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Si B, Yang Y, Naveed M, Wang F, Chan MWH. Characterizations of biogenic selenium nanoparticles and their anti-biofilm potential against Streptococcus mutans ATCC 25175. J Trace Elem Med Biol 2024; 84:127448. [PMID: 38626650 DOI: 10.1016/j.jtemb.2024.127448] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/26/2023] [Revised: 04/03/2024] [Accepted: 04/05/2024] [Indexed: 04/18/2024]
Abstract
INTRODUCTION S. mutans has been identified as the primary pathogenic bacterium in biofilm-mediated dental caries. The biogenic selenium nanoparticles (SeNPs) produced by L. plantarum KNF-5 were used in this study against S. mutans ATCC 25175. OBJECTIVES The aims of this study were: (1) the biosynthesis of SeNPs by L. plantarum KNF-5, (2) the characterization of SeNPs, (3) the investigation of the inhibitory effect of biogenic SeNPs against S. mutans ATCC 25175, and (4) the determination of the anti-biofilm potential of SeNPS against S. mutans ATCC 25175. METHODOLOGY 3 mL of the culture was added to 100 mL of MRS medium and incubated. After 4 h, Na2SeO3 solution (concentration 100 μg/mL) was added and incubated at 37 °C for 36 h. The color of the culture solution changed from brownish-yellow to reddish, indicating the formation of SeNPs. The characterization of SeNPs was confirmed by UV-Vis spectrophotometry, FTIR, SEM-EDS and a particle size analyzer. The antibacterial activity was determined by the disk diffusion method, the MIC by the micro-double dilution method, and the biofilm inhibitory potential by the crystal violet method and the MTT assay. The effect of SeNPs on S. mutans ATCC 25175 was determined using SEM and CLSM spectrometry techniques. The sulfate-anthrone method was used to analyze the effect of SeNPs on insoluble extracellular polysaccharides. The expression of genes in S. mutans ATCC 25175 was analyzed by real-time quantitative polymerase chain reaction (RT-qPCR). PREPARATION OF NANOPARTICLES SeNPs produced by probiotic bacteria are considered a safe method. In this study, L. plantarum KNF-5 (probiotic strain) was used for the production of SeNPs. RESULTS The biogenic SeNPs were spherical and coated with proteins and polysaccharides and had a diameter of about 270 nm. The MIC of the SeNPs against S. mutans ATCC 25175 was 3.125 mg/mL. Biofilm growth was also significantly suppressed at this concentration. The expression of genes responsible for biofilm formation (GtfB, GtfC, BrpA and GbpB,) was reduced when S. mutans ATCC 25175 was treated with SeNPs. CONCLUSION It was concluded that the biogenic SeNPs produced by L. plantarum KNF-5 was highly effective to inhibit the growth of S. mutans ATCC 25175. NOVELTY STATEMENT The application of biogenic SeNPs, a natural anti-biofilm agent against S. mutans ATCC 25175. In the future, this study will provide a new option for the prevention and treatment of dental caries.
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Affiliation(s)
- Binbin Si
- Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing Technology & Business University (BTBU), Beijing 100048, China; School of Light Industry, Beijing Technology & Business University (BTBU), Beijing 100048, China
| | - Yang Yang
- Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing Technology & Business University (BTBU), Beijing 100048, China; School of Light Industry, Beijing Technology & Business University (BTBU), Beijing 100048, China
| | - Muhammad Naveed
- Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing Technology & Business University (BTBU), Beijing 100048, China; School of Light Industry, Beijing Technology & Business University (BTBU), Beijing 100048, China
| | - Fenghuan Wang
- Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing Technology & Business University (BTBU), Beijing 100048, China; School of Light Industry, Beijing Technology & Business University (BTBU), Beijing 100048, China.
| | - Malik Wajid Hussain Chan
- Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing Technology & Business University (BTBU), Beijing 100048, China; School of Light Industry, Beijing Technology & Business University (BTBU), Beijing 100048, China.
