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Zeng L, Noeparvar P, Burne RA, Glezer BS. Genetic characterization of glyoxalase pathway in oral streptococci and its contribution to interbacterial competition. J Oral Microbiol 2024; 16:2322241. [PMID: 38440286 PMCID: PMC10911100 DOI: 10.1080/20002297.2024.2322241] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2024] [Accepted: 02/16/2024] [Indexed: 03/06/2024] Open
Abstract
Objectives To analyze contributions to microbial ecology of Reactive Electrophile Species (RES), including methylglyoxal, generated during glycolysis. Methods Genetic analyses were performed on the glyoxalase pathway in Streptococcus mutans (SM) and Streptococcus sanguinis (SS), followed by phenotypic assays and transcription analysis. Results Deleting glyoxalase I (lguL) reduced RES tolerance to a far greater extent in SM than in SS, decreasing the competitiveness of SM against SS. Although SM displays a greater RES tolerance than SS, lguL-null mutants of either species showed similar tolerance; a finding consistent with the ability of methylglyoxal to induce the expression of lguL in SM, but not in SS. A novel paralogue of lguL (named gloA2) was identified in most streptococci. SM mutant ∆gloA2SM showed little change in methylglyoxal tolerance yet a significant growth defect and increased autolysis on fructose, a phenotype reversed by the addition of glutathione, or by the deletion of a fructose: phosphotransferase system (PTS) that generates fructose-1-phosphate (F-1-P). Conclusions Fructose contributes to RES generation in a PTS-specific manner, and GloA2 may be required to degrade certain RES derived from F-1-P. This study reveals the critical roles of RES in fitness and interbacterial competition and the effects of PTS in modulating RES metabolism.
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Affiliation(s)
- Lin Zeng
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, USA
| | - Payam Noeparvar
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, USA
| | - Robert A. Burne
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, USA
| | - Benjamin S. Glezer
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, USA
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Kim YY, Kim JC, Kim S, Yang JE, Kim HM, Park HW. Heterotypic stress-induced adaptive evolution enhances freeze-drying tolerance and storage stability of Leuconostoc mesenteroides WiKim33. Food Res Int 2024; 175:113731. [PMID: 38128991 DOI: 10.1016/j.foodres.2023.113731] [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: 08/31/2023] [Revised: 11/15/2023] [Accepted: 11/22/2023] [Indexed: 12/23/2023]
Abstract
Lactic acid bacteria (LAB) are currently being investigated for their potential use as probiotics and starter cultures. Researchers have developed powdering processes for the commercialization of LAB. Previous studies have focused on identifying innovative cryoprotective agents and freeze-drying (FD) techniques to enhance the stability of LAB. In this study, adaptive laboratory evolution (ALE) was employed to develop a strain with high FD tolerance and enhanced storage stability. Leuconostoc mesenteroids WiKim33 was subjected to heterotypic shock (heat and osmosis shock) to induce the desired phenotype and genotype. An FD-tolerant enhanced Leu. mesenteroides WiKim33 strain (ALE50) was obtained, which harbored a modified fatty acid composition and cell envelope characteristics. Specifically, ALE50 showed a lower unsaturated fatty acid (UFA)/saturated fatty acid (SFA) ratio and a higher cyclic fatty acid (CFA) composition. Moreover, the exopolysaccharide (EPS) thickness increased significantly by 331% compared to that of the wild type (WT). FD tolerance, which was evaluated using viability testing after FD, was enhanced by 33.4%. Overall, we demonstrated the feasibility of ALE to achieve desirable characteristics and provided insights into the mechanisms underlying increased FD tolerance.
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Affiliation(s)
- Yeong Yeol Kim
- Technology Innovation Research Division, World Institute of Kimchi, Gwangju 61755, Republic of Korea; Department of Integrative Food, Bioscience and Biotechnology, Chonnam National University, Gwangju 61186, Republic of Korea
| | - Jong-Cheol Kim
- Technology Innovation Research Division, World Institute of Kimchi, Gwangju 61755, Republic of Korea
| | - Seulbi Kim
- Technology Innovation Research Division, World Institute of Kimchi, Gwangju 61755, Republic of Korea; Division of Applied Bioscience & Biotechnology, Chonnam National University, Gwangju 61186, Republic of Korea
| | - Jung Eun Yang
- Technology Innovation Research Division, World Institute of Kimchi, Gwangju 61755, Republic of Korea
| | - Ho Myeong Kim
- Technology Innovation Research Division, World Institute of Kimchi, Gwangju 61755, Republic of Korea.
| | - Hae Woong Park
- Technology Innovation Research Division, World Institute of Kimchi, Gwangju 61755, Republic of Korea.
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The fruB Gene of Streptococcus mutans Encodes an Endo-Levanase That Enhances Growth on Levan and Influences Global Gene Expression. Microbiol Spectr 2022; 10:e0052222. [PMID: 35588281 PMCID: PMC9241797 DOI: 10.1128/spectrum.00522-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Streptococcus mutans, the primary etiologic agent of human dental caries, and a variety of oral Streptococcus and Actinomyces spp. synthesize high molecular mass homopolymers of fructose (fructans) with predominantly β2,1- (inulins) or β2,6-linkages (levans). The ability of S. mutans to degrade fructans contributes to the severity of dental caries. The extracellular product of fruA of S. mutans is an exo- β-d-fructofuranosidase that releases fructose from levan and inulin. Located 70 bp downstream of fruA, fruB encodes a member of the glycoside hydrolase family 32, but the function of FruB has not been established. Growth assays performed using wild-type UA159 and fruB-deficient derivatives, with fructans as the sole carbohydrate source, showed a significant reduction in the growth rate of a fruB mutant on levan, but not on inulin. A purified, recombinant FruB protein degraded levan to release mainly fructooligosaccharides. Driven by the fruA promoter and a secondary promoter located in the 3′ region of the fruA sequence, the fruB gene is inducible by fructose and especially by levan, but a stable stem-loop structure in the intergenic region likely modulates transcriptional read-through from fruA. Transcriptomic analysis of UA159 and a fruB mutant grown on 0.2% levan revealed differential expression of genes encoding ABC transporters, transcriptional regulators and genes involved in growth and stress tolerance. The ability of FruB to enhance levan metabolism and the high degree of conservation of FruB across S. mutans isolates imply a significant contribution of FruB to the fitness and virulence of this pathogen in human dental biofilms. IMPORTANCE Carbohydrate metabolism and acid production are essential for the development of dental caries. As a by-product of sucrose metabolism, formation, and degradation of fructans enhances the severity of caries by S. mutans in animal models. This study highlights a significant breakthrough in identifying FruB in S. mutans as an endolevanase that contributes to efficient utilization of levan, a specific type of fructan produced by certain commensals but not S. mutans. Transcriptomic analysis revealed that FruB-dependent levan metabolism impacted global gene regulation, including a large number of novel genes. Considering the preference for levan by both FruA and FruB, the conservation of fruAB in S. mutans might represent a competitive advantage in access to the energy storage produced by dental microbiome. This is the first report demonstrating the presence of an endolevanase in S. mutans, therefore should be of broad interest to the fields of dental caries and complex carbohydrate metabolism.
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Transcriptional Profiling Reveals the Importance of RcrR in the Regulation of Multiple Sugar Transportation and Biofilm Formation in Streptococcus mutans. mSystems 2021; 6:e0078821. [PMID: 34427509 PMCID: PMC8407328 DOI: 10.1128/msystems.00788-21] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The ability of Streptococcus mutans to survive and cause dental caries is dependent on its ability to metabolize various carbohydrates, accompanied by extracellular polysaccharide synthesis and biofilm formation. Here, the role of an rel competence-related regulator (RcrR) in the regulation of multiple sugar transportation and biofilm formation is reported. The deletion of the rcrR gene in S. mutans caused delayed growth, decreased biofilm formation ability, and affected the expression level of its multiple sugar transportation-related genes. Transcriptional profiling revealed 17 differentially expressed genes in the rcrR mutant. Five were downregulated and clustered with the sugar phosphotransferase (PTS) systems (mannitol- and trehalose-specific PTS systems). The conserved sites bound by the rcrR promoter were then determined by electrophoretic mobility shift assays (EMSAs) and DNase I footprinting assays. Furthermore, a potential binding motif in the promoters of the two PTS operons was predicted using MEME Suite 5.1.1. RcrR could bind to the promoter regions of the two operons in vitro, and the sugar transporter-related genes of the two operons were upregulated in an rcrR-overexpressing strain. In addition, when RcrR-binding sites were deleted, the growth rates and final yield of S. mutans were significantly decreased in tryptone-vitamin (TV) medium supplemented with different sugars, but not in absolute TV medium. These results revealed that RcrR acted as a transcription activator to regulate the two PTS systems, accompanied by multiple sugar transportation and biofilm formation. Collectively, these results indicate that RcrR is a critical transcription factor in S. mutans that regulates bacterial growth, biofilm formation, and multiple sugar transportation. IMPORTANCE The human oral cavity is a constantly changing environment. Tooth decay is a commonly prevalent chronic disease mainly caused by the cariogenic bacterium Streptococcus mutans. S. mutans is an oral pathogen that metabolizes various carbohydrates into extracellular polysaccharides (EPSs), biofilm, and tooth-destroying lactic acid. The host diet strongly influences the availability of multiple carbohydrates. Here, we showed that the RcrR transcription regulator plays a significant role in the regulation of biofilm formation and multiple sugar transportation. Further systematic evaluation of how RcrR regulates the transportation of various sugars and biofilm formation was also conducted. Notably, this study decrypts the physiological functions of RcrR as a potential target for the better prevention of dental caries.
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Yi X, Lin L, Mei J, Wang W. Transporter proteins in Zymomonas mobilis contribute to the tolerance of lignocellulose-derived phenolic aldehyde inhibitors. Bioprocess Biosyst Eng 2021; 44:1875-1882. [PMID: 33839896 DOI: 10.1007/s00449-021-02567-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Accepted: 03/31/2021] [Indexed: 01/29/2023]
Abstract
Transporter proteins are of great importance for improving the tolerance of fermentation strains to lignocellulose-derived furans and phenolic inhibitors. Different from the documented transporter proteins responsible for the tolerance of furfural and 5-hydroxymethyl-furfural (HMF), transporters responsible for that of varied phenolic aldehyde inhibitors were less investigated and elucidated. Here, an interesting phenomenon was found that no phenolic alcohols were accumulated from phenolic aldehydes degradation in Zymomonas mobilis. A transcriptional profiling of transporter genes was established in Z. mobilis ZM4 under phenolic aldehydes stress using DNA microarray. Six transporter proteins were identified as the potential candidates responsible for the tolerance of phenolic aldehydes including ABC transporter (ZMO0799 and ZMO0800), MFS transporter (ZMO1288 and ZMO1856), and RND transporter (ZMO0282 and ZMO0798). Furthermore, the analysis showed that the key transporters were significantly correlated with oxidoreductases and transcriptional regulators. This work would provide several important transporter genes serving as synthetic biology tools for improving the robustness of biorefinery strains.
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Affiliation(s)
- Xia Yi
- Jiangxi Provincial Key Laboratory of Systems Biomedicine, Jiujiang University, 17 Lufeng Road, Jiujiang, 332000, China.
| | - Ling Lin
- Jiangxi Provincial Key Laboratory of Systems Biomedicine, Jiujiang University, 17 Lufeng Road, Jiujiang, 332000, China
| | - Jun Mei
- Jiangxi Provincial Key Laboratory of Systems Biomedicine, Jiujiang University, 17 Lufeng Road, Jiujiang, 332000, China
| | - Wei Wang
- State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, China
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Chen J, Zhang A, Xiang Z, Lu M, Huang P, Gong T, Pan Y, Lin Y, Zhou X, Li Y. EpsR Negatively Regulates Streptococcus mutans Exopolysaccharide Synthesis. J Dent Res 2021; 100:968-976. [PMID: 33749354 DOI: 10.1177/00220345211000668] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Streptococcus mutans is considered the primary etiological agent of human dental caries. Glucosyltransferases (Gtfs) from S. mutans play important roles in the formation of biofilm matrix and the development of cariogenic oral biofilm. Therefore, Gtfs are considered an important target to prevent the development of dental caries. However, the role of transcription factors in regulating gtf expression is not yet clear. Here, we identify a MarR (multiple antibiotic resistance regulator) family transcription factor named EpsR (exopolysaccharide synthesis regulator), which negatively regulates gtfB expression and exopolysaccharide (EPS) production in S. mutans. The epsR in-frame deletion strain grew slowly, aggregated more easily in the presence of dextran, and displayed different colony morphology and biofilm structure. Notably, epsR deletion resulted in altered 3-dimensional biofilm architecture, increased water-insoluble EPS production, and upregulated GtfB protein content and activity. In addition, global gene expression profiling revealed differences in the expression levels of 69 genes in which gtfB was markedly upregulated. The conserved DNA motif for EpsR binding was determined by electrophoretic mobility shift assay and DNase I footprinting assays. Moreover, analysis of β-galactosidase activity suggested that EpsR acted as a repressor and inhibited gtfB expression. Taken together, our findings indicate that EpsR is an important transcription factor that regulates gtfB expression and EPS production in S. mutans. These results add new aspects to the complexity of regulating the expression of genes involved in the cariogenicity of S. mutans, which might lead to novel strategies to prevent the formation of cariogenic biofilm that may favor diseases.
