Microbial production of 2-keto-L-gulonic acid from L-sorbose and D-sorbitol by Gluconobacter melanogenus.

The strain SPO1 producing 13 g of 2-keto-L-gulonic acid (2KGA) per liter was isolated as a spontaneous mutant of Gluconobacter melanogenus IFO 3293. For the enhancement of 2KGA productivity, we did further strain improvement studies of the mutant. As a result, the mutant U13, producing about 60 g of 2KGA per liter from 100 g of L-sorbose per liter, was obtained. In addition, the mutant Z84, producing about 60 g of 2KGA per liter from 100 g of o-sorbitol per liter, was also obtained. During the fermentation from L-sorbose and D-sorbitoI, 5 to 10 g of L-idonic acid per liter was produced as a by-product, but L-idonic acid was converted to 2KGA before the end of fermentation.