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Merritt J, Kreth J. Illuminating the oral microbiome and its host interactions: tools and approaches for molecular microbiology studies. FEMS Microbiol Rev 2023; 47:fuac050. [PMID: 36549660 PMCID: PMC10719069 DOI: 10.1093/femsre/fuac050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2022] [Accepted: 12/19/2022] [Indexed: 12/24/2022] Open
Abstract
Advancements in DNA sequencing technologies within the last decade have stimulated an unprecedented interest in the human microbiome, largely due the broad diversity of human diseases found to correlate with microbiome dysbiosis. As a direct consequence of these studies, a vast number of understudied and uncharacterized microbes have been identified as potential drivers of mucosal health and disease. The looming challenge in the field is to transition these observations into defined molecular mechanistic studies of symbiosis and dysbiosis. In order to meet this challenge, many of these newly identified microbes will need to be adapted for use in experimental models. Consequently, this review presents a comprehensive overview of the molecular microbiology tools and techniques that have played crucial roles in genetic studies of the bacteria found within the human oral microbiota. Here, we will use specific examples from the oral microbiome literature to illustrate the biology supporting these techniques, why they are needed in the field, and how such technologies have been implemented. It is hoped that this information can serve as a useful reference guide to help catalyze molecular microbiology studies of the many new understudied and uncharacterized species identified at different mucosal sites in the body.
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Affiliation(s)
- Justin Merritt
- Department of Restorative Dentistry, School of Dentistry, Oregon Health and Science University, Portland, OR, United States
- Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, OR 97239, United States
| | - Jens Kreth
- Department of Restorative Dentistry, School of Dentistry, Oregon Health and Science University, Portland, OR, United States
- Department of Molecular Microbiology and Immunology, Oregon Health and Science University, Portland, OR 97239, United States
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Ko SY, Kim N, Park SY, Kim SY, Shin M, Lee JC. Acinetobacter baumannii under Acidic Conditions Induces Colistin Resistance through PmrAB Activation and Lipid A Modification. Antibiotics (Basel) 2023; 12:antibiotics12050813. [PMID: 37237716 DOI: 10.3390/antibiotics12050813] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Revised: 04/24/2023] [Accepted: 04/24/2023] [Indexed: 05/28/2023] Open
Abstract
Colistin is a last-resort antimicrobial agent for treating carbapenem-resistant Acinetobacter baumannii infections. The activation of PmrAB by several environmental signals induces colistin resistance in Gram-negative bacteria. This study investigated the molecular mechanisms of colistin resistance in A. baumannii under acidic conditions using wild-type (WT) A. baumannii 17978, ΔpmrA and ΔpmrB mutants, and pmrA-complemented strains. The pmrA or pmrB deletion did not affect the growth of A. baumannii under acidic or aerobic conditions. A. baumannii under acidic (pH 5.5) and high-iron (1 mM) conditions showed 32- and 8-fold increases in the minimum inhibitory concentrations (MICs) of colistin, respectively. The ΔpmrA and ΔpmrB mutants at pH 5.5 showed a significant decrease in colistin MICs compared to the WT strain at pH 5.5. No difference in colistin MICs was observed between WT and mutant strains under high-iron conditions. The pmrCAB expression significantly increased in the WT strain at pH 5.5 compared to the WT strain at pH 7.0. The pmrC expression significantly decreased in two mutant strains at pH 5.5 compared to the WT strain at pH 5.5. The PmrA protein was expressed in the ΔpmrA strain carrying ppmrA_FLAG plasmids at pH 5.5 but not at pH 7.0. Lipid A modification by the addition of phosphoethanolamine was observed in the WT strain at pH 5.5. In conclusion, this study demonstrated that A. baumannii under acidic conditions induces colistin resistance via the activation of pmrCAB operon and subsequent lipid A modification.
