A Quorum-Sensing Signaling System Essential for Genetic Competence in Streptococcus mutans Is Involved in Biofilm Formation

Abstract

In a previous study, a quorum-sensing signaling system essential for genetic competence in Streptococcus mutans was identified, characterized, and found to function optimally in biofilms (Li et al., J. Bacteriol. 183:897-908, 2001). Here, we demonstrate that this system also plays a role in the ability of S. mutans to initiate biofilm formation. To test this hypothesis, S. mutans wild-type strain NG8 and its knockout mutants defective in comC, comD, comE, and comX, as well as a comCDE deletion mutant, were assayed for their ability to initiate biofilm formation. The spatial distribution and architecture of the biofilms were examined by scanning electron microscopy and confocal scanning laser microscopy. The results showed that inactivation of any of the individual genes under study resulted in the formation of an abnormal biofilm. The comC mutant, unable to produce or secrete a competence-stimulating peptide (CSP), formed biofilms with altered architecture, whereas the comD and comE mutants, which were defective in sensing and responding to the CSP, formed biofilms with reduced biomass. Exogenous addition of the CSP and complementation with a plasmid containing the wild-type comC gene into the cultures restored the wild-type biofilm architecture of comC mutants but showed no effect on the comD, comE, or comX mutant biofilms. The fact that biofilms formed by comC mutants differed from the comD, comE, and comX mutant biofilms suggested that multiple signal transduction pathways were affected by CSP. Addition of synthetic CSP into the culture medium or introduction of the wild-type comC gene on a shuttle vector into the comCDE deletion mutant partially restored the wild-type biofilm architecture and further supported this idea. We conclude that the quorum-sensing signaling system essential for genetic competence in S. mutans is important for the formation of biofilms by this gram-positive organism.

Antimicrobial and anti-biofilm activities of Lactobacillus kefiranofaciens DD2 against oral pathogens

“…Thus, our results demonstrated that supplementation with the DD2 culture supernatant could influence fructan production in S. mutans . Furthermore, the downregulation of ftf was accompanied by decreases in the expression levels of comDE and brpA (Figure 4), which are also involved in the biofilm formation and play a critical role in the regulation of stress responses [9,37]. Interestingly, the expression level of vicR (Figure 4) – which encodes proteins that regulate the expression of virulence factors involved in polysaccharide synthesis and those that integrate external signals in a regulatory network composed of ftf, gtfB , and gtfC [37] – was significantly decreased.…”

“…Streptococci are also known to aggregate to form oral biofilms; for instance, S. mutans rapidly increases biofilm thickness by producing surface-associated and biofilm regulatory proteins [7,9,10]. As such, reducing the size of cariogenic bacterial populations and suppressing biofilm formation are essential strategies for the prevention of oral diseases [11].…”

Antimicrobial peptide GH12 suppresses cariogenic virulence factors of Streptococcus mutans

“…The VicRKX and LiaFSR two-component signal transduction systems (TCSTS) have been reported as the master regulatory system involved in expression of GTFs, biofilm formation and environment stress tolerance in S. mutans [8,9]. The ComCDE system quorum sensing (QS) system enables intra-species cell–cell communication [10]. As these TCSTS are selective for the bacteria and not the host, they are regarded as excellent therapeutic targets for antimicrobial agents [11].…”

Inhibition ofSteptococcus mutansbiofilm formation by extracts ofTenacibaculumsp. 20J, a bacterium with wide-spectrum quorum quenching activity

“…The QS system typical of streptococci is regulated by a peptide pheromone signal called competence stimulating peptide (CSP) [9], which is species-specific and detected by a histidine-kinase [10]. The inactivation of any of the genes related to the CSP QS system results in the alteration of biofilm architecture [11]. The other QS signal related to biofilm formation in S. mutans is AI-2 [7,12,13], which has been proposed as a universal signalling molecule due to its wide distribution among prokaryotes [14,15], including important oral pathogens [16].…”