Competence-Dependent Bacteriocin Production by Streptococcus gordonii DL1 (Challis)

Abstract

The production of streptocins STH 1 and STH 2 by Streptococcus gordonii DL1 (Challis) is directly controlled by the competence regulon, which requires intact comR and comAB loci. The streptocin (sth) locus comprises two functional genes, sthA and sthB. Whereas STH 1 activity requires sthA alone, STH 2 activity depends on both genes.In the 1970s, reported the production of streptocin STH 1 , a proteinaceous antimicrobial agent (bacteriocin), by the naturally transformable Streptococcus gordonii (formerly Streptococcus sanguis) strain Challis (also known as DL1 and NCTC 7868). Streptocin STH 1 biosynthesis coincided with the development of competence for genetic transformation (20, 21), a relationship supported by later studies (8,23). The inhibitory spectrum of streptocin STH 1 was initially reported to include other S. gordonii strains (e.g., strains Wicky and C219) and select strains of Streptococcus mitis and Streptococcus oralis (8,23). However, we have observed that the bacteriocin activity targeting S. mitis and S. oralis appears to be linked to the beta-hemolytic phenotype of strain Challis because S. gordonii OB164 (originally designated DL1-Challis), a non-beta-hemolytic strain indistinguishable from DL1 biochemically (API 20 Strep; bioMérieux, France) and genotypically (18), exhibited inhibitory activity only against S. gordonii isolates. This suggested that strain DL1 produces two bacteriocins: the previously described STH 1 (20) and the newly designated STH 2 , a bacteriocin that targets certain non-S. gordonii strains and is associated with the beta-hemolytic phenotype. Based on our speculation that genetic competence and bacteriocin production may be functionally related in strain DL1 (23), the aims of the present study were to determine whether bacteriocin biosynthesis is genetically associated with competence development and to define the locus encoding the inhibitory/hemolytic agents.(Parts of this work were presented at the 7th ASM Conference on Streptococcal Genetics, Saint Malo, France [7a].)Association of competence and bacteriocin/␤-hemolysin production. Competence development in S. gordonii is analogous to competence development in Streptococcus pneumoniae, occurring in two distinct stages, early and late (10, 13). The early stage involves a quorum-sensing signal transduction circuit comprising a secreted competence-stimulating peptide (CSP), its cell surface receptor ComD (a histidine kinase), and ComE, the primary transcriptional regulator of competence (10, 13). ComE, when activated by ComD, upregulates the comCDE (signal transduction), comAB (CSP secretion), and comX operons (13). ComX, an alternative sigma factor, connects the early and late stages by activating expression of the late competence operons that are responsible for DNA uptake and processing (17). Several key components of the S. gordonii competence regulon have been identified, including comCDE, comAB, comYA (DNA uptake), and duplicate comR (comX homologue) loci (6,7,15,16).In this study, early (comC, comE, comA, comB, an...

Functional Analysis of Paralogous Thiol-disulfide Oxidoreductases in Streptococcus gordonii

“…This situation is exemplified by a previous report that inactivation of the S. gordonii surface antigens SspA and SspB resulted in up-regulation of other surface proteins and a 20% increase biofilm formation (46). Moreover, the lack of competence and bacteriocin activity in the sdbA mutant strongly suggests an effect on the ComDE two-component system, which in turn could affect all of the genes in the regulon (24). We are currently investigating the relationship between SdbA and the ComDE system.…”

“…Activity of Sth 1 and Sth 2 was tested exactly as described by Heng et al (24), using S. oralis 34 and S. mitis I18 as the indicator strain, respectively.…”

“…This indicates that SdbA is required for either processing or production of both Sth 1 and Sth 2 bacteriocins. Because bacteriocin activity coincides with development of genetic competence, and both are controlled under the ComDE regulon, we tested the transformation efficiency of the sdbA mutant (24). The sdbA mutant showed a dramatic defect in transformation frequency compared with the parent strain ( Table 1).…”

“…As an adaptation to the fluctuating environment of oral cavity, S. gordonii exhibits biofilm formation, extracellular DNA (eDNA) release, autolysis, bacteriocin production, and natural genetic competence. Regulation of these phenotypes is interconnected, and conditions at the cell envelope are closely monitored by multiple two-component systems (21)(22)(23)(24). These diverse and testable phenotypes exhibited by S. gordonii create a sensitive system to potentially detect disulfide bond formation.…”

Mutation of the Thiol-Disulfide Oxidoreductase SdbA Activates the CiaRH Two-Component System, Leading to Bacteriocin Expression Shutdown in Streptococcus gordonii

“…For example, S. gordonii produces hydrogen peroxide as a metabolic byproduct, which inhibits the growth of neighboring species that are more sensitive to oxidative stress (8,9). It also targets closely related species more directly, by secreting small antimicrobial peptides called bacteriocins (10). To defend itself from similar counterattacks, it secretes a protease that degrades the signaling peptide required for bacteriocin production and biofilm formation in a competitor, Streptococcus mutans (11).…”