Two glyceraldehyde-3-phosphate dehydrogenases with opposite physiological roles in a nonphotosynthetic bacterium

Bacillus subtilis possesses two similar putative phosphorylating glyceralde hyde-3-phosphate dehydrogenase (GAPDH) encoding genes, gap (renamed gapA) a nd gapB. A gapA mutant was unable to grow on glycolytic carbon sources, alt hough it developed as well as the wild-type strain on gluconeogenic carbon sources. A gapB mutant showed the opposite phenotype, Purified GrapB showed a 50-fold higher GAPDHase activity with NADP(+) than with NAD(+), with K-m values of 0.86 and 5.7 mM, respectively. lacZ reporter gene fusions reveal ed that the gapB gene is transcribed during gluconeogenesis and repressed d uring glycolysis, Conversely, gapA transcription is 5-fold higher under gly colytic conditions than during gluconeogenesis. GAPDH activity assays in cr ude extracts of wild-type and mutant strains confirmed this differential ex pression pattern at the enzymatic level. Genetic analyses demonstrated that gapA transcription is repressed by the yvbQ (renamed cggR) gene product an d indirectly stimulated by CcpA Thus, the same enzymatic step is catalyzed in B. 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 c entral carbon metabolism is described for the first time in a nonphotosynth etic eubacterium, but genomic analyses suggest that it could be a widesprea d feature.