Characterization of glucose-repression-resistant mutants of Bacillus subtilis: identification of the glcR gene

In Bacillus subtilis, carbon catabolite repression (CCR) is mediated by the pleiotropic repressor CcpA and by ATP-dependent phosphorylation of the HPr protein of the phosphotransferase system (PTS). In this study, we attempted to identify novel genes that are involved in the signal transduction pathway that ultimately results in CCR in the presence of repressing carbon sources such as glucose. Seven mutants resistant to glucose repression of the levanase operon were isolated and characterized. All mutations were trans-acting and pleiotropic as determined by analyzing CCR of beta-xylosidase and of the sacPA and bglPH operon. Moreover, all mutations specifically affected repression exerted by glucose but not by other sugars. The mutations were mapped to three different loci on the genetic map, ptsG, glcR, and pgi. These three genes encode proteins involved in glucose metabolism. A novel repressor gene, glcR (ywpI), defined by two mutations, was studied in more detail. The glcR mutants exhibit loss of glucose repression of catabolic operons, a deficiency in glucose transport, and absence of expression of the ptsG gene. The mutant GlcR proteins act as super-repressors of ptsG expression.