Production of 2-keto-L-gulonic acid by metabolically engineered Escherichia coli.

The 2-keto-L-gulonic acid (2-KLG) is the direct precursor for industrial vitamin C production. The main biosynthetic method for 2-KLG production is the classical two-step fermentation route. However, disadvantages of this method are emerging, including high consumption of energy, difficulties in strain screening, complex operation, and poor stability. In this study, five recombinant Escherichia coli strains overexpressing different sorbose/sorbosone dehydrogenases were constructed and used for 2-KLG production. By optimizing catalytic conditions and further expressing pyrroloquinoline quinone in the recombinant strain, the titer of 2-KLG reached 72.4 g/L, with a conversion ratio from L-sorbose of 71.2% in a 5-L bioreactor. To achieve direct biosynthesis of 2-KLG from D-sorbitol, a co-culture system consisting of Gluconobacter oxydans and recombinant E. coli was designed. With this co-culture system, 16.8 g/L of 2-KLG was harvested, with a conversion ratio from D-sorbitol of 33.6%. The approaches developed here provide alternative routes for the efficient biosynthesis of 2-KLG.