Process design and economic studies of two-step fermentation for production of ascorbic acid

Strain Development, Substrate Utilization, and Downstream Purification of Vitamin C

Vitamin C, C6H8O6, is a water-soluble vitamin that is widespread in nature. It is an essential nutrient involved in many biological processes in the living organisms: it enhances collagen biosynthesis, ensures the optimal functioning of enzymes and the immune system, has a major role in lipid and iron metabolism, and it enhances the biosynthesis of l-carnitine. Due to its antioxidant activity, vitamin C can neutralize the tissue-damaging effects of free radicals. Vitamin C is being related to the prevention of cancer and cardiovascular diseases. This review includes current information on the biosynthesis of ascorbic acid, as new methods are now challenging the traditional Reichstein process for vitamin C’s industrial-scale production. Different strains were analyzed in correlation with their ability to synthesize ascorbic acid, and several separation techniques were investigated for a more effective production of vitamin C.

Combined evolutionary and metabolic engineering improve 2-keto-L-gulonic acid production in Gluconobacter oxydans WSH-004

The direct fermentation of the precursor of vitamin C, 2-keto-L-gulonic acid (2-KLG), has been a long-pursued goal. Previously, a strain of Gluconobacter oxydans