1
|
Chen H, Zhou X, Dai W. Identification of antimicrobial-susceptible Pseudomonas aeruginosa RpoA variant strains through positional conservation pattern. J Antimicrob Chemother 2024:dkae228. [PMID: 38990679 DOI: 10.1093/jac/dkae228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2024] [Accepted: 06/18/2024] [Indexed: 07/13/2024] Open
Abstract
BACKGROUND Bacterial RNA polymerase (RNAP) is a promising target for antimicrobial chemotherapy due to its indispensable role in bacterial growth and survival. Among its components, only the rpoB gene encoding the β-subunit is known for its association with rifampicin resistance. We recently identified a variant of the RNAP α-subunit (RpoA) in Pseudomonas aeruginosa, conferring heightened bacterial susceptibility to antimicrobials. This susceptibility was attributed to the specific down-regulation of the MexEF-OprN efflux pump. OBJECTIVES We asked how to distinguish antimicrobial-susceptible variant strains from clinical isolates. METHODS In this study, we identified various P. aeruginosa RpoA variants from clinical sources. Using the sequence alignment of different bacterial RpoA species, we computed the positional conservation of substitutions in RpoA variants using Shannon Entropy. RESULTS Our findings revealed that selective RpoA variant strains exhibited distinct profiles of antimicrobial susceptibility. Notably, RpoA variant strains, containing single-substitutions in the C-terminal domain (α-CTD) but not the N-terminal domain (α-NTD), showed attenuated MexEF-OprN expression and increased susceptibility to MexEF-OprN-specific antibiotics. Furthermore, we observed a close correlation between the susceptibility of these α-CTD RpoA variant strains to antibiotics and the conservation degrees of positional substitutions. CONCLUSIONS Our findings demonstrate the prevalence of antimicrobial-susceptible RpoA variant strains among P. aeruginosa clinical isolates. The identified positional conservation pattern in our study facilitates the rapid classification of RpoA variant strains with distinct drug resistances. Given the high conservation of RNAP across bacterial species, our findings open a new therapeutic perspective for precisely and efficiently combating pathogenic RpoA variant strains with specific antimicrobials.
Collapse
Affiliation(s)
- Huali Chen
- Integrative Microbiology Research Center, College of Plant Protection, South China Agricultural University, Guangzhou 510642, China
| | - Xiaoqing Zhou
- Integrative Microbiology Research Center, College of Plant Protection, South China Agricultural University, Guangzhou 510642, China
| | - Weijun Dai
- Integrative Microbiology Research Center, College of Plant Protection, South China Agricultural University, Guangzhou 510642, China
| |
Collapse
|
2
|
Tewary A, Prajapati RK, Mukhopadhyay J. Mechanism of δ Mediated Transcription Activation in Bacillus subtilis: Interaction with α CTD of RNA Polymerase Stabilizes δ and Successively Facilitates the Open Complex Formation. J Mol Biol 2023; 435:168366. [PMID: 37972688 DOI: 10.1016/j.jmb.2023.168366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Revised: 11/08/2023] [Accepted: 11/09/2023] [Indexed: 11/19/2023]
Abstract
The α CTD (C-terminal domain of the α subunit) of RNA polymerase (RNAP) is a target for transcriptional regulators. In the transcription activation at Class I, Class II, and Class III promoters of bacteria, the transcriptional regulator, binds to DNA at different sites and interacts with the α CTD to stabilize the RNAP at the promoter or it binds to the α CTD to form a prerecruitment complex that searches for its cognate binding site. This 'simple recruitment mechanism' of the transcriptional machinery at the promoter is responsible for the activation of transcription. Strikingly, in B. subtilis the binding of RNAP at the promoter stabilizes the transcriptional regulator, δ at the -41 site of the promoter DNA through an interaction with its α CTD and successively facilitates the open complex formation. Two residues R293 and K294 of α CTD (equivalent to K297 and K298 of E. coli) are involved in the interactions with δ and essential for the activation of transcription. R293 is responsible for the stabilization of δ, while K294 is responsible for facilitating the open complex formation. Based on our data we propose a new model of transcription activation by δ of B. subtilis that is similar to (its binding location and interaction with α CTD), but distinct from (the recruitment of transcription factor by RNAP at the DNA, and enhancement of the open complex formation) the model Class II promoters in bacteria.
