid-associated protein, H-NS

Molecular Microbiology, 2001

Despite many years of intense work investigating the function of nucleoid-associated proteins in ... more Despite many years of intense work investigating the function of nucleoid-associated proteins in prokaryotes, their role in bacterial physiology remains largely unknown. The two-dimensional protein patterns were compared and expression profiling was carried out on H-NS-deficient and wild-type strains of Escherichia coli K-12. The expression of approximately 5% of the genes and/or the accumulation of their protein was directly or indirectly altered in the hns mutant strain. About one-fifth of these genes encode proteins that are involved in transcription or translation and one-third are known to or were in silico predicted to encode cell envelope components or proteins that are usually involved in bacterial adaptation to changes in environmental conditions. The increased expression of several genes in the mutant resulted in a better ability of this strain to survive at low pH and high osmolarity than the wildtype strain. In particular, the putative regulator, YhiX, plays a central role in the H-NS control of genes required in the glutamate-dependent acid stress response. These results suggest that there is a strong relationship between the H-NS regulon and the maintenance of intracellular homeostasis.

Research paper thumbnail of Global Control of Cysteine Metabolism by CymR in Bacillus subtilis

Journal of Bacteriology, 2006

YrzC has previously been identified as a repressor controlling ytmI expression via its regulation... more YrzC has previously been identified as a repressor controlling ytmI expression via its regulation of YtlI activator synthesis in Bacillus subtilis. We identified YrzC as a master regulator of sulfur metabolism. Gene expression profiles of B. subtilis ⌬yrzC mutant and wild-type strains grown in minimal medium with sulfate as the sole sulfur source were compared. In the mutant, increased expression was observed for 24 genes previously identified as repressed in the presence of sulfate. Since several genes involved in the pathways leading to cysteine formation were found, we propose to rename YrzC CymR, for "cysteine metabolism repressor." A CymR-dependent binding to the promoter region of the ytlI, ssuB, tcyP, yrrT, yxeK, cysK, or ydbM gene was demonstrated using gel shift experiments. A potential CymR target site, TAAWNCN 2 ANTWNAN 3 ATMGGAA TTW, was found in the promoter region of these genes. In a DNase footprint experiment, the protected region in the ytlI promoter region contained this consensus sequence. Partial deletion or introduction of point mutations in this sequence confirmed its involvement in ytlI, yrrT, and yxeK regulation. The addition of O-acetylserine in gel shift experiments prevented CymR-dependent binding to DNA for all of the targets characterized. Transcriptome analysis of a ⌬cymR mutant and the wild-type strain also brought out significant changes in the expression level of a large set of genes related to stress response or to transition toward anaerobiosis.

Research paper thumbnail of Conversion of Methionine to Cysteine in Bacillus subtilis and Its Regulation

Journal of Bacteriology, 2007

Bacillus subtilis can use methionine as the sole sulfur source, indicating an efficient conversio... more Bacillus subtilis can use methionine as the sole sulfur source, indicating an efficient conversion of methionine to cysteine. To characterize this pathway, the enzymatic activities of CysK, YrhA and YrhB purified in Escherichia coli were tested. Both CysK and YrhA have an O-acetylserine-thiol-lyase activity, but YrhA was 75-fold less active than CysK. An atypical cystathionine ␤-synthase activity using O-acetylserine and homocysteine as substrates was observed for YrhA but not for CysK. The YrhB protein had both cystathionine lyase and homocysteine ␥-lyase activities in vitro. Due to their activity, we propose that YrhA and YrhB should be renamed MccA and MccB for methionine-to-cysteine conversion. Mutants inactivated for cysK or yrhB grew similarly to the wild-type strain in the presence of methionine. In contrast, the growth of an ⌬yrhA mutant or a luxS mutant, inactivated for the S-ribosyl-homocysteinase step of the S-adenosylmethionine recycling pathway, was strongly reduced with methionine, whereas a ⌬yrhA ⌬cysK or cysE mutant did not grow at all under the same conditions. The yrhB and yrhA genes form an operon together with yrrT, mtnN, and yrhC. The expression of the yrrT operon was repressed in the presence of sulfate or cysteine. Both purified CysK and CymR, the global repressor of cysteine metabolism, were required to observe the formation of a protein-DNA complex with the yrrT promoter region in gel-shift experiments. The addition of O-acetyl-serine prevented the formation of this protein-DNA complex.

