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Susan Gottesman - One of the best experts on this subject based on the ideXlab platform.
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Stress Sigma Factor RpoS degradation and translation are sensitive to the state of central metabolism
Proceedings of the National Academy of Sciences of the United States of America, 2015Co-Authors: Aurelia Battesti, Nadim Majdalani, Susan GottesmanAbstract:RpoS, the stationary phase/stress Sigma Factor of Escherichia coli, regulates a large cohort of genes important for the cell to deal with suboptimal conditions. Its level increases quickly in the cell in response to many stresses and returns to low levels when growth resumes. Increased RpoS results from increased translation and decreased RpoS degradation. Translation is positively regulated by small RNAs (sRNAs). Protein stability is positively regulated by anti-adaptors, which prevent the RssB adaptor-mediated degradation of RpoS by the ClpXP protease. Inactivation of aceE, a subunit of pyruvate dehydrogenase (PDH), was found to increase levels of RpoS by affecting both translation and protein degradation. The stabilization of RpoS in aceE mutants is dependent on increased transcription and translation of IraP and IraD, two known anti-adaptors. The aceE mutation also leads to a significant increase in RpoS translation. The sRNAs known to positively regulate RpoS are not responsible for the increased translation; sequences around the start codon are sufficient for the induction of translation. PDH synthesizes acetyl-CoA; acetate supplementation allows the cell to synthesize acetyl-CoA by an alternative, less favored pathway, in part dependent upon RpoS. Acetate addition suppressed the effects of the aceE mutant on induction of the anti-adaptors, RpoS stabilization, and RpoS translation. Thus, the bacterial cell responds to lowered levels of acetyl-CoA by inducing RpoS, allowing reprogramming of E. coli metabolism.
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the RpoS mediated general stress response in escherichia coli
Annual Review of Microbiology, 2011Co-Authors: Aurelia Battesti, Nadim Majdalani, Susan GottesmanAbstract:Under conditions of nutrient deprivation or stress, or as cells enter stationary phase, Escherichia coli and related bacteria increase the accumulation of RpoS, a specialized Sigma Factor. RpoS-dependent gene expression leads to general stress resistance of cells. During rapid growth, RpoS translation is inhibited and any RpoS protein that is synthesized is rapidly degraded. The complex transition from exponential growth to stationary phase has been partially dissected by analyzing the induction of RpoS after specific stress treatments. Different stress conditions lead to induction of specific sRNAs that stimulate RpoS translation or to induction of small-protein antiadaptors that stabilize the protein. Recent progress has led to a better, but still far from complete, understanding of how stresses lead to RpoS induction and what RpoS-dependent genes help the cell deal with the stress.
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the phop phoq two component system stabilizes the alternative Sigma Factor RpoS in salmonella enterica
Proceedings of the National Academy of Sciences of the United States of America, 2006Co-Authors: Tammy Latifi, Susan Gottesman, Alexandre Bougdour, Eduardo A GroismanAbstract:The Sigma Factor RpoS regulates the expression of many stress response genes and is required for virulence in several bacterial species. We now report that RpoS accumulates when Salmonella enterica serovar Typhimurium is growing logarithmically in media with low Mg2+ concentrations. This process requires the two-component regulatory system PhoP/PhoQ, which is specifically activated in low Mg2+. We show that PhoP controls RpoS protein turnover by serving as a transcriptional activator of the iraP (yaiB) gene, which encodes a product that enhances RpoS stability by interacting with RssB, the protein that normally delivers RpoS to the ClpXP protease for degradation. Mutation of the phoP gene rendered Salmonella as sensitive to hydrogen peroxide as an RpoS mutant after growth in low Mg2+. In Escherichia coli, low Mg2+ leads to only modest RpoS stabilization, and iraP is not regulated by PhoP/PhoQ. These findings add the Sigma Factor RpoS to the regulatory proteins and two-component systems that are elevated in a PhoP/PhoQ-dependent fashion when Salmonella face low Mg2+ environments. Our data also exemplify the critical differences in regulatory circuits that exist between the closely related enteric bacteria Salmonella and E. coli.
