scholarly journals ThefsrQuorum-Sensing System and Cognate Gelatinase Orchestrate the Expression and Processing of Proprotein EF_1097 into the Mature Antimicrobial Peptide Enterocin O16

2015 ◽  
Vol 197 (13) ◽  
pp. 2112-2121 ◽  
Author(s):  
Halil Dundar ◽  
Dag A. Brede ◽  
Sabina Leanti La Rosa ◽  
Ahmed Osama El-Gendy ◽  
Dzung B. Diep ◽  
...  
Keyword(s):  
Antimicrobial Activity ◽  
Quorum Sensing ◽  
Antimicrobial Peptide ◽  
Bioinformatic Analysis ◽  
Dependent Manner ◽  
Content Type ◽  
Sensing System ◽  
Quorum Sensing System ◽  
Inhibitory Spectrum ◽  
A Cell

ABSTRACTA novel antimicrobial peptide designated enterocin O16 was purified fromEnterococcus faecalis. Mass spectrometry showed a monoisotopic mass of 7,231 Da, and N-terminal Edman degradation identified a 29-amino-acid sequence corresponding to residues 90 to 119 of the EF_1097 protein. Bioinformatic analysis showed that enterocin O16 is composed of the 68 most C-terminal residues of the EF_1097 protein. Introduction of an in-frame isogenic deletion in theef1097gene abolished the production of enterocin O16. Enterocin O16 has a narrow inhibitory spectrum, as it inhibits mostly lactobacilli. Apparently,E. faecalisis intrinsically resistant to the antimicrobial peptide, as no immunity connected to the production of enterocin O16 could be identified.ef1097has previously been identified as one of three loci regulated by thefsrquorum-sensing system. The introduction of a nonsense mutation intofsrBconsistently impaired enterocin O16 production, but externally added gelatinase biosynthesis-activating pheromone restored the antimicrobial activity. Functional genetic analysis showed that the EF_1097 proprotein is processed extracellularly into enterocin O16 by the metalloprotease GelE. Thus, it is evident that thefsrquorum-sensing system constitutes the regulatory unit that controls the expression of the EF_1097 precursor protein and the protease GelE and that the latter is required for the formation of enterocin O16. On the basis of these results, this study identified antibacterial antagonism as a novel aspect related to the function offsrand provides a rationale for whyef1097is part of thefsrregulon.IMPORTANCEThefsrquorum-sensing system modulates important physiological functions inE. faecalisvia the activity of GelE. The present study presents a new facet offsrsignaling. The system controls the expression of three primary target operons (fsrABCD,gelE-sprE, andef1097-ef1097b). We demonstrate that the concerted expression of these operons constitutes the elements necessary for the production of a bacteriocin-type peptide and that antimicrobial antagonism is an intrinsic function offsr. The bacteriocin enterocin O16 consists of the 68 most C-terminal residues of the EF_1097 secreted proprotein. The GelE protease processes the EF_1097 proprotein into enterocin O16. In this manner,fsrsignaling enablesE. faecalispopulations to express antimicrobial activity in a cell density-dependent manner.

scholarly journals Pseudomonas aeruginosa Regulatory Protein AnvM Controls Pathogenicity in Anaerobic Environments and Impacts Host Defense

mBio ◽  
2019 ◽  
Vol 10 (4) ◽  
Author(s):  
Yingchao Zhang ◽  
Chuan-min Zhou ◽  
Qinqin Pu ◽  
Qun Wu ◽  
Shirui Tan ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Immune Response ◽  
Pseudomonas Aeruginosa ◽  
Quorum Sensing ◽  
Anaerobic Conditions ◽  
Content Type ◽  
Sensing System ◽  
Quorum Sensing System ◽  
Aerobic And Anaerobic ◽  
Aerobic And Anaerobic Conditions

