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Horvat M, Pannuri A, Romeo T, Dogsa I, Stopar D. Viscoelastic response of Escherichia coli biofilms to genetically altered expression of extracellular matrix components. SOFT MATTER 2019; 15:5042-5051. [PMID: 31179461 DOI: 10.1039/c9sm00297a] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
How the viscoelastic properties of the extracellular matrix affect the various biological functions conferred by biofilms is an important question in microbiology. In this study, the viscoelastic response of Escherichia coli biofilms to the genetically altered expression of extracellular matrix components was studied. Biofilms of the wild type E. coli MG1655 and its mutant strains producing different amounts of extracellular matrix components (curli, colanic acid, and poly-β-1,6-N-acetyl-d-glucosamine) were used to examine the viscoelastic behavior of biofilms grown at the solid-atmosphere interface. The results suggest that the presence of curli proteins dominates biofilm mechanical behavior. The rheological data indicate that the cohesive energy of the biofilm was the highest in the wild type strain. The results demonstrate the importance of extracellular matrix composition for biofilm mechanical properties. We propose that by genetically altering the expression of extracellular matrix polymers, bacteria are able to modulate the mechanical properties of their local environment in accordance with bulk environmental conditions.
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Affiliation(s)
- Maruša Horvat
- University of Ljubljana, Biotechnical Faculty, Chair of Microbiology, Department of Food Science and Technology, Večna pot 111, 1000 Ljubljana, Slovenia.
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102
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Vibrio cholerae CsrA Directly Regulates varA To Increase Expression of the Three Nonredundant Csr Small RNAs. mBio 2019; 10:mBio.01042-19. [PMID: 31164471 PMCID: PMC6550530 DOI: 10.1128/mbio.01042-19] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
CsrA, an RNA-binding global regulator, is an essential protein in Vibrio choleraeV. cholerae CsrA is regulated by three small RNAs (sRNAs), namely, CsrB, CsrC, and CsrD, which act to sequester and antagonize the activity of CsrA. Although the sRNAs were considered to be largely redundant, we found that they differ in expression, half-life, and the ability to regulate CsrA. Further, we identified a feedback loop in the Csr system in which CsrA increases the synthesis of these antagonistic sRNAs. Because the Csr sRNAs are positively regulated by VarA, we determined the effects of CsrA on VarA levels. The level of VarA was reduced in a csrA mutant, and we found that CsrA directly bound to varA mRNA in an electrophoretic mobility shift assay in vitro and in an CsrA-RNA immunoprecipitation assay in vivo Thus, varA mRNA is an in vivo-verified direct target of CsrA in V. cholerae, and this is the first demonstration of CsrA directly binding to a varA/uvrY/gacA homolog. Additionally, we demonstrated that a varA translational fusion was less active in a csrA mutant than in wild-type V. cholerae, suggesting that CsrA enhances varA translation. We propose that this autoregulatory feedback loop, in which CsrA increases the production of the nonredundant Csr sRNAs by regulating the amount of VarA, provides a mechanism for fine-tuning the availability of CsrA and, thus, of its downstream targets.IMPORTANCEVibrio cholerae is a major human pathogen, causing epidemics and pandemics of cholera. V. cholerae persists in the aquatic environment, providing a constant source for human infection. Success in transitioning from the environment to the human host and back requires the bacterium to rapidly respond and to adjust its gene expression and metabolism to these two very different habitats. Our findings show that CsrA, an RNA-binding regulatory protein, plays a central role in regulating these transitions. CsrA activity is controlled by the antagonistic sRNAs CsrB, CsrC, and CsrD, and these sRNAs respond to changes in the availability of nutrients. CsrA autoregulates its own activity by controlling these sRNAs via their primary regulator VarA. Thus, the change in CsrA availability in response to nutrient availability allows V. cholerae to alter gene expression in response to environmental cues.
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103
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Robust Stoichiometry of FliW-CsrA Governs Flagellin Homeostasis and Cytoplasmic Organization in Bacillus subtilis. mBio 2019; 10:mBio.00533-19. [PMID: 31113895 PMCID: PMC6529632 DOI: 10.1128/mbio.00533-19] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The intracellular concentration of flagellar filament protein Hag is restricted by the Hag-FliW-CsrA system in B. subtilis. Here we show that the Hag-FliW-CsrAdimer system functions at nearly 1:1:1 stoichiometry and that the system is both robust with respect to perturbation and hypersensitive to the Hag intracellular concentration. Moreover, restriction of cytoplasmic Hag levels is important for maintaining proper intracellular architecture, as artificial Hag hyperaccumulation led to generalized spatial defects and a high frequency of minicell production. The Hag-FliW-CsrA system is conserved in the deeper branches of bacterial phylogeny, and we note that the Hag-FliW-CsrA “homeostasis module” resembles a toxin-antitoxin system where, by analogy, CsrA is the “toxin,” FliW is the “antitoxin,” and Hag is the target. Flagellin (Hag) is one of the most abundant proteins in Bacillus subtilis. Here we show that each flagellar filament is assembled from ∼12,000 Hag monomers and that there is a cytoplasmic pool of Hag that is restricted to 5% of the total. Hag is thought to be restricted at the level of translation by a partner-switching mechanism involving FliW and the homodimeric RNA-binding protein CsrA (CsrAdimer). We further show that the mechanism of translation inhibition is hypersensitive due to a 1:1 ratio of Hag to FliW, a 1:1 inhibitory ratio of FliW to CsrAdimer, and a nearly 1:1 ratio of CsrAdimer to hag transcripts. Equimolarity of all components couples single-molecule detection of Hag export to compensatory translation and causes cytoplasmic Hag concentrations to oscillate around the level of FliW. We found that stoichiometry is ensured by genetic architecture, translational coupling, and the ability of CsrAdimer to restrict hag transcript accumulation. We further show that homeostasis prevents Hag hyperaccumulation that would otherwise cause severe defects in intracellular architecture, perhaps due to increased molecular crowding. We note that FliW-CsrA-mediated structural homeostasis has similarities to that seen with some toxin-antitoxin systems.