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regulation and mode of action of the second small rna activator of RpoS translation rpra
Molecular Microbiology, 2002Co-Authors: Nadim Majdalani, David Hernandez, Susan GottesmanAbstract:Translation of the stationary phase Sigma Factor RpoS is stimulated by at least two small RNAs, DsrA and RprA. DsrA disrupts an inhibitory secondary structure in the RpoS leader mRNA by pairing with the upstream RNA. Mutations in rprA and compensating mutations in the RpoS leader demonstrate that RprA interacts with the same region of the RpoS leader as DsrA. This is the first example of two different small RNAs regulating a common target. Regulation of these RNAs differs. DsrA synthesis is increased at low temperature. We find that RprA synthesis is regulated by the RcsC/RcsB phosphorelay system, previously found to regulate capsule synthesis and promoters of ftsZ and osmC. An rcsB null mutation abolishes the basal level, whereas mutations in rcsC that activate capsule synthesis also activate expression of the rprA promoter. An essential site with similarity to other RcsB-regulated promoters was defined in the rprA promoter. Activation of the RcsC/RcsB system leads to increased RpoS synthesis, in an RprA-dependent fashion. This work suggests a new signal for RpoS translation and extends the global regulation effected by the RcsC/RcsB system to coregulation of RpoS with capsule and FtsZ.
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regulation of RpoS by a novel small rna the characterization of rpra
Molecular Microbiology, 2001Co-Authors: Nadim Majdalani, Susan Gottesman, Suann Chen, Jonathan R Murrow, Kristin St JohnAbstract:Translational regulation of the stationary phase Sigma Factor RpoS is mediated by the formation of a double-stranded RNA stem-loop structure in the upstream region of the RpoS messenger RNA, occluding the translation initiation site. The interaction of the RpoS mRNA with a small RNA, DsrA, disrupts the double-strand pairing and allows high levels of translation initiation. We screened a multicopy library of Escherichia coli DNA fragments for novel activators of RpoS translation when DsrA is absent. Clones carrying rprA (RpoS regulator RNA) increased the translation of RpoS. The rprA gene encodes a 106 nucleotide regulatory RNA. As with DsrA, RprA is predicted to form three stem-loops and is highly conserved in Salmonella and Klebsiella species. Thus, at least two small RNAs, DsrA and RprA, participate in the positive regulation of RpoS translation. Unlike DsrA, RprA does not have an extensive region of complementarity to the RpoS leader, leaving its mechanism of action unclear. RprA is non-essential. Mutations in the gene interfere with the induction of RpoS after osmotic shock when DsrA is absent, demonstrating a physiological role for RprA. The existence of two very different small RNA regulators of RpoS translation suggests that such additional regulatory RNAs are likely to exist, both for regulation of RpoS and for regulation of other important cellular components.
Justin D Radolf - One of the best experts on this subject based on the ideXlab platform.
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borrelia burgdorferi requires the alternative Sigma Factor RpoS for dissemination within the vector during tick to mammal transmission
PLOS Pathogens, 2012Co-Authors: Star Dunhamems, Christian H Eggers, Melissa J Caimano, Justin D RadolfAbstract:While the roles of RpoSBb and RpoS-dependent genes have been studied extensively within the mammal, the contribution of the RpoS regulon to the tick-phase of the Borrelia burgdorferi enzootic cycle has not been examined. Herein, we demonstrate that RpoS-dependent gene expression is prerequisite for the transmission of spirochetes by feeding nymphs. RpoS-deficient organisms are confined to the midgut lumen where they transform into an unusual morphotype (round bodies) during the later stages of the blood meal. We show that round body formation is rapidly reversible, and in vitro appears to be attributable, in part, to reduced levels of Coenzyme A disulfide reductase, which among other functions, provides NAD+ for glycolysis. Our data suggest that spirochetes default to an RpoS-independent program for round body formation upon sensing that the energetics for transmission are unfavorable.