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Affiliation(s)
- Seo-Yeon Ko
- Department of Microbiology, School of Medicine, Kyungpook National University, Daegu 41944, Republic of Korea
| | - Nayeong Kim
- Department of Microbiology, School of Medicine, Kyungpook National University, Daegu 41944, Republic of Korea
| | - Seong-Yong Park
- Department of Microbiology, School of Medicine, Kyungpook National University, Daegu 41944, Republic of Korea
| | - Seong-Yeop Kim
- Department of Microbiology, School of Medicine, Kyungpook National University, Daegu 41944, Republic of Korea
| | - Minsang Shin
- Department of Microbiology, School of Medicine, Kyungpook National University, Daegu 41944, Republic of Korea
| | - Je-Chul Lee
- Department of Microbiology, School of Medicine, Kyungpook National University, Daegu 41944, Republic of Korea
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A Genome-Wide CRISPR Interference Screen Reveals an StkP-Mediated Connection between Cell Wall Integrity and Competence in Streptococcus salivarius. mSystems 2022; 7:e0073522. [PMID: 36342134 PMCID: PMC9765292 DOI: 10.1128/msystems.00735-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Competence is one of the most efficient bacterial evolutionary and adaptative strategies by synchronizing production of antibacterial compounds and integration of DNA released by dead cells. In most streptococci, this tactic is orchestrated by the ComRS system, a pheromone communication device providing a short time window of activation in which only part of the population is responsive. Understanding how this developmental process integrates multiple inputs to fine-tune the adequate response is a long-standing question. However, essential genes involved in the regulation of ComRS have been challenging to study. In this work, we built a conditional mutant library using CRISPR interference and performed three complementary screens to investigate competence genetic regulation in the human commensal Streptococcus salivarius. We show that initiation of competence increases upon cell wall impairment, suggesting a connection between cell envelope stress and competence activation. Notably, we report a key role for StkP, a serine-threonine kinase known to regulate cell wall homeostasis. We show that StkP controls competence by a mechanism that reacts to peptidoglycan fragments. Together, our data suggest a key cell wall sensing mechanism coupling competence to cell envelope integrity. IMPORTANCE Survival of human commensal streptococci in the digestive tract requires efficient strategies which must be tightly and collectively controlled for responding to competitive pressure and drastic environmental changes. In this context, the autocrine signaling system ComRS controlling competence for natural transformation and predation in salivarius streptococci could be seen as a multi-input device integrating a variety of environmental stimuli. In this work, we revealed novel positive and negative competence modulators by using a genome-wide CRISPR interference strategy. Notably, we highlighted an unexpected connection between bacterial envelope integrity and competence activation that involves several cell wall sensors. Together, these results showcase how commensal streptococci can fine-tune the pheromone-based competence system by responding to multiple inputs affecting their physiological status in order to calibrate an appropriate collective behavior.
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Pandey SD, Biswas I. Clp ATPases differentially affect natural competence development in Streptococcus mutans. Microbiologyopen 2022; 11:e1288. [PMID: 35765180 PMCID: PMC9108599 DOI: 10.1002/mbo3.1288] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Accepted: 04/27/2022] [Indexed: 11/25/2022] Open
Abstract
In naturally competent bacteria, DNA transformation through horizontal gene transfer is an evolutionary mechanism to receive extracellular DNA. Bacteria need to maintain a state of competence to accept foreign DNA, and this is an energy-driven phenomenon that is tightly controlled. In Streptococcus, competence development is a complex process that is not fully understood. In this study, we used Streptococcus mutans, an oral bacterium, to determine how cell density affects competence development. We found that in S. mutans the transformation efficiency is maximum when the transforming DNA was added at low cell density and incubated for 2.5 h before selecting for transformants. We also found that S. mutans cells remain competent until the mid-logarithmic phase, after which the competence decreases drastically. Surprisingly, we observed that individual components of Clp proteolytic complexes differentially regulate competence. If the transformation is carried out at the early growth phase, both ClpP protease and ClpX ATPase are needed for competence. In contrast, we found that both ClpC and ClpE negatively affect competence. We also found that if the transformation is carried out at the mid-logarithmic growth phase ClpX is still required for competence, but ClpP negatively affects competence. While the exact reason for this differential effect of ClpP and ClpX on transformation is currently unknown, we found that both ClpC and ClpE have a negative effect on transformation, which was not reported before.
