Characterization of Streptococcus mutans Strains Deficient in EIIABMan of the Sugar Phosphotransferase System
ABSTRACT The phosphoenolpyruvate:sugar phosphotransferase system (PTS) is the major sugar uptake system in oral streptococci. The role of EIIABMan (encoded by manL) in gene regulation and sugar transport was investigated in Streptococcus mutans UA159. The manL knockout strain, JAM1, grew more slowly than the wild-type strain in glucose but grew faster in mannose and did not display diauxic growth, indicating that EIIABMan is involved in sugar uptake and in carbohydrate catabolite repression. PTS assays of JAM1, and of strains lacking the inducible (fruI) and constitutive (fruCD) EII fructose, revealed that S. mutans EIIABMan transported mannose and glucose and provided evidence that there was also a mannose-inducible or glucose-repressible mannose PTS. Additionally, there appears to be a fructose PTS that is different than FruI and FruCD. To determine whether EIIABMan controlled expression of the known virulence genes, glucosyltransferases (gtfBC) and fructosyltransferase (ftf) promoter fusions of these genes were established in the wild-type and EIIABMan-deficient strains. In the manL mutant, the level of chloramphenicol acetyltransferase activity expressed from the gtfBC promoter was up to threefold lower than that seen with the wild-type strain at pH 6 and 7, indicating that EIIABMan is required for optimal expression of gtfBC. No significant differences were observed between the mutant and the wild-type background in ftf regulation, with the exception that under glucose-limiting conditions at pH 7, the mutant exhibited a 2.1-fold increase in ftf expression. Two-dimensional gel analysis of batch-grown cells of the EIIABMan-deficient strain indicated that the expression of at least 38 proteins was altered compared to that seen with the wild-type strain, revealing that EIIABMan has a pleiotropic effect on gene expression.