Two Glyceraldehyde-3-phosphate Dehydrogenases with Opposite Physiological Roles in a Nonphotosynthetic Bacterium

Bacillus subtilis possesses two similar putative phosphorylating glyceraldehyde-3-phosphate dehydrogenase (GAPDH) encoding genes, gap (renamedgapA) and gapB. A gapA mutant was unable to grow on glycolytic carbon sources, although it developed as well as the wild-type strain on gluconeogenic carbon sources. AgapB mutant showed the opposite phenotype. Purified GapB showed a 50-fold higher GAPDHase activity with NADP+ than with NAD+, with Km values of 0.86 and 5.7 mm, respectively. lacZ reporter gene fusions revealed that the gapB gene is transcribed during gluconeogenesis and repressed during glycolysis. Conversely,gapA transcription is 5-fold higher under glycolytic conditions than during gluconeogenesis. GAPDH activity assays in crude extracts of wild-type and mutant strains confirmed this differential expression pattern at the enzymatic level. Genetic analyses demonstrated that gapA transcription is repressed by theyvbQ (renamed cggR) gene product and indirectly stimulated by CcpA. Thus, the same enzymatic step is catalyzed inB. subtilis by two enzymes specialized, through the regulation of their synthesis and their enzymatic characteristics, either in catabolism (GapA) or in anabolism (GapB). Such a dual enzymatic system for this step of the central carbon metabolism is described for the first time in a nonphotosynthetic eubacterium, but genomic analyses suggest that it could be a widespread feature.