ABSTRACT Pseudomonas aeruginosa, one of the most common pathogens in hospital-acquired infections, is tightly controlled by a multilayered regulatory network, including the quorum sensing system (QS), the type VI secretion system (T6SS), and resistance to host immunity. We found that the P. aeruginosa 3880 (PA3880) gene, which encodes an unknown protein, acts as a regulator of anaerobic metabolism in response to oxidative stress and virulence in P. aeruginosa. More than 30 PA3880 homologs were found in other bacterial genomes, indicating that PA3880 is widely distributed in the Bacteria kingdom as a highly conserved gene. Deletion of the PA3880 gene changed the expression levels of more than 700 genes, including a group of virulence genes, under both aerobic and anaerobic conditions. To further study the mechanisms of PA3880-mediated regulation in virulence, we utilized a bacterial two-hybrid assay and found that the PA3880 protein interacted directly with QS regulator MvfR and anaerobic regulator Anr. Loss of the PA3880 protein significantly blunted the pathogenicity of P. aeruginosa, resulting in increased host survival, decreased bacterial burdens, reduced inflammatory responses, and fewer lung injuries in challenged mice hosts. Mechanistically, we found that Cys44 was a critical site for the full function of PA3880 in influencing alveolar macrophage phagocytosis and bacterial clearance. We also found that AnvM directly interacted with host receptors Toll-like receptor 2 (TLR2) and TLR5, which might lead to activation of the host immune response. Hence, we gave the name AnvM (anaerobic and virulence modulator) to the PA3880 protein. This characterization of AnvM could help to uncover new targets and strategies to treat P. aeruginosa infections. IMPORTANCE Infections by Pseudomonas aeruginosa, one of the most frequently isolated human pathogens, can create huge financial burdens. However, knowledge of the molecular mechanisms involved in the pathogenesis of P. aeruginosa remains elusive. We identified AnvM as a novel regulator of virulence in P. aeruginosa. Deletion of anvM altered the expression levels of more than 700 genes under aerobic and anaerobic conditions, including quorum sensing system genes and oxidative stress resistance genes. AnvM directly interacted with MvfR and Anr, thus regulating their downstream genes. More importantly, AnvM directly bound to TLR2 and TLR5, which turn on the host immune response. These findings provide insights into the significance of AnvM homologs in pathogenic bacteria and suggest a potential drug target against bacterial infection.

scholarly journals The LuxS-Dependent Quorum-Sensing System Regulates Early Biofilm Formation by Streptococcus pneumoniae Strain D39

2011 ◽  
Vol 79 (10) ◽  
pp. 4050-4060 ◽  
Author(s):  
Jorge E. Vidal ◽  
Herbert P. Ludewick ◽  
Rebekah M. Kunkel ◽  
Dorothea Zähner ◽  
Keith P. Klugman
Keyword(s):  
Streptococcus Pneumoniae ◽  
Quorum Sensing ◽  
Biofilm Formation ◽  
Single Copy ◽  
Middle Ear Mucosa ◽  
Transcript Levels ◽  
Content Type ◽  
Sensing System ◽  
Quorum Sensing System

ABSTRACTStreptococcus pneumoniaeis the leading cause of death in children worldwide and forms highly organized biofilms in the nasopharynx, lungs, and middle ear mucosa. TheluxS-controlled quorum-sensing (QS) system has recently been implicated in virulence and persistence in the nasopharynx, but its role in biofilms has not been studied. Here we show that this QS system plays a major role in the control ofS. pneumoniaebiofilm formation. Our results demonstrate that theluxSgene is contained by invasive isolates and normal-flora strains in a region that contains genes involved in division and cell wall biosynthesis. TheluxSgene was maximally transcribed, as a monocistronic message, in the early mid-log phase of growth, and this coincides with the appearance of early biofilms. Demonstrating the role of the LuxS system in regulatingS. pneumoniaebiofilms, at 24 h postinoculation, two different D39ΔluxSmutants produced ∼80% less biofilm biomass than wild-type (WT) strain D39 did. Complementation of these strains withluxS, either in a plasmid or integrated as a single copy in the genome, restored their biofilm level to that of the WT. Moreover, a soluble factor secreted by WT strain D39 or purified AI-2 restored the biofilm phenotype of D39ΔluxS. Our results also demonstrate that during the early mid-log phase of growth, LuxS regulates the transcript levels oflytA, which encodes an autolysin previously implicated in biofilms, and also the transcript levels ofply, which encodes the pneumococcal pneumolysin. In conclusion, theluxS-controlled QS system is a key regulator of early biofilm formation byS. pneumoniaestrain D39.

scholarly journals The Agr-Like Quorum-Sensing System Regulates Sporulation and Production of Enterotoxin and Beta2 Toxin by Clostridium perfringens Type A Non-Food-Borne Human Gastrointestinal Disease Strain F5603