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Affiliation(s)
- Satya D. Pandey
- Department of MicrobiologyUniversity of Kansas Medical CenterKansas CityKansasUSA
| | - Indranil Biswas
- Department of MicrobiologyUniversity of Kansas Medical CenterKansas CityKansasUSA
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Alves LA, Ganguly T, Harth-Chú ÉN, Kajfasz J, Lemos JA, Abranches J, Mattos-Graner RO. PepO is a target of the two-component systems VicRK and CovR required for systemic virulence of Streptococcus mutans. Virulence 2020; 11:521-536. [PMID: 32427040 PMCID: PMC7239026 DOI: 10.1080/21505594.2020.1767377] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Revised: 03/10/2020] [Accepted: 03/29/2020] [Indexed: 12/14/2022] Open
Abstract
Streptococcus mutans, a cariogenic species, is often associated with cardiovascular infections. Systemic virulence of specific S. mutans serotypes has been associated with the expression of the collagen- and laminin-binding protein Cnm, which is transcriptionally regulated by VicRK and CovR. In this study, we characterized a VicRK- and CovR-regulated gene, pepO, coding for a conserved endopeptidase. Transcriptional and protein analyses revealed that pepO is highly expressed in S. mutans strains resistant to complement immunity (blood isolates) compared to oral isolates. Gel mobility assay, transcriptional, and Western blot analyses revealed that pepO is repressed by VicR and induced by CovR. Deletion of pepO in the Cnm+ strain OMZ175 (OMZpepO) or in the Cnm- UA159 (UApepO) led to an increased susceptibility to C3b deposition, and to low binding to complement proteins C1q and C4BP. Additionally, pepO mutants showed diminished ex vivo survival in human blood and impaired capacity to kill G. mellonella larvae. Inactivation of cnm in OMZ175 (OMZcnm) resulted in increased resistance to C3b deposition and unaltered blood survival, although both pepO and cnm mutants displayed attenuated virulence in G. mellonella. Unlike OMZcnm, OMZpepO could invade HCAEC endothelial cells. Supporting these phenotypes, recombinant proteins rPepO and rCnmA showed specific profiles of binding to C1q, C4BP, and to other plasma (plasminogen, fibronectin) and extracellular matrix proteins (type I collagen, laminin). Therefore this study identifies a novel VicRK/CovR-target required for immune evasion and host persistence, pepO, expanding the roles of VicRK and CovR in regulating S. mutans virulence.
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Affiliation(s)
- Lívia A. Alves
- Department of Oral Diagnosis, Piracicaba Dental School – State University of Campinas, Piracicaba, SP, Brazil
| | - Tridib Ganguly
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, USA
| | - Érika N. Harth-Chú
- Department of Oral Diagnosis, Piracicaba Dental School – State University of Campinas, Piracicaba, SP, Brazil
| | - Jessica Kajfasz
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, USA
| | - José A. Lemos
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, USA
| | - Jacqueline Abranches
- Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, USA
| | - Renata O. Mattos-Graner
- Department of Oral Diagnosis, Piracicaba Dental School – State University of Campinas, Piracicaba, SP, Brazil
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7
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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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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: 306] [Impact Index Per Article: 61.2] [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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CovR and VicRKX Regulate Transcription of the Collagen Binding Protein Cnm of Streptococcus mutans. J Bacteriol 2018; 200:JB.00141-18. [PMID: 30201780 DOI: 10.1128/jb.00141-18] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2018] [Accepted: 09/04/2018] [Indexed: 11/20/2022] Open
Abstract
Cnm is a surface-associated protein present in a subset of Streptococcus mutans strains that mediates binding to extracellular matrices, intracellular invasion, and virulence. Here, we showed that cnm transcription is controlled by the global regulators CovR and VicRKX. In silico analysis identified multiple putative CovR- and VicR-binding motifs in the regulatory region of cnm as well as in the downstream gene pgfS, which is associated with the posttranslational modification of Cnm. Electrophoretic mobility shift assays revealed that CovR and VicR specifically and independently bind to the cnm and pgfS promoter regions. Quantitative real-time PCR and Western blot analyses of ΔcovR and ΔvicK strains as well as of a strain overexpressing vicRKX revealed that CovR functions as a positive regulator of cnm, whereas VicRKX acts as a negative regulator. In agreement with the role of VicRKX as a repressor, the ΔvicK strain showed enhanced binding to collagen and laminin and higher intracellular invasion rates. Overexpression of vicRKX was associated with decreased rates of intracellular invasion but did not affect collagen or lamin binding activities, suggesting that this system controls additional genes involved in binding to these extracellular matrix proteins. As expected, based on the role of CovR in cnm regulation, the ΔcovR strain showed decreased intracellular invasion rates, but, unexpectedly collagen and laminin binding activities were increased in this mutant strain. Collectively, the results presented here expand the repertoire of virulence-related genes regulated by CovR and VicRKX to include the core gene pgfS and the noncore gene cnm IMPORTANCE Streptococcus mutans is a major pathogen associated with dental caries and also implicated in systemic infections, in particular, infective endocarditis. The Cnm adhesin of S. mutans is an important virulence factor associated with systemic infections and caries severity. Despite its role in virulence, the regulatory mechanisms governing cnm expression are poorly understood. Here, we describe the identification of two independent regulatory systems controlling the transcription of cnm and the downstream pgfS-pgfM1-pgfE-pgfM2 operon. A better understanding of the mechanisms controlling expression of virulence factors like Cnm can facilitate the development of new strategies to treat bacterial infections.