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Affiliation(s)
- J Chen
- Department of Operative Dentistry and Endodontics, State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China
| | - A Zhang
- Department of Operative Dentistry and Endodontics, State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China
| | - Z Xiang
- Department of Operative Dentistry and Endodontics, State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China
| | - M Lu
- Department of Operative Dentistry and Endodontics, State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China
| | - P Huang
- Department of Operative Dentistry and Endodontics, State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China
| | - T Gong
- Department of Operative Dentistry and Endodontics, State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China
| | - Y Pan
- Department of Operative Dentistry and Endodontics, State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China
| | - Y Lin
- Department of Operative Dentistry and Endodontics, State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China
| | - X Zhou
- Department of Operative Dentistry and Endodontics, State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China
| | - Y Li
- Department of Operative Dentistry and Endodontics, State Key Laboratory of Oral Diseases, National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, China
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Shields RC, Kim JN, Ahn SJ, Burne RA. Peptides encoded in the Streptococcus mutans RcrRPQ operon are essential for thermotolerance. MICROBIOLOGY-SGM 2020; 166:306-317. [PMID: 31935187 DOI: 10.1099/mic.0.000887] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The MarR-like transcriptional regulator and two ABC transporters encoded by the rcrRPQ operon in the dental caries pathogen Streptococcus mutans have important regulatory roles related to oxidative stress tolerance, genetic competence and (p)ppGpp metabolism. A unique feature of the rcrRPQ operon, when compared to other bacteria, is the presence of two peptides, designated Pep1 and Pep2, encoded in alternative reading frames at the 3' end of rcrQ. Here, we show that the rcrRPQ operon, including Pep1 and 2, is essential for S. mutans to survive and maintain viability at elevated temperatures. No major changes in the levels of the heat shock proteins DnaK or GroEL that could account for the thermosensitivity of rcrRPQ mutants were observed. By introducing a single amino acid substitution into the comX gene that deletes an internally encoded peptide, XrpA, we found that XrpA is a contributing factor to the thermosensitive phenotype of a ΔrcrR strain. Overexpression of XrpA on a plasmid also caused a significant growth defect at 42 °C. Interestingly, loss of the gene for the RelA/SpoT homologue (RSH) enzyme, relA, restored growth of the ΔrcrR strain at 42 °C. During heat stress and when a stringent response was induced, levels of (p)ppGpp were elevated in the ΔrcrR strain. Deletion of relA in the ΔrcrR strain lowered the basal levels of (p)ppGpp to those observed in wild-type S. mutans. Thus, (p)ppGpp pools are dysregulated in ΔrcrR, which likely leads to aberrant control of transcriptional/translational processes and the thermosensitive phenotype. In summary, the genes and peptides encoded in the rcrRPQ operon are critical for thermotolerance, and in some strains these phenotypes are related to altered (p)ppGpp metabolism and increased production of the XrpA peptide.
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Affiliation(s)
- Robert C Shields
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida, USA
| | - Jeong Nam Kim
- Department of Microbiology, College of Natural Sciences, Pusan National University, Busan 46241, Republic of Korea
| | - Sang-Joon Ahn
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida, USA
| | - Robert A Burne
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida, USA
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Puccio T, Kunka KS, Zhu B, Xu P, Kitten T. Manganese Depletion Leads to Multisystem Changes in the Transcriptome of the Opportunistic Pathogen Streptococcus sanguinis. Front Microbiol 2020; 11:592615. [PMID: 33250881 PMCID: PMC7674665 DOI: 10.3389/fmicb.2020.592615] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Accepted: 10/07/2020] [Indexed: 12/13/2022] Open
Abstract
Streptococcus sanguinis is a primary colonizer of teeth and is typically considered beneficial due to its antagonistic relationship with the cariogenic pathogen Streptococcus mutans. However, S. sanguinis can also act as an opportunistic pathogen should it enter the bloodstream and colonize a damaged heart valve, leading to infective endocarditis. Studies have implicated manganese acquisition as an important virulence determinant in streptococcal endocarditis. A knockout mutant lacking the primary manganese import system in S. sanguinis, SsaACB, is severely attenuated for virulence in an in vivo rabbit model. Manganese is a known cofactor for several important enzymes in S. sanguinis, including superoxide dismutase, SodA, and the aerobic ribonucleotide reductase, NrdEF. To determine the effect of manganese depletion on S. sanguinis, we performed transcriptomic analysis on a ΔssaACB mutant grown in aerobic fermentor conditions after the addition of the metal chelator EDTA. Despite the broad specificity of EDTA, analysis of cellular metal content revealed a decrease in manganese, but not in other metals, that coincided with a drop in growth rate. Subsequent supplementation with manganese, but not iron, zinc, or magnesium, restored growth in the fermentor post-EDTA. Reduced activity of Mn-dependent SodA and NrdEF likely contributed to the decreased growth rate post-EDTA, but did not appear entirely responsible. With the exception of the Dps-like peroxide resistance gene, dpr, manganese depletion did not induce stress response systems. By comparing the transcriptome of ΔssaACB cells pre- and post-EDTA, we determined that manganese deprivation led to altered expression of diverse systems. Manganese depletion also led to an apparent induction of carbon catabolite repression in a glucose-independent manner. The combined results suggest that manganese limitation produces effects in S. sanguinis that are diverse and complex, with no single protein or system appearing entirely responsible for the observed growth rate decrease. This study provides further evidence for the importance of this trace element in streptococcal biology. Future studies will focus on determining mechanisms for regulation, as the multitude of changes observed in this study indicate that multiple regulators may respond to manganese levels.
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Affiliation(s)
| | | | | | | | - Todd Kitten
- Philips Institute for Oral Health Research, Virginia Commonwealth University, Richmond, VA, United States
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Krishnan S, Chatterji D. Pleiotropic Effects of Bacterial Small Alarmone Synthetases: Underscoring the Dual-Domain Small Alarmone Synthetases in Mycobacterium smegmatis. Front Microbiol 2020; 11:594024. [PMID: 33154743 PMCID: PMC7591505 DOI: 10.3389/fmicb.2020.594024] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2020] [Accepted: 09/17/2020] [Indexed: 11/13/2022] Open
Abstract
The nucleotide alarmone (p)ppGpp, signaling the stringent response, is known for more than 5 decades. The cellular turnover of the alarmone is regulated by RelA/SpoT homolog (RSH) superfamily of enzymes. There are long RSHs (RelA, SpoT, and Rel) and short RSHs [small alarmone synthetases (SAS) and small alarmone hydrolases (SAH)]. Long RSHs are multidomain proteins with (p)ppGpp synthesis, hydrolysis, and regulatory functions. Short RSHs are single-domain proteins with a single (p)ppGpp synthesis/hydrolysis function with few exceptions having two domains. Mycobacterial RelZ is a dual-domain SAS with RNase HII and the (p)ppGpp synthetase activity. SAS is known to impact multiple cellular functions independently and in accordance with the long RSH. Few SAS in bacteria including RelZ synthesize pGpp, the third small alarmone, along with the conventional (p)ppGpp. SAS can act as an RNA-binding protein for the negative allosteric inhibition of (p)ppGpp synthesis. Here, we initially recap the important features and molecular functions of different SAS that are previously characterized to understand the obligation for the “alarmone pool” produced by the long and short RSHs. Then, we focus on the RelZ, especially the combined functions of RNase HII and (p)ppGpp synthesis from a single polypeptide to connect with the recent findings of SAS as an RNA-binding protein. Finally, we conclude with the possibilities of using single-stranded RNA (ssRNA) as an additional therapeutic strategy to combat the persistent infections by inhibiting the redundant (p)ppGpp synthetases.
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Turner ME, Huynh K, Carney OV, Gross D, Carroll RK, Ahn SJ, Rice KC. Genomic instability of TnSMU2 contributes to Streptococcus mutans biofilm development and competence in a cidB mutant. Microbiologyopen 2019; 8:e934. [PMID: 31599128 PMCID: PMC6925190 DOI: 10.1002/mbo3.934] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Revised: 08/20/2019] [Accepted: 08/21/2019] [Indexed: 02/06/2023] Open
Abstract
Streptococcus mutans is a key pathogenic bacterium in the oral cavity and a primary contributor to dental caries. The S. mutans Cid/Lrg system likely contributes to tolerating stresses encountered in this environment as cid and/or lrg mutants exhibit altered oxidative stress sensitivity, genetic competence, and biofilm phenotypes. It was recently noted that the cidB mutant had two stable colony morphologies: a “rough” phenotype (similar to wild type) and a “smooth” phenotype. In our previously published work, the cidB rough mutant exhibited increased sensitivity to oxidative stress, and RNAseq identified widespread transcriptomic changes in central carbon metabolism and oxidative stress response genes. In this current report, we conducted Illumina‐based genome resequencing of wild type, cidB rough, and cidB smooth mutants and compared their resistance to oxidative and acid stress, biofilm formation, and competence phenotypes. Both cidB mutants exhibited comparable aerobic growth inhibition on agar plates, during planktonic growth, and in the presence of 1 mM hydrogen peroxide. The cidB smooth mutant displayed a significant competence defect in BHI, which was rescuable by synthetic CSP. Both cidB mutants also displayed reduced XIP‐mediated competence, although this reduction was more pronounced in the cidB smooth mutant. Anaerobic biofilms of the cidB smooth mutant displayed increased propidium iodide staining, but corresponding biofilm CFU data suggest this phenotype is due to cell damage and not increased cell death. The cidB rough anaerobic biofilms showed altered structure relative to wild type (reduced biomass and average thickness) which correlated with decreased CFU counts. Sequencing data revealed that the cidB smooth mutant has a unique “loss of read coverage” of ~78 kb of DNA, corresponding to the genomic island TnSMU2 and genes flanking its 3′ end. It is therefore likely that the unique biofilm and competence phenotypes of the cidB smooth mutant are related to its genomic changes in this region.
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Affiliation(s)
- Matthew E Turner
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, USA
| | - Khanh Huynh
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, USA
| | - O'neshia V Carney
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, USA
| | - Dennis Gross
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, USA
| | - Ronan K Carroll
- Department of Biological Sciences, Ohio University, Athens, OH, USA
| | - Sang-Joon Ahn
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, FL, USA
| | - Kelly C Rice
- Department of Microbiology and Cell Science, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL, USA
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Lichev A, Angelov A, Cucurull I, Liebl W. Amino acids as nutritional factors and (p)ppGpp as an alarmone of the stringent response regulate natural transformation in Micrococcus luteus. Sci Rep 2019; 9:11030. [PMID: 31363120 PMCID: PMC6667448 DOI: 10.1038/s41598-019-47423-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Accepted: 07/15/2019] [Indexed: 11/10/2022] Open
Abstract
Natural competence for genetic transformation refers to the natural ability of various bacteria to take up exogenous DNA from their surroundings and to incorporate internalized genetic information into their genomes. By promoting bacterial diversification and adaptability, this process represents a major driving force in bacterial evolution. Micrococcus luteus was one of the first organisms used to study natural transformation in bacteria. Since then, however, only very little information about this phenomenon has been reported in M. luteus or in any member of the Actinobacteria phylum (low-GC Gram-positive bacteria). Previous work in our group indicated major differences between the transformation apparatus of M. luteus and the transformation machinery described for various Gram-negative and Gram-positive model bacteria belonging to the phyla Proteobacteria and Firmicutes (high-GC Gram-positive bacteria). This prompted us to initiate a study concerning the regulation mechanism of competence development in M. luteus. In this report, we identify amino acids as a nutritional factor that influences competence in a concentration-dependent manner. By using a transcriptional reporter strain for one of the late competence genes, we demonstrate how increasing concentrations of both amino acids mixtures and single amino acids supplemented to the growth medium affect transformability on transcriptional and post-transcriptional level. Furthermore, we revisit previously generated auxotrophic mutants to show that the transformation machinery is turned down during a state of extreme hunger for amino acids presumably as a part of a general response to auxotrophy. Finally, by generating and analysing knockout mutants for two predicted stringent response enzymes, we provide evidence for the involvement of the alarmone (p)ppGpp as a putative mediator of the effects on transformation development caused by amino acids. As a member of the Actinobacteria phylum, M. luteus could serve as a model for other representatives of the phylum, including a number of important human pathogens.
