The transcriptional regulation of the Streptococcus mutans bgl regulon

A beta-glucoside utilization regulon recently isolated from Streptococcus mutans has been shown to contain genes involved in beta-glucoside hydrolysis and a putative regulator. The bglP gene encodes a beta-glucoside-specific enzyme II (EII) component of the phosphoenolpyruvate-dependent phosphotransferase system, the bglC gene encodes a putative transcriptional regulator, and the bglA gene encodes a putative phospho-beta-glucosidase. To investigate the transcriptional activity of these genes, the putative promoter regions of the bglP, bglC and bglA genes were fused with the E. coli lacZ reporter gene. The resultant reporter plasmids were used to monitor the transcriptional activity of these loci in S. mutans. The results illustrate that these genes are not repressed by glucose in the presence of an inducing beta-glucoside, esculin, to the levels of expression observed in the absence of esculin. Therefore, these loci are not subject to catabolite repression by glucose to noninduced levels of expression. The bglC gene product was determined to be a positive transcriptional regulator of the bglA gene but does not regulate the expression of the bglP gene. Thus, regulation of these loci requires different and multiple control mechanisms.