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analysis of the RpoS regulon in borrelia burgdorferi in response to mammalian host signals provides insight into RpoS function during the enzootic cycle
Molecular Microbiology, 2007Co-Authors: Melissa J Caimano, Christian H Eggers, Cynthia M Gonzalez, Elizabeth A Morton, Michael A Gilbert, Radha Iyer, Ira Schwartz, Justin D RadolfAbstract:Borrelia burgdorferi (Bb) adapts to its arthropod and mammalian hosts by altering its transcriptional and antigenic profiles in response to environmental signals associated with each of these milieus. In studies presented here, we provide evidence to suggest that mammalian host signals are important for modulating and maintaining both the positive and negative aspects of mammalian host adaptation mediated by the alternative Sigma Factor RpoS in Bb. Although considerable overlap was observed between genes induced by RpoS during growth within the mammalian host and following temperature-shift, comparative microarray analyses demonstrated unequivocally that RpoS-mediated repression requires mammalian host-specific signals. A substantial portion of the in vivo RpoS regulon was uniquely upregulated within dialysis membrane chambers, further underscoring the importance of host-derived environmental stimuli for differential gene expression in Bb. Expression profiling of genes within the RpoS regulon by quantitative reverse transcription polymerase chain reaction (qRT-PCR) revealed a level of complexity to RpoS-dependent gene regulation beyond that observed by microarray, including a broad range of expression levels and the presence of genes whose expression is only partially dependent on RpoS. Analysis of Bb-infected ticks by qRT-PCR established that expression of RpoS is induced during the nymphal blood meal but not within unfed nymphs or engorged larvae. Together, these data have led us to postulate that RpoS acts as a gatekeeper for the reciprocal regulation of genes involved in the establishment of infection within the mammalian host and the maintenance of spirochetes within the arthropod vector.
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alternate Sigma Factor RpoS is required for the in vivo specific repression of borrelia burgdorferi plasmid lp54 borne ospa and lp6 6 genes
Journal of Bacteriology, 2005Co-Authors: Melissa J Caimano, Christian H Eggers, Cynthia A Gonzalez, Justin D RadolfAbstract:While numerous positively regulated loci have been characterized during the enzootic cycle of Borrelia burgdorferi, very little is known about the mechanism(s) involved in the repression of borrelial loci either during tick feeding or within the mammalian host. Here, we report that the alternative Sigma Factor RpoS is required for the in vivo-specific repression of at least two RpoD-dependent B. burgdorferi loci, ospA and lp6.6. The downregulation of ospA and Ip6.6 appears to require either a repressor molecule whose expression is RpoS dependent or an accessory Factor which enables RpoS to directly interact with the ospA and Ip6.6 promoter elements, thereby blocking transcription by RpoD. The central role for RpoS during the earliest stages of host adaptation suggests that tick feeding imparts signals to spirochetes that trigger the RpoS-dependent repression, as well as expression, of in vivo-specific virulence Factors critical for the tick-to-mammalian host transition.
Daniel Segura - One of the best experts on this subject based on the ideXlab platform.
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the gacs a rsma signal transduction pathway controls the synthesis of alkylresorcinol lipids that replace membrane phospholipids during encystment of azotobacter vinelandii sw136
PLOS ONE, 2016Co-Authors: Yanet Romero, Miguel Cocotlyanez, Miguel Castaneda, Josefina Guzman, Miguel Angel Vencesguzman, Soledad Moreno, Guadalupe Espin, Daniel SeguraAbstract:Azotobacter vinelandii is a soil bacterium that undergoes a differentiation process that forms cysts resistant to desiccation. During encystment, a family of alkylresorcinols lipids (ARs) are synthesized and become part of the membrane and are also components of the outer layer covering the cyst, where they play a structural role. The synthesis of ARs in A. vinelandii has been shown to occur by the activity of enzymes encoded in the arsABCD operon. The expression of this operon is activated by ArpR, a LysR-type transcriptional regulator whose transcription occurs during encystment and is dependent on the alternative Sigma Factor RpoS. In this study, we show that the two component response regulator GacA, the small RNA RsmZ1 and the translational repressor protein RsmA, implicated in the control of the synthesis of other cysts components (i.e., alginate and poly-s-hydroxybutyrate), are also controlling alkylresorcinol synthesis. This control affects the expression of arsABCD and is exerted through the regulation of arpR expression. We show that RsmA negatively regulates arpR expression by binding its mRNA, repressing its translation. GacA in turn, positively regulates arpR expression through the activation of transcription of RsmZ1, that binds RsmA, counteracting its repressor activity. This regulatory cascade is independent of RpoS. We also show evidence suggesting that GacA exerts an additional regulation on arsABCD expression through an ArpR independent route.