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Affiliation(s)
- Antoni Lichev
- Chair of Microbiology, Technical University of Munich, Freising-Weihenstephan, Germany
| | - Angel Angelov
- Chair of Microbiology, Technical University of Munich, Freising-Weihenstephan, Germany
| | - Inigo Cucurull
- Chair of Microbiology, Technical University of Munich, Freising-Weihenstephan, Germany
| | - Wolfgang Liebl
- Chair of Microbiology, Technical University of Munich, Freising-Weihenstephan, Germany.
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Spontaneously Arising Streptococcus mutans Variants with Reduced Susceptibility to Chlorhexidine Display Genetic Defects and Diminished Fitness. Antimicrob Agents Chemother 2019; 63:AAC.00161-19. [PMID: 31036688 DOI: 10.1128/aac.00161-19] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2019] [Accepted: 04/20/2019] [Indexed: 01/10/2023] Open
Abstract
Chlorhexidine (CHX) has been used to control dental caries caused by acid-tolerant bacteria such as Streptococcus mutans since the 1970s. Repeat CHX exposure for other bacterial species results in the development of variants with reduced susceptibility that also become more resistant to other antimicrobials. It has not been tested if such variants arise when streptococci are exposed to CHX. Here, we passaged S. mutans in increasing concentrations of CHX and isolated spontaneously arising reduced susceptibility variants (RSVs) from separate lineages that have MICs that are up to 3-fold greater than the parental strain. The RSVs have increased growth rates at neutral pH and under acidic conditions in the presence of CHX but accumulate less biomass in biofilms. RSVs display higher MICs for daptomycin and clindamycin but increased sensitivity to dental-relevant antimicrobials triclosan and sodium fluoride. Plate-based assays for competition with health-associated oral streptococci revealed decreased bacteriocin production by the RSVs, increased sensitivity to hydrogen peroxide, and diminished competitive fitness in a human-derived ex vivo biofilm consortium. Whole-genome sequencing identified common single nucleotide polymorphisms (SNPs) within a diacylglycerol kinase homolog and a glycolipid synthesis enzyme, which could alter the accumulation of lipoteichoic acids and other envelope constituents, as well as a variety of mutations in other genes. Collectively, these findings confirm that S. mutans and likely other streptococci can develop tolerance to CHX but that increased tolerance comes at a fitness cost, such that CHX-induced variants that spontaneously arise in the human oral cavity may not persist.
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13
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Kaspar JR, Walker AR. Expanding the Vocabulary of Peptide Signals in Streptococcus mutans. Front Cell Infect Microbiol 2019; 9:194. [PMID: 31245303 PMCID: PMC6563777 DOI: 10.3389/fcimb.2019.00194] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Accepted: 05/21/2019] [Indexed: 12/18/2022] Open
Abstract
Streptococci, including the dental pathogen Streptococcus mutans, undergo cell-to-cell signaling that is mediated by small peptides to control critical physiological functions such as adaptation to the environment, control of subpopulation behaviors and regulation of virulence factors. One such model pathway is the regulation of genetic competence, controlled by the ComRS signaling system and the peptide XIP. However, recent research in the characterization of this pathway has uncovered novel operons and peptides that are intertwined into its regulation. These discoveries, such as cell lysis playing a critical role in XIP release and importance of bacterial self-sensing during the signaling process, have caused us to reevaluate previous paradigms and shift our views on the true purpose of these signaling systems. The finding of new peptides such as the ComRS inhibitor XrpA and the peptides of the RcrRPQ operon also suggests there may be more peptides hidden in the genomes of streptococci that could play critical roles in the physiology of these organisms. In this review, we summarize the recent findings in S. mutans regarding the integration of other circuits into the ComRS signaling pathway, the true mode of XIP export, and how the RcrRPQ operon controls competence activation. We also look at how new technologies can be used to re-annotate the genome to find new open reading frames that encode peptide signals. Together, this summary of research will allow us to reconsider how we perceive these systems to behave and lead us to expand our vocabulary of peptide signals within the genus Streptococcus.
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Affiliation(s)
- Justin R. Kaspar
- Department of Oral Biology, University of Florida, Gainesville, FL, United States
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14
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Zeng L, Burne RA. Essential Roles of the sppRA Fructose-Phosphate Phosphohydrolase Operon in Carbohydrate Metabolism and Virulence Expression by Streptococcus mutans. J Bacteriol 2019; 201:e00586-18. [PMID: 30348833 PMCID: PMC6304665 DOI: 10.1128/jb.00586-18] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Accepted: 10/16/2018] [Indexed: 11/20/2022] Open
Abstract
The dental caries pathogen Streptococcus mutans can ferment a variety of sugars to produce organic acids. Exposure of S. mutans to certain nonmetabolizable carbohydrates, such as xylitol, impairs growth and can cause cell death. Recently, the presence of a sugar-phosphate stress in S. mutans was demonstrated using a mutant lacking 1-phosphofructokinase (FruK) that accumulates fructose-1-phosphate (F-1-P). Here, we studied an operon in S. mutans, sppRA, which was highly expressed in the fruK mutant. Biochemical characterization of a recombinant SppA protein indicated that it possessed hexose-phosphate phosphohydrolase activity, with preferences for F-1-P and, to a lesser degree, fructose-6-phosphate (F-6-P). SppA activity was stimulated by Mg2+ and Mn2+ but inhibited by NaF. SppR, a DeoR family regulator, repressed the expression of the sppRA operon to minimum levels in the absence of the fructose-derived metabolite F-1-P and likely also F-6-P. The accumulation of F-1-P, as a result of growth on fructose, not only induced sppA expression, but it significantly altered biofilm maturation through increased cell lysis and enhanced extracellular DNA release. Constitutive expression of sppA, via a plasmid or by deleting sppR, greatly alleviated fructose-induced stress in a fruK mutant, enhanced resistance to xylitol, and reversed the effects of fructose on biofilm formation. Finally, by identifying three additional putative phosphatases that are capable of promoting sugar-phosphate tolerance, we show that S. mutans is capable of mounting a sugar-phosphate stress response by modulating the levels of certain glycolytic intermediates, functions that are interconnected with the ability of the organism to manifest key virulence behaviors.IMPORTANCEStreptococcus mutans is a major etiologic agent for dental caries, primarily due to its ability to form biofilms on the tooth surface and to convert carbohydrates into organic acids. We have discovered a two-gene operon in S. mutans that regulates fructose metabolism by controlling the levels of fructose-1-phosphate, a potential signaling compound that affects bacterial behaviors. With fructose becoming increasingly common and abundant in the human diet, we reveal the ways that fructose may alter bacterial development, stress tolerance, and microbial ecology in the oral cavity to promote oral diseases.
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Affiliation(s)
- Lin Zeng
- Department of Oral Biology, University of Florida, Gainesville, Florida, USA
| | - Robert A Burne
- Department of Oral Biology, University of Florida, Gainesville, Florida, USA
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15
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Junges R, Salvadori G, Chen T, Morrison DA, Petersen FC. Hidden Gems in the Transcriptome Maps of Competent Streptococci. Front Mol Biosci 2019; 5:116. [PMID: 30662898 PMCID: PMC6328492 DOI: 10.3389/fmolb.2018.00116] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2018] [Accepted: 12/11/2018] [Indexed: 11/22/2022] Open
Abstract
Natural transformation is regarded as an important mechanism in bacteria that allows for adaptation to different environmental stressors by ensuring genome plasticity. Since the discovery of this phenomenon in Streptococcus pneumoniae, remarkable progress has been made in the understanding of the molecular mechanisms and pathways coordinating this process. Recently, the advent of high-throughput sequencing allows the posing of questions that address the system at a larger scale but also allow for the creation of high-resolution maps of transcription. Thus, while much is already known about genetic competence in streptococci, recent studies continue to reveal intricate novel regulation pathways and components. In this perspective article, we highlight the use of transcriptional profiling and mapping as a valuable resource in the identification and characterization of “hidden gems” pertinent to the natural transformation system. Such strategies have recently been employed in a variety of different species. In S. mutans, for example, genome editing combined with the power of promoter mapping and RNA-Seq allowed for the identification of a link between the ComCDE and the ComRS systems, a ComR positive feedback loop mediated by SigX, and the XrpA peptide, encoded within sigX, which inhibits competence. In S. pneumoniae, a novel member of the competence regulon termed BriC was found to be directly under control of ComE and to promote biofilm formation and nasopharyngeal colonization but not competence. Together these new technologies enable us to discover new links and to revisit old pathways in the compelling study of natural genetic transformation.
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Affiliation(s)
- Roger Junges
- Faculty of Dentistry, Institute of Oral Biology, University of Oslo, Oslo, Norway
| | - Gabriela Salvadori
- Faculty of Dentistry, Institute of Oral Biology, University of Oslo, Oslo, Norway
| | - Tsute Chen
- Department of Microbiology, The Forsyth Institute, Cambridge, MA, United States
| | - Donald A Morrison
- Department of Biological Sciences, College of Liberal Arts and Sciences, University of Illinois at Chicago, Chicago, IL, United States
| | - Fernanda C Petersen
- Faculty of Dentistry, Institute of Oral Biology, University of Oslo, Oslo, Norway
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16
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Lemos JA, Palmer SR, Zeng L, Wen ZT, Kajfasz JK, Freires IA, Abranches J, Brady LJ. The Biology of Streptococcus mutans. Microbiol Spectr 2019; 7:10.1128/microbiolspec.GPP3-0051-2018. [PMID: 30657107 PMCID: PMC6615571 DOI: 10.1128/microbiolspec.gpp3-0051-2018] [Citation(s) in RCA: 287] [Impact Index Per Article: 57.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Indexed: 12/30/2022] Open
Abstract
As a major etiological agent of human dental caries, Streptococcus mutans resides primarily in biofilms that form on the tooth surfaces, also known as dental plaque. In addition to caries, S. mutans is responsible for cases of infective endocarditis with a subset of strains being indirectly implicated with the onset of additional extraoral pathologies. During the past 4 decades, functional studies of S. mutans have focused on understanding the molecular mechanisms the organism employs to form robust biofilms on tooth surfaces, to rapidly metabolize a wide variety of carbohydrates obtained from the host diet, and to survive numerous (and frequent) environmental challenges encountered in oral biofilms. In these areas of research, S. mutans has served as a model organism for ground-breaking new discoveries that have, at times, challenged long-standing dogmas based on bacterial paradigms such as Escherichia coli and Bacillus subtilis. In addition to sections dedicated to carbohydrate metabolism, biofilm formation, and stress responses, this article discusses newer developments in S. mutans biology research, namely, how S. mutans interspecies and cross-kingdom interactions dictate the development and pathogenic potential of oral biofilms and how next-generation sequencing technologies have led to a much better understanding of the physiology and diversity of S. mutans as a species.
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Affiliation(s)
- JA Lemos
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL
| | - SR Palmer
- Division of Biosciences, College of Dentistry, Ohio State University, Columbus, OH
| | - L Zeng
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL
| | - ZT Wen
- Dapartment of Comprehensive Dentistry and Biomaterials and Department of Microbiology, Immunology and Parasitology, Louisiana State University Health Sciences Center, New Orleans, LA
| | - JK Kajfasz
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL
| | - IA Freires
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL
| | - J Abranches
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL
| | - LJ Brady
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL
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17
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Son M, Kaspar J, Ahn SJ, Burne RA, Hagen SJ. Threshold regulation and stochasticity from the MecA/ClpCP proteolytic system in Streptococcus mutans competence. Mol Microbiol 2018; 110:914-930. [PMID: 29873131 PMCID: PMC6281771 DOI: 10.1111/mmi.13992] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/21/2018] [Indexed: 12/28/2022]
Abstract
Many bacterial species use the MecA/ClpCP proteolytic system to block entry into genetic competence. In Streptococcus mutans, MecA/ClpCP degrades ComX (also called SigX), an alternative sigma factor for the comY operon and other late competence genes. Although the mechanism of MecA/ClpCP has been studied in multiple Streptococcus species, its role within noisy competence pathways is poorly understood. S. mutans competence can be triggered by two different peptides, CSP and XIP, but it is not known whether MecA/ClpCP acts similarly for both stimuli, how it affects competence heterogeneity, and how its regulation is overcome. We have studied the effect of MecA/ClpCP on the activation of comY in individual S. mutans cells. Our data show that MecA/ClpCP is active under both XIP and CSP stimulation, that it provides threshold control of comY, and that it adds noise in comY expression. Our data agree quantitatively with a model in which MecA/ClpCP prevents adventitious entry into competence by sequestering or intercepting low levels of ComX. Competence is permitted when ComX levels exceed a threshold, but cell‐to‐cell heterogeneity in MecA levels creates variability in that threshold. Therefore, MecA/ClpCP provides a stochastic switch, located downstream of the already noisy comX, that enhances phenotypic diversity.
