Transcriptional analysis of gtfB, gtfC, and gbpB and their putative response regulators in several isolates of Streptococcus mutans

Abstract

Streptococcus mutans, a major dental caries pathogen, expresses several virulence genes that mediate its growth, accumulation on tooth surfaces, and acid-mediated tooth demineralization. GtfB and GtfC catalyze the extracellular synthesis of water-insoluble glucan matrix from sucrose, and are essential for accumulation of bacteria in the dental biofilm. GbpB, an essential protein of S. mutans, might also mediate cell-surface interaction with glucan. In this study, we determined the transcription levels of gtfB, gtfC, and gbpB, and several putative transcriptional response regulators (rr) at different phases of planktonic growth in 11 S. mutans strains. Activities of gtfB and gtfC were growth-phase dependent and assumed divergent patterns in several strains during specific phases of growth, while gbpB activities appeared to be under modest influence of the growth phase. Transcription patterns of the rr vicR, covR, comE, ciaR, and rr1 were growth-phase dependent and some of these genes were expressed in a highly coordinated way. Each rr, except comE, was expressed by all the strains. Patterns of virulence and regulatory genes were, however, strain-specific. The findings suggest that mechanisms controlling virulence gene expression are variable among genotypes, providing the notion that the genetic diversity of S. mutans may have important implications for understanding mechanisms that regulate the expression of virulence genes in this species.