Identification of hydrogen peroxide production-related genes in Streptococcus sanguinis and their functional relationship with pyruvate oxidase

Hydrogen peroxide (H2O2), an important substance produced by many members of the genus Streptococcus, plays important roles in virulence and antagonism within a microbial community such as oral biofilms. The spxB gene, which encodes pyruvate oxidase, is involved in H2O2 production in many streptococcal species. However, knowledge about its regulation and relation with other genes putatively involved in the same pathway is limited. In this study, three genes ackA, spxR and tpk - were identified as contributing to H2O2 production in Streptococcus sanguinis by screening mutants for opaque colony appearance. Mutations in all three genes resulted in significant decreases in H2O2 production, with 16-31% of that of the wild-type. H2O2 production was restored in the complemented strains. Antagonism against Streptococcus mutans by these three S. sanguinis mutants was reduced, both on plates and in liquid cultures, indicating the critical roles of these three genes for conferring the competitive advantage of S. sanguinis. Analysis by qPCR indicated that the expression of spxB was decreased in the ackA and spxR mutants and significantly increased in the tpk mutant.