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Affiliation(s)
- M Son
- Department of Physics, University of Florida, Gainesville, FL 32611, USA
| | - J Kaspar
- Department of Oral Biology, University of Florida, Gainesville, FL 32610, USA
| | - S J Ahn
- Department of Oral Biology, University of Florida, Gainesville, FL 32610, USA
| | - R A Burne
- Department of Oral Biology, University of Florida, Gainesville, FL 32610, USA
| | - S J Hagen
- Department of Physics, University of Florida, Gainesville, FL 32611, USA
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18
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Characterization of the Trehalose Utilization Operon in Streptococcus mutans Reveals that the TreR Transcriptional Regulator Is Involved in Stress Response Pathways and Toxin Production. J Bacteriol 2018; 200:JB.00057-18. [PMID: 29632089 DOI: 10.1128/jb.00057-18] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Accepted: 03/30/2018] [Indexed: 11/20/2022] Open
Abstract
Streptococcus mutans, the organism most frequently associated with the development of dental caries, is able to utilize a diverse array of carbohydrates for energy metabolism. One such molecule is trehalose, a disaccharide common in human foods, which has been recently implicated in enhancing the virulence of epidemic strains of the pathogen Clostridium difficile In this study, mutants with deletions of all three genes in the putative S. mutans trehalose utilization operon were characterized, and the genes were shown to be required for wild-type levels of growth when trehalose was the only carbohydrate source provided. Interestingly, the TreR transcriptional regulator appeared to be critical for responding to oxidative stress and for mounting a protective stress tolerance response following growth at moderately acidic pH. mRNA sequencing (RNA-seq) of a treR deletion mutant suggested that in S. mutans, TreR acts as a trehalose-sensing activator of transcription of the tre operon, rather than as a repressor, as described in other species. In addition, deletion of treR caused the downregulation of a number of genes involved in genetic competence and bacteriocin production, supporting the results of a recent study linking trehalose and the S. mutans competence pathways. Finally, deletion of treR compromised the ability of S. mutans to inhibit the growth of the competing species Streptococcus gordonii and Lactococcus lactis Taking the results together, this study solidifies the role of the S. mutans tre operon in trehalose utilization and suggests novel functions for the TreR regulator, including roles in the stress response and competitive fitness.IMPORTANCES. mutans is the primary etiologic agent of dental caries, which globally is the most common chronic disease. S. mutans must be able to outcompete commensal organisms in its dental plaque niche in order to establish persistence and pathogenesis. To that end, S. mutans metabolizes a diverse array of carbohydrates to generate acid and impede its acid-sensitive neighbors. Additionally, S. mutans utilizes quorum signaling through genetic competence-associated pathways to induce production of toxins to kill its rivals. This study definitively shows that the S. mutans trehalose utilization operon is required for growth in trehalose. Furthermore, this study suggests that the S. mutans TreR transcriptional regulator has a novel role in virulence through regulation of genes involved in genetic competence and toxin production.
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19
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Shields RC, Zeng L, Culp DJ, Burne RA. Genomewide Identification of Essential Genes and Fitness Determinants of Streptococcus mutans UA159. mSphere 2018; 3:e00031-18. [PMID: 29435491 PMCID: PMC5806208 DOI: 10.1128/msphere.00031-18] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Accepted: 01/19/2018] [Indexed: 11/20/2022] Open
Abstract
Transposon mutagenesis coupled with next-generation DNA sequencing (Tn-seq) is a powerful tool for discovering regions of the genome that are required for the survival of bacteria in different environments. We adapted this technique to the dental caries pathogen Streptococcus mutans UA159 and identified 11% of the genome as essential, with many genes encoding products required for replication, translation, lipid metabolism, and cell wall biogenesis. Comparison of the essential genome of S. mutans UA159 with those of selected other streptococci for which such information is available revealed several metabolic pathways and genes that are required in S. mutans, but not in some Streptococcus spp. We further identified genes that are essential for sustained growth in rich or defined medium, as well as for persistence in vivo in a rodent model of oral infection. Collectively, our results provide a novel and comprehensive view of the genes required for essential processes of S. mutans, many of which could represent potential targets for therapeutics. IMPORTANCE Tooth decay (dental caries) is a common cause of pain, impaired quality of life, and tooth loss in children and adults. It begins because of a compositional change in the microorganisms that colonize the tooth surface driven by repeated and sustained carbohydrate intake. Although several bacterial species are associated with tooth decay, Streptococcus mutans is the most common cause. Therefore, it is important to identify biological processes that contribute to the survival of S. mutans in the human mouth, with the aim of disrupting the processes with antimicrobial agents. We successfully applied Tn-seq to S. mutans, discovering genes that are required for survival, growth, and persistence, both in laboratory environments and in a mouse model of tooth decay. This work highlights new avenues for the control of an important human pathogen.
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Affiliation(s)
- Robert C. Shields
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida, USA
| | - Lin Zeng
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida, USA
| | - David J. Culp
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida, USA
| | - Robert A. Burne
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida, USA
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20
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Genome-Wide Screens Reveal New Gene Products That Influence Genetic Competence in Streptococcus mutans. J Bacteriol 2017; 200:JB.00508-17. [PMID: 29109185 DOI: 10.1128/jb.00508-17] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Accepted: 10/26/2017] [Indexed: 12/11/2022] Open
Abstract
A network of genes and at least two peptide signaling molecules tightly control when Streptococcus mutans becomes competent to take up DNA from its environment. Widespread changes in the expression of genes occur when S. mutans is presented with competence signal peptides in vitro, including the increased production of the alternative sigma factor, ComX, which activates late competence genes. Still, the way that gene products that are regulated by competence peptides influence DNA uptake and cellular physiology are not well understood. Here, we developed and employed comprehensive transposon mutagenesis of the S. mutans genome, with a screen to identify mutants that aberrantly expressed comX, coupled with transposon sequencing (Tn-seq) to gain a more thorough understanding of the factors modulating comX expression and progression to the competent state. The screens effectively identified genes known to affect competence, e.g., comR, comS, comD, comE, cipB, clpX, rcrR, and ciaH, but disclosed an additional 20 genes that were not previously competence associated. The competence phenotypes of mutants were characterized, including by fluorescence microscopy to determine at which stage the mutants were impaired for comX activation. Among the novel genes studied were those implicated in cell division, the sensing of cell envelope stress, cell envelope biogenesis, and RNA stability. Our results provide a platform for determining the specific chemical and physical cues that are required for genetic competence in S. mutans, while highlighting the effectiveness of using Tn-seq in S. mutans to discover and study novel biological processes.IMPORTANCE Streptococcus mutans acquires DNA from its environment by becoming genetically competent, a physiologic state triggered by cell-cell communication using secreted peptides. Competence is important for acquiring novel genetic traits and has a strong influence on the expression of virulence-associated traits of S. mutans Here, we used transposon mutagenesis and genomic technologies to identify novel genes involved in competence development. In addition to identifying genes previously known to be required for comX expression, 20 additional genes were identified and characterized. The findings create opportunities to diminish the pathogenic potential of S. mutans, while validating technologies that can rapidly advance our understanding of the physiology, biology, and genetics of S. mutans and related pathogens.
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21
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Kajfasz JK, Ganguly T, Hardin EL, Abranches J, Lemos JA. Transcriptome responses of Streptococcus mutans to peroxide stress: identification of novel antioxidant pathways regulated by Spx. Sci Rep 2017; 7:16018. [PMID: 29167560 PMCID: PMC5700188 DOI: 10.1038/s41598-017-16367-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Accepted: 11/02/2017] [Indexed: 01/12/2023] Open
Abstract
The oxidative stress regulator Spx is ubiquitously found among Gram-positive bacteria. Previously, we reported identification of two Spx proteins in Streptococcus mutans - SpxA1 was the primary activator of oxidative stress genes whereas SpxA2 served a backup role. Here, we used RNA sequencing to uncover the scope of the H2O2 (peroxide)-stress regulon and to further explore the significance of Spx regulation in S. mutans. The transcriptome data confirmed the relationship between Spx and genes typically associated with oxidative stress, but also identified novel genes and metabolic pathways controlled by Spx during peroxide stress. While individual inactivation of newly identified peroxide stress genes had modest or no obvious consequences to bacterial survival, a phenotype enhancement screen using the ∆spxA1 strain as background for creation of double mutants revealed that four of the five genes inactivated were required for stress survival. Physiological and biochemical assays validated, at least in part, the transcriptome data indicating that SpxA1 coordinates transcriptional changes during peroxide stress that modify global metabolism and facilitate production of antioxidants. Collectively, our findings unraveled the scope of the peroxide stress regulon and expand the repertoire of oxidative stress genes in S. mutans, shedding new light on the role of Spx regulation.
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Affiliation(s)
- Jessica K Kajfasz
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, 32608, USA
| | - Tridib Ganguly
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, 32608, USA
| | - Emily L Hardin
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, 32608, USA
| | - Jacqueline Abranches
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, 32608, USA
| | - José A Lemos
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, 32608, USA.
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22
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Intercellular Communication via the comX-Inducing Peptide (XIP) of Streptococcus mutans. J Bacteriol 2017; 199:JB.00404-17. [PMID: 28808131 DOI: 10.1128/jb.00404-17] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Accepted: 08/08/2017] [Indexed: 12/29/2022] Open
Abstract
Gram-positive bacteria utilize exported peptides to coordinate genetic and physiological processes required for biofilm formation, stress responses, and ecological competitiveness. One example is activation of natural genetic competence by ComR and the com X -inducing peptide (XIP) in Streptococcus mutans Although the competence pathway can be activated by the addition of synthetic XIP in defined medium, the hypothesis that XIP is able to function as an intercellular signaling molecule has not been rigorously tested. Coculture model systems were developed that included a "sender" strain that overexpressed the XIP precursor (ComS) and a "responder" strain harboring a green fluorescent protein (GFP) reporter fused to a ComR-activated gene (comX) promoter. The ability of the sender strain to provide a signal to activate GFP expression was monitored at the individual cell and population levels using (i) planktonic culture systems, (ii) cells suspended in an agarose matrix, or (iii) cells growing in biofilms. XIP was shown to be freely diffusible, and XIP signaling between the S. mutans sender and responder strains did not require cell-to-cell contact. The presence of a sucrose-derived exopolysaccharide matrix diminished the efficiency of XIP signaling in biofilms, possibly by affecting the spatial distribution of XIP senders and potential responders. Intercellular signaling was greatly impaired in a strain lacking the primary autolysin, AtlA, and was substantially greater when the sender strain underwent lysis. Collectively, these data provide evidence that S. mutans XIP can indeed function as a peptide signal between cells and highlight the importance of studying signaling with an endogenously produced peptide(s) in populations in various environments and physiologic states.IMPORTANCE The comX-inducing peptide (XIP) of Streptococcus mutans is a key regulatory element in the activation of genetic competence, which allows cells to take up extracellular DNA. XIP has been found in cell culture fluids, and the addition of synthetic XIP to physiologically receptive cells can robustly induce competence gene expression. However, there is a lack of consensus as to whether XIP can function as an intercellular communication signal. Here, we show that XIP indeed signals between cells in S. mutans, but that cell lysis may be a critical factor, as opposed to a dedicated secretion/processing system, in allowing for release of XIP into the environment. The results have important implications in the context of the ecology, virulence, and evolution of a ubiquitous human pathogen and related organisms.
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23
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Silva AF, Antunes S, Freitas F, Carvalho G, Reis MAM, Barreto Crespo MT. Impact of sludge retention time on MBR fouling: role of extracellular polymeric substances determined through membrane autopsy. BIOFOULING 2017; 33:556-566. [PMID: 28675051 DOI: 10.1080/08927014.2017.1333112] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2016] [Accepted: 05/16/2017] [Indexed: 06/07/2023]
Abstract
The impact of sludge retention time (SRT) on the biofouling of a membrane bioreactor (MBR) by extracellular polymeric substances (EPS) was investigated. The MBR was operated at 60 and 20 d SRT. The gel layer (recovered through optimized membrane autopsy methods) and the cake layer were analyzed for their content and profile of EPS proteins and polysaccharides. The change to a shorter SRT led to decreased membrane filterability, concomitant with a higher expression of EPS proteins in the cake layer, which were identified as being mainly related with biosynthesis and stress functions. The gel layer was more substantial in internal fibers, with polysaccharides being the major component in this layer. With the decrease in SRT (and filterability decrease), the overall polysaccharide content and sugar variety increased. In conclusion, SRT impacted not only on the quantity but also the composition of EPS molecules, and both were shown to be important in biofouling.