Collapse
Affiliation(s)
- Aniruddha Tewary
- Department of Chemical Science, Bose Institute, EN80 Sector V, Kolkata 700091, India.
| | | | - Jayanta Mukhopadhyay
- Department of Chemical Science, Bose Institute, EN80 Sector V, Kolkata 700091, India.
| |
Collapse
|
3
|
Cai W, Liao H, Lu M, Zhou X, Cheng X, Staehelin C, Dai W. New Evolutionary Insights into RpoA: A Novel Quorum Sensing Reprograming Factor in Pseudomonas aeruginosa. Mol Biol Evol 2023; 40:msad203. [PMID: 37708386 PMCID: PMC10566545 DOI: 10.1093/molbev/msad203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2023] [Revised: 08/19/2023] [Accepted: 08/22/2023] [Indexed: 09/16/2023] Open
Abstract
Quorum-sensing (QS) coordinates the expression of virulence factors in Pseudomonas aeruginosa, an opportunistic pathogen known for causing severe infections in immunocompromised patients. QS has a master regulator, the lasR gene, but in clinical settings, P. aeruginosa isolates have been found that are QS-active but LasR-null. In this study, we developed an experimental evolutionary approach to identify additional QS-reprogramming determinants. We began the study with a LasR-null mutant with an extra copy of mexT, a transcriptional regulator gene that is known to be able to reprogram QS in laboratory LasR-null strains. In this strain, spontaneous single mexT mutations are expected to have no or little phenotypic consequences. Using this novel method, which we have named "targeted gene duplication followed by mutant screening", we identified QS-active revertants with mutations in genes other than mexT. One QS-active revertant had a point mutation in rpoA, a gene encoding the α-subunit of RNA polymerase. QS activation in this mutant was found to be associated with the downregulated expression of mexEF-oprN efflux pump genes. Our study therefore uncovers a new functional role for RpoA in regulating QS activity. Our results indicate that a RpoA-dependent regulatory circuit controlling the expression of the mexEF-oprN operon is critical for QS-reprogramming. In conclusion, our study reports on the identification of non-MexT proteins associated with QS-reprogramming in a laboratory strain, shedding light on possible QS activation mechanisms in clinical P. aeruginosa isolates.
Collapse
Affiliation(s)
- Wenjie Cai
- Guangdong Laboratory for Lingnan Modern Agriculture, South China Agricultural University, Guangzhou, China
- College of Plant Protection, Integrative Microbiology Research Center, South China Agricultural University, Guangzhou, China
| | - Huimin Liao
- Guangdong Laboratory for Lingnan Modern Agriculture, South China Agricultural University, Guangzhou, China
- College of Plant Protection, Integrative Microbiology Research Center, South China Agricultural University, Guangzhou, China
| | - Mingqi Lu
- Guangdong Laboratory for Lingnan Modern Agriculture, South China Agricultural University, Guangzhou, China
- College of Plant Protection, Integrative Microbiology Research Center, South China Agricultural University, Guangzhou, China
| | - Xiangting Zhou
- Guangdong Laboratory for Lingnan Modern Agriculture, South China Agricultural University, Guangzhou, China
- College of Plant Protection, Integrative Microbiology Research Center, South China Agricultural University, Guangzhou, China
| | - Xiaoyan Cheng
- Guangdong Laboratory for Lingnan Modern Agriculture, South China Agricultural University, Guangzhou, China
- College of Plant Protection, Integrative Microbiology Research Center, South China Agricultural University, Guangzhou, China
| | - Christian Staehelin
- State Key Laboratory of Biocontrol and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Weijun Dai
- Guangdong Laboratory for Lingnan Modern Agriculture, South China Agricultural University, Guangzhou, China
- College of Plant Protection, Integrative Microbiology Research Center, South China Agricultural University, Guangzhou, China
| |
Collapse
|
4
|
Cai W, Lu M, Dai W. Novel antibiotic susceptibility of an RNA polymerase α-subunit mutant in Pseudomonas aeruginosa. J Antimicrob Chemother 2023; 78:2162-2169. [PMID: 37428003 DOI: 10.1093/jac/dkad207] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2022] [Accepted: 06/14/2023] [Indexed: 07/11/2023] Open
Abstract
