Pgf Glycosylation Affects Competence and Mutacin Production in Streptococcus Mutans

Objectives: To determine whether glycosylation by the Pgf machinery influences genetic competence and competence associated phenotypes in Streptococcus mutans.
Methods: S. mutans OMZ175 (WT) and deletion mutants of the pgf genes (pgfS, pgfM1, pgfE, pgfM2, and a quadruple mutant, pgf) were compared in a series of competence frequency assays in the presence of CSP and XIP peptides. Also, autolytic activity and mutacin V production was assessed. The ability of mutant strains to tolerate different environmental stresses was compared to that of the WT strain.
Results: Deletion of pgfS did not cause a significant difference in the responsiveness to CSP and XIP compared to the WT. On the other hand, deletion of pgfM1, pgfE, pgfM2, or all four genes significantly increased the responsiveness to both CSP and XIP (p < 0.05). These mutants were also found to be naturally more competent in nutrient deficient media without addition of peptides. In line with the competence findings, the mutants that were are naturally more competent were also more autolytic in poor media. Inactivation of pgfS, pgfM1, pgfE, and of all four pgf genes resulted in decreased production of mutacin V, while ΔpgfM2 shares a phenotype similar to the wild type. With the exception of ΔpgfM2, all mutant strains were more susceptible to oxidative stress when compared to the wild type.
Conclusions: The Pgf glycosylation machinery is important for competence associated phenotypes and oxidative stress tolerance in Streptococcus mutans OMZ175.