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104
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Müller P, Gimpel M, Wildenhain T, Brantl S. A new role for CsrA: promotion of complex formation between an sRNA and its mRNA target in Bacillus subtilis. RNA Biol 2019; 16:972-987. [PMID: 31043113 PMCID: PMC6546359 DOI: 10.1080/15476286.2019.1605811] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
CsrA is a widely conserved, abundant small RNA binding protein that has been found in E. coli and other Gram-negative bacteria where it is involved in the regulation of carbon metabolism, biofilm formation and virulence. CsrA binds to single-stranded GGA motifs around the SD sequence of target mRNAs where it inhibits or activates translation or influences RNA processing. Small RNAs like CsrB or CsrC containing 13–22 GGA motifs can sequester CsrA, thereby abrogating the effect of CsrA on its target mRNAs. In B. subtilis, CsrA has so far only been found to regulate one target, hag mRNA and to be sequestered by a protein (FliW) and not by an sRNA. Here, we employ a combination of in vitro and in vivo methods to investigate the effect of CsrA on the small regulatory RNA SR1 from B. subtilis, its primary target ahrC mRNA and its downstream targets, the rocABC and rocDEF operons. We demonstrate that CsrA can promote the base-pairing interactions between SR1 and ahrC mRNA, a function that has so far only been found for Hfq or ProQ. Abbreviations: aa, amino acid; bp, basepair; nt, nucleotide; PAA, polyacrylamide; SD, Shine Dalgarno.
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Affiliation(s)
- Peter Müller
- a Matthias-Schleiden-Institut für Genetik, Bioinformatik und Molekulare Botanik, AG Bakteriengenetik , Friedrich-Schiller-Universität Jena , Jena , Germany
| | - Matthias Gimpel
- a Matthias-Schleiden-Institut für Genetik, Bioinformatik und Molekulare Botanik, AG Bakteriengenetik , Friedrich-Schiller-Universität Jena , Jena , Germany.,b Institut für Biotechnologie , Fachgebiet Bioverfahrenstechnik , Berlin , Germany
| | - Theresa Wildenhain
- a Matthias-Schleiden-Institut für Genetik, Bioinformatik und Molekulare Botanik, AG Bakteriengenetik , Friedrich-Schiller-Universität Jena , Jena , Germany
| | - Sabine Brantl
- a Matthias-Schleiden-Institut für Genetik, Bioinformatik und Molekulare Botanik, AG Bakteriengenetik , Friedrich-Schiller-Universität Jena , Jena , Germany
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105
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González-Flores YE, de Dios R, Reyes-Ramírez F, Santero E. The response of Sphingopyxis granuli strain TFA to the hostile anoxic condition. Sci Rep 2019; 9:6297. [PMID: 31000749 PMCID: PMC6472365 DOI: 10.1038/s41598-019-42768-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Accepted: 04/05/2019] [Indexed: 01/02/2023] Open
Abstract
Sphingomonads comprises a group of interesting aerobic bacteria because of their ubiquity and metabolic capability of degrading many recalcitrant contaminants. The tetralin-degrader Sphingopyxis granuli strain TFA has been recently reported as able to anaerobically grow using nitrate as the alternative electron acceptor and so far is the only bacterium with this ability within the sphingomonads group. To understand how strain TFA thrives under anoxic conditions, a differential transcriptomic analysis while growing under aerobic or anoxic conditions was performed. This analysis has been validated and complemented with transcription kinetics of representative genes of different functional categories. Results show an extensive change of the expression pattern of this strain in the different conditions. Consistently, the most induced operon in anoxia codes for proteases, presumably required for extensive changes in the protein profile. Besides genes that respond to lack of oxygen in other bacteria, there are a number of genes that respond to stress or to damage of macromolecules, including genes of the SOS DNA-damage response, which suggest that anoxic conditions represent a hostile environment for this bacterium. Interestingly, growth under anoxic conditions also resulted in repression of all flagellar and type IV pilin genes, which suggested that this strain shaves its appendages off while growing in anaerobiosis.
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Affiliation(s)
- Yolanda Elisabet González-Flores
- Centro Andaluz de Biología del Desarrollo/CSIC/Universidad Pablo de Olavide/Junta de Andalucía. Departamento de Biología Molecular e Ingeniería Bioquímica, Seville, Spain
| | - Rubén de Dios
- Centro Andaluz de Biología del Desarrollo/CSIC/Universidad Pablo de Olavide/Junta de Andalucía. Departamento de Biología Molecular e Ingeniería Bioquímica, Seville, Spain
| | - Francisca Reyes-Ramírez
- Centro Andaluz de Biología del Desarrollo/CSIC/Universidad Pablo de Olavide/Junta de Andalucía. Departamento de Biología Molecular e Ingeniería Bioquímica, Seville, Spain.