Research paper thumbnail of MvaT proteins in Pseudomonas spp.: a novel class of H-NS-like proteins

Research paper thumbnail of Formation of D-tyrosyl-tRNATyr accounts for the toxicity of D-tyrosine toward Escherichia coli

The Journal of biological chemistry, Jan 8, 2004

D-Tyr-tRNATyr deacylase cleaves the ester bond between a tRNA molecule and a D-amino acid. In Esc... more D-Tyr-tRNATyr deacylase cleaves the ester bond between a tRNA molecule and a D-amino acid. In Escherichia coli, inactivation of the gene (dtd) encoding this deacylase increases the toxicity of several D-amino acids including D-tyrosine, D-tryptophan, and D-aspartic acid. Here, we demonstrate that, in a Deltadtd cell grown in the presence of 2.4 mm D-tyrosine, approximately 40% of the total tRNATyr pool is converted into D-Tyr-tRNATyr. No D-Tyr-tRNATyr is observed in dtd+ cells. In addition, we observe that overproduction of tRNATyr, tRNATrp, or tRNAAsp protects a Deltadtd mutant strain against the toxic effect of D-tyrosine, D-tryptophan, or D-aspartic acid, respectively. In the case of D-tyrosine, we show that the protection is accounted for by an increase in the concentration of L-Tyr-tRNATyr proportional to that of overproduced tRNATyr. Altogether, these results indicate that, by accumulating in vivo, high amounts of D-Tyr-tRNATyr cause a starvation for L-Tyr-tRNATyr. The deacyla...

Research paper thumbnail of Global analysis of gene expression in mammalian kidney

Pfl�gers Archiv - European Journal of Physiology, 2005

The past decade has seen the achievement of sequencing of human, rat and mouse genomes and the de... more The past decade has seen the achievement of sequencing of human, rat and mouse genomes and the development of high-throughput methods for quantitative monitoring of gene expression. The aim of the beginning post-genomic era is to determine the function of all these genes, a challenge in which the community of physiologists should have a leading role. In this short review, we discuss the relevance, feasibility and impact of transcriptome analysis in renal physiology. Comparison of transcriptomes demonstrates that cell lines are poor physiological models, making it necessary to work on native kidney tissue. Palliating kidney heterogeneity therefore requires the development of methods for transcriptome analysis sensitive enough to be compatible with microdissected nephron segments. Axial comparison of transcriptomes along the human nephron unexpectedly points out that the segmentation of nephrons concerns not only genes involved in solute and water transport functions and their regulation, but also genes related to the control of cell division, differentiation and apoptosis. Comparison of transcriptome of a same nephron segment from mice under different pathophysiological conditions outlines the wide pleiotropy of kidney function regulations. Both types of comparative studies also identify yet unknown transcripts specifically expressed along the nephron or under pathophysiological conditions.

Research paper thumbnail of A Novel H-NS-like Protein from an Antarctic Psychrophilic Bacterium Reveals a Crucial Role for the N-terminal Domain in Thermal Stability

Journal of Biological Chemistry, 2003

We describe here new members of the H-NS protein family identified in a psychrotrophic Acinetobac... more We describe here new members of the H-NS protein family identified in a psychrotrophic Acinetobacter spp. bacterium collected in Siberia and in a psychrophilic Psychrobacter spp. bacterium collected in Antarctica. Both are phylogenetically closely related to the HvrA and SPB Rhodobacter transcriptional regulators. Their amino acid sequence shares 40% identity, and their pre- dicted secondary structure displays a structural and

Research paper thumbnail of Environmental control of flagellar motility in prokaryotes: implication of DNA topology and nucleoid-associated proteins

Research paper thumbnail of Global Control of Cysteine Metabolism by CymR in Bacillus subtilis

