Function of the mdxR gene encoding a novel regulator for carbohydrate metabolism and sporulation in Bacillus subtilis 168

The mdx R gene located upstream of mdx D , encoding a maltogenic amylase, has been annotated as a member of LacI-type transcriptional regulator in Bacillus subtilis 168 but its function has not been investigated yet. In this study, expression pattern of the mdx R promoter ( P mdx R ) and effects of mdx R were investigated to elucidate the function of mdx R. Expression of P mdx R was monitored by the β-galactosidase activity expressed from the P mdx R - lac Z fusion integrated at the amy E locus on the chromosome. The promoter was induced by starch, β-cyclomaltodextrin, or maltose at early exponential phase and kept expressed until late stationary phase. However, it was repressed by glucose, sucrose, or glycerol, suggesting that it was under catabolite repression. Furthermore, interactions of MdxR and Spo0A to the DNA fragment carrying P mdx R or P mdx D were detected by mobility-shift assay, implying that MdxR was a novel transcription regulator for both genes, which were regulated also by Spo0A. The mdx R mutant impaired the expressions of mdx D and mal L (encoding an α-glucosidase); degraded accumulated glycogen slower than the wild type and the mdx D mutant. Both of the mdx R and the mdx D mutants formed more endospores (50.95% and 47.10%) than the wild type (23.90%). Enhanced sporulation by these mutations could be of industrial interest where sporulation or endospores of B. subtilis matters. These results indicate that MdxR functions as a transcriptional regulator for mdx R, mdx D, and other genes in the gene cluster that is related to the maltose/maltodextrin metabolism. MdxR and MdxD are also involved in glycogen metabolism and sporulation, tentatively by modulating the net energy balance in the cell.