| | - Eduardo Santero
- Centro Andaluz de Biología del Desarrollo/CSIC/Universidad Pablo de Olavide/Junta de Andalucía. Departamento de Biología Molecular e Ingeniería Bioquímica, Seville, Spain
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106
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Monson RE, Apagyi K, Bowden SD, Simpson N, Williamson NR, Cubitt MF, Harris S, Toth IK, Salmond GPC. The rsmS (ybaM) mutation causes bypass suppression of the RsmAB post-transcriptional virulence regulation system in enterobacterial phytopathogens. Sci Rep 2019; 9:4525. [PMID: 30872786 PMCID: PMC6418279 DOI: 10.1038/s41598-019-40970-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2018] [Accepted: 02/22/2019] [Indexed: 11/09/2022] Open
Abstract
Plant cell wall degrading enzymes (PCWDEs) are the primary virulence determinants of soft rotting bacteria such as the potato pathogen, Pectobacterium atrosepticum. The regulation of secondary metabolite (Rsm) system controls production of PCWDEs in response to changing nutrient conditions. This work identified a new suppressor of an rsmB mutation - ECA1172 or rsmS (rsmB suppressor). Mutants defective in rsmB (encoding a small regulatory RNA), show reduced elaboration of the quorum sensing molecule (N-3-oxohexanoyl-homoserine lactone; OHHL) and PCWDEs. However, OHHL and PCWDE production were partially restored in an rsmB, rsmS double mutant. Single rsmS mutants, overproduced PCWDEs and OHHL relative to wild type P. atrosepticum and exhibited hypervirulence in potato. RsmS overproduction also resulted in increased PCWDEs and OHHL. Homology searches revealed rsmS conservation across pathogens such as Escherichia coli (ybaM), Dickeya solani, Klebsiella pneumoniae and Shigella flexneri. An rsmS mutant of Pectobacterium carotovorum ATCC39048 showed bypass of rsmB-dependent repression of PCWDEs and OHHL production. P. carotovorum ATCC39048 produces the β-lactam antibiotic, 1-carbapen-2-em-3-carboxylic acid (a carbapenem). Production of the antibiotic was repressed in an rsmB mutant but partially restored in an rsmB, rsmS double mutant. This work highlights the importance of RsmS, as a conserved pleiotropic regulator of virulence and antibiotic biosynthesis.
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Affiliation(s)
- Rita E Monson
- Department of Biochemistry, Hopkins Building, Tennis Court Road, University of Cambridge, Cambridge, CB2 1QW, UK
| | - Katinka Apagyi
- Department of Biochemistry, Hopkins Building, Tennis Court Road, University of Cambridge, Cambridge, CB2 1QW, UK
- Faculty of Medicine, School of Public Health, Imperial College, London, St Mary's Campus, Norfolk Place, W2 1PG, UK
| | - Steven D Bowden
- Department of Biochemistry, Hopkins Building, Tennis Court Road, University of Cambridge, Cambridge, CB2 1QW, UK
- Department of Food Science and Nutrition, University of Minnesota-Twin Cities, St. Paul, Minnesota, USA
| | - Natalie Simpson
- Department of Biochemistry, Hopkins Building, Tennis Court Road, University of Cambridge, Cambridge, CB2 1QW, UK
| | - Neil R Williamson
- Department of Biochemistry, Hopkins Building, Tennis Court Road, University of Cambridge, Cambridge, CB2 1QW, UK
| | - Marion F Cubitt
- Department of Biochemistry, Hopkins Building, Tennis Court Road, University of Cambridge, Cambridge, CB2 1QW, UK
| | - Steve Harris
- Department of Biochemistry, Hopkins Building, Tennis Court Road, University of Cambridge, Cambridge, CB2 1QW, UK
- School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, LE11 3TU, UK
| | - Ian K Toth
- Cell and Molecular Sciences, James Hutton Institute, Invergowrie, Dundee, DD2 5DA, UK
| | - George P C Salmond
- Department of Biochemistry, Hopkins Building, Tennis Court Road, University of Cambridge, Cambridge, CB2 1QW, UK.
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107
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Nguyen HL, Duviau MP, Cocaign-Bousquet M, Nouaille S, Girbal L. Multiplexing polysome profiling experiments to study translation in Escherichia coli. PLoS One 2019; 14:e0212297. [PMID: 30779773 PMCID: PMC6380557 DOI: 10.1371/journal.pone.0212297] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2018] [Accepted: 01/30/2019] [Indexed: 12/01/2022] Open
Abstract
Polysome profiling is a widely used method to monitor the translation status of mRNAs. Although it is theoretically a simple technique, it is labor intensive. Repetitive polysome fractionation rapidly generates a large number of samples to be handled in the downstream processes of protein elimination, RNA extraction and quantification. Here, we propose a multiplex polysome profiling experiment in which distinct cellular extracts are pooled before loading on the sucrose gradient for fractionation. We used the multiplexing method to study translation in E. coli. Multiplexing polysome profiling experiments provided similar mRNA translation status to that obtained with the non-multiplex method with comparable distribution of mRNA copies between the polysome profiling fractions, similar ribosome occupancy and ribosome density. The multiplexing method was used for parallel characterization of gene translational responses to changing mRNA levels. When the mRNA level of two native genes, cysZ and lacZ was increased by transcription induction, their global translational response was similar, with a higher ribosome load leading to increased ribosome occupancy and ribosome densities. However the pattern and the magnitude of the translational response were gene specific. By reducing the number of polysome profiling experiments, the multiplexing method saved time and effort and reduced cost and technical bias. This method would be useful to study the translational effect of mRNA sequence-dependent parameters that often require testing multiple samples and conditions in parallel.