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Avilés-Reyes A, Freires IA, Kajfasz JK, Barbieri D, Miller JH, Lemos JA, Abranches J. Whole genome sequence and phenotypic characterization of a Cbm + serotype e strain of Streptococcus mutans. Mol Oral Microbiol 2018; 33:257-269. [PMID: 29524318 PMCID: PMC5945312 DOI: 10.1111/omi.12222] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/05/2018] [Indexed: 12/27/2022]
Abstract
We report the whole genome sequence of the serotype e Cbm+ strain LAR01 of Streptococcus mutans, a dental pathogen frequently associated with extra-oral infections. The LAR01 genome is a single circular chromosome of 2.1 Mb with a GC content of 36.96%. The genome contains 15 phosphotransferase system gene clusters, seven cell wall-anchored (LPxTG) proteins, all genes required for the development of natural competence and genes coding for mutacins VI and K8. Interestingly, the cbm gene is genetically linked to a putative type VII secretion system that has been found in Mycobacteria and few other Gram-positive bacteria. When compared with the UA159 type strain, phenotypic characterization of LAR01 revealed increased biofilm formation in the presence of either glucose or sucrose but similar abilities to withstand acid and oxidative stresses. LAR01 was unable to inhibit the growth of Strpetococcus gordonii, which is consistent with the genomic data that indicate absence of mutacins that can kill mitis streptococci. On the other hand, LAR01 effectively inhibited growth of other S. mutans strains, suggesting that it may be specialized to outcompete strains from its own species. In vitro and in vivo studies using mutational and heterologous expression approaches revealed that Cbm is a virulence factor of S. mutans by mediating binding to extracellular matrix proteins and intracellular invasion. Collectively, the whole genome sequence analysis and phenotypic characterization of LAR01 provides new insights on the virulence properties of S. mutans and grants further opportunities to understand the genomic fluidity of this important human pathogen.
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Affiliation(s)
- Alejandro Avilés-Reyes
- Department of Oral Biology, University of Florida, College of Dentistry, Gainesville, FL
| | - Irlan Almeida Freires
- Department of Oral Biology, University of Florida, College of Dentistry, Gainesville, FL
| | - Jessica K. Kajfasz
- Department of Oral Biology, University of Florida, College of Dentistry, Gainesville, FL
| | - Dicler Barbieri
- Center for Oral Biology, University of Rochester School of Medicine and Dentistry, Rochester, NY
| | - James H. Miller
- Center for Oral Biology, University of Rochester School of Medicine and Dentistry, Rochester, NY
| | - José A. Lemos
- Department of Oral Biology, University of Florida, College of Dentistry, Gainesville, FL
| | - Jacqueline Abranches
- Department of Oral Biology, University of Florida, College of Dentistry, Gainesville, FL
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Suzuki Y, Nagasawa R, Senpuku H. Inhibiting effects of fructanase on competence-stimulating peptide-dependent quorum sensing system in Streptococcus mutans. J Infect Chemother 2017; 23:634-641. [PMID: 28729051 DOI: 10.1016/j.jiac.2017.06.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Revised: 05/22/2017] [Accepted: 06/16/2017] [Indexed: 11/28/2022]
Abstract
Streptococcus mutans produces glucosyltransferases encoded by the gtfB and gtfC genes, which synthesize insoluble glucan, and both insoluble and soluble glucans by conversion of sucrose, and are known as principal agents to provide strong biofilm formation and demineralization on tooth surfaces. S. mutans possess a Com-dependent quorum sensing (QS) system, which is important for survival in severe conditions. The QS system is stimulated by the interaction between ComD {Receptor to competence-stimulating peptide (CSP)} encoded by the comD and CSP encoded by the comC, and importantly associated with bacteriocin production and genetic competence. Previously, we found enzyme fructanase (FruA) as a new inhibitor for the glucan-dependent biofilm formation. In the present study, inhibiting effects by FruA on glucan-independent biofilm formation of S. mutans UA159, UA159.gtfB-, UA159.gtfC-, and UA159.gtfBC- were observed in sucrose and no sucrose sugars-supplemented conditions using the plate assay. The reduction of UA159.comC- and UA159.comD- biofilm formation were also observed as compared with UA159 in same conditions. These results suggested that inhibitions of glucan-independent and Com-dependent biofilm formation were involved in the inhibiting mechanism by FruA. To more thoroughly investigate effects by FruA on the QS system, we examined on CSP-stimulated and Com-dependent bacteriocin production and genetic transformation. FruA inhibited bacteriocin production in collaboration with CSP and genetic transformation in bacterial cell conditions treated with FruA. Our findings show that FruA has multiple effects that inhibit survival functions of S. mutans, including biofilm formation and CSP-dependent QS responses, indicating its potential use as an agent for prevention of dental caries.