2011 ◽  
Vol 79 (6) ◽  
pp. 2451-2459 ◽  
Author(s):  
Jihong Li ◽  
Jianming Chen ◽  
Jorge E. Vidal ◽  
Bruce A. McClane
Keyword(s):  
Quorum Sensing ◽  
Gastrointestinal Disease ◽  
Alpha Toxin ◽  
Null Mutant ◽  
Content Type ◽  
Perfringolysin O ◽  
Sensing System ◽  
Food Borne ◽  
Quorum Sensing System ◽  
Beta2 Toxin

ABSTRACTClostridium perfringenstype A strains producing enterotoxin (CPE) cause one of the most common bacterial food-borne illnesses, as well as many cases of non-food-borne human gastrointestinal disease. Recent studies have shown that an Agr-like quorum-sensing system controls production of chromosomally encoded alpha-toxin and perfringolysin O byC. perfringens, as well as sporulation byClostridium botulinumandClostridium sporogenes. The current study explored whether the Agr-like quorum-sensing system also regulates sporulation and production of two plasmid-encoded toxins (CPE and beta2 toxin) that may contribute to the pathogenesis of non-food-borne human gastrointestinal disease strain F5603. An isogenicagrBnull mutant was inhibited for production of beta2 toxin during vegetative growth and in sporulating culture, providing the first evidence that, inC. perfringens, this system can control production of plasmid-encoded toxins as well as chromosomally encoded toxins. This mutant also showed reduced production of alpha-toxin and perfringolysin O during vegetative growth. Importantly, when cultured in sporulation medium, the mutant failed to efficiently form spores and was blocked for CPE production. Complementation partially or fully reversed all phenotypic changes in the mutant, confirming that they were specifically due to inactivation of theagrlocus. Western blots suggest that this loss of sporulation and sporulation-specific CPE production for theagrBnull mutant involves, at least in part, Agr-mediated regulation of production of Spo0A and alternative sigma factors, which are essential forC. perfringenssporulation.

scholarly journals Pseudomonas aeruginosa synthesizes the autoinducers of its oxylipin-dependent quorum sensing system extracellularly

2021 ◽  
Author(s):  
Eriel Martínez ◽  
Carlos J. Orihuela ◽  
Javier Campos-Gomez
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Quorum Sensing ◽  
Outer Membrane ◽  
Biofilm Formation ◽  
Octadecenoic Acid ◽  
Secretion System ◽  
Genetic Screen ◽  
Dependent Manner ◽  
Sensing System ◽  
Quorum Sensing System

ABSTRACTThe oxylipin-dependent quorum sensing system (ODS) of Pseudomonas aeruginosa relies on the production and sensing of two oxylipin autoinducers, 10S-hydroxy-(8E)-octadecenoic acid (10-HOME) and 7S,10S dihydroxy-(8E)-octadecenoic acid (7,10-DiHOME). Here, and contrary to the prevailing notion that bacterial autoinducers are synthesized intracellularly, we show that 10-HOME and 7,10-DiHOME biosynthesis occurs extracellularly, and this requires the secretion of the oxylipin synthases. We implemented a genetic screen of P. aeruginosa strain PAO1, which identified fourteen genes required for the synthesis of oxylipins. Among the identified genes, four encoded components of the ODS system and the other ten were part of the Xcp type II secretion system (T2SS). We created a deletion mutant of xcpQ, which encodes the outer membrane component of Xcp, and found it recapitulated the impaired functionality of the transposon mutants. Upon further examination, the lack of ODS function was demonstrated to be caused by the blocking of the DS enzymes secretion. Notably, the xcpQ mutant activated the ODS system when exposed to 10-HOME and 7,10-DiHOME, indicating that the sensing component of this quorum sensing system remains fully functional. In contrast with the detrimental effect previously described for T2SS in biofilm formation, here we observed that T2SS was required for robust in vitro and in vivo biofilm formation in an ODS dependent manner. To the best of our knowledge, this study is the first to find QS autoinducers that are synthetized in the extracellular space and provides new evidence for the role of the T2SS for biofilm formation in P. aeruginosa.IMPORTANCEWe previously showed that the ODS quorum sensing system of P. aeruginosa produces and responds to oxylipins derived from host oleic acid by enhancing biofilm formation and virulence. Herein, we developed a genetic screen strategy to explore the molecular basis for oxylipins synthesis and detection. Unexpectedly, we found that the ODS autoinducer synthases cross the outer membrane using the Xcp Type 2 secretion system of P. aeruginosa and thus, the biosynthesis of oxylipins occur extracellularly. Biofilm formation, which was thought to be impaired as result of Xcp activity, was found to be enhanced as result of ODS activation. This is a unique QS system strategy and reveals a new way by which P. aeruginosa interacts with the host environment.

