Environmental Influences on Competitive Hydrogen Peroxide Production in Streptococcus gordonii

Abstract

Streptococcus gordonii is an important member of the oral biofilm. One of its phenotypic traits is the production of hydrogen peroxide (H ₂ O ₂ ). H ₂ O ₂ is an antimicrobial component produced by S. gordonii that is able to antagonize the growth of cariogenic Streptococcus mutans . Strategies that modulate H ₂ O ₂ production in the oral cavity may be useful as a simple therapeutic mechanism to improve oral health, but little is known about the regulation of H ₂ O ₂ production. The enzyme responsible for H ₂ O ₂ production is pyruvate oxidase, encoded by spxB . The functional studies of spxB expression and SpxB abundance presented in this report demonstrate a strong dependence on environmental oxygen tension and carbohydrate availability. Carbon catabolite repression (CCR) modulates spxB expression carbohydrate dependently. Catabolite control protein A (CcpA) represses spxB expression by direct binding to the spxB promoter, as shown by electrophoretic mobility shift assays (EMSA). Promoter mutation studies revealed the requirement of two catabolite-responsive elements (CRE) for CcpA-dependent spxB regulation, as evaluated by spxB expression and phenotypic H ₂ O ₂ production assays. Thus, molecular mechanisms for the control of S. gordonii spx B expression are presented for the first time, demonstrating the possibility of manipulating H ₂ O ₂ production for increased competitive fitness.