BACKGROUND RNA polymerase (RNAP) is highly conserved and essential for prokaryotic housekeeping activities, making it an important target for the development of new antibiotics. The rpoB gene, encoding a β-subunit of bacterial RNAP, has a well-known association with rifampicin resistance. However, the roles of other RNAP component genes such as rpoA, encoding an α-subunit of RNAP, in antibiotic resistance remain unexplored. OBJECTIVES To characterize the antibiotic resistance-related role of RpoA. METHODS We measured the expression of the MexEF-OprN efflux pump in an RpoA mutant using a transcriptional reporter. The MICs of various antibiotics for this RpoA mutant were determined. RESULTS We uncover a novel role of antibiotic susceptibility for an RpoA mutant in Pseudomonas aeruginosa. We found that a single amino acid substitution in RpoA resulted in reduced activity of the MexEF-OprN efflux pump, which is responsible for the exportation of various antibiotics, including ciprofloxacin, chloramphenicol, ofloxacin and norfloxacin. This attenuated efflux pump activity, caused by the RpoA mutation, conferred the bacteria further susceptibility to antibiotics regulated by MexEF-OprN. Our work further revealed that certain clinical P. aeruginosa isolates also contained the same RpoA mutation, providing clinical relevance to our findings. Our results elucidate why this new antibiotic-susceptible function of RpoA mutants would have remained undetected in conventional screens for mutants involving antibiotic resistance. CONCLUSIONS The discovery of antibiotic susceptibility in an RpoA mutant implicates a new therapeutic approach for treating clinical isolates of P. aeruginosa with RpoA mutations, using specific antibiotics regulated by MexEF-OprN. More generally, our work suggests that RpoA could serve as a promising candidate target for anti-pathogen therapeutic purposes.
Collapse
Affiliation(s)
- Wenjie Cai
- Guangdong Laboratory for Lingnan Modern Agriculture, South China Agricultural University, Guangzhou 510642, China
- College of Plant Protection, Integrative Microbiology Research Center, South China Agricultural University, Guangzhou, 510642, China
| | - Mingqi Lu
- Guangdong Laboratory for Lingnan Modern Agriculture, South China Agricultural University, Guangzhou 510642, China
- College of Plant Protection, Integrative Microbiology Research Center, South China Agricultural University, Guangzhou, 510642, China
| | - Weijun Dai
- Guangdong Laboratory for Lingnan Modern Agriculture, South China Agricultural University, Guangzhou 510642, China
- College of Plant Protection, Integrative Microbiology Research Center, South China Agricultural University, Guangzhou, 510642, China
| |
Collapse
|
5
|
Ogura M, Matsutani M, Asai K, Suzuki M. Glucose controls manganese homeostasis through transcription factors regulating known and newly identified manganese transporter genes in Bacillus subtilis. J Biol Chem 2023; 299:105069. [PMID: 37468100 PMCID: PMC10448178 DOI: 10.1016/j.jbc.2023.105069] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2023] [Revised: 07/06/2023] [Accepted: 07/12/2023] [Indexed: 07/21/2023] Open
Abstract
Mn2+ is an essential nutrient whose concentration is tightly controlled in bacteria. In Bacillus subtilis, the Mn2+-activated transcription factor MntR controls Mn2+ transporter genes. However, factors regulating intracellular Mn2+ concentration are incompletely understood. Here, we found that glucose addition induces an increase in intracellular Mn2+ concentration. We determined this upshift was mediated by glucose induction of the major Mn2+ importer gene mntH by the transcription factor AhrC, which is known to be involved in arginine metabolism and to be indirectly induced by glucose. In addition, we identified novel AhrC-regulated genes encoding the Mn2+ importer YcsG and the ABC-type exporter YknUV. We found the expression of these genes was also regulated by glucose and contributes to the glucose induction of Mn2+ concentrations. ycsG expression is regulated by MntR as well. Furthermore, we analyzed the interaction of AhrC and MntR with the promoter driving ycsG expression and examined the Mn2+-dependent induction of this promoter to identify the transcription factors responsible for the Mn2+ induction. RNA-Seq revealed that disruption of ahrC and mntR affected the expression of 502 and 478 genes, respectively (false discovery rate, <0.001, log2[fold change] ≥ |2|. The AhrC- and/or MntR-dependent expression of twenty promoters was confirmed by LacZ analysis, and AhrC or MntR binding to some of these promoters was observed via EMSA. The finding that glucose promotes an increase in intracellular Mn2+ levels without changes in extracellular Mn2+ concentrations is reasonable for the bacterium, as intracellular Mn2+ is required for enzymes and pathways mediating glucose metabolism.
