Enhancement of L-ornithine production by disruption of three genes encoding putative oxidoreductases in Corynebacterium glutamicum

Recently, Corynebacterium glutamicum has been shown to exhibit gluconate bypass activity, with two key enzymes, glucose dehydrogenase (GDH) and gluconate kinase, that provides an alternate route to 6-phosphogluconate formation. In this study, gene disruption analysis was used to examine possible metabolic functions of three proteins encoded by open reading frames having significant sequence similarity to GDH of Bacillus subtilis. Chromosomal in-frame deletion of three genes (NCgl0281, NCgl2582, and NCgl2053) encoding putative NADP(+)-dependent oxidoreductases led to the absence of GDH activity and correlated with increased specific glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities. This finding suggested that enhanced carbon flux from glucose was directed toward the oxidative pentose phosphate (PP) pathway, when the mutant was cultivated with 6 % glucose. Consequently, the mutant showed 72.4 % increased intracellular NADPH and 66.3 % increased extracellular l-ornithine production. The enhanced activities of the oxidative PP pathway in the mutant explain both the increased intracellular NADPH and the high extracellular concentration of l-ornithine. Thus, the observed metabolic changes in this work corroborate the importance of NADPH in l-ornithine production from C. glutamicum.