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Affiliation(s)
- Yusuke Suzuki
- Department of Maxillofacial Surgery, Nihon University Graduate School of Dentistry at Matsudo, Chiba, Japan; Department of Bacteriology I, National Institute of Infectious Diseases, Tokyo, Japan
| | - Ryo Nagasawa
- Department of Bacteriology I, National Institute of Infectious Diseases, Tokyo, Japan
| | - Hidenobu Senpuku
- Department of Bacteriology I, National Institute of Infectious Diseases, Tokyo, Japan.
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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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Effects of Carbohydrate Source on Genetic Competence in Streptococcus mutans. Appl Environ Microbiol 2016; 82:4821-4834. [PMID: 27260355 DOI: 10.1128/aem.01205-16] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Accepted: 05/25/2016] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED The capacity to internalize and catabolize carbohydrates is essential for dental caries pathogens to persist and cause disease. The expression of many virulence-related attributes by Streptococcus mutans, an organism strongly associated with human dental caries, is influenced by the peptide signaling pathways that control genetic competence. Here, we demonstrate a relationship between the efficiency of competence signaling and carbohydrate source. A significant increase in the activity of the promoters for comX, comS, and comYA after exposure to competence-stimulating peptide (CSP) was observed in cells growing on fructose, maltose, sucrose, or trehalose as the primary carbohydrate source, compared to cells growing on glucose. However, only cells grown in the presence of trehalose or sucrose displayed a significant increase in transformation frequency. Notably, even low concentrations of these carbohydrates in the presence of excess glucose could enhance the expression of comX, encoding a sigma factor needed for competence, and the effects on competence were dependent on the cognate sugar:phosphotransferase permease for each carbohydrate. Using green fluorescent protein (GFP) reporter fusions, we observed that growth in fructose or trehalose resulted in a greater proportion of the population activating expression of comX and comS, encoding the precursor of comX-inducing peptide (XIP), after addition of CSP, than growth in glucose. Thus, the source of carbohydrate significantly impacts the stochastic behaviors that regulate subpopulation responses to CSP, which can induce competence in S. mutans IMPORTANCE The signaling pathways that regulate development of genetic competence in Streptococcus mutans are intimately intertwined with the pathogenic potential of the organism, impacting biofilm formation, stress tolerance, and expression of known virulence determinants. Induction of the gene for the master regulator of competence, ComX, by competence-stimulating peptide (CSP) occurs in a subpopulation of cells. Here, we show that certain carbohydrates that are common in the human diet enhance the ability of CSP to activate transcription of comX and that a subset of these carbohydrates stimulates progression to the competent state. The cognate sugar:phosphotransferase permeases for each sugar are needed for these effects. Interestingly, single-cell analysis shows that the carbohydrates that increase com gene expression do so by enhancing the proportion of cells that respond to CSP. A mathematical model is developed to explain how carbohydrates modulate bistable behavior in the system via the ComRS pathway and ComX stability.