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The GacS/A-RsmA Signal Transduction Pathway Controls the Synthesis of Alkylresorcinol Lipids that Replace Membrane Phospholipids during Encystment of Azotobacter vinelandii SW136
2016Co-Authors: Yanet Romero, Miguel Castaneda, Josefina Guzman, Soledad Moreno, Guadalupe Espin, Miguel Cocotl-yañez, Miguel Ángel Vences-guzmán, Daniel SeguraAbstract:Azotobacter vinelandii is a soil bacterium that undergoes a differentiation process that forms cysts resistant to desiccation. During encystment, a family of alkylresorcinols lipids (ARs) are synthesized and become part of the membrane and are also components of the outer layer covering the cyst, where they play a structural role. The synthesis of ARs in A. vinelandii has been shown to occur by the activity of enzymes encoded in the arsABCD operon. The expression of this operon is activated by ArpR, a LysR-type transcriptional regulator whose transcription occurs during encystment and is dependent on the alternative Sigma Factor RpoS. In this study, we show that the two component response regulator GacA, the small RNA RsmZ1 and the translational repressor protein RsmA, implicated in the control of the synthesis of other cysts components (i.e., alginate and poly-ß-hydroxybutyrate), are also controlling alkylresorcinol synthesis. This control affects the expression of arsABCD and is exerted through the regulation of arpR expression. We show that RsmA negatively regulates arpR expression by binding its mRNA, repressing its translation. GacA in turn, positively regulates arpR expression through the activation of transcription of RsmZ1, that binds RsmA, counteracting its repressor activity. This regulatory cascade is independent of RpoS. We also show evidence suggesting that GacA exerts an additional regulation on arsABCD expression through an ArpR independent route.
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Sigma Factor RpoS controls alkylresorcinol synthesis through arpr a lysr type regulatory protein during encystment of azotobacter vinelandii
Journal of Bacteriology, 2013Co-Authors: Yanet Romero, Josefina Guzman, Soledad Moreno, Guadalupe Espin, Daniel SeguraAbstract:Azotobacter vinelandii is a bacterium which undergoes a differentiation process leading to the formation of metabolically dormant cysts. During the encystment process, A. vinelandii produces alkylresorcinol lipids (ARs) that replace the membrane phospholipids and are also components of the layers covering the cyst. The synthesis of ARs in A. vinelandii has been shown to occur by the activity of enzymes encoded by the arsABCD operon, which is expressed only during the differentiation process. Also, the production of ARs has been shown to be dependent on the stationary-phase Sigma Factor RpoS, which is also implicated in the control of the synthesis of other cyst components (i.e., alginate and poly-β-hydroxybutyrate). In this study, we identified ArpR, a LysR-type transcriptional regulator expressed only during encystment that positively regulates arsABCD transcription. We show that this activation is dependent on acetoacetyl-coenzyme A (acetoacetyl-CoA), which might provide a metabolic signal for encystment. We also show that RpoS regulates arsABCD expression through the control of arpR transcription.