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Affiliation(s)
- Huong Le Nguyen
- LISBP, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France
| | | | | | | | - Laurence Girbal
- LISBP, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France
- * E-mail: (MCB); (LG)
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108
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Potts AH, Guo Y, Ahmer BMM, Romeo T. Role of CsrA in stress responses and metabolism important for Salmonella virulence revealed by integrated transcriptomics. PLoS One 2019; 14:e0211430. [PMID: 30682134 PMCID: PMC6347204 DOI: 10.1371/journal.pone.0211430] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2018] [Accepted: 01/14/2019] [Indexed: 12/31/2022] Open
Abstract
To cause infection, Salmonella must survive and replicate in host niches that present dramatically different environmental conditions. This requires a flexible metabolism and physiology, responsive to conditions of the local milieu. The sequence specific RNA binding protein CsrA serves as a global regulator that governs gene expression required for pathogenicity, metabolism, biofilm formation, and motility in response to nutritional conditions. Its activity is determined by two noncoding small RNAs (sRNA), CsrB and CsrC, which sequester and antagonize this protein. Here, we used ribosome profiling and RNA-seq analysis to comprehensively examine the effects of CsrA on mRNA occupancy with ribosomes, a measure of translation, transcript stability, and the steady state levels of transcripts under in vitro SPI-1 inducing conditions, to simulate growth in the intestinal lumen, and under in vitro SPI-2-inducing conditions, to simulate growth in the Salmonella containing vacuole (SCV) of the macrophage. Our findings uncovered new roles for CsrA in controlling the expression of structural and regulatory genes involved in stress responses, metabolism, and virulence systems required for infection. We observed substantial variation in the CsrA regulon under the two growth conditions. In addition, CsrB/C sRNA levels were greatly reduced under the simulated intracellular conditions and were responsive to nutritional factors that distinguish the intracellular and luminal environments. Altogether, our results reveal CsrA to be a flexible regulator, which is inferred to be intimately involved in maintaining the distinct gene expression patterns associated with growth in the intestine and the macrophage.
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Affiliation(s)
- Anastasia H Potts
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, United States of America
| | - Yinping Guo
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, United States of America
| | - Brian M M Ahmer
- Department of Microbial Infection and Immunity, The Ohio State University, Columbus, OH, United States of America
| | - Tony Romeo
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, United States of America
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109
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Elhenawy W, Tsai CN, Coombes BK. Host-Specific Adaptive Diversification of Crohn's Disease-Associated Adherent-Invasive Escherichia coli. Cell Host Microbe 2019; 25:301-312.e5. [PMID: 30683582 DOI: 10.1016/j.chom.2018.12.010] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Revised: 10/05/2018] [Accepted: 12/13/2018] [Indexed: 12/12/2022]
Abstract
Crohn's disease (CD) is an inflammatory bowel disease influenced by bacteria. Adherent-invasive E. coli (AIEC) is associated with CD, yet the adaptations facilitating AIEC gut colonization are unknown. AIEC isolates exhibit high genetic diversity, suggesting strains evolve independently across different gut environments. We tracked the adaptive evolution of AIEC in a murine model of chronic colonization across multiple hosts and transmission events. We detected evolved lineages that outcompeted the ancestral strain in the host through independent mechanisms. One lineage was hypermotile because of a mobile insertion sequence upstream of the master flagellar regulator, flhDC, which enhanced AIEC invasion and establishment of a mucosal niche. Another lineage outcompeted the ancestral strain through improved use of acetate, a short-chain fatty acid in the gut. The presence of hypermotile and acetate-consuming lineages discriminated E. coli isolated from CD patients from healthy controls, suggesting an evolutionary trajectory that distinguishes AIEC from commensal E. coli.
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Affiliation(s)
- Wael Elhenawy
- Michael G. DeGroote Institute for Infectious Disease Research, Hamilton, ON, Canada
| | - Caressa N Tsai
- Michael G. DeGroote Institute for Infectious Disease Research, Hamilton, ON, Canada
| | - Brian K Coombes
- Michael G. DeGroote Institute for Infectious Disease Research, Hamilton, ON, Canada; Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Hamilton, ON, Canada.
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110
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Metabolome and transcriptome-wide effects of the carbon storage regulator A in enteropathogenic Escherichia coli. Sci Rep 2019; 9:138. [PMID: 30644424 PMCID: PMC6333774 DOI: 10.1038/s41598-018-36932-w] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2018] [Accepted: 11/28/2018] [Indexed: 02/06/2023] Open
Abstract
The carbon storage regulator A (CsrA) is a conserved global regulatory system known to control central carbon pathways, biofilm formation, motility, and pathogenicity. The aim of this study was to characterize changes in major metabolic pathways induced by CsrA in human enteropathogenic Escherichia coli (EPEC) grown under virulence factor-inducing conditions. For this purpose, the metabolomes and transcriptomes of EPEC and an isogenic ∆csrA mutant derivative were analyzed by untargeted mass spectrometry and RNA sequencing, respectively. Of the 159 metabolites identified from untargeted GC/MS and LC/MS data, 97 were significantly (fold change ≥ 1.5; corrected p-value ≤ 0.05) regulated between the knockout and the wildtype strain. A lack of csrA led to an accumulation of fructose-6-phosphate (F6P) and glycogen synthesis pathway products, whereas metabolites in lower glycolysis and the citric acid cycle were downregulated. Associated pathways from the citric acid cycle like aromatic amino acid and siderophore biosynthesis were also negatively influenced. The nucleoside salvage pathways were featured by an accumulation of nucleosides and nucleobases, and a downregulation of nucleotides. In addition, a pronounced downregulation of lyso-lipid metabolites was observed. A drastic change in the morphology in the form of vesicle-like structures of the ∆csrA knockout strain was visible by electron microscopy. Colanic acid synthesis genes were strongly (up to 50 fold) upregulated, and the abundance of colanic acid was 3 fold increased according to a colorimetric assay. The findings expand the scope of pathways affected by the csrA regulon and emphasize its importance as a global regulator.