Journal of Bacteriology, 2006

YrzC has previously been identified as a repressor controlling ytmI expression via its regulation... more YrzC has previously been identified as a repressor controlling ytmI expression via its regulation of YtlI activator synthesis in Bacillus subtilis. We identified YrzC as a master regulator of sulfur metabolism. Gene expression profiles of B. subtilis yrzC mutant and wild-type strains grown in minimal medium with sulfate as the sole sulfur source were compared. In the mutant, increased expression

Research paper thumbnail of Regulation of bacterial motility in response to low pH in Escherichia coli: the role of H-NS protein

Microbiology (Reading, England), 2002

The effect of detrimental conditions on bacterial motility in Escherichia coli was investigated. ... more The effect of detrimental conditions on bacterial motility in Escherichia coli was investigated. Expression profiling of mutant E. coli strains by DNA arrays and analysis of phenotypic traits demonstrated that motility and low-pH resistance are coordinately regulated. Analysis of transcriptional fusions suggests that bacterial motility in response to an acidic environment is mediated via the control by H-NS of flhDC expression. Moreover, the results suggested that the presence of an extended mRNA 5' end and DNA topology are required in this process. Finally, the presence of a similar regulatory region in several Gram-negative bacteria implies that this mechanism is largely conserved.

Research paper thumbnail of Riboswitch Discovery by Combining RNA-Seq and Genome-Wide Identification of Transcriptional Start Sites

Methods in Enzymology, 2014

Deep-sequencing technologies applied to RNA have tremendous potential to identify novel transcrip... more Deep-sequencing technologies applied to RNA have tremendous potential to identify novel transcripts with single-nucleotide resolution. By combining whole-transcript cDNA sequencing (RNA-seq) and genome-wide identification of transcription start sites (dRNA-seq), it is possible to characterize long 5'-untranslated regions potentially endowed with regulatory capacities and to detect premature termination of transcription. This can be used to identify new potential riboswitches. In this chapter, we provide a detailed protocol of the dRNA-seq method based on differential pretreatment of RNAs with tobacco acid pyrophosphatase to differentiate between 5'-ends of primary and processed RNAs. We also give a briefer protocol of the preparation of RNA-seq libraries and of how to go through data bioinformatics analysis and data visualization using genome browsers. This approach is powerful to identify novel riboswitches and to demonstrate the functionality of riboswitches predicted in silico.

Research paper thumbnail of Pleiotropic Role of the RNA Chaperone Protein Hfq in the Human Pathogen Clostridium difficile

Journal of Bacteriology, 2014

Clostridium difficile is an emergent human pathogen and the most common cause of nosocomial diarr... more Clostridium difficile is an emergent human pathogen and the most common cause of nosocomial diarrhea. Our recent data strongly suggest the importance of RNA-based mechanisms for the control of gene expression in C. difficile. In an effort to understand the function of the RNA chaperone protein Hfq, we constructed and characterized an Hfq-depleted strain in C. difficile. Hfq depletion led to a growth defect, morphological changes, an increased sensitivity to stresses, and a better ability to sporulate and to form biofilms. The transcriptome analysis revealed pleiotropic effects of Hfq depletion on gene expression in C. difficile, including genes encoding proteins involved in sporulation, stress response, metabolic pathways, cell wall-associated proteins, transporters, and transcriptional regulators and genes of unknown function. Remarkably, a great number of genes of the regulon dependent on sporulation-specific sigma factor, SigK, were upregulated in the Hfq-depleted strain. The altered accumulation of several sRNAs and interaction of Hfq with selected sRNAs suggest potential involvement of Hfq in these regulatory RNA functions. Altogether, these results suggest the pleiotropic role of Hfq protein in C. difficile physiology, including processes important for the C. difficile infection cycle, and expand our knowledge of Hfq-dependent regulation in Gram-positive bacteria.