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roles of RpoS and psra in cyst formation and alkylresorcinol synthesis in azotobacter vinelandii
Microbiology, 2011Co-Authors: Miguel Cocotlyanez, Aristides Iii Sampieri, Miguel Castaneda, Cinthia Núñez, Soledad Moreno, Daniel Segura, Guadalupe EspinAbstract:Azotobacter vinelandii is a soil bacterium that undergoes differentiation to form cysts that are resistant to desiccation. Upon induction of cyst formation, the bacterium synthesizes alkylresorcinols that are present in cysts but not in vegetative cells. Alternative Sigma Factors play important roles in differentiation. In A. vinelandii, AlgU (Sigma E) is involved in controlling the loss of flagella upon induction of encystment. We investigated the involvement of the Sigma Factor RpoS in cyst formation in A. vinelandii. We analysed the transcriptional regulation of the RpoS gene by PsrA, the main regulator of RpoS in Pseudomonas species, which are closely related to A. vinelandii. Inactivation of RpoS resulted in the inability to form cysts resistant to desiccation and to produce cyst-specific alkylresorcinols, whereas inactivation of psrA reduced by 50 % both production of alkylresorcinols and formation of cysts resistant to desiccation. Electrophoretic mobility shift assays revealed specific binding of PsrA to the RpoS promoter region and that inactivation of psrA reduced RpoS transcription by 60 %. These results indicate that RpoS and PsrA are involved in regulation of encystment and alkylresorcinol synthesis in A. vinelandii.
Dieter Haas - One of the best experts on this subject based on the ideXlab platform.
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role of the stress Sigma Factor RpoS in gaca rsma controlled secondary metabolism and resistance to oxidative stress in pseudomonas fluorescens cha0
Fems Microbiology Letters, 2005Co-Authors: Stephan Heeb, Claudio Valverde, Ca Cile Gigotbonnefoy, Dieter HaasAbstract:In Pseudomonas fluorescens biocontrol strain CHA0, the two-component system GacS/GacA positively controls the synthesis of extracellular products such as hydrogen cyanide, protease, and 2,4-diacetylphloroglucinol, by upregulating the transcription of small regulatory RNAs which relieve RsmA-mediated translational repression of target genes. The expression of the stress Sigma Factor SigmaS (RpoS) was controlled positively by GacA and negatively by RsmA. By comparison with the wild-type CHA0, both a gacS and an RpoS null mutant were more sensitive to H2O2 in stationary phase. Overexpression of RpoS or of rsmZ, encoding a small RNA antagonistic to RsmA, restored peroxide resistance to a gacS mutant. By contrast, the RpoS mutant showed a slight increase in the expression of the hcnA (HCN synthase subunit) gene and of the aprA (major exoprotease) gene, whereas overexpression of SigmaS strongly reduced the expression of these genes. These results suggest that in strain CHA0, regulation of exoproduct synthesis does not involve SigmaS as an intermediate in the Gac/Rsm signal transduction pathway whereas SigmaS participates in Gac/Rsm-mediated resistance to oxidative stress.
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regulatory rna as mediator in gaca rsma dependent global control of exoproduct formation in pseudomonas fluorescens cha0
Journal of Bacteriology, 2002Co-Authors: Stephan Heeb, Caroline Blumer, Dieter HaasAbstract:In Pseudomonas fluorescens CHA0, an antagonist of root-pathogenic fungi, the GacS/GacA two-component system tightly controls the expression of antifungal secondary metabolites and exoenzymes at a posttranscriptional level, involving the RNA-binding protein and global regulator of secondary metabolism RsmA. This protein was purified from P. fluorescens, and RNA bound to it was converted to cDNA, which served as a probe to isolate the corresponding chromosomal locus, rsmZ. This gene encoded a regulatory RNA of 127 nucleotides and a truncated form lacking 35 nucleotides at the 3" end. Expression of rsmZ depended on GacA, increased with increasing population density, and was stimulated by the addition of a solvent-extractable extracellular signal produced by strain CHA0 at the end of exponential growth. This signal appeared to be unrelated to N-acyl-homoserine lactones. A conserved upstream element in the rsmZ promoter, but not the stress Sigma Factor RpoS, was involved in rsmZ expression. Overexpression of rsmZ effectively suppressed the negative effect of gacS and gacA mutations on target genes, i.e., hcnA (for hydrogen cyanide synthase) and aprA (for the major exoprotease). Mutational inactivation of rsmZ resulted in reduced expression of these target genes in the presence of added signal. Overexpression of rsmA had a similar, albeit stronger negative effect. These results support a model in which GacA upregulates the expression of regulatory RNAs, such as RsmZ of strain CHA0, in response to a bacterial signal. By a titration effect, RsmZ may then alleviate the repressing activity of RsmA on the expression of target mRNAs.