scholarly journals Loci identification of a N-acyl homoserine lactone type quorum sensing system and a new LysR-type transcriptional regulator associated with antimicrobial activity and swarming in Burkholderia gladioli UAPS07070

2019 ◽  
Vol 14 (1) ◽  
pp. 165-178
Author(s):  
E. Seynos-García ◽  
M. Castañeda-Lucio ◽  
J. Muñoz-Rojas ◽  
L. López-Pliego ◽  
M. Villalobos ◽  
...  
Keyword(s):  
Antimicrobial Activity ◽  
Quorum Sensing ◽  
Transcriptional Regulator ◽  
Homoserine Lactone ◽  
Sensing System ◽  
Gene Coding ◽  
Burkholderia Gladioli ◽  
Quorum Sensing System ◽  
First Time ◽  
Random Transposition

AbstractA random transposition mutant library of B. gladioli UAPS07070 was analyzed for searching mutants with impaired microbial antagonism. Three derivates showed diminished antimicrobial activity against a sensitive strain. The mutated loci showed high similarity to the quorum sensing genes of the AHL-synthase and its regulator. Another mutant was affected in a gene coding for a LysrR-type transcriptional regulator. The production of toxoflavin, the most well known antimicrobial-molecule and a major virulence factor of plant-pathogenic B. glumae and B. gladioli was explored. The absence of a yellowish pigment related to toxoflavin and the undetectable transcription of toxA in the mutants indicated the participation of the QS system and of the LysR-type transcriptional regulator in the regulation of toxoflavin. Additionally, those genes were found to be related to the swarming phenotype. Lettuce inoculated with the AHL synthase and the lysR mutants showed less severe symptoms. We present evidence of the participation of both, the quorum sensing and for the first time, of a LysR-type transcriptional regulator in antibiosis and swarming phenotype in a strain of B. gladioli

scholarly journals A Quorum-Sensing System That Regulates Streptococcus pneumoniae Biofilm Formation and Surface Polysaccharide Production

mSphere ◽  
2017 ◽  
Vol 2 (5) ◽  
Author(s):  
Roger Junges ◽  
Gabriela Salvadori ◽  
Sudhanshu Shekhar ◽  
Heidi A. Åmdal ◽  
Jimstan N. Periselneris ◽  
...  
Keyword(s):  
Quorum Sensing ◽  
Gene Cluster ◽  
Biofilm Formation ◽  
Parent Strain ◽  
Single Gene ◽  
Content Type ◽  
Sensing System ◽  
Quorum Sensing System ◽  
Surface Polysaccharide ◽  
Capsule Size