Research paper thumbnail of Genome-Wide Identification of Regulatory RNAs in the Human Pathogen Clostridium difficile

PLoS Genetics, 2013

Clostridium difficile is an emergent pathogen, and the most common cause of nosocomial diarrhea. ... more Clostridium difficile is an emergent pathogen, and the most common cause of nosocomial diarrhea. In an effort to understand the role of small noncoding RNAs (sRNAs) in C. difficile physiology and pathogenesis, we used an in silico approach to identify 511 sRNA candidates in both intergenic and coding regions. In parallel, RNA-seq and differential 59-end RNA-seq were used for global identification of C. difficile sRNAs and their transcriptional start sites at three different growth conditions (exponential growth phase, stationary phase, and starvation). This global experimental approach identified 251 putative regulatory sRNAs including 94 potential trans riboregulators located in intergenic regions, 91 cis-antisense RNAs, and 66 riboswitches. Expression of 35 sRNAs was confirmed by gene-specific experimental approaches. Some sRNAs, including an antisense RNA that may be involved in control of C. difficile autolytic activity, showed growth phase-dependent expression profiles. Expression of each of 16 predicted c-di-GMP-responsive riboswitches was observed, and experimental evidence for their regulatory role in coordinated control of motility and biofilm formation was obtained. Finally, we detected abundant sRNAs encoded by multiple C. difficile CRISPR loci. These RNAs may be important for C. difficile survival in bacteriophage-rich gut communities. Altogether, this first experimental genome-wide identification of C. difficile sRNAs provides a firm basis for future RNome characterization and identification of molecular mechanisms of sRNA-based regulation of gene expression in this emergent enteropathogen.

Research paper thumbnail of Genome-Wide Analysis of Cell Type-Specific Gene Transcription during Spore Formation in Clostridium difficile

PLoS Genetics, 2013

Clostridium difficile, a Gram positive, anaerobic, spore-forming bacterium is an emergent pathoge... more Clostridium difficile, a Gram positive, anaerobic, spore-forming bacterium is an emergent pathogen and the most common cause of nosocomial diarrhea. Although transmission of C. difficile is mediated by contamination of the gut by spores, the regulatory cascade controlling spore formation remains poorly characterized. During Bacillus subtilis sporulation, a cascade of four sigma factors, s F and s G in the forespore and s E and s K in the mother cell governs compartment-specific gene expression. In this work, we combined genome wide transcriptional analyses and promoter mapping to define the C. difficile s F , s E , s G and s K regulons. We identified about 225 genes under the control of these sigma factors: 25 in the s F regulon, 97 s E -dependent genes, 50 s G -governed genes and 56 genes under s K control. A significant fraction of genes in each regulon is of unknown function but new candidates for spore coat proteins could be proposed as being synthesized under s E or s K control and detected in a previously published spore proteome. SpoIIID of C. difficile also plays a pivotal role in the mother cell line of expression repressing the transcription of many members of the s E regulon and activating sigK expression. Global analysis of developmental gene expression under the control of these sigma factors revealed deviations from the B. subtilis model regarding the communication between mother cell and forespore in C. difficile. We showed that the expression of the s E regulon in the mother cell was not strictly under the control of s F despite the fact that the forespore product SpoIIR was required for the processing of pro-s E . In addition, the s K regulon was not controlled by s G in C. difficile in agreement with the lack of pro-s K processing. This work is one key step to obtain new insights about the diversity and evolution of the sporulation process among Firmicutes.

Research paper thumbnail of Characterization of the SigD Regulon of C. difficile and Its Positive Control of Toxin Production through the Regulation of tcdR

Research paper thumbnail of Insights into the Rrf2 repressor family - the structure of CymR, the global cysteine regulator of Bacillus subtilis

Research paper thumbnail of RcsB plays a central role in H-NS-dependent regulation of motility and acid stress resistance in Escherichia coli

Research in Microbiology, 2010

In Escherichia coli, hns mutants lack flagellar motility and display an increase in acid stress r... more In Escherichia coli, hns mutants lack flagellar motility and display an increase in acid stress resistance. Spontaneous phenotypic revertants showed reversion of both H-NS-controlled phenotypes. In the present study, suppressor mutations were identified in the rcsB gene. In addition to RcsA, our experiments establish that H-NS indirectly controlled the RcsB regulator via repression of RcsD. We also show that RcsB D56E , mimicking phosphorylated RcsB, interacts with GadE to form a RcsB-P/GadE complex, a general direct regulator of glutamate-, arginine-and lysine-dependent acid resistance pathways. In addition, we showed that H-NS positively affects motility via the flhDC master operon repression by RcsB. This substantiates the central role of RcsB in H-NS-mediated control of motility and acid stress resistance.

