RegM is required for optimal fructosyltransferase and glucosyltransferase gene expression in Streptococcus mutans

Glucosyltransferases (Gtfs) and fructosyltransferase (Ftf), and the exopolysaccharides they produce, facilitate bacterial adherence and biofilm formation, and enhance the virulence of Streptococcus mutans. In this study, we used continuous chemostat cultures and reporter gene fusions to study the expression of ftf and gtfBC in response to carbohydrate availability and pH, and to asses the role of a protein similar to catabolite control protein A (CcpA), RegM, in regulation of these genes. Expression of ftf was efficient at pH 7.0 and 6.0, but was repressed at pH 5.0 under glucose-excess conditions. At pH 7.0, ftf expression was 5-fold lower under glucose-limiting conditions than in cells growing with an excess of glucose. Expression of gtfBC was also sensitive, albeit to a lesser extent, to pH and glucose availability. Inactivation of regM resulted in decreases of as much as 10-fold in both ftf and gtfBC expression, depending on growth conditions. These findings reinforce the importance of pH and carbohydrate availability for expression of two primary virulence attributes of S. mutans and reveal a critical role for RegM in regulation of expression of both gtfBC and ftf.