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Affiliation(s)
- Ana F Silva
- a IBET - Instituto de Biologia Experimental , Oeiras , Portugal
- b Instituto de Tecnologia Química e Biológica António Xavier , Universidade Nova de Lisboa , Oeiras , Portugal
| | - Silvia Antunes
- c UCIBIO-REQUIMTE, Chemistry Department, Faculdade de Ciências e Tecnologia , Universidade Nova de Lisboa , Caparica , Portugal
| | - Filomena Freitas
- c UCIBIO-REQUIMTE, Chemistry Department, Faculdade de Ciências e Tecnologia , Universidade Nova de Lisboa , Caparica , Portugal
| | - Gilda Carvalho
- c UCIBIO-REQUIMTE, Chemistry Department, Faculdade de Ciências e Tecnologia , Universidade Nova de Lisboa , Caparica , Portugal
| | - Maria A M Reis
- c UCIBIO-REQUIMTE, Chemistry Department, Faculdade de Ciências e Tecnologia , Universidade Nova de Lisboa , Caparica , Portugal
| | - Maria T Barreto Crespo
- a IBET - Instituto de Biologia Experimental , Oeiras , Portugal
- b Instituto de Tecnologia Química e Biológica António Xavier , Universidade Nova de Lisboa , Oeiras , Portugal
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24
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Effects of Arginine on Streptococcus mutans Growth, Virulence Gene Expression, and Stress Tolerance. Appl Environ Microbiol 2017; 83:AEM.00496-17. [PMID: 28526785 DOI: 10.1128/aem.00496-17] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Accepted: 05/11/2017] [Indexed: 11/20/2022] Open
Abstract
Streptococcus mutans is a common constituent of oral biofilms and a primary etiologic agent of human dental caries. The bacteria associated with dental caries have potent abilities to produce organic acids from dietary carbohydrates and to grow and metabolize in acidic conditions. By contrast, many commensal bacteria produce ammonia through the arginine deiminase system (ADS), which moderates the pH of oral biofilms. Arginine metabolism by the ADS is a significant deterrent to the initiation and progression of dental caries. In this study, we observed how exogenously provided l-arginine affects the growth, the virulence properties, and the tolerance of environmental stresses of S. mutans Supplementation with 1.5% arginine (final concentration) had an inhibitory effect on the growth of S. mutans in complex and chemically defined media, particularly when cells were exposed to acid or oxidative stress. The genes encoding virulence factors required for attachment/accumulation (gtfB and spaP), bacteriocins (nlmA, nlmB, nlmD, and cipB), and the sigma factor required for competence development (comX) were downregulated during growth with 1.5% arginine. Deep sequencing of RNA (RNA-Seq) comparing the transcriptomes of S. mutans growing in chemically defined media with and without 1.5% arginine revealed differential expression of genes encoding ATP-binding cassette transporters, metal transporters, and constituents required for survival, metabolism, and biofilm formation. Therefore, the mechanisms of action by which arginine inhibits dental caries include direct adverse effects on multiple virulence-related properties of the most common human dental caries pathogen.IMPORTANCE Metabolism of the amino acid arginine by the arginine deiminase system (ADS) of certain oral bacteria raises the pH of dental plaque and provides a selective advantage to health-associated bacteria, thereby protecting the host from dental caries (cavities). Here, we examine the effects of arginine on the cavity-causing bacterium Streptococcus mutans We find that arginine negatively impacts the growth, the pathogenic potential, and the tolerance of environmental stresses in a way that is likely to compromise the ability of S. mutans to cause disease. Using genetic and genomic techniques, multiple mechanisms by which arginine exerts its influence on virulence-related properties of S. mutans are discovered. This report demonstrates that a primary mechanism of action by which arginine inhibits the initiation and progression of dental caries may be by reducing the pathogenic potential of S. mutans.
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Zeng H, Liu J, Ling J. Efflux inhibitor suppresses Streptococcus mutans virulence properties. FEMS Microbiol Lett 2017; 364:2975576. [DOI: 10.1093/femsle/fnx033] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Accepted: 02/07/2017] [Indexed: 01/26/2023] Open
Affiliation(s)
- Huihui Zeng
- Guanghua School of Stomatology, Guangdong Province Key Laboratory of Stomatology, Sun Yat-Sen University, Guangzhou, China
- Applied Oral Sciences, Faculty of Dentistry, University of HongKong, HongKong
| | - Jia Liu
- Guanghua School of Stomatology, Guangdong Province Key Laboratory of Stomatology, Sun Yat-Sen University, Guangzhou, China
| | - Junqi Ling
- Guanghua School of Stomatology, Guangdong Province Key Laboratory of Stomatology, Sun Yat-Sen University, Guangzhou, China
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Investigation of simulated microgravity effects on Streptococcus mutans physiology and global gene expression. NPJ Microgravity 2017. [PMID: 28649626 PMCID: PMC5460135 DOI: 10.1038/s41526-016-0006-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Astronauts have been previously shown to exhibit decreased salivary lysozyme and increased dental calculus and gingival inflammation in response to space flight, host factors that could contribute to oral diseases such as caries and periodontitis. However, the specific physiological response of caries-causing bacteria such as Streptococcus mutans to space flight and/or ground-based simulated microgravity has not been extensively investigated. In this study, high aspect ratio vessel S. mutans simulated microgravity and normal gravity cultures were assessed for changes in metabolite and transcriptome profiles, H2O2 resistance, and competence in sucrose-containing biofilm media. Stationary phase S. mutans simulated microgravity cultures displayed increased killing by H2O2 compared to normal gravity control cultures, but competence was not affected. RNA-seq analysis revealed that expression of 153 genes was up-regulated ≥2-fold and 94 genes down-regulated ≥2-fold during simulated microgravity high aspect ratio vessel growth. These included a number of genes located on extrachromosomal elements, as well as genes involved in carbohydrate metabolism, translation, and stress responses. Collectively, these results suggest that growth under microgravity analog conditions promotes changes in S. mutans gene expression and physiology that may translate to an altered cariogenic potential of this organism during space flight missions. The gene expression patterns, metabolism and physiology of tooth cavities-causing microbes change in a space-like gravity environment. These findings could help explain why astronauts are at a greater risk for dental diseases when in space. Kelly Rice and colleagues from the University of Florida, Gainesville, USA, cultured Streptococcus mutans bacteria under simulated microgravity and normal gravity conditions. The bacteria grown in microgravity were more susceptible to killing with hydrogen peroxide, tended to aggregate in more compact cellular structures, showed changes in their metabolite profile and expressed around 250 genes at levels that were either much higher or lower than normal gravity control cultures. These genes included many involved in carbohydrate metabolism, protein production and stress responses. The observed changes collectively suggest that space flight and microgravity could alter the cavities-causing potential of S. mutans.
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Quorum Sensing Regulation of Competence and Bacteriocins in Streptococcus pneumoniae and mutans. Genes (Basel) 2017; 8:genes8010015. [PMID: 28067778 PMCID: PMC5295010 DOI: 10.3390/genes8010015] [Citation(s) in RCA: 110] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Revised: 12/25/2016] [Accepted: 12/27/2016] [Indexed: 11/17/2022] Open
Abstract
The human pathogens Streptococcus pneumoniae and Streptococcus mutans have both evolved complex quorum sensing (QS) systems that regulate the production of bacteriocins and the entry into the competent state, a requirement for natural transformation. Natural transformation provides bacteria with a mechanism to repair damaged genes or as a source of new advantageous traits. In S. pneumoniae, the competence pathway is controlled by the two-component signal transduction pathway ComCDE, which directly regulates SigX, the alternative sigma factor required for the initiation into competence. Over the past two decades, effectors of cellular killing (i.e., fratricides) have been recognized as important targets of the pneumococcal competence QS pathway. Recently, direct interactions between the ComCDE and the paralogous BlpRH pathway, regulating bacteriocin production, were identified, further strengthening the interconnections between these two QS systems. Interestingly, a similar theme is being revealed in S. mutans, the primary etiological agent of dental caries. This review compares the relationship between the bacteriocin and the competence QS pathways in both S. pneumoniae and S. mutans, and hopes to provide clues to regulatory pathways across the genus Streptococcus as a potential tool to efficiently investigate putative competence pathways in nontransformable streptococci.
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Transcriptional Profiling of the Oral Pathogen Streptococcus mutans in Response to Competence Signaling Peptide XIP. mSystems 2017; 2:mSystems00102-16. [PMID: 28066817 PMCID: PMC5209530 DOI: 10.1128/msystems.00102-16] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Accepted: 11/28/2016] [Indexed: 11/20/2022] Open
Abstract
In the cariogenic Streptococcus mutans, competence development is regulated by the ComRS signaling system comprised of the ComR regulator and the ComS prepeptide to the competence signaling peptide XIP (ComX-inducing peptide). Aside from competence development, XIP signaling has been demonstrated to regulate cell lysis, and recently, the expression of bacteriocins, small antimicrobial peptides used by bacteria to inhibit closely related species. Our study further explores the effect of XIP signaling on the S. mutans transcriptome. RNA sequencing revealed that XIP induction resulted in a global change in gene expression that was consistent with a stress response. An increase in several membrane-bound regulators, including HdrRM and BrsRM, involved in bacteriocin production, and the VicRKX system, involved in acid tolerance and biofilm formation, was observed. Furthermore, global changes in gene expression corresponded to changes observed during the stringent response to amino acid starvation. Effects were also observed on genes involved in sugar transport and carbon catabolite repression and included the levQRST and levDEFG operons. Finally, our work identified a novel heat shock-responsive intergenic region, encoding a small RNA, with a potential role in competence shutoff. IMPORTANCE Genetic competence provides bacteria with an opportunity to increase genetic diversity or acquire novel traits conferring a survival advantage. In the cariogenic pathogen Streptococcus mutans, DNA transformation is regulated by the competence stimulating peptide XIP (ComX-inducing peptide). The present study utilizes high-throughput RNA sequencing (RNAseq) to provide a greater understanding of how global gene expression patterns change in response to XIP. Overall, our work demonstrates that in S. mutans, XIP signaling induces a response that resembles the stringent response to amino acid starvation. We further identify a novel heat shock-responsive intergenic region with a potential role in competence shutoff. Together, our results provide further evidence that multiple stress response mechanisms are linked through the genetic competence signaling pathway in S. mutans.
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Zaccaria E, Wels M, van Baarlen P, Wells JM. Temporal Regulation of the Transformasome and Competence Development in Streptococcus suis. Front Microbiol 2016; 7:1922. [PMID: 28066332 PMCID: PMC5167698 DOI: 10.3389/fmicb.2016.01922] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Accepted: 11/16/2016] [Indexed: 11/19/2022] Open
Abstract
In S. suis the ComX-inducing peptide (XIP) pheromone regulates ComR-dependent transcriptional activation of comX (or sigX) the regulator of the late competence regulon. The aims of this study were to identify the ComR-regulated genes and in S. suis using genome-wide transcriptomics and identify their function based on orthology and the construction of specific knockout mutants. The ComX regulon we identified, includes all homologs of the “transformasome” a type 4-like pilus DNA binding and transport apparatus identified in Streptococcus pneumoniae, Streptococcus mutans, and Streptococcus thermophilus. A conserved CIN-box (YTACGAAYW), predicted to be bound by ComX, was found in the promoters of operons encoding genes involved in expression of the transformasome. Mutants lacking the major pilin gene comYC were not transformable demonstrating that the DNA uptake pilus is indeed required for competence development in S. suis. Competence was a transient state with the comX regulon shut down after ~15 min even when transcription of comX had not returned to basal levels, indicating other mechanisms control the exit from competence. The ComX regulon also included genes involved in DNA repair including cinA which we showed to be required for high efficiency transformation. In contrast to S. pneumoniae and S. mutans the ComX regulon of S. suis did not include endA which converts the transforming DNA into ssDNA, or ssbA, which protects the transforming ssDNA from degradation. EndA appeared to be essential in S. suis so we could not generate mutants and confirm its role in DNA transformation. Finally, we identified a putative homolog of fratricin, and a putative bacteriocin gene cluster, that were also part of the CIN-box regulon and thus may play a role in DNA release from non-competent cells, enabling gene transfer between S. suis pherotypes or S. suis and other species. S. suis mutants of oppA, the binding subunit of the general oligopeptide transporter were not transformable, suggesting that it is required for the import of XIP.