Research paper thumbnail of Effect of mild acid pH on the functioning of bacterial membranes in Vibrio cholerae

PROTEOMICS, 2002

In this paper, we initiated the first two-dimensional electrophoresis map of Vibrio cholerae, the... more In this paper, we initiated the first two-dimensional electrophoresis map of Vibrio cholerae, the aetiological agent of cholera disease. In this pathogen the efficient adaptation to detrimental conditions plays an important role in its survival in both the aquatic reservoir and human intestine. By proteome analysis we investigated the effect of mild acid treatment on the physiology of V. cholerae. More than 50 proteins were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry and database searching. Amongst them, pH regulated proteins belong to various functional classes such as intermediary metabolism and bacterial envelope. Several proteins whose accumulation level was decreased in response to acidic pH are known to be involved in the organization and the functioning of membranes, including lipopolysaccharide. Consistent with this, we observed an increased susceptibility to hydrophobic drugs, a loss of motility and a reduction in the ability to form a biofilm in cells grown at pH 6. Our results suggest that V. cholerae is able to sense a moderate decrease in pH and to modify accordingly its structure and physiology.

Research paper thumbnail of Tissue Compartment Analysis for Biomarker Discovery by Gene Expression Profiling

PLoS ONE, 2009

Background: Although high throughput technologies for gene profiling are reliable tools, sample/t... more Background: Although high throughput technologies for gene profiling are reliable tools, sample/tissue heterogeneity limits their outcomes when applied to identify molecular markers. Indeed, inter-sample differences in cell composition contribute to scatter the data, preventing detection of small but relevant changes in gene expression level. To date, attempts to circumvent this difficulty were based on isolation of the different cell structures constituting biological samples. As an alternate approach, we developed a tissue compartment analysis (TCA) method to assess the cell composition of tissue samples, and applied it to standardize data and to identify biomarkers.

Research paper thumbnail of S-box and T-box riboswitches and antisense RNA control a sulfur metabolic operon of Clostridium acetobutylicum

Nucleic Acids Research, 2008

The ubiGmccBA operon of Clostridium acetobutylicum is involved in methionine to cysteine conversi... more The ubiGmccBA operon of Clostridium acetobutylicum is involved in methionine to cysteine conversion. We showed that its expression is controlled by a complex regulatory system combining several RNA-based mechanisms. Two functional convergent promoters associated with transcriptional antitermination systems, a cysteine-specific T-box and an S-box riboswitch, are located upstream of and downstream from the ubiG operon, respectively. Several antisense RNAs were synthesized from the downstream S-box-dependent promoter, resulting in modulation of the level of ubiG transcript and of MccB activity. In contrast, the upstream T-box system did not appear to play a major role in regulation, leaving antisense transcription as the major regulatory mechanism for the ubiG operon. The abundance of sense and antisense transcripts was inversely correlated with the sulfur source availability. Deletion of the downstream promoter region completely abolished the sulfur-dependent control of the ubiG operon, and the expression of antisense transcripts in trans did not restore the regulation of the operon. Our data revealed important insights into the molecular mechanism of cis-antisensemediated regulation, a control system only rarely observed in prokaryotes. We proposed a regulatory model in which the antisense RNA controlled the expression of the ubiG operon in cis via transcriptional interference at the ubiG locus.