Stephan Heeb - One of the best experts on this subject based on the ideXlab platform.
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role of the stress Sigma Factor RpoS in gaca rsma controlled secondary metabolism and resistance to oxidative stress in pseudomonas fluorescens cha0
Fems Microbiology Letters, 2005Co-Authors: Stephan Heeb, Claudio Valverde, Ca Cile Gigotbonnefoy, Dieter HaasAbstract:In Pseudomonas fluorescens biocontrol strain CHA0, the two-component system GacS/GacA positively controls the synthesis of extracellular products such as hydrogen cyanide, protease, and 2,4-diacetylphloroglucinol, by upregulating the transcription of small regulatory RNAs which relieve RsmA-mediated translational repression of target genes. The expression of the stress Sigma Factor SigmaS (RpoS) was controlled positively by GacA and negatively by RsmA. By comparison with the wild-type CHA0, both a gacS and an RpoS null mutant were more sensitive to H2O2 in stationary phase. Overexpression of RpoS or of rsmZ, encoding a small RNA antagonistic to RsmA, restored peroxide resistance to a gacS mutant. By contrast, the RpoS mutant showed a slight increase in the expression of the hcnA (HCN synthase subunit) gene and of the aprA (major exoprotease) gene, whereas overexpression of SigmaS strongly reduced the expression of these genes. These results suggest that in strain CHA0, regulation of exoproduct synthesis does not involve SigmaS as an intermediate in the Gac/Rsm signal transduction pathway whereas SigmaS participates in Gac/Rsm-mediated resistance to oxidative stress.
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regulatory rna as mediator in gaca rsma dependent global control of exoproduct formation in pseudomonas fluorescens cha0
Journal of Bacteriology, 2002Co-Authors: Stephan Heeb, Caroline Blumer, Dieter HaasAbstract:In Pseudomonas fluorescens CHA0, an antagonist of root-pathogenic fungi, the GacS/GacA two-component system tightly controls the expression of antifungal secondary metabolites and exoenzymes at a posttranscriptional level, involving the RNA-binding protein and global regulator of secondary metabolism RsmA. This protein was purified from P. fluorescens, and RNA bound to it was converted to cDNA, which served as a probe to isolate the corresponding chromosomal locus, rsmZ. This gene encoded a regulatory RNA of 127 nucleotides and a truncated form lacking 35 nucleotides at the 3" end. Expression of rsmZ depended on GacA, increased with increasing population density, and was stimulated by the addition of a solvent-extractable extracellular signal produced by strain CHA0 at the end of exponential growth. This signal appeared to be unrelated to N-acyl-homoserine lactones. A conserved upstream element in the rsmZ promoter, but not the stress Sigma Factor RpoS, was involved in rsmZ expression. Overexpression of rsmZ effectively suppressed the negative effect of gacS and gacA mutations on target genes, i.e., hcnA (for hydrogen cyanide synthase) and aprA (for the major exoprotease). Mutational inactivation of rsmZ resulted in reduced expression of these target genes in the presence of added signal. Overexpression of rsmA had a similar, albeit stronger negative effect. These results support a model in which GacA upregulates the expression of regulatory RNAs, such as RsmZ of strain CHA0, in response to a bacterial signal. By a titration effect, RsmZ may then alleviate the repressing activity of RsmA on the expression of target mRNAs.