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Comprehensive Transcriptome Profiles of Streptococcus mutans UA159 Map Core Streptococcal Competence Genes. mSystems 2016; 1:mSystems00038-15. [PMID: 27822519 PMCID: PMC5069739 DOI: 10.1128/msystems.00038-15] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2015] [Accepted: 03/10/2016] [Indexed: 12/15/2022] Open
Abstract
In Streptococcus mutans, an oral colonizer associated with dental caries, development of competence for natural genetic transformation is triggered by either of two types of peptide pheromones, competence-stimulating peptides (CSPs) (18 amino acids [aa]) or SigX-inducing peptides (XIPs) (7 aa). Competence induced by CSP is a late response to the pheromone that requires the response regulator ComE and the XIP-encoding gene comS. XIP binds to ComR to allow expression of the alternative sigma factor SigX and the effector genes it controls. While these regulatory links are established, the precise set of effectors controlled by each regulator is poorly defined. To improve the definition of all three regulons, we used a high-resolution tiling array to map global changes in gene expression in the early and late phases of the CSP response. The early phase of the CSP response was limited to increased gene expression at four loci associated with bacteriocin production and immunity. In the late phase, upregulated regions expanded to a total of 29 loci, including comS and genes required for DNA uptake and recombination. The results indicate that the entire late response to CSP depends on the expression of comS and that the immediate transcriptional response to CSP, mediated by ComE, is restricted to just four bacteriocin-related loci. Comparison of the new data with published transcriptome data permitted the identification of all of the operons in each regulon: 4 for ComE, 2 for ComR, and 21 for SigX. Finally, a core set of 27 panstreptococcal competence genes was identified within the SigX regulon by comparison of transcriptome data from diverse streptococcal species. IMPORTANCES. mutans has the hard surfaces of the oral cavity as its natural habitat, where it depends on its ability to form biofilms in order to survive. The comprehensive identification of S. mutans regulons activated in response to peptide pheromones provides an important basis for understanding how S. mutans can transition from individual to social behavior. Our study placed 27 of the 29 transcripts activated during competence within three major regulons and revealed a core set of 27 panstreptococcal competence-activated genes within the SigX regulon.
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Peng X, Zhang Y, Bai G, Zhou X, Wu H. Cyclic di-AMP mediates biofilm formation. Mol Microbiol 2016; 99:945-59. [PMID: 26564551 PMCID: PMC5003771 DOI: 10.1111/mmi.13277] [Citation(s) in RCA: 104] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/11/2015] [Indexed: 12/27/2022]
Abstract
Cyclic di-AMP (c-di-AMP) is an emerging second messenger in bacteria. It has been shown to play important roles in bacterial fitness and virulence. However, transduction of c-di-AMP signaling in bacteria and the role of c-di-AMP in biofilm formation are not well understood. The level of c-di-AMP is modulated by activity of di-adenylyl cyclase that produces c-di-AMP and phosphodiesterase (PDE) that degrades c-di-AMP. In this study, we determined that increased c-di-AMP levels by deletion of the pdeA gene coding for a PDE promoted biofilm formation in Streptococcus mutans. Deletion of pdeA upregulated expression of gtfB, the gene coding for a major glucan producing enzyme. Inactivation of gtfB blocked the increased biofilm by the pdeA mutant. Two c-di-AMP binding proteins including CabPA (SMU_1562) and CabPB (SMU_1708) were identified. Interestingly, only CabPA deficiency inhibited both the increased biofilm formation and the upregulated expression of GtfB observed in the pdeA mutant. In addition, CabPA but not CabPB interacted with VicR, a known transcriptional factor that regulates expression of gtfB, suggesting that a signaling link between CabPA and GtfB through VicR. Increased biofilm by the pdeA deficiency also enhanced bacterial colonization of Drosophila in vivo. Taken together, our studies reveal a new role of c-di-AMP in mediating biofilm formation through a CabPA/VicR/GtfB signaling network in S. mutans.
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Affiliation(s)
- Xian Peng
- Department of Pediatric Dentistry, University of Alabama at Birmingham, School of Dentistry, Birmingham, AL, USA
- State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, China
| | - Yang Zhang
- Center for Immunology and Microbial Disease, MC-151, Albany Medical College, 47 New Scotland Avenue, Albany, NY, USA
| | - Guangchun Bai
- Center for Immunology and Microbial Disease, MC-151, Albany Medical College, 47 New Scotland Avenue, Albany, NY, USA
| | - Xuedong Zhou
- State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, China
| | - Hui Wu
- Department of Pediatric Dentistry, University of Alabama at Birmingham, School of Dentistry, Birmingham, AL, USA
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Haustenne L, Bastin G, Hols P, Fontaine L. Modeling of the ComRS Signaling Pathway Reveals the Limiting Factors Controlling Competence in Streptococcus thermophilus. Front Microbiol 2015; 6:1413. [PMID: 26733960 PMCID: PMC4686606 DOI: 10.3389/fmicb.2015.01413] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2015] [Accepted: 11/27/2015] [Indexed: 12/25/2022] Open
Abstract
In streptococci, entry in competence is dictated by ComX abundance. In Streptococcus thermophilus, production of ComX is transient and tightly regulated during growth: it is positively regulated by the cell-cell communication system ComRS during the activation phase and negatively regulated during the shut-off phase by unidentified late competence gene(s). Interestingly, most S. thermophilus strains are not or weakly transformable in permissive growth conditions (i.e., chemically defined medium, CDM), suggesting that some players of the ComRS regulatory pathway are limiting. Here, we combined mathematical modeling and experimental approaches to identify the components of the ComRS system which are critical for both dynamics and amplitude of ComX production in S. thermophilus. We built a deterministic, population-scaled model of the time-course regulation of specific ComX production in CDM growth conditions. Strains LMD-9 and LMG18311 were respectively selected as representative of highly and weakly transformable strains. Results from in silico simulations and in vivo luciferase activities show that ComR concentration is the main limiting factor for the level of comX expression and controls the kinetics of spontaneous competence induction in strain LMD-9. In addition, the model predicts that the poor transformability of strain LMG18311 results from a 10-fold lower comR expression level compared to strain LMD-9. In agreement, comR overexpression in both strains was shown to induce higher competence levels with deregulated kinetics patterns during growth. In conclusion, we propose that the level of ComR production is one important factor that could explain competence heterogeneity among S. thermophilus strains.