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Affiliation(s)
- Edoardo Zaccaria
- Host-Microbe Interactomics, Animal Sciences, Wageningen University Wageningen, Netherlands
| | | | - Peter van Baarlen
- Host-Microbe Interactomics, Animal Sciences, Wageningen University Wageningen, Netherlands
| | - Jerry M Wells
- Host-Microbe Interactomics, Animal Sciences, Wageningen University Wageningen, Netherlands
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Liu L, Fang H, Yang H, Zhang Y, Han Y, Zhou D, Yang R. Reciprocal regulation of Yersinia pestis biofilm formation and virulence by RovM and RovA. Open Biol 2016; 6:rsob.150198. [PMID: 26984293 PMCID: PMC4821237 DOI: 10.1098/rsob.150198] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
RovA is known to enhance Yersinia pestis virulence by directly upregulating the psa loci. This work presents a complex gene regulatory paradigm involving the reciprocal regulatory action of RovM and RovA on the expression of biofilm and virulence genes as well as on their own genes. RovM and RovA enhance and inhibit Y. pestis biofilm production, respectively, whereas RovM represses virulence in mice. RovM directly stimulates the transcription of hmsT, hmsCDE and rovM, while indirectly enhancing hmsHFRS transcription. It also indirectly represses hmsP transcription. By contrast, RovA directly represses hmsT transcription and indirectly inhibits waaAE-coaD transcription, while RovM inhibits psaABC and psaEF transcription by directly repressing rovA transcription. rovM expression is significantly upregulated at 26°C (the temperature of the flea gut) relative to 37°C (the warm-blooded host temperature). We speculate that upregulation of rovM together with downregulation of rovA in the flea gut would promote Y. pestis biofilm formation while inhibiting virulence gene expression, leading to a more transmissible infection of this pathogen in fleas. Once the bacterium shifts to a lifestyle in the warm-blooded hosts, inhibited RovM production accompanied by recovered RovA synthesis would encourage virulence factor production and inhibit biofilm gene expression.
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Affiliation(s)
- Lei Liu
- State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China
| | - Haihong Fang
- State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China
| | - Huiying Yang
- State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China
| | - Yiquan Zhang
- State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China School of Medicine, Jiangsu University, Zhenjiang 212013, Jiangsu, People's Republic of China
| | - Yanping Han
- State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China
| | - Dongsheng Zhou
- State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China
| | - Ruifu Yang
- State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing 100071, People's Republic of China
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Kaspar J, Kim JN, Ahn SJ, Burne RA. An Essential Role for (p)ppGpp in the Integration of Stress Tolerance, Peptide Signaling, and Competence Development in Streptococcus mutans. Front Microbiol 2016; 7:1162. [PMID: 27516759 PMCID: PMC4963387 DOI: 10.3389/fmicb.2016.01162] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Accepted: 07/12/2016] [Indexed: 11/25/2022] Open
Abstract
The microbes that inhabit the human oral cavity are subjected to constant fluctuations in their environment. To overcome these challenges and gain a competitive advantage, oral streptococci employ numerous adaptive strategies, many of which appear to be intertwined with the development of genetic competence. Here, we demonstrate that the regulatory circuits that control development of competence in Streptococcus mutans, a primary etiological agent of human dental caries, are integrated with key stress tolerance pathways by the molecular alarmone (p)ppGpp. We first observed that the growth of a strain that does not produce (p)ppGpp (ΔrelAPQ, (p)ppGpp0) is not sensitive to growth inhibition by comXinducing peptide (XIP), unlike the wild-type strain UA159, even though XIP-dependent activation of the alternative sigma factor comX by the ComRS pathway is not impaired in the (p)ppGpp0 strain. Overexpression of a (p)ppGpp synthase gene (relP) in the (p)ppGpp0 mutant restored growth inhibition by XIP. We also demonstrate that exposure to micromolar concentrations of XIP elicited changes in (p)ppGpp accumulation in UA159. Loss of the RelA/SpoT homolog (RSH) enzyme, RelA, lead to higher basal levels of (p)ppGpp accumulation, but to decreased sensitivity to XIP and to decreases in comR promoter activity and ComX protein levels. By introducing single amino acid substitutions into the RelA enzyme, the hydrolase activity of the enzyme was shown to be crucial for full com gene induction and transformation by XIP. Finally, loss of relA resulted in phenotypic changes to ΔrcrR mutants, highlighted by restoration of transformation and ComX protein production in the otherwise non-transformable ΔrcrR-NP mutant. Thus, RelA activity and its influence on (p)ppGpp pools appears to modulate competence signaling and development through RcrRPQ and the peptide effectors encoded within rcrQ. Collectively, this study provides new insights into the molecular mechanisms that integrate intercellular communication with the physiological status of the cells and the regulation of key virulence-related phenotypes in S. mutans.
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Affiliation(s)
- Justin Kaspar
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville FL, USA
| | - Jeong N Kim
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville FL, USA
| | - Sang-Joon Ahn
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville FL, USA
| | - Robert A Burne
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville FL, USA
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Abstract
Lactic acid bacteria (LAB) are important starter, commensal, or pathogenic microorganisms. The stress physiology of LAB has been studied in depth for over 2 decades, fueled mostly by the technological implications of LAB robustness in the food industry. Survival of probiotic LAB in the host and the potential relatedness of LAB virulence to their stress resilience have intensified interest in the field. Thus, a wealth of information concerning stress responses exists today for strains as diverse as starter (e.g., Lactococcus lactis), probiotic (e.g., several Lactobacillus spp.), and pathogenic (e.g., Enterococcus and Streptococcus spp.) LAB. Here we present the state of the art for LAB stress behavior. We describe the multitude of stresses that LAB are confronted with, and we present the experimental context used to study the stress responses of LAB, focusing on adaptation, habituation, and cross-protection as well as on self-induced multistress resistance in stationary phase, biofilms, and dormancy. We also consider stress responses at the population and single-cell levels. Subsequently, we concentrate on the stress defense mechanisms that have been reported to date, grouping them according to their direct participation in preserving cell energy, defending macromolecules, and protecting the cell envelope. Stress-induced responses of probiotic LAB and commensal/pathogenic LAB are highlighted separately due to the complexity of the peculiar multistress conditions to which these bacteria are subjected in their hosts. Induction of prophages under environmental stresses is then discussed. Finally, we present systems-based strategies to characterize the "stressome" of LAB and to engineer new food-related and probiotic LAB with improved stress tolerance.
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Shields RC, Burne RA. Growth of Streptococcus mutans in Biofilms Alters Peptide Signaling at the Sub-population Level. Front Microbiol 2016; 7:1075. [PMID: 27471495 PMCID: PMC4946182 DOI: 10.3389/fmicb.2016.01075] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Accepted: 06/27/2016] [Indexed: 11/30/2022] Open
Abstract
Streptococcus mutans activates multiple cellular processes in response to the formation of a complex between comX-inducing peptide (XIP) and the ComR transcriptional regulator. Bulk phase and microfluidic experiments previously revealed that ComR-dependent activation of comX is altered by pH and by carbohydrate source. Biofilm formation is a major factor in bacterial survival and virulence in the oral cavity. Here, we sought to determine the response of S. mutans biofilm cells to XIP during different stages of biofilm maturation. Using flow cytometry and confocal microscopy, we showed that exogenous addition of XIP to early biofilms resulted in robust comX activation. However, as the biofilms matured, increasing amounts of XIP were required to activate comX expression. Single-cell analysis demonstrated that the entire population was responding to XIP with activation of comX in early biofilms, but only a sub-population was responding in mature biofilms. The sub-population response of mature biofilms was retained when the cells were dispersed and then treated with XIP. The proportion and intensity of the bi-modal response of mature biofilm cells was altered in mutants lacking the Type II toxins MazF and RelE, or in a strain lacking the (p)ppGpp synthase/hydrolase RelA. Thus, competence signaling is markedly altered in cells growing in mature biofilms, and pathways that control cell death and growth/survival decisions modulate activation of comX expression in these sessile populations.
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Affiliation(s)
- Robert C Shields
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville FL, USA
| | - Robert A Burne
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville FL, USA
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He Z, Huang Z, Zhou W, Tang Z, Ma R, Liang J. Anti-biofilm Activities from Resveratrol against Fusobacterium nucleatum. Front Microbiol 2016; 7:1065. [PMID: 27458454 PMCID: PMC4932316 DOI: 10.3389/fmicb.2016.01065] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Accepted: 06/24/2016] [Indexed: 11/24/2022] Open
Abstract
Fusobacterium nucleatum is a Gram-negative, anaerobic bacterium that plays an important role in dental plaque biofilm formation. In this study, we evaluate the effect of resveratrol, a phytoalexin compound, on F. nucleatum biofilm formation. The effects of different concentrations of resveratrol on biofilms formed on 96-well microtiter plates at different time points were determined by the MTT assay. The structures and thicknesses of the biofilm were observed by confocal laser scanning microscopy (CLSM), and gene expression was investigated by real-time PCR. The results showed that resveratrol at sub-MIC levels can significantly decrease biofilm formation, whereas it does not affect the bacterial growth rate. It was observed by CLSM images that the biofilm was visually decreased with increasing concentrations of resveratrol. Gene expression was down regulated in the biofilm in the presence of resveratrol. Our results revealed that resveratrol can effectively inhibit biofilm formation.
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Affiliation(s)
- Zhiyan He
- Department of Endodontics, Shanghai Research Institute of Stomatology, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology Shanghai, China
| | - Zhengwei Huang
- Department of Endodontics, Shanghai Research Institute of Stomatology, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology Shanghai, China
| | - Wei Zhou
- Department of Endodontics, Shanghai Research Institute of Stomatology, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology Shanghai, China
| | - Zisheng Tang
- Department of Endodontics, Shanghai Research Institute of Stomatology, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology Shanghai, China
| | - Rui Ma
- Department of Endodontics, Shanghai Research Institute of Stomatology, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology Shanghai, China
| | - Jingping Liang
- Department of Endodontics, Shanghai Research Institute of Stomatology, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology Shanghai, China
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Impact of sludge retention time on the fine composition of the microbial community and extracellular polymeric substances in a membrane bioreactor. Appl Microbiol Biotechnol 2016; 100:8507-21. [DOI: 10.1007/s00253-016-7617-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Revised: 05/01/2016] [Accepted: 05/07/2016] [Indexed: 10/21/2022]
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Sucrose- and Fructose-Specific Effects on the Transcriptome of Streptococcus mutans, as Determined by RNA Sequencing. Appl Environ Microbiol 2015; 82:146-56. [PMID: 26475108 DOI: 10.1128/aem.02681-15] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Accepted: 10/13/2015] [Indexed: 11/20/2022] Open
Abstract
Recent genome-scale studies have begun to establish the scope and magnitude of the impacts of carbohydrate source and availability on the regulation of gene expression in bacteria. The effects of sugars on gene expression are particularly profound in a group of lactic acid bacteria that rely almost entirely on their saccharolytic activities for energy production and growth. For Streptococcus mutans, the major etiologic agent of human dental caries, sucrose is the carbohydrate that contributes in the most significant manner to establishment, persistence, and virulence of the organism. However, because this organism produces multiple extracellular sucrolytic enzymes that can release hexoses from sucrose, it has not been possible to study the specific effects of sucrose transport and metabolism on gene expression in the absence of carbohydrates that by themselves can elicit catabolite repression and induce expression of multiple genes. By employing RNA deep-sequencing (RNA-Seq) technology and mutants that lacked particular sucrose-metabolizing enzymes, we compared the transcriptomes of S. mutans bacteria growing on glucose, fructose, or sucrose as the sole carbohydrate source. The results provide a variety of new insights into the impact of sucrose transport and metabolism by S. mutans, including the likely expulsion of fructose after sucrose internalization and hydrolysis, and identify a set of genes that are differentially regulated by sucrose versus fructose. The findings significantly enhance our understanding of the genetics and physiology of this cariogenic pathogen.
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Shields RC, Burne RA. Conserved and divergent functions of RcrRPQ in Streptococcus gordonii and S. mutans. FEMS Microbiol Lett 2015; 362:fnv119. [PMID: 26229070 DOI: 10.1093/femsle/fnv119] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/20/2015] [Indexed: 01/18/2023] Open
Abstract
In the dental caries pathogen Streptococcus mutans, an MarR-like transcriptional regulator (RcrR), two ABC efflux pumps (RcrPQ) and two effector peptides encoded in the rcrRPQ operon provide molecular connections between stress tolerance, (p)ppGpp metabolism and genetic competence. Here, we examined the role of RcrRPQ in the oral commensal S. gordonii. Unlike in S. mutans, introduction of polar or non-polar rcrR mutations into S. gordonii elicited no significant changes in transformation efficiency. However, S. gordonii rcrR mutants were markedly impaired in their ability to grow in the presence of hydrogen peroxide, paraquat, low pH or elevated temperature. Sensitivity to paraquat could also be conferred by mutation of cysteine residues that are present in the RcrR protein of S. gordonii, but not in S. mutans RcrR. Thus, stress tolerance is a conserved function of RcrRPQ in a commensal and pathogenic streptococcus, but the study reveals additional differences in regulation of genetic competence development between S. mutans and S. gordonii.