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111
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Król JE. Regulatory loop between the CsrA system and NhaR, a high salt/high pH regulator. PLoS One 2018; 13:e0209554. [PMID: 30589862 PMCID: PMC6307784 DOI: 10.1371/journal.pone.0209554] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Accepted: 12/07/2018] [Indexed: 11/24/2022] Open
Abstract
In E. coli, under high pH/high salt conditions, a major Na+/H+ antiporter (NhaA) is activated to maintain an internal pH level. Its expression is induced by a specific regulator NhaR, which is also responsible for osmC and pgaA regulation. Here I report that the NhaR regulator affects the carbon storage regulatory Csr system. I found that the expression of all major components of the Csr system-CsrA regulator, CsrB and CsrC small RNAs, and the CsrB and CsrC stability were indirectly affected by nhaR mutation under stress conditions. Using a combination of experimental and in silico analyses, I concluded that the mechanism of regulation included direct and indirect activation of a two-component system (TCS) response regulator-UvrY. NhaR regulation involved interactions with the regulators H-NS and SdiA and was affected by a naturally occurring spontaneous IS5 insertion in the promoter region. A regulatory circuit was proposed and discussed.
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Affiliation(s)
- Jarosław E. Król
- Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida, United States of America
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112
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Abstract
The sequence-specific RNA binding protein CsrA is employed by diverse bacteria in the posttranscriptional regulation of gene expression. Its binding interactions with RNA have been documented at atomic resolution and shown to alter RNA secondary structure, RNA stability, translation, and/or Rho-mediated transcription termination through a growing number of molecular mechanisms. In Gammaproteobacteria, small regulatory RNAs (sRNAs) that contain multiple CsrA binding sites compete with mRNA for binding to CsrA, thereby sequestering and antagonizing this protein. Both the synthesis and turnover of these sRNAs are regulated, allowing CsrA activity to be rapidly and efficiently adjusted in response to nutritional conditions and stresses. Feedback loops between the Csr regulatory components improve the dynamics of signal response by the Csr system. The Csr system of Escherichia coli is intimately interconnected with other global regulatory systems, permitting it to contribute to regulation by those systems. In some species, a protein antagonist of CsrA functions as part of a checkpoint for flagellum biosynthesis. In other species, a protein antagonist participates in a mechanism in which a type III secretion system is used for sensing interactions with host cells. Recent transcriptomics studies reveal vast effects of CsrA on gene expression through direct binding to hundreds of mRNAs, and indirectly through its effects on the expression of dozens of transcription factors. CsrA binding to base-pairing sRNAs and novel mRNA segments, such as the 3' untranslated region and deep within coding regions, predict its participation in yet-to-be-discovered regulatory mechanisms.
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113
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Andresen L, Holmqvist E. CLIP-Seq in Bacteria: Global Recognition Patterns of Bacterial RNA-Binding Proteins. Methods Enzymol 2018; 612:127-145. [PMID: 30502939 DOI: 10.1016/bs.mie.2018.08.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/02/2023]
Abstract
RNA-protein interactions are at the heart of many central cellular processes, and RNA-binding proteins (RBPs) associate with virtually all RNA molecules in a cell. In bacteria, global RBPs, often in conjunction with small regulatory RNAs, affect physiology and virulence by controlling transcription, translation, and RNA decay. To understand how these regulatory proteins orchestrate global gene expression, detailed maps of their cellular RNA binding sites are required. To this end, cross-linking and immunoprecipitation followed by deep sequencing (CLIP-seq) has revolutionized RBP studies by providing knowledge about global recognition patterns of RBPs in both eukaryotic and bacterial cells. In this chapter, we provide a step-by-step protocol for global mapping of bona fide RBP binding sites using CLIP-seq in bacteria. This protocol has been successfully applied for charting the binding sites of Hfq, CsrA, and ProQ, three global regulatory RBPs in Salmonella enterica and Escherichia coli, and should be readily applicable to other RBPs and bacterial species.
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Affiliation(s)
- Liis Andresen
- Department of Cell and Molecular Biology, Biomedical Center, Uppsala University, Uppsala, Sweden
| | - Erik Holmqvist
- Department of Cell and Molecular Biology, Biomedical Center, Uppsala University, Uppsala, Sweden.
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114
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Schachterle JK, Stewart RM, Schachterle MB, Calder JT, Kang H, Prince JT, Erickson DL. Yersinia pseudotuberculosis BarA-UvrY Two-Component Regulatory System Represses Biofilms via CsrB. Front Cell Infect Microbiol 2018; 8:323. [PMID: 30280093 PMCID: PMC6153318 DOI: 10.3389/fcimb.2018.00323] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Accepted: 08/24/2018] [Indexed: 01/07/2023] Open
Abstract
The formation of biofilms by Yersinia pseudotuberculosis (Yptb) and Y. pestis requires the hmsHFRS genes, which direct production of a polysaccharide extracellular matrix (Hms-ECM). Despite possessing identical hmsHFRS sequences, Yptb produces much less Hms-ECM than Y. pestis. The regulatory influences that control Yptb Hms-ECM production and biofilm formation are not fully understood. In this study, negative regulators of biofilm production in Yptb were identified. Inactivation of the BarA/UvrY two-component system or the CsrB regulatory RNA increased binding of Congo Red dye, which correlates with extracellular polysaccharide production. These mutants also produced biofilms that were substantially more cohesive than the wild type strain. Disruption of uvrY was not sufficient for Yptb to cause proventricular blockage during infection of Xenopsylla cheopis fleas. However, this strain was less acutely toxic toward fleas than wild type Yptb. Flow cytometry measurements of lectin binding indicated that Yptb BarA/UvrY/CsrB mutants may produce higher levels of other carbohydrates in addition to poly-GlcNAc Hms-ECM. In an effort to characterize the relevant downstream targets of the BarA/UvrY system, we conducted a proteomic analysis to identify proteins with lower abundance in the csrB::Tn5 mutant strain. Urease subunit proteins were less abundant and urease enzymatic activity was lower, which likely reduced toxicity toward fleas. Loss of CsrB impacted expression of several potential regulatory proteins that may influence biofilms, including the RcsB regulator. Overexpression of CsrB did not alter the Congo-red binding phenotype of an rcsB::Tn5 mutant, suggesting that the effect of CsrB on biofilms may require RcsB. These results underscore the regulatory and compositional differences between Yptb and Y. pestis biofilms. By activating CsrB expression, the Yptb BarA/UvrY two-component system has pleiotropic effects that impact biofilm production and stability.
