A physical and functional analysis of the newly-identified bglGPT operon of Lactobacillus plantarum

A newly-identified bglGPT operon of Lactobacillus plantarum was isolated and expressed in Escherichia coli. The sequence analysis of the cloned DNA fragment showed three open reading frames encoding (i) a 237-amino acid protein (BglG), (ii) a 577-amino acid protein (BglP) and (iii) a 486-amino acid protein (BglT). BglG, BglP and BglT were shown to be homologous to the BglG family of transcriptional antiterminators, to permeases of the phosphoenolpyruvate-dependent phosphotransferase system and to β-glucosidases, respectively. Complementation of E. coli mutant strains showed that BglP and BglT are a permease and a β-glucosidase active on the β-glucosides, 5-bromo-4-chloro-3-indolyl-β- D-glucopyranoside and p-nitrophenyl-β- D-glucoside, respectively. BglG was also shown to promote expression of a bglG– lacZ gene fusion in an E. coli bglG − background. A ribonucleic antiterminator sequence, the antiterminator-responsive cis-element and a ‘catabolite responsive element’, were found downstream of the transcriptional start point. Transcription of the operon was repressed 10-fold in L. plantarum cells grown on glucose as compared to ribose.