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Affiliation(s)
- Robert C Shields
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, FL 32610, USA
| | - Robert A Burne
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, FL 32610, USA
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From (p)ppGpp to (pp)pGpp: Characterization of Regulatory Effects of pGpp Synthesized by the Small Alarmone Synthetase of Enterococcus faecalis. J Bacteriol 2015; 197:2908-19. [PMID: 26124242 DOI: 10.1128/jb.00324-15] [Citation(s) in RCA: 73] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Accepted: 06/23/2015] [Indexed: 02/08/2023] Open
Abstract
UNLABELLED The bacterial stringent response (SR) is a conserved stress tolerance mechanism that orchestrates physiological alterations to enhance cell survival. This response is mediated by the intracellular accumulation of the alarmones pppGpp and ppGpp, collectively called (p)ppGpp. In Enterococcus faecalis, (p)ppGpp metabolism is carried out by the bifunctional synthetase/hydrolase E. faecalis Rel (RelEf) and the small alarmone synthetase (SAS) RelQEf. Although Rel is the main enzyme responsible for SR activation in Firmicutes, there is emerging evidence that SASs can make important contributions to bacterial homeostasis. Here, we showed that RelQEf synthesizes ppGpp more efficiently than pppGpp without the need for ribosomes, tRNA, or mRNA. In addition to (p)ppGpp synthesis from GDP and GTP, RelQEf also efficiently utilized GMP to form GMP 3'-diphosphate (pGpp). Based on this observation, we sought to determine if pGpp exerts regulatory effects on cellular processes affected by (p)ppGpp. We found that pGpp, like (p)ppGpp, strongly inhibits the activity of E. faecalis enzymes involved in GTP biosynthesis and, to a lesser extent, transcription of rrnB by Escherichia coli RNA polymerase. Activation of E. coli RelA synthetase activity was observed in the presence of both pGpp and ppGpp, while RelQEf was activated only by ppGpp. Furthermore, enzymatic activity of RelQEf is insensitive to relacin, a (p)ppGpp analog developed as an inhibitor of "long" RelA/SpoT homolog (RSH) enzymes. We conclude that pGpp can likely function as a bacterial alarmone with target-specific regulatory effects that are similar to what has been observed for (p)ppGpp. IMPORTANCE Accumulation of the nucleotide second messengers (p)ppGpp in bacteria is an important signal regulating genetic and physiological networks contributing to stress tolerance, antibiotic persistence, and virulence. Understanding the function and regulation of the enzymes involved in (p)ppGpp turnover is therefore critical for designing strategies to eliminate the protective effects of this molecule. While characterizing the (p)ppGpp synthetase RelQ of Enterococcus faecalis (RelQEf), we found that, in addition to (p)ppGpp, RelQEf is an efficient producer of pGpp (GMP 3'-diphosphate). In vitro analysis revealed that pGpp exerts complex, target-specific effects on processes known to be modulated by (p)ppGpp. These findings provide a new regulatory feature of RelQEf and suggest that pGpp may represent a new member of the (pp)pGpp family of alarmones.
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Genetics and Physiology of Acetate Metabolism by the Pta-Ack Pathway of Streptococcus mutans. Appl Environ Microbiol 2015; 81:5015-25. [PMID: 25979891 DOI: 10.1128/aem.01160-15] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2015] [Accepted: 05/12/2015] [Indexed: 12/24/2022] Open
Abstract
In the dental caries pathogen Streptococcus mutans, phosphotransacetylase (Pta) catalyzes the conversion of acetyl coenzyme A (acetyl-CoA) to acetyl phosphate (AcP), which can be converted to acetate by acetate kinase (Ack), with the concomitant generation of ATP. A ΔackA mutant displayed enhanced accumulation of AcP under aerobic conditions, whereas little or no AcP was observed in the Δpta or Δpta ΔackA mutant. The Δpta and Δpta ΔackA mutants also had diminished ATP pools compared to the size of the ATP pool for the parental or ΔackA strain. Surprisingly, when exposed to oxidative stress, the Δpta ΔackA strain appeared to regain the capacity to produce AcP, with a concurrent increase in the size of the ATP pool compared to that for the parental strain. The ΔackA and Δpta ΔackA mutants exhibited enhanced (p)ppGpp accumulation, whereas the strain lacking Pta produced less (p)ppGpp than the wild-type strain. The ΔackA and Δpta ΔackA mutants displayed global changes in gene expression, as assessed by microarrays. All strains lacking Pta, which had defects in AcP production under aerobic conditions, were impaired in their abilities to form biofilms when glucose was the growth carbohydrate. Collectively, these data demonstrate the complex regulation of the Pta-Ack pathway and critical roles for these enzymes in processes that appear to be essential for the persistence and pathogenesis of S. mutans.
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Kaspar J, Ahn SJ, Palmer SR, Choi SC, Stanhope MJ, Burne RA. A unique open reading frame within the comX gene of Streptococcus mutans regulates genetic competence and oxidative stress tolerance. Mol Microbiol 2015; 96:463-82. [PMID: 25620525 DOI: 10.1111/mmi.12948] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/08/2015] [Indexed: 01/19/2023]
Abstract
Streptococcus mutans displays complex regulation of genetic competence, with ComX controlling late competence gene transcription. The rcrRPQ operon has been shown to link oxidative stress tolerance, (p)ppGpp metabolism and competence in S. mutans. Importantly, an rcrR polar (ΔrcrR-P) mutant is hyper-transformable, but an rcrR non-polar (ΔrcrR-NP) mutant cannot be transformed. Transcriptome comparisons of the rcrR mutants using RNA-Seq and quantitative real-time polymerase chain reaction revealed little expression in the 5' region of comX in ΔrcrR-NP, but high level expression in the 3' region. Northern blotting with comX probes revealed two distinct transcripts in the ΔrcrR-P and ΔrcrR-NP strains, and 5' Rapid Amplification of cDNA Ends mapped the 5' terminus of the shorter transcript to nt +140 of the comX structural gene, where a unique 69-aa open reading frame, termed XrpA, was encoded in a different reading frame than ComX. Two single-nucleotide substitution mutants (comX::T162C; comX::T210A) were introduced to disrupt XrpA without affecting the sequence of ComX. When the mutations were in the ΔrcrR-NP genetic background, ComX production and transformation were restored. Overexpression of xrpA led to impaired growth in aerobic conditions and decreased transformability. These results reveal an unprecedented mechanism for competence regulation and stress tolerance by a gene product encoded within the comX gene that appears unique to S. mutans.
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Affiliation(s)
- Justin Kaspar
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, FL, 32610, USA
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Many means to a common end: the intricacies of (p)ppGpp metabolism and its control of bacterial homeostasis. J Bacteriol 2015; 197:1146-56. [PMID: 25605304 DOI: 10.1128/jb.02577-14] [Citation(s) in RCA: 142] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
In nearly all bacterial species examined so far, amino acid starvation triggers the rapid accumulation of the nucleotide second messenger (p)ppGpp, the effector of the stringent response. While for years the enzymes involved in (p)ppGpp metabolism and the significance of (p)ppGpp accumulation to stress survival were considered well defined, a recent surge of interest in the field has uncovered an unanticipated level of diversity in how bacteria metabolize and utilize (p)ppGpp to rapidly synchronize a variety of biological processes important for growth and stress survival. In addition to the classic activation of the stringent response, it has become evident that (p)ppGpp exerts differential effects on cell physiology in an incremental manner rather than simply acting as a biphasic switch that controls growth or stasis. Of particular interest is the intimate relationship of (p)ppGpp with persister cell formation and virulence, which has spurred the pursuit of (p)ppGpp inhibitors as a means to control recalcitrant infections. Here, we present an overview of the enzymes responsible for (p)ppGpp metabolism, elaborate on the intricacies that link basal production of (p)ppGpp to bacterial homeostasis, and discuss the implications of targeting (p)ppGpp synthesis as a means to disrupt long-term bacterial survival strategies.
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Seaton K, Ahn SJ, Burne RA. Regulation of competence and gene expression in Streptococcus mutans by the RcrR transcriptional regulator. Mol Oral Microbiol 2014; 30:147-159. [PMID: 25146832 DOI: 10.1111/omi.12079] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/15/2014] [Indexed: 01/19/2023]
Abstract
An intimate linkage between the regulation of biofilm formation, stress tolerance and genetic competence exists in the dental caries pathogen Streptococcus mutans. The rcrRPQ genes encode ABC exporters (RcrPQ) and a MarR-family transcriptional repressor of the rcr operon (RcrR) that play a dominant role in the regulation of the development of genetic competence and connect competence with stress tolerance and (p)ppGpp production in S. mutans. Here we identify the target for efficient RcrR binding in the rcr promoter region using purified recombinant RcrR (rRcrR) protein in electrophoretic mobility shift assays and show that DNA fragments carrying mutations in the binding region were not bound as efficiently by rRcrR in vitro. Mutations in the RcrR binding site impacted expression from the rcrR promoter in vivo and elicited changes in transformation efficiency, competence gene expression, and growth inhibition by competence-stimulating peptide; even when the changes in rcrRPQ transcription were minor. An additional mechanistic linkage of RcrR with competence and (p)ppGpp metabolism was identified by showing that the rRcrR protein could bind to the promoter regions of comX, comYA and relP, although the binding was not as efficient as to the rcrRPQ promoter under the conditions tested. Hence, tightly controlled autogenous regulation of the rcrRPQ operon by RcrR binding to specific target sites is essential for cellular homeostasis, and RcrR contributes to the integration of genetic competence, (p)ppGpp metabolism, and acid and oxidative stress tolerance in S. mutans through both direct and indirect mechanisms.
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Affiliation(s)
- Kinda Seaton
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida 32610
| | - Sang-Joon Ahn
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida 32610
| | - Robert A Burne
- Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida 32610
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Ayala E, Downey JS, Mashburn-Warren L, Senadheera DB, Cvitkovitch DG, Goodman SD. A biochemical characterization of the DNA binding activity of the response regulator VicR from Streptococcus mutans. PLoS One 2014; 9:e108027. [PMID: 25229632 PMCID: PMC4168254 DOI: 10.1371/journal.pone.0108027] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2014] [Accepted: 08/18/2014] [Indexed: 02/03/2023] Open
Abstract
Two-component systems (TCSs) are ubiquitous among bacteria and are among the most elegant and effective sensing systems in nature. They allow for efficient adaptive responses to rapidly changing environmental conditions. In this study, we investigated the biochemical characteristics of the Streptococcus mutans protein VicR, an essential response regulator that is part of the VicRK TCS. We dissected the DNA binding requirements of the recognition sequences for VicR in its phosphorylated and unphosphorylated forms. In doing so, we were able to make predictions for the expansion of the VicR regulon within S. mutans. With the ever increasing number of bacteria that are rapidly becoming resistant to even the antibiotics of last resort, TCSs such as the VicRK provide promising targets for a new class of antimicrobials.
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Affiliation(s)
- Eduardo Ayala
- Department of Molecular and Computational Biology, Division of Biomedical Science, Herman Ostrow School of Dentistry, The University of Southern California, Los Angeles, California, United States of America
| | - Jennifer S. Downey
- Department of Molecular and Computational Biology, Division of Biomedical Science, Herman Ostrow School of Dentistry, The University of Southern California, Los Angeles, California, United States of America
| | - Lauren Mashburn-Warren
- Center for Microbial Pathogenesis, The Research Institute, Nationwide Children’s Hospital, Columbus, Ohio, United States of America
| | - Dilani B. Senadheera
- Dental Research Institute, Faculty of Dentistry, University of Toronto, Toronto, Canada
| | - Dennis G. Cvitkovitch
- Dental Research Institute, Faculty of Dentistry, University of Toronto, Toronto, Canada
| | - Steven D. Goodman
- Department of Molecular and Computational Biology, Division of Biomedical Science, Herman Ostrow School of Dentistry, The University of Southern California, Los Angeles, California, United States of America
- Center for Microbial Pathogenesis, The Research Institute, Nationwide Children’s Hospital, Columbus, Ohio, United States of America
- * E-mail:
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Discovery of novel peptides regulating competence development in Streptococcus mutans. J Bacteriol 2014; 196:3735-45. [PMID: 25135217 DOI: 10.1128/jb.01942-14] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A MarR-like transcriptional repressor (RcrR) and two predicted ABC efflux pumps (RcrPQ) encoded by a single operon were recently shown to be dominant regulators of stress tolerance and development of genetic competence in the oral pathogen Streptococcus mutans. Here, we focused on polar (ΔrcrR-P) and nonpolar (ΔrcrR-NP) rcrR mutants, which are hyper- and nontransformable, respectively, to dissect the mechanisms by which these mutations impact competence. We discovered two open reading frames (ORFs) in the 3' end of the rcrQ gene that encode peptides of 27 and 42 amino acids (aa) which are also dramatically upregulated in the ΔrcrR-NP strain. Deletion of, or start codon mutations in, the ORFs for the peptides in the ΔrcrR-NP background restored competence and sensitivity to competence-stimulating peptide (CSP) to levels seen in the ΔrcrR-P strain. Overexpression of the peptides adversely affected competence development. Importantly, overexpression of mutant derivatives of the ABC exporters that lacked the peptides also resulted in impaired competence. FLAG-tagged versions of the peptides could be detected in S. mutans, and FLAG tagging of the peptides impaired their function. The competence phenotypes associated with the various mutations, and with overexpression of the peptides and ABC transporters, were correlated with the levels of ComX protein in cells. Collectively, these studies revealed multiple novel mechanisms for regulation of competence development by the components of the rcrRPQ operon. Given their intimate role in competence and stress tolerance, the rcrRPQ-encoded peptides may prove to be useful targets for therapeutics to diminish the virulence of S. mutans.