ABSTRACT Quorum sensing regulates bacterial social behaviors by production, secretion, and sensing of pheromones. In this study, we characterized a new quorum-sensing system of the Rgg/SHP class in S. pneumoniae D39. The system was found to directly induce the expression of a single gene cluster comprising the gene for the SHP pheromone and genes with putative functions in capsule synthesis. Capsule size, as measured by dextran exclusion, was increased by SHP exposure in R36A, an unencapsulated derivative of D39. In the encapsulated parent strain, overexpression of the gene cluster increased capsule size, supporting the role of Rgg/SHP in the synthesis of surface polysaccharides. Further, we found that biofilm formation on epithelial cells was reduced by overexpression of the system and increased in a mutant with an rgg deletion. Placing surface polysaccharide expression under quorum-sensing regulation may enable S. pneumoniae to tune interactions with the host and other bacteria in accordance with environmental and cell density conditions. Despite vaccines, Streptococcus pneumoniae kills more than a million people yearly. Thus, understanding how pneumococci transition from commensals to pathogens is particularly relevant. Quorum sensing regulates collective behaviors and thus represents a potential driver of commensal-to-pathogen transitions. Rgg/small hydrophobic peptide (SHP) quorum-sensing systems are widespread in streptococci, yet they remain largely uncharacterized in S. pneumoniae. Using directional transcriptome sequencing, we show that the S. pneumoniae D39 Rgg0939/SHP system induces the transcription of a single gene cluster including shp and capsule gene homologs. Capsule size measurements determined by fluorescein isothiocyanate-dextran exclusion allowed assignment of the system to the regulation of surface polysaccharide expression. We found that the SHP pheromone induced exopolysaccharide expression in R36A, an unencapsulated derivative of D39. In the encapsulated parent strain, overexpression of the Rgg system resulted in a mutant with increased capsule size. In line with previous studies showing that capsule expression is inversely associated with biofilm formation, we found that biofilm formed on lung epithelial cells was decreased in the overexpression strain and increased in an rgg deletion mutant. Although no significant differences were observed between D39 and the rgg deletion mutant in a mouse model of lung infection, in competitive assays, overexpression reduced fitness. This is the first study to reveal a quorum-sensing system in streptococci that regulates exopolysaccharide synthesis from a site distinct from the original capsule locus. IMPORTANCE Quorum sensing regulates bacterial social behaviors by production, secretion, and sensing of pheromones. In this study, we characterized a new quorum-sensing system of the Rgg/SHP class in S. pneumoniae D39. The system was found to directly induce the expression of a single gene cluster comprising the gene for the SHP pheromone and genes with putative functions in capsule synthesis. Capsule size, as measured by dextran exclusion, was increased by SHP exposure in R36A, an unencapsulated derivative of D39. In the encapsulated parent strain, overexpression of the gene cluster increased capsule size, supporting the role of Rgg/SHP in the synthesis of surface polysaccharides. Further, we found that biofilm formation on epithelial cells was reduced by overexpression of the system and increased in a mutant with an rgg deletion. Placing surface polysaccharide expression under quorum-sensing regulation may enable S. pneumoniae to tune interactions with the host and other bacteria in accordance with environmental and cell density conditions.

scholarly journals LuxS/AI-2 Quorum Sensing System in Edwardsiella piscicida Promotes Biofilm Formation and Pathogenicity

2020 ◽  
Vol 88 (5) ◽  
Author(s):  
Yongcan Sun ◽  
Yu Li ◽  
Qian Luo ◽  
Jinjing Huang ◽  
Jiakang Chen ◽  
...  
Keyword(s):  
Quorum Sensing ◽  
Biofilm Formation ◽  
Type Strain ◽  
Wild Type Strain ◽  
Wild Type ◽  
Content Type ◽  
Sensing System ◽  
Gene Mutant ◽  
Quorum Sensing System ◽  
Edwardsiella Piscicida

ABSTRACT LuxS/AI-2 is an important quorum sensing system which affects the growth, biofilm formation, virulence, and metabolism of bacteria. LuxS is encoded by the luxS gene, but how this gene is associated with a diverse array of physiological activities in Edwardsiella piscicida (E. piscicida) is not known. Here, we constructed an luxS gene mutant strain, the △luxS strain, to identify how LuxS/AI-2 affects pathogenicity. The results showed that LuxS was not found in the luxS gene mutant strain, and this gene deletion decreased E. piscicida growth compared to that of the wild-type strain. Meanwhile, the wild-type strain significantly increased penetration and motility in mucin compared to levels with the △luxS strain. The 50% lethal dose (LD50) of the E. piscicida △luxS strain for zebrafish was significantly higher than that of the wild-type strain, which suggested that the luxS gene deletion could attenuate the strain’s virulence. The AI-2 activities of EIB202 were 56-fold higher than those in the △luxS strain, suggesting that the luxS gene promotes AI-2 production. Transcriptome results demonstrated that between cells infected with the △luxS strain and those infected with the wild-type strain 46 genes were significantly differentially regulated, which included 34 upregulated genes and 12 downregulated genes. Among these genes, the largest number were closely related to cell immunity and signaling systems. In addition, the biofilm formation ability of EIB202 was significantly higher than that of the △luxS strain. The supernatant of EIB202 increased the biofilm formation ability of the △luxS strain, which suggested that the luxS gene and its product LuxS enhanced biofilm formation in E. piscicida. All results indicate that the LuxS/AI-2 quorum sensing system in E. piscicida promotes its pathogenicity through increasing a diverse array of physiological activities.

