A novel β-glucoside-specific PTS locus from Streptococcus mutans that is not inhibited by glucose

A regulon from Streptococcus mutans that plays a role in the utilization of beta-glucosides has been isolated, sequenced and subjected to sequence analysis. This regulon encodes a beta-glucoside-specific Enzyme II (EII) component (bglP) of the phosphoenolpyruvate-dependent phosphotransferase system (PTS) and a phospho-beta-glucosidase (bglA) which is responsible for the breakdown of the phospho-beta-glucosides within the cell. Both the bglP and bglA gene products have significant similarity with proteins that have similar functions from Clostridium longisporum, Listeria monocytogenes, Erwinia chrysanthemi, Escherichia coli, Klebsellia oxytoca and Bacillus subtilis. The potential functions of the BglP and BglA proteins are supported by phenotypic data from both S. mutans and E. coli. A chromosomal deletion in S. mutans spanning the bglP and bglA genes resulted in a strain that was unable to hydrolyse the beta-glucoside aesculin in the presence of glucose. When glucose was removed from the medium, the deletion strain regained the ability to break down aesculin. These data suggest that S. mutans possesses an alternative mechanism from the one described in this report for breaking down beta-glucosides. This second mechanism was repressed by glucose while the regulon described here was not. Complementation studies in E. coli CC118 also suggest a potential role for this regulon in the utilization of other beta-glucosides. When a plasmid containing the 8 kb beta-glucoside-specific regulon was transformed into E. coli CC118, the transformed strain was able to break down the beta-glucoside arbutin.