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Yi L, Wang Y, Ma Z, Zhang H, Li Y, Zheng JX, Yang YC, Fan HJ, Lu CP. Biofilm Formation of Streptococcus equi ssp. zooepidemicus and Comparative Proteomic Analysis of Biofilm and Planktonic Cells. Curr Microbiol 2014; 69:227-33. [DOI: 10.1007/s00284-014-0574-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2013] [Accepted: 02/08/2014] [Indexed: 10/25/2022]
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Ceruso M, Fratamico P, Chirollo C, Taglialatela R, Cortesi ML, Pepe T. The Capacity of Listeria Monocytogenes Mutants with In-Frame Deletions in Putative ATP-Binding Cassette Transporters to form Biofilms and Comparison with the Wild Type. Ital J Food Saf 2014; 3:1657. [PMID: 27800311 PMCID: PMC5076661 DOI: 10.4081/ijfs.2014.1657] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2013] [Revised: 09/02/2013] [Accepted: 09/02/2013] [Indexed: 11/23/2022] Open
Abstract
Listeria monocytogenes (Lm) is a food-borne pathogen responsible for human listeriosis, an invasive infection with high mortality rates. Lm has developed efficient strategies for survival under stress conditions such as starvation and wide variations in temperature, pH, and osmolarity. Therefore, Lm can survive in food under multiple stress conditions. Detailed studies to determine the mode of action of this pathogen for survival under stress conditions are important to control Lm in food. It has been shown that genes encoding for ATP-binding cassette (ABC) transporters are induced in Lm in food, in particular under stress conditions. Previous studies showed that these genes are involved in sensitivity to nisin, acids, and salt. The aim of this study was to determine the involvement of some ABC transporters in biofilm formation. Therefore, deletion mutants of ABC transporter genes (LMOf2365_1875 and LMOf2365_1877) were created in Lm F2365, and then were compared to the wild type for their capacity to form biofilms. Lm strain F2365 was chosen as reference since the genome is fully sequenced and furthermore this strain is particularly involved in food-borne outbreaks of listeriosis. Our results showed that ΔLMOf2365_1875 had an increased capacity to form biofilms compared to the wild type, indicating that LMOf2365_1875 negatively regulates biofilm formation. A deeper knowledge on the ability to form biofilms in these mutants may help in the development of intervention strategies to control Lm in food and in the environment.
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Affiliation(s)
- Marina Ceruso
- Dipartimento di Medicina Veterinaria e Produzioni animali, Università degli Studi Federico II, Napoli, Italy
| | - Pina Fratamico
- Molecular Characterization of Foodborne Pathogens (MCFP), Eastern Regional Research Center (ERRC), United States Department of Agriculture (USDA), Wyndmoor, PA, USA
| | - Claudia Chirollo
- Dipartimento di Medicina Veterinaria e Produzioni animali, Università degli Studi Federico II, Napoli, Italy
| | - Rosanna Taglialatela
- Dipartimento di Medicina Veterinaria e Produzioni animali, Università degli Studi Federico II, Napoli, Italy
| | - Maria Luisa Cortesi
- Dipartimento di Medicina Veterinaria e Produzioni animali, Università degli Studi Federico II, Napoli, Italy
| | - Tiziana Pepe
- Dipartimento di Medicina Veterinaria e Produzioni animali, Università degli Studi Federico II, Napoli, Italy
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Growth phase and pH influence peptide signaling for competence development in Streptococcus mutans. J Bacteriol 2013; 196:227-36. [PMID: 24163340 DOI: 10.1128/jb.00995-13] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The development of competence by the dental caries pathogen Streptococcus mutans is mediated primarily through the alternative sigma factor ComX (SigX), which is under the control of multiple regulatory systems and activates the expression of genes involved in DNA uptake and recombination. Here we report that the induction of competence and competence gene expression by XIP (sigX-inducing peptide) and CSP (competence-stimulating peptide) is dependent on the growth phase and that environmental pH has a potent effect on the responses to XIP. A dramatic decline in comX and comS expression was observed in mid- and late-exponential-phase cells. XIP-mediated competence development and responses to XIP were optimal around a neutral pH, although mid-exponential-phase cells remained refractory to XIP treatment, and acidified late-exponential-phase cultures were resistant to killing by high concentrations of XIP. Changes in the expression of the genes for the oligopeptide permease (opp), which appears to be responsible for the internalization of XIP, could not entirely account for the behaviors observed. Interestingly, comS and comX expression was highly induced in response to endogenously overproduced XIP or ComS in mid-exponential-phase cells. In contrast to the effects of pH on XIP, competence induction and responses to CSP in complex medium were not affected by pH, although a decreased response to CSP in cells that had exited early-exponential phase was observed. Collectively, these results indicate that competence development may be highly sensitive to microenvironments within oral biofilms and that XIP and CSP signaling in biofilms could be spatially and temporally heterogeneous.
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Palmer SR, Miller JH, Abranches J, Zeng L, Lefebure T, Richards VP, Lemos JA, Stanhope MJ, Burne RA. Phenotypic heterogeneity of genomically-diverse isolates of Streptococcus mutans. PLoS One 2013; 8:e61358. [PMID: 23613838 PMCID: PMC3628994 DOI: 10.1371/journal.pone.0061358] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Accepted: 03/07/2013] [Indexed: 11/18/2022] Open
Abstract
High coverage, whole genome shotgun (WGS) sequencing of 57 geographically- and genetically-diverse isolates of Streptococcus mutans from individuals of known dental caries status was recently completed. Of the 57 sequenced strains, fifteen isolates, were selected based primarily on differences in gene content and phenotypic characteristics known to affect virulence and compared with the reference strain UA159. A high degree of variability in these properties was observed between strains, with a broad spectrum of sensitivities to low pH, oxidative stress (air and paraquat) and exposure to competence stimulating peptide (CSP). Significant differences in autolytic behavior and in biofilm development in glucose or sucrose were also observed. Natural genetic competence varied among isolates, and this was correlated to the presence or absence of competence genes, comCDE and comX, and to bacteriocins. In general strains that lacked the ability to become competent possessed fewer genes for bacteriocins and immunity proteins or contained polymorphic variants of these genes. WGS sequence analysis of the pan-genome revealed, for the first time, components of a Type VII secretion system in several S. mutans strains, as well as two putative ORFs that encode possible collagen binding proteins located upstream of the cnm gene, which is associated with host cell invasiveness. The virulence of these particular strains was assessed in a wax-worm model. This is the first study to combine a comprehensive analysis of key virulence-related phenotypes with extensive genomic analysis of a pathogen that evolved closely with humans. Our analysis highlights the phenotypic diversity of S. mutans isolates and indicates that the species has evolved a variety of adaptive strategies to persist in the human oral cavity and, when conditions are favorable, to initiate disease.
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Affiliation(s)
- Sara R. Palmer
- Department of Oral Biology, University of Florida, Gainesville, Florida, United States of America
| | - James H. Miller
- Center for Oral Biology, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Jacqueline Abranches
- Center for Oral Biology, University of Rochester Medical Center, Rochester, New York, United States of America
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Lin Zeng
- Department of Oral Biology, University of Florida, Gainesville, Florida, United States of America
| | - Tristan Lefebure
- Université de Lyon, CNRS, Ecologie des Hydrosystèmes Naturels et Anthropisés; Université Lyon, Villeurbanne, France
- Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, United States of America
| | - Vincent P. Richards
- Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, United States of America
| | - José A. Lemos
- Center for Oral Biology, University of Rochester Medical Center, Rochester, New York, United States of America
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Michael J. Stanhope
- Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, United States of America
| | - Robert A. Burne
- Department of Oral Biology, University of Florida, Gainesville, Florida, United States of America
- * E-mail:
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Cornejo OE, Lefébure T, Pavinski Bitar PD, Lang P, Richards VP, Eilertson K, Do T, Beighton D, Zeng L, Ahn SJ, Burne RA, Siepel A, Bustamante CD, Stanhope MJ. Evolutionary and population genomics of the cavity causing bacteria Streptococcus mutans. Mol Biol Evol 2013; 30:881-93. [PMID: 23228887 PMCID: PMC3603310 DOI: 10.1093/molbev/mss278] [Citation(s) in RCA: 129] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Streptococcus mutans is widely recognized as one of the key etiological agents of human dental caries. Despite its role in this important disease, our present knowledge of gene content variability across the species and its relationship to adaptation is minimal. Estimates of its demographic history are not available. In this study, we generated genome sequences of 57 S. mutans isolates, as well as representative strains of the most closely related species to S. mutans (S. ratti, S. macaccae, and S. criceti), to identify the overall structure and potential adaptive features of the dispensable and core components of the genome. We also performed population genetic analyses on the core genome of the species aimed at understanding the demographic history, and impact of selection shaping its genetic variation. The maximum gene content divergence among strains was approximately 23%, with the majority of strains diverging by 5-15%. The core genome consisted of 1,490 genes and the pan-genome approximately 3,296. Maximum likelihood analysis of the synonymous site frequency spectrum (SFS) suggested that the S. mutans population started expanding exponentially approximately 10,000 years ago (95% confidence interval [CI]: 3,268-14,344 years ago), coincidental with the onset of human agriculture. Analysis of the replacement SFS indicated that a majority of these substitutions are under strong negative selection, and the remainder evolved neutrally. A set of 14 genes was identified as being under positive selection, most of which were involved in either sugar metabolism or acid tolerance. Analysis of the core genome suggested that among 73 genes present in all isolates of S. mutans but absent in other species of the mutans taxonomic group, the majority can be associated with metabolic processes that could have contributed to the successful adaptation of S. mutans to its new niche, the human mouth, and with the dietary changes that accompanied the origin of agriculture.
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Affiliation(s)
- Omar E. Cornejo
- Department of Genetics, School of Medicine, Stanford University
| | - Tristan Lefébure
- Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University
| | - Paulina D. Pavinski Bitar
- Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University
| | - Ping Lang
- Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University
| | - Vincent P. Richards
- Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University
| | - Kirsten Eilertson
- Department of Biological Statistics and Computational Biology, Cornell University
| | - Thuy Do
- Department of Microbiology, King’s College London Dental Institute and NIHR Biomedical Research Centre at Guy's and St. Thomas’s NHS Foundation Trust, Guy’s Hospital, London, United Kingdom
| | - David Beighton
- Department of Microbiology, King’s College London Dental Institute and NIHR Biomedical Research Centre at Guy's and St. Thomas’s NHS Foundation Trust, Guy’s Hospital, London, United Kingdom
| | - Lin Zeng
- Department of Oral Biology, University of Florida
| | | | | | - Adam Siepel
- Department of Biological Statistics and Computational Biology, Cornell University
| | | | - Michael J. Stanhope
- Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University
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The stringent response controls catalases in Pseudomonas aeruginosa and is required for hydrogen peroxide and antibiotic tolerance. J Bacteriol 2013; 195:2011-20. [PMID: 23457248 DOI: 10.1128/jb.02061-12] [Citation(s) in RCA: 119] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Pseudomonas aeruginosa, a human opportunistic pathogen, possesses a number of antioxidant defense enzymes under the control of multiple regulatory systems. We recently reported that inactivation of the P. aeruginosa stringent response (SR), a starvation stress response controlled by the alarmone (p)ppGpp, caused impaired antioxidant defenses and antibiotic tolerance. Since catalases are key antioxidant enzymes in P. aeruginosa, we compared the levels of H2O2 susceptibility and catalase activity in P. aeruginosa wild-type and ΔrelA ΔspoT (ΔSR) mutant cells. We found that the SR was required for optimal catalase activity and mediated H2O2 tolerance during both planktonic and biofilm growth. Upon amino acid starvation, induction of the SR upregulated catalase activity. Full expression of katA and katB also required the SR, and this regulation occurred through both RpoS-independent and RpoS-dependent mechanisms. Furthermore, overexpression of katA was sufficient to restore H2O2 tolerance and to partially rescue the antibiotic tolerance of ΔSR cells. All together, these results suggest that the SR regulates catalases and that this is an important mechanism in protecting nutrient-starved and biofilm bacteria from H2O2- and antibiotic-mediated killing.
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