Research paper thumbnail of Large-scale monitoring of pleiotropic regulation of gene expression by the prokaryotic nucleoid-associated protein, H-NS

Molecular Microbiology, 2001

Despite many years of intense work investigating the function of nucleoid-associated proteins in ... more Despite many years of intense work investigating the function of nucleoid-associated proteins in prokaryotes, their role in bacterial physiology remains largely unknown. The two-dimensional protein patterns were compared and expression profiling was carried out on H-NS-deficient and wild-type strains of Escherichia coli K-12. The expression of approximately 5% of the genes and/or the accumulation of their protein was directly or indirectly altered in the hns mutant strain. About one-fifth of these genes encode proteins that are involved in transcription or translation and one-third are known to or were in silico predicted to encode cell envelope components or proteins that are usually involved in bacterial adaptation to changes in environmental conditions. The increased expression of several genes in the mutant resulted in a better ability of this strain to survive at low pH and high osmolarity than the wildtype strain. In particular, the putative regulator, YhiX, plays a central role in the H-NS control of genes required in the glutamate-dependent acid stress response. These results suggest that there is a strong relationship between the H-NS regulon and the maintenance of intracellular homeostasis.

Research paper thumbnail of Global Control of Cysteine Metabolism by CymR in Bacillus subtilis

Journal of Bacteriology, 2006

YrzC has previously been identified as a repressor controlling ytmI expression via its regulation... more YrzC has previously been identified as a repressor controlling ytmI expression via its regulation of YtlI activator synthesis in Bacillus subtilis. We identified YrzC as a master regulator of sulfur metabolism. Gene expression profiles of B. subtilis ⌬yrzC mutant and wild-type strains grown in minimal medium with sulfate as the sole sulfur source were compared. In the mutant, increased expression was observed for 24 genes previously identified as repressed in the presence of sulfate. Since several genes involved in the pathways leading to cysteine formation were found, we propose to rename YrzC CymR, for "cysteine metabolism repressor." A CymR-dependent binding to the promoter region of the ytlI, ssuB, tcyP, yrrT, yxeK, cysK, or ydbM gene was demonstrated using gel shift experiments. A potential CymR target site, TAAWNCN 2 ANTWNAN 3 ATMGGAA TTW, was found in the promoter region of these genes. In a DNase footprint experiment, the protected region in the ytlI promoter region contained this consensus sequence. Partial deletion or introduction of point mutations in this sequence confirmed its involvement in ytlI, yrrT, and yxeK regulation. The addition of O-acetylserine in gel shift experiments prevented CymR-dependent binding to DNA for all of the targets characterized. Transcriptome analysis of a ⌬cymR mutant and the wild-type strain also brought out significant changes in the expression level of a large set of genes related to stress response or to transition toward anaerobiosis.

Research paper thumbnail of Conversion of Methionine to Cysteine in Bacillus subtilis and Its Regulation

Journal of Bacteriology, 2007

Bacillus subtilis can use methionine as the sole sulfur source, indicating an efficient conversio... more Bacillus subtilis can use methionine as the sole sulfur source, indicating an efficient conversion of methionine to cysteine. To characterize this pathway, the enzymatic activities of CysK, YrhA and YrhB purified in Escherichia coli were tested. Both CysK and YrhA have an O-acetylserine-thiol-lyase activity, but YrhA was 75-fold less active than CysK. An atypical cystathionine ␤-synthase activity using O-acetylserine and homocysteine as substrates was observed for YrhA but not for CysK. The YrhB protein had both cystathionine lyase and homocysteine ␥-lyase activities in vitro. Due to their activity, we propose that YrhA and YrhB should be renamed MccA and MccB for methionine-to-cysteine conversion. Mutants inactivated for cysK or yrhB grew similarly to the wild-type strain in the presence of methionine. In contrast, the growth of an ⌬yrhA mutant or a luxS mutant, inactivated for the S-ribosyl-homocysteinase step of the S-adenosylmethionine recycling pathway, was strongly reduced with methionine, whereas a ⌬yrhA ⌬cysK or cysE mutant did not grow at all under the same conditions. The yrhB and yrhA genes form an operon together with yrrT, mtnN, and yrhC. The expression of the yrrT operon was repressed in the presence of sulfate or cysteine. Both purified CysK and CymR, the global repressor of cysteine metabolism, were required to observe the formation of a protein-DNA complex with the yrrT promoter region in gel-shift experiments. The addition of O-acetyl-serine prevented the formation of this protein-DNA complex.