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Affiliation(s)
- Jeffrey K Schachterle
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT, United States
| | - Ryan M Stewart
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT, United States
| | - M Brett Schachterle
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT, United States
| | - Joshua T Calder
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT, United States
| | - Huan Kang
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT, United States
| | - John T Prince
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT, United States
| | - David L Erickson
- Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT, United States
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115
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Raina M, King A, Bianco C, Vanderpool CK. Dual-Function RNAs. Microbiol Spectr 2018; 6:10.1128/microbiolspec.RWR-0032-2018. [PMID: 30191807 PMCID: PMC6130917 DOI: 10.1128/microbiolspec.rwr-0032-2018] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2018] [Indexed: 12/30/2022] Open
Abstract
Bacteria are known to use RNA, either as mRNAs encoding proteins or as noncoding small RNAs (sRNAs), to regulate numerous biological processes. However, a few sRNAs have two functions: they act as base-pairing RNAs and encode a small protein with additional regulatory functions. Thus, these so called "dual-function" sRNAs can serve as both a riboregulator and an mRNA. In some cases, these two functions can act independently within the same pathway, while in other cases, the base-pairing function and protein function act in different pathways. Here, we discuss the five known dual-function sRNAs-SgrS from enteric species, RNAIII and Psm-mec from Staphylococcus aureus, Pel RNA from Streptococcus pyogenes, and SR1 from Bacillus subtilis-and review their mechanisms of action and roles in regulating diverse biological processes. We also discuss the prospect of finding additional dual-function sRNAs and future challenges in studying the overlap and competition between the functions.
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Affiliation(s)
- Medha Raina
- Division of Molecular and Cellular Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD 20892
| | - Alisa King
- Department of Microbiology, University of Illinois, Urbana, IL 61801
| | - Colleen Bianco
- Department of Microbiology, University of Illinois, Urbana, IL 61801
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116
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Laguerre S, González I, Nouaille S, Moisan A, Villa-Vialaneix N, Gaspin C, Bouvier M, Carpousis AJ, Cocaign-Bousquet M, Girbal L. Large-Scale Measurement of mRNA Degradation in Escherichia coli: To Delay or Not to Delay. Methods Enzymol 2018; 612:47-66. [PMID: 30502954 DOI: 10.1016/bs.mie.2018.07.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
In this study, we compared different computational methods used for genome-wide determination of mRNA half-lives in Escherichia coli with a special focus on the impact on considering a delay before the onset of mRNA decay after transcription arrest. A wide variety of datasets were analyzed coming from different technical methods for mRNA quantification (microarrays, RNA-seq, and RT-qPCR) and different bacterial growth conditions. The exponential decay of mRNA levels was fitted using both linear and exponential models and with or without a delay. We showed that for all the models, independently of mRNA quantification methods and growth conditions, ignoring the delay resulted in only a modest overestimation of the half-life. For approximately 80% of the mRNAs, differences in mRNA half-life values were less than 34s. The correlation between half-lives estimated with and without a delay was extremely high. However, the slope of the linear regression between the half-lives with and without a delay tended to decrease with the delay. For the few mRNAs for which taking into account the delay influenced the estimated half-life, the impact was dependent on the model and the growth condition. The smallest impact was obtained for the linear model.
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Affiliation(s)
| | | | | | - Annick Moisan
- MIAT, Université de Toulouse, INRA, Castanet-Tolosan, France
| | | | | | - Marie Bouvier
- LMGM, CBI, Université de Toulouse, CNRS, Toulouse, France
| | | | | | - Laurence Girbal
- LISBP, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France
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117
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El Mouali Y, Balsalobre C. 3'untranslated regions: regulation at the end of the road. Curr Genet 2018; 65:127-131. [PMID: 30120519 DOI: 10.1007/s00294-018-0877-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2018] [Revised: 08/10/2018] [Accepted: 08/12/2018] [Indexed: 01/07/2023]
Abstract
Post-transcriptional gene regulation in bacteria plays a major role in the adaptation of bacterial cells to the changing conditions encountered in the environment. In bacteria, most of the regulation at the level of mRNA seems to be targeting the 5'untranslated regions where accessibility to the ribosome-binding site can be modulated to alter gene expression. In recent years, the role of 3'untranslated regions has gained attention also as a site for post-transcriptional regulation. In addition to be a source of trans-encoded small RNAs, the 3'untranslated regions can be targets to modulate gene expression. Taking recent findings in the post-transcriptional regulation of the hilD gene, encoding for the main regulator of virulence in Salmonella enterica serovar Typhimurium, we highlight the role of 3'untranslated regions as targets of post-transcriptional regulation mediated by small RNAs and discuss the implications of transcriptional elongation in the 3'UTR-mediated regulation in bacteria.
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Affiliation(s)
- Youssef El Mouali
- RNA Biology Group, Institute for Molecular Infection Biology, University of Würzburg, Würzburg, Germany
| | - Carlos Balsalobre
- Department of Genetics, Microbiology and Statistics, School of Biology, University of Barcelona, Barcelona, Spain.