Collapse
Affiliation(s)
- Mitsuo Ogura
- Institute of Oceanic Research and Development, Tokai University, Shizuoka, Japan.
| | | | - Kei Asai
- Department of Bioscience, Tokyo University of Agriculture, Tokyo, Japan
| | - Michio Suzuki
- Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan
| |
Collapse
|
6
|
Krishna A, Liu B, Peacock SJ, Wigneshweraraj S. The prevalence and implications of single nucleotide polymorphisms in genes encoding the RNA polymerase of clinical isolates of Staphylococcus aureus. Microbiologyopen 2020; 9:e1058. [PMID: 32419302 PMCID: PMC7349150 DOI: 10.1002/mbo3.1058] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2020] [Revised: 04/23/2020] [Accepted: 04/25/2020] [Indexed: 01/22/2023] Open
Abstract
Central to the regulation of bacterial gene expression is the multisubunit enzyme RNA polymerase (RNAP), which is responsible for catalyzing transcription. As all adaptive processes are underpinned by changes in gene expression, the RNAP can be considered the major mediator of any adaptive response in the bacterial cell. In bacterial pathogens, theoretically, single nucleotide polymorphisms (SNPs) in genes that encode subunits of the RNAP and associated factors could mediate adaptation and confer a selective advantage to cope with biotic and abiotic stresses. We investigated this possibility by undertaking a systematic survey of SNPs in genes encoding the RNAP and associated factors in a collection of 1,429 methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates. We present evidence for the existence of several, hitherto unreported, nonsynonymous SNPs in genes encoding the RNAP and associated factors of MRSA ST22 clinical isolates and propose that the acquisition of amino acid substitutions in the RNAP could represent an adaptive strategy that contributes to the pathogenic success of MRSA.
Collapse
Affiliation(s)
- Aishwarya Krishna
- MRC Centre for Molecular Bacteriology and InfectionImperial College LondonLondonUK
| | - Bing Liu
- MRC Centre for Molecular Bacteriology and InfectionImperial College LondonLondonUK
| | - Sharon J. Peacock
- Department of MedicineAddenbrooke's HospitalUniversity of CambridgeCambridgeUK
- Cambridge University Hospitals NHS Foundation TrustCambridgeUK
- Wellcome Trust Sanger InstituteCambridgeUK
- London School of Hygiene and Tropical MedicineLondonUK
| | | |
Collapse
|
7
|
Wu Y, Liu Y, Lv X, Li J, Du G, Liu L. CAMERS‐B: CRISPR/Cpf1 assisted multiple‐genes editing and regulation system for
Bacillus subtilis. Biotechnol Bioeng 2020; 117:1817-1825. [DOI: 10.1002/bit.27322] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2019] [Revised: 02/20/2020] [Accepted: 03/02/2020] [Indexed: 12/13/2022]
Affiliation(s)
- Yaokang Wu
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of EducationJiangnan University Wuxi Jiangsu China
- Key Laboratory of Industrial Biotechnology, Ministry of EducationJiangnan University Wuxi Jiangsu China
| | - Yanfeng Liu
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of EducationJiangnan University Wuxi Jiangsu China
- Key Laboratory of Industrial Biotechnology, Ministry of EducationJiangnan University Wuxi Jiangsu China
| | - Xueqin Lv
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of EducationJiangnan University Wuxi Jiangsu China
- Key Laboratory of Industrial Biotechnology, Ministry of EducationJiangnan University Wuxi Jiangsu China
| | - Jianghua Li
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of EducationJiangnan University Wuxi Jiangsu China
- Key Laboratory of Industrial Biotechnology, Ministry of EducationJiangnan University Wuxi Jiangsu China
| | - Guocheng Du
- Key Laboratory of Industrial Biotechnology, Ministry of EducationJiangnan University Wuxi Jiangsu China
| | - Long Liu
- Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of EducationJiangnan University Wuxi Jiangsu China
- Key Laboratory of Industrial Biotechnology, Ministry of EducationJiangnan University Wuxi Jiangsu China
| |
Collapse
|
8
|
