LuxS-Based Signaling Affects Streptococcus mutans Biofilm Formation

Abstract

Streptococcus mutans is implicated as a major etiological agent in human dental caries, and one of the important virulence properties of this organism is its ability to form biofilms (dental plaque) on tooth surfaces. We examined the role of autoinducer-2 (AI-2) on S. mutans biofilm formation by constructing a GS-5 luxS-null mutant. Biofilm formation by the luxS mutant in 0.5% sucrose defined medium was found to be markedly attenuated compared to the wild type. Scanning electron microscopy also revealed that biofilms of the luxS mutant formed larger clumps in sucrose medium compared to the parental strain. Therefore, the expression of glucosyltransferase genes was examined and the gtfB and gtfC genes, but not the gtfD gene, in the luxS mutant were upregulated in the mid-log growth phase. Furthermore, we developed a novel two-compartment system to monitor AI-2 production by oral streptococci and periodontopathic bacteria. The biofilm defect of the luxS mutant was complemented by strains of S. gordonii, S. sobrinus, and S. anginosus; however, it was not complemented by S. oralis, S. salivarius, or S. sanguinis. Biofilm formation by the luxS mutant was also complemented by Porphyromonas gingivalis 381 and Actinobacillus actinomycetemcomitans Y4 but not by a P. gingivalis luxS mutant. These results suggest that the regulation of the glucosyltransferase genes required for sucrosedependent biofilm formation is regulated by AI-2. Furthermore, these results provide further confirmation of previous proposals that quorum sensing via AI-2 may play a significant role in oral biofilm formation.Quorum sensing (QS) is a process whereby bacteria communicate with one another by means of the secretion of chemical signal molecules called autoinducers (AIs) (3,4,35,38). In the bioluminescent gram-negative marine bacterium Vibrio harveyi, two distinct AIs, AI-1 (6, 9) and AI-2, regulate light emission (36). LuxS is an enzyme involved in the catabolism of S-adenosylmethionine and converts ribose homocysteine into homocysteine and 4,5-dihydroxy-2,3-pentanedione, the precursor of 46,51). This system has been referred to as an interspecies quorum system and may operate as a universal quorum system for many bacteria possessing the characteristic luxS gene (5). The luxS gene is highly conserved across a diverse range of gram-negative and gram-positive bacterial species, and AI-2 is produced by many of these species. QS enables a population of bacteria collectively to regulate gene expression including expression of virulence factors (21, 39), competence for genetic transformation (1, 28, 37), conjugal DNA transfer (20,52,56), and the production of antibiotics and secondary metabolites (31, 49), as well as biofilm formation (13). However, more recent investigations have also indicated that AI-2 production is regulated at the level of LuxS substrate availability and not at the level of luxS expression. Consequently, AI-2-dependent signaling can also reflect the metabolic state of the cell and not necessarily cell density (7).Biofilms are se...

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

“…Given that biofilm formation is regulated by AI-2 signalling in S. mutans [7,12,13], we decided to assess whether 20J extracts could interfere with biofilm formation of this early dental plaque colonizer. Indeed, the biofilm-inhibitory activity recorded in extracts of strain 20J suggested that it could be derived from the interference with the AI-2 QS system in S. mutans .…”

“…Among them, Streptococcus species are the initial colonizers of clean teeth surfaces and the main components of early dental plaque. Although Streptococcus mutans was considered one of the major cariogenic bacteria in humans in the past [6,7], recent DNA- and RNA-based studies from carious lesions indicate that this bacterium represents only a small fraction of the bacterial community present in these lesions [8]. Biofilm formation by S. mutans is regulated by two QS systems, although the hierarchy of their organization is unknown.…”

“…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]. The mutation of the gene of luxS which codifies the enzyme required for AI-2 production affects biofilm formation in S. mutans [12,17].…”

“…The mutation of the gene of luxS which codifies the enzyme required for AI-2 production affects biofilm formation in S. mutans [12,17]. The QS signal AI-2 seems to be relevant also in other oral pathogens such as Porphyromonas gingivalis, Aggregatibacteractinomycetencomitans Y4, Treponema denticola , and Tannerella forsythia [7,18], which indicates complex signalling networks in the oral biofilm. According to the hypothesis proposed by Kolenbrander et al [19], high levels of AI-2 would accelerate the growth of pathogens while reducing growth of commensal bacteria, contributing to subgingival plaque formation and maturation and leading to periodontal diseases.…”

Synergy in biofilm formation between Fusobacterium nucleatum and Prevotella species

“…Gram-positive bacteria, and the AI-2 pathway can control the expression of genes involved in a variety of metabolic pathways and pathogenic mechanisms (25,43,44,45). Fries et al (46) showed that strains of F. nucleatum, P.…”