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118
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Leistra AN, Gelderman G, Sowa SW, Moon-Walker A, Salis HM, Contreras LM. A Canonical Biophysical Model of the CsrA Global Regulator Suggests Flexible Regulator-Target Interactions. Sci Rep 2018; 8:9892. [PMID: 29967470 PMCID: PMC6028588 DOI: 10.1038/s41598-018-27474-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2018] [Accepted: 06/04/2018] [Indexed: 02/04/2023] Open
Abstract
Bacterial global post-transcriptional regulators execute hundreds of interactions with targets that display varying molecular features while retaining specificity. Herein, we develop, validate, and apply a biophysical, statistical thermodynamic model of canonical target mRNA interactions with the CsrA global post-transcriptional regulator to understand the molecular features that contribute to target regulation. Altogether, we model interactions of CsrA with a pool of 236 mRNA: 107 are experimentally regulated by CsrA and 129 are suspected interaction partners. Guided by current understanding of CsrA-mRNA interactions, we incorporate (i) mRNA nucleotide sequence, (ii) cooperativity of CsrA-mRNA binding, and (iii) minimization of mRNA structural changes to identify an ensemble of likely binding sites and their free energies. The regulatory impact of bound CsrA on mRNA translation is determined with the RBS calculator. Predicted regulation of 66 experimentally regulated mRNAs adheres to the principles of canonical CsrA-mRNA interactions; the remainder implies that other, diverse mechanisms may underlie CsrA-mRNA interaction and regulation. Importantly, results suggest that this global regulator may bind targets in multiple conformations, via flexible stretches of overlapping predicted binding sites. This novel observation expands the notion that CsrA always binds to its targets at specific consensus sequences.
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Affiliation(s)
- A N Leistra
- McKetta Department of Chemical Engineering, University of Texas at Austin, 200 E. Dean Keeton St. Stop C0400, Austin, TX, 78712, USA
| | - G Gelderman
- McKetta Department of Chemical Engineering, University of Texas at Austin, 200 E. Dean Keeton St. Stop C0400, Austin, TX, 78712, USA
| | - S W Sowa
- Microbiology Graduate Program, University of Texas at Austin, 100 E. 24th St. Stop A6500, Austin, TX, 78712, USA
| | - A Moon-Walker
- Biological Sciences Program College of Natural Sciences, University of Texas at Austin, 120 Inner Campus Drive Stop G2500, Austin, TX, 78712, USA
| | - H M Salis
- Department of Chemical Engineering, Pennsylvania State University, 210 Agricultural Engineering Building, University Park, PA, 16802, USA
| | - L M Contreras
- McKetta Department of Chemical Engineering, University of Texas at Austin, 200 E. Dean Keeton St. Stop C0400, Austin, TX, 78712, USA.
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119
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Santiago-Frangos A, Woodson SA. Hfq chaperone brings speed dating to bacterial sRNA. WILEY INTERDISCIPLINARY REVIEWS. RNA 2018; 9:e1475. [PMID: 29633565 PMCID: PMC6002925 DOI: 10.1002/wrna.1475] [Citation(s) in RCA: 109] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2018] [Revised: 02/22/2018] [Accepted: 02/26/2018] [Indexed: 11/11/2022]
Abstract
Hfq is a ubiquitous, Sm-like RNA binding protein found in most bacteria and some archaea. Hfq binds small regulatory RNAs (sRNAs), facilitates base pairing between sRNAs and their mRNA targets, and directly binds and regulates translation of certain mRNAs. Because sRNAs regulate many stress response pathways in bacteria, Hfq is essential for adaptation to different environments and growth conditions. The chaperone activities of Hfq arise from multipronged RNA binding by three different surfaces of the Hfq hexamer. The manner in which the structured Sm core of Hfq binds RNA has been well studied, but recent work shows that the intrinsically disordered C-terminal domain of Hfq modulates sRNA binding, creating a kinetic hierarchy of RNA competition for Hfq and ensuring the release of double-stranded sRNA-mRNA complexes. A combination of structural, biophysical, and genetic experiments reveals how Hfq recognizes its RNA substrates and plays matchmaker for sRNAs and mRNAs in the cell. The interplay between structured and disordered domains of Hfq optimizes sRNA-mediated post-transcriptional regulation, and is a common theme in RNA chaperones. This article is categorized under: Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes RNA Structure and Dynamics > RNA Structure, Dynamics, and Chemistry.
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Affiliation(s)
- Andrew Santiago-Frangos
- Program in Cellular, Molecular and Developmental Biology and Biophysics, Johns Hopkins University, Baltimore, Maryland
| | - Sarah A Woodson
- T. C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, Maryland
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120
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Holmqvist E, Li L, Bischler T, Barquist L, Vogel J. Global Maps of ProQ Binding In Vivo Reveal Target Recognition via RNA Structure and Stability Control at mRNA 3′ Ends. Mol Cell 2018; 70:971-982.e6. [DOI: 10.1016/j.molcel.2018.04.017] [Citation(s) in RCA: 92] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2017] [Revised: 04/05/2018] [Accepted: 04/19/2018] [Indexed: 12/17/2022]
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121
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Examination of Csr regulatory circuitry using epistasis analysis with RNA-seq (Epi-seq) confirms that CsrD affects gene expression via CsrA, CsrB and CsrC. Sci Rep 2018; 8:5373. [PMID: 29599472 PMCID: PMC5876332 DOI: 10.1038/s41598-018-23713-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2017] [Accepted: 03/19/2018] [Indexed: 01/14/2023] Open
Abstract
The Csr global regulatory system coordinates gene expression in response to metabolic status. This system utilizes the RNA binding protein CsrA to regulate gene expression by binding to transcripts of structural and regulatory genes, thus affecting their structure, stability, translation, and/or transcription elongation. CsrA activity is controlled by sRNAs, CsrB and CsrC, which sequester CsrA away from other transcripts. CsrB/C levels are partly determined by their rates of turnover, which requires CsrD to render them susceptible to RNase E cleavage. Previous epistasis analysis suggested that CsrD affects gene expression through the other Csr components, CsrB/C and CsrA. However, those conclusions were based on a limited analysis of reporters. Here, we reassessed the global behavior of the Csr circuitry using epistasis analysis with RNA seq (Epi-seq). Because CsrD effects on mRNA levels were entirely lost in the csrA mutant and largely eliminated in a csrB/C mutant under our experimental conditions, while the majority of CsrA effects persisted in the absence of csrD, the original model accounts for the global behavior of the Csr system. Our present results also reflect a more nuanced role of CsrA as terminal regulator of the Csr system than has been recognized.