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Affiliation(s)
- Laurie Haustenne
- Biochimie, Biophysique et Génétique des Microorganismes, Institut des Sciences de la Vie, Université catholique de Louvain Louvain-la-Neuve, Belgium
| | - Georges Bastin
- Center for Systems Engineering and Applied Mechanics, ICTEAM, Université catholique de Louvain Louvain-la-Neuve, Belgium
| | - Pascal Hols
- Biochimie, Biophysique et Génétique des Microorganismes, Institut des Sciences de la Vie, Université catholique de Louvain Louvain-la-Neuve, Belgium
| | - Laetitia Fontaine
- Biochimie, Biophysique et Génétique des Microorganismes, Institut des Sciences de la Vie, Université catholique de Louvain Louvain-la-Neuve, Belgium
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Fontaine L, Wahl A, Fléchard M, Mignolet J, Hols P. Regulation of competence for natural transformation in streptococci. INFECTION GENETICS AND EVOLUTION 2015; 33:343-60. [DOI: 10.1016/j.meegid.2014.09.010] [Citation(s) in RCA: 68] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2014] [Revised: 08/28/2014] [Accepted: 09/07/2014] [Indexed: 02/02/2023]
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18
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Morphological and proteomic analyses of the biofilms generated by Streptococcus mutans isolated from caries-active and caries-free adults. J Dent Sci 2015. [DOI: 10.1016/j.jds.2014.09.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
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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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Jakubovics NS, Yassin SA, Rickard AH. Community interactions of oral streptococci. ADVANCES IN APPLIED MICROBIOLOGY 2014; 87:43-110. [PMID: 24581389 DOI: 10.1016/b978-0-12-800261-2.00002-5] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
It is now clear that the most common oral diseases, dental caries and periodontitis, are caused by mixed-species communities rather than by individual pathogens working in isolation. Oral streptococci are central to these disease processes since they are frequently the first microorganisms to colonize oral surfaces and they are numerically the dominant microorganisms in the human mouth. Numerous interactions between oral streptococci and other bacteria have been documented. These are thought to be critical for the development of mixed-species oral microbial communities and for the transition from oral health to disease. Recent metagenomic studies are beginning to shed light on the co-occurrence patterns of streptococci with other oral bacteria. Refinements in microscopy techniques and biofilm models are providing detailed insights into the spatial distribution of streptococci in oral biofilms. Targeted genetic manipulation is increasingly being applied for the analysis of specific genes and networks that modulate interspecies interactions. From this work, it is clear that streptococci produce a range of extracellular factors that promote their integration into mixed-species communities and enable them to form social networks with neighboring taxa. These "community integration factors" include coaggregation-mediating adhesins and receptors, small signaling molecules such as peptides or autoinducer-2, bacteriocins, by-products of metabolism including hydrogen peroxide and lactic acid, and a range of extracellular enzymes. Here, we provide an overview of various types of community interactions between oral streptococci and other microorganisms, and we consider the possibilities for the development of new technologies to interfere with these interactions to help control oral biofilms.
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Affiliation(s)
- Nicholas S Jakubovics
- Oral Biology, School of Dental Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom.
| | - Sufian A Yassin
- Oral Biology, School of Dental Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Alexander H Rickard
- Department of Epidemiology, School of Public Health, University of Michigan, Ann Arbor, Michigan, USA
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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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