The Formation of Streptococcus mutans Persisters Induced by the Quorum-Sensing Peptide Pheromone Is Affected by the LexA Regulator

Abstract

bThe presence of multidrug-tolerant persister cells within microbial populations has been implicated in the resiliency of bacterial survival against antibiotic treatments and is a major contributing factor in chronic infections. The mechanisms by which these phenotypic variants are formed have been linked to stress response pathways in various bacterial species, but many of these mechanisms remain unclear. We have previously shown that in the cariogenic organism Streptococcus mutans, the quorumsensing peptide CSP (competence-stimulating peptide) pheromone was a stress-inducible alarmone that triggered an increased formation of multidrug-tolerant persisters. In this study, we characterized SMU.2027, a CSP-inducible gene encoding a LexA ortholog. We showed that in addition to exogenous CSP exposure, stressors, including heat shock, oxidative stress, and ofloxacin antibiotic, were capable of triggering expression of lexA in an autoregulatory manner akin to that of LexA-like transcriptional regulators. We demonstrated the role of LexA and its importance in regulating tolerance toward DNA damage in a noncanonical SOS mechanism. We showed its involvement and regulatory role in the formation of persisters induced by the CSP-ComDE quorum-sensing regulatory system. We further identified key genes involved in sugar and amino acid metabolism, the clustered regularly interspaced short palindromic repeat (CRISPR) system, and autolysin from transcriptomic analyses that contribute to the formation of quorum-sensing-induced persister cells.T he classical view of bacterial survival against antibiotic killing has usually been seen as the expression of genetic resistance mechanisms that arise from mutations or gained through horizontal gene transfer. These resistance mechanisms include host target modification, degradation or modification of the antibiotic itself, and reduction in the permeability or increase in the efflux of the drug (1). A major survival mechanism of bacteria is antibiotic tolerance, whereby bacterial cells that have a slower or reduced growth rate become more tolerant toward antibiotic killing (2, 3). This reduction in bacterial growth is prominently perceived as one of the main survival mechanisms elicited in bacterial biofilms, by which the slower growth of biofilm cells contributes toward the highly recalcitrant nature of biofilm infections, even in biofilm populations that lack genetically encoded antibiotic resistance markers (4, 5).Formation of persister cells is the main factor responsible for the tolerance of pathogens to antibiotics. Persisters are nongrowing dormant cells that are produced in a clonal population of genetically identical cells. They constitute a small fraction of the bacterial population. Persisters are not mutants but phenotypic variants of the wildtype population (6). In contrast to the case with the aforementioned drug resistance mechanisms, which allow for bacterial cells to actively grow and divide unimpeded in the presence of specific antimicrobials, persisters are capable of sur...

A tripartite toxin‐antitoxin module induced by quorum sensing is associated with the persistence phenotype in Streptococcus mutans

“…20 However, this stress-inducible persistence phenotype was abolished in any quorum sensing-deficient mutants. 20,23 This confirmed the importance of quorum sensing signaling in mounting an adaptive stress response within a subpopulation of S. mutans to form persisters for survival of the species. We previously identified the CSP regulon of S. mutans 21 and found that a novel putative tripartite type II TA system, named SmuATR, was up-regulated under CSP conditions.…”

“…It was demonstrated that different stresses encountered in the oral cavity increased the level of persisters . However, this stress‐inducible persistence phenotype was abolished in any quorum sensing‐deficient mutants . This confirmed the importance of quorum sensing signaling in mounting an adaptive stress response within a subpopulation of S. mutans to form persisters for survival of the species.…”

“…Therefore, it is not surprising that the CSP‐ComDE quorum sensing system is used by S. mutans as a deterministic mechanism for persister formation. This stress inducible phenotype was abolished in any quorum sensing‐deficient mutants unable to produce (∆ comC ), detect (∆ comD ), or respond (∆ comE , ∆ comR , ∆ comS , ∆ sigX ) to the CSP pheromone …”

Ecological Approaches to Dental Caries Prevention: Paradigm Shift or Shibboleth?

“…For MS, the stress-dependent QS system is primarily comprised of the CSP and its ComD/ComE 2-component signal transduction system for communication between biofilm cells of the same species, while interspecies signalling is mediated via the autoinducer-2 molecule produced by LuxS [Senadheera and Cvitkovitch, 2008]. The CSP-mediated QS system in S. mutans affects biofilm formation, acidogenicity, aciduricity, genetic transformation, bacteriocin production, stress response, and the ability to produce persister phenotypes [Leung et al, 2015]. Targeting QS signalling pathways could provide a promising avenue in the development of novel therapeutics to alter cariogenic biofilms.…”

Transcriptional Repressor PtvR Regulates Phenotypic Tolerance to Vancomycin in Streptococcus pneumoniae

“…Also, ATP depletion is associated with persister formation in S. aureus (22). LexA, a DNA-binding protein that represses the SOS response in bacteria, is involved in the formation of Streptococcus mutans persisters induced by the competence-stimulating peptide (CSP) (26). Lastly, Streptococcus pneumoniae (pneumococcus) exhibits phenotypic tolerance to vancomycin and penicillin in a capsuledependent fashion (27), and this tolerance is epigenetically inherited by daughter cells (28).…”