Inhibition of Biogenic Amines in Shewanella baltica by Anthocyanins Involving a Quorum Sensing System

2019 ◽  
Vol 82 (4) ◽  
pp. 589-596
Author(s):  
YANBO WANG ◽  
FEIFEI WANG ◽  
XINGYUE BAO ◽  
JIE FENG ◽  
LINGLIN FU
Keyword(s):  
Quorum Sensing ◽  
Transcriptional Analysis ◽  
Large Yellow Croaker ◽  
Sensing System ◽  
Quorum Sensing System ◽  
A Cell ◽  
Culture Extract ◽  
Purple Sweet Potato ◽  
Positive Correlations ◽  
Shewanella Baltica

ABSTRACT Quorum sensing (QS) is a cell density-dependent signaling system responsible for various physiological activities in bacteria. We initially investigated the relation between a QS system and biogenic amine (BA) production in Shewanella baltica, the specific spoilage organism of refrigerated large yellow croaker (Pseudosciaene crocea). In addition, the inhibition effects of anthocyanins from blueberry and purple sweet potato against QS signals and putrescine production were explored. Two kinds of diketopiperazines, cyclo-(l-Pro-l-Leu) and cyclo-(l-Pro-l-Pro), and two kinds of BAs, putrescine and cadaverine, were detected in the culture extract of S. baltica cultivated in sterile large yellow croaker juice, wherein putrescine presented significantly positive correlations with cyclo-(l-Pro-l-Leu) and cyclo-(l-Pro-l-Pro). In addition, anthocyanins at subminimum inhibitory concentration inhibited the production of diketopiperazines and putrescine in S. baltica 23, a strain with strong putrescine production. Furthermore, a transcriptional analysis showed that anthocyanins suppressed the expression of the odc gene in S. baltica, the gene responsible for the production of putrescine from decarboxylation of ornithine. These results established a correlation of the main BA putrescine with the QS system in S. baltica and revealed that anthocyanins could be developed as new QS inhibitors and seafood preservative candidates. HIGHLIGHTS

scholarly journals Quorum Sensing in Streptococcus mutans Regulates Production of Tryglysin, a Novel RaS-RiPP Antimicrobial Compound

mBio ◽  
2021 ◽  
Vol 12 (2) ◽  
Author(s):  
Britta E. Rued ◽  
Brett C. Covington ◽  
Leah B. Bushin ◽  
Gabriella Szewczyk ◽  
Irina Laczkovich ◽  
...  
Keyword(s):  
Quorum Sensing ◽  
Streptococcus Mutans ◽  
Opportunistic Pathogen ◽  
Oral Microbiota ◽  
Content Type ◽  
Sensing System ◽  
Regulatory Systems ◽  
Quorum Sensing System ◽  
Streptococcal Species ◽  
Bona Fide

ABSTRACT The genus Streptococcus encompasses a large bacterial taxon that commonly colonizes mucosal surfaces of vertebrates and is capable of disease etiologies originating from diverse body sites, including the respiratory, digestive, and reproductive tracts. Identifying new modes of treating infections is of increasing importance, as antibiotic resistance has escalated. Streptococcus mutans is an important opportunistic pathogen that is an agent of dental caries and is capable of systemic diseases such as endocarditis. As such, understanding how it regulates virulence and competes in the oral niche is a priority in developing strategies to defend from these pathogens. We determined that S. mutans UA159 possesses a bona fide short hydrophobic peptide (SHP)/Rgg quorum-sensing system that regulates a specialized biosynthetic operon featuring a radical-SAM (S-adenosyl-l-methionine) (RaS) enzyme and produces a ribosomally synthesized and posttranslationally modified peptide (RiPP). The pairing of SHP/Rgg regulatory systems with RaS biosynthetic operons is conserved across streptococci, and a locus similar to that in S. mutans is found in Streptococcus ferus, an oral streptococcus isolated from wild rats. We identified the RaS-RiPP product from this operon and solved its structure using a combination of analytical methods; we term these RiPPs tryglysin A and B for the unusual Trp-Gly-Lys linkage. We report that tryglysins specifically inhibit the growth of other streptococci, but not other Gram-positive bacteria such as Enterococcus faecalis or Lactococcus lactis. We predict that tryglysin is produced by S. mutans in its oral niche, thus inhibiting the growth of competing species, including several medically relevant streptococci. IMPORTANCE Bacteria interact and compete with a large community of organisms in their natural environment. Streptococcus mutans is one such organism, and it is an important member of the oral microbiota. We found that S. mutans uses a quorum-sensing system to regulate production of a novel posttranslationally modified peptide capable of inhibiting growth of several streptococcal species. We find inhibitory properties of a similar peptide produced by S. ferus and predict that these peptides play a role in interspecies competition in the oral niche.

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