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122
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Durica-Mitic S, Göpel Y, Görke B. Carbohydrate Utilization in Bacteria: Making the Most Out of Sugars with the Help of Small Regulatory RNAs. Microbiol Spectr 2018; 6. [PMID: 29573258 DOI: 10.1128/microbiolspec.rwr-0013-2017] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Indexed: 12/11/2022] Open
Abstract
Survival of bacteria in ever-changing habitats with fluctuating nutrient supplies requires rapid adaptation of their metabolic capabilities. To this end, carbohydrate metabolism is governed by complex regulatory networks including posttranscriptional mechanisms that involve small regulatory RNAs (sRNAs) and RNA-binding proteins. sRNAs limit the response to substrate availability and set the threshold or time required for induction and repression of carbohydrate utilization systems. Carbon catabolite repression (CCR) also involves sRNAs. In Enterobacteriaceae, sRNA Spot 42 cooperates with the transcriptional regulator cyclic AMP (cAMP)-receptor protein (CRP) to repress secondary carbohydrate utilization genes when a preferred sugar is consumed. In pseudomonads, CCR operates entirely at the posttranscriptional level, involving RNA-binding protein Hfq and decoy sRNA CrcZ. Moreover, sRNAs coordinate fluxes through central carbohydrate metabolic pathways with carbohydrate availability. In Gram-negative bacteria, the interplay between RNA-binding protein CsrA and its cognate sRNAs regulates glycolysis and gluconeogenesis in response to signals derived from metabolism. Spot 42 and cAMP-CRP jointly downregulate tricarboxylic acid cycle activity when glycolytic carbon sources are ample. In addition, bacteria use sRNAs to reprogram carbohydrate metabolism in response to anaerobiosis and iron limitation. Finally, sRNAs also provide homeostasis of essential anabolic pathways, as exemplified by the hexosamine pathway providing cell envelope precursors. In this review, we discuss the manifold roles of bacterial sRNAs in regulation of carbon source uptake and utilization, substrate prioritization, and metabolism.
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Affiliation(s)
- Svetlana Durica-Mitic
- Department of Microbiology, Immunobiology and Genetics, Max F. Perutz Laboratories, University of Vienna, Vienna Biocenter, Vienna, Austria
| | - Yvonne Göpel
- Department of Microbiology, Immunobiology and Genetics, Max F. Perutz Laboratories, University of Vienna, Vienna Biocenter, Vienna, Austria
| | - Boris Görke
- Department of Microbiology, Immunobiology and Genetics, Max F. Perutz Laboratories, University of Vienna, Vienna Biocenter, Vienna, Austria
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123
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Circuitry Linking the Global Csr- and σ E-Dependent Cell Envelope Stress Response Systems. J Bacteriol 2017; 199:JB.00484-17. [PMID: 28924029 DOI: 10.1128/jb.00484-17] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Accepted: 09/08/2017] [Indexed: 01/23/2023] Open
Abstract
CsrA of Escherichia coli is an RNA-binding protein that globally regulates a wide variety of cellular processes and behaviors, including carbon metabolism, motility, biofilm formation, and the stringent response. CsrB and CsrC are small RNAs (sRNAs) that sequester CsrA, thereby preventing CsrA-mRNA interaction. RpoE (σE) is the extracytoplasmic stress response sigma factor of E. coli Previous RNA sequencing (RNA-seq) studies identified rpoE mRNA as a CsrA target. Here, we explored the regulation of rpoE by CsrA and found that CsrA represses rpoE translation. Gel mobility shift, footprint, and toeprint studies identified three CsrA binding sites in the rpoE leader transcript, one of which overlaps the rpoE Shine-Dalgarno (SD) sequence, while another overlaps the rpoE translation initiation codon. Coupled in vitro transcription-translation experiments showed that CsrA represses rpoE translation by binding to these sites. We further demonstrate that σE indirectly activates the transcription of csrB and csrC, leading to increased sequestration of CsrA, such that repression of rpoE by CsrA is reduced. We propose that the Csr system fine-tunes the σE-dependent cell envelope stress response. We also identified a 51-amino-acid coding sequence whose stop codon overlaps the rpoE start codon and demonstrate that rpoE is translationally coupled with this upstream open reading frame (ORF51). The loss of coupling reduces rpoE translation by more than 50%. Identification of a translationally coupled ORF upstream of rpoE suggests that this previously unannotated protein may participate in the cell envelope stress response. In keeping with existing nomenclature, we named ORF51 rseD, resulting in an operon arrangement of rseD-rpoE-rseA-rseB-rseC IMPORTANCE CsrA posttranscriptionally represses genes required for bacterial stress responses, including the stringent response, catabolite repression, and the RpoS (σS)-mediated general stress response. We show that CsrA represses the translation of rpoE, encoding the extracytoplasmic stress response sigma factor, and that σE indirectly activates the transcription of csrB and csrC, resulting in reciprocal regulation of these two global regulatory systems. These findings suggest that extracytoplasmic stress leads to derepression of rpoE translation by CsrA, and CsrA-mediated repression helps reset RpoE abundance to prestress levels once envelope damage is repaired. The discovery of an ORF, rseD, translationally coupled with rpoE adds further complexity to translational control of rpoE.
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