High-yield production of 5-keto-D-gluconic acid via regulated fermentation strategy of Gluconobacter oxydans and its conversion to L-(+)-tartaric acid

Herein, we propose the production of 5-keto-D-gluconic acid (5KGA) by fermentation using <i>Gluconobacter oxydans</i> (<i>G. oxydans</i>) as the starting strain, from an initial concentration of 100 g/L glucose as substrate and the chemical conversion of 5KGA to L-(+)-tartaric acid (L-TA). The results show the efficacy and feasibility of two-stage pH (5.50→natural) linkage ventilation (0.5 vvm and 1.0 vvm, L/L/min) control of batch fermentation for 5KGA production. The final 5KGA yield of 100.2 g/L of 1.0 vvm is much higher than 0.5 vvm with an average productivity of 1.95 g/L/h. Changing the method of fermentation from batch to fed-batch can efficently prolong the high activity of <i>G. oxydans</i> for 5KGA production with an increased average productivity of 3.10 g/L/h, and the conversion rate of glucose to 5KGA is 92.50 %. The chemical conversion of 5KGA to L-TA catalyzed by metal ions <i>in vitro</i> indicates that the optimal catalyst is Cu²⁺ with a conversion rate of 35.09 % of 5KGA to L-TA. Our method can provide a practical and effective alternative for the industrial production of 5KGA and its conversion to L-TA.