Ogura M, Sato T, Abe K. Bacillus subtilis YlxR, Which Is Involved in Glucose-Responsive Metabolic Changes, Regulates Expression of tsaD for Protein Quality Control of Pyruvate Dehydrogenase. Front Microbiol 2019; 10:923. [PMID: 31118925 PMCID: PMC6504816 DOI: 10.3389/fmicb.2019.00923] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2018] [Accepted: 04/11/2019] [Indexed: 01/09/2023] Open
Abstract
Glucose is the most favorable carbon source for many bacteria, which have several glucose-responsive gene networks. Recently, we found that in Bacillus subtilis glucose induces the expression of the extracellular sigma factor genes sigX and sigM through the acetylation of CshA (RNA helicase), which associates with RNA polymerase (RNAP). We performed a transposon mutagenesis screen for mutants with no glucose induction (GI) of sigX-lacZ. While screening for such mutants, we recently found that the GI of sigX/M involves YlxR, a nucleoid-associated protein (NAP) that regulates nearly 400 genes, including metabolic genes. It has been shown that acetylated CshA positively regulates expression of ylxR-containing operon. Here, we report additional mutations in yqfO or tsaD required for the GI of sigX. YqfO contains a universally conserved domain with unknown function. YqfO and YlxR were found to regulate expression of the tsaEBD-containing operon. Mutational analysis using lacZ fusions revealed the adenine-rich cis-element for YlxR. TsaD is a component of the TsaEBD enzyme required for the synthesis of threonylcarbamoyl adenosine (t6A). The t6A modification of tRNA is universal across the three domains of life. Western blot analysis showed that the tsaD mutation in the presence of glucose reduced levels of soluble PdhA, PdhB, and PdhD, which are subunits of the pyruvate dehydrogenase complex (PDHc). This resulted in severely defective PDHc function and thus reduced concentrations of cellular acetyl-CoA, a reaction product of PDHc and plausible source for CshA acetylation. Thus, we discuss a suggested glucose-responsive system (GRS) involving self-reinforcing CshA acetylation. This self-reinforcing pathway may contribute to the maintenance of the acetyl-CoA pool for protein acetylation.
Collapse
Affiliation(s)
- Mitsuo Ogura
- Institute of Oceanic Research and Development, Tokai University, Shizuoka, Japan
| | - Tsutomu Sato
- Department of Frontier Bioscience, Hosei University, Koganei, Japan
| | - Kimihiro Abe
- Research Center for Micro-Nano Technology, Hosei University, Koganei, Japan
| |
Collapse
|
9
|
Schäfer H, Heinz A, Sudzinová P, Voß M, Hantke I, Krásný L, Turgay K. Spx, the central regulator of the heat and oxidative stress response in B. subtilis, can repress transcription of translation-related genes. Mol Microbiol 2018; 111:514-533. [PMID: 30480837 DOI: 10.1111/mmi.14171] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/21/2018] [Indexed: 12/19/2022]
Abstract
Spx is a Bacillus subtilis transcription factor that interacts with the alpha subunits of RNA polymerase. It can activate the thiol stress response regulon and interfere with the activation of many developmental processes. Here, we show that Spx is a central player orchestrating the heat shock response by up-regulating relevant stress response genes as revealed by comparative transcriptomic experiments. Moreover, these experiments revealed the potential of Spx to inhibit transcription of translation-related genes. By in vivo and in vitro experiments, we confirmed that Spx can inhibit transcription from rRNA. This inhibition depended mostly on UP elements and the alpha subunits of RNA polymerase. However, the concurrent up-regulation activity of stress genes by Spx, but not the inhibition of translation related genes, was essential for mediating stress response and antibiotic tolerance under the applied stress conditions. The observed inhibitory activity might be compensated in vivo by additional stress response processes interfering with translation. Nevertheless, the impact of Spx on limiting translation becomes apparent under conditions with high cellular Spx levels. Interestingly, we observed a subpopulation of stationary phase cells that contains raised Spx levels, which may contribute to growth inhibition and a persister-like behaviour of this subpopulation during outgrowth.
Collapse
Affiliation(s)
- Heinrich Schäfer
- Institute of Microbiology, Leibniz Universität Hannover, Herrenhäuser Str. 2, D-30419, Hannover, Germany
| | - Anja Heinz
- Institute of Biology-Microbiology, Freie Universität Berlin, Königin-Luise-Str. 12-16, D-14195, Berlin, Germany
| | - Petra Sudzinová
- Institute of Microbiology, Czech Academy of Sciences, Vídeňská 1083, 142 20, Prague, Czech Republic
| | - Michelle Voß
- Institute of Microbiology, Leibniz Universität Hannover, Herrenhäuser Str. 2, D-30419, Hannover, Germany
| | - Ingo Hantke
- Institute of Microbiology, Leibniz Universität Hannover, Herrenhäuser Str. 2, D-30419, Hannover, Germany
| | - Libor Krásný
- Institute of Microbiology, Czech Academy of Sciences, Vídeňská 1083, 142 20, Prague, Czech Republic
| | - Kürşad Turgay
- Institute of Microbiology, Leibniz Universität Hannover, Herrenhäuser Str. 2, D-30419, Hannover, Germany
| |
Collapse
|
10
|
Novel Genes and Regulators That Influence Production of Cell Surface Exopolysaccharides in Sinorhizobium meliloti. J Bacteriol 2018; 200:JB.00501-17. [PMID: 29158240 DOI: 10.1128/jb.00501-17] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 11/10/2017] [Indexed: 12/21/2022] Open
Abstract
Sinorhizobium meliloti is a soil-dwelling alphaproteobacterium that engages in a nitrogen-fixing root nodule symbiosis with leguminous plants. Cell surface polysaccharides are important both for adapting to stresses in the soil and for the development of an effective symbiotic interaction. Among the polysaccharides characterized to date, the acidic exopolysaccharides I (EPS-I; succinoglycan) and II (EPS-II; galactoglucan) are particularly important for protection from abiotic stresses, biofilm formation, root colonization, and infection of plant roots. Previous genetic screens discovered mutants with impaired EPS production, allowing the delineation of EPS biosynthetic pathways. Here we report on a genetic screen to isolate mutants with mucoid colonial morphologies that suggest EPS overproduction. Screening with Tn5-110, which allows the recovery of both null and upregulation mutants, yielded 47 mucoid mutants, most of which overproduce EPS-I; among the 30 unique genes and intergenic regions identified, 14 have not been associated with EPS production previously. We identified a new protein-coding gene, emmD, which may be involved in the regulation of EPS-I production as part of the EmmABC three-component regulatory circuit. We also identified a mutant defective in EPS-I production, motility, and symbiosis, where Tn5-110 was not responsible for the mutant phenotypes; these phenotypes result from a missense mutation in rpoA corresponding to the domain of the RNA polymerase alpha subunit known to interact with transcription regulators.IMPORTANCE The alphaproteobacterium Sinorhizobium meliloti converts dinitrogen to ammonium while inhabiting specialized plant organs termed root nodules. The transformation of S. meliloti from a free-living soil bacterium to a nitrogen-fixing plant symbiont is a complex developmental process requiring close interaction between the two partners. As the interface between the bacterium and its environment, the S. meliloti cell surface plays a critical role in adaptation to varied soil environments and in interaction with plant hosts. We isolated and characterized S. meliloti mutants with increased production of exopolysaccharides, key cell surface components. Our diverse set of mutants suggests roles for exopolysaccharide production in growth, metabolism, cell division, envelope homeostasis, biofilm formation, stress response, motility, and symbiosis.
Collapse
|