2-Ketogluconic acid production by Klebsiella pneumoniae CGMCC 1.6366.

Klebsiella pneumoniae CGMCC 1.6366 is a bacterium isolated for 1,3-propanediol or 2,3-butanediol production previously. K. pneumoniae ΔbudA, a 2,3-butanediol synthesis pathway truncated mutant with the gene deletion of budA which encodes alpha-acetolactate decarboxylase, was found to execrate an unknown chemical at a high titer when grown in the broth using glucose as carbon source. Later this chemical was identified to be 2-ketogluconic acid, which was formed through the glucose oxidation pathway in K. pneumoniae. It was found that 2-ketogluconic can also be produced by the wild strain. The fermentation studies showed that the production of this metabolite is strictly pH dependent, when the fermenting broth was maintained at pH 6-7, the main metabolite produced by K. pneumoniae CGMCC 1.6366 was 2,3-butanediol, or some organic acids in the budA mutated strain. However, if the cells were fermented at pH 4.7, 2-ketogluconic acid was formed, and the secretion of all other organic acids or 2,3-butanediol were limited. In the 5L bioreactors, a final level of 38.2 and 30.2 g/L 2-ketogluconic acid were accumulated by the wild type and the budA mutant K. pneumoniae, respectively, in 26 and 56 h; and the conversion ratios of glucose to 2-ketogluconic acid reached 0.86 and 0.91 mol/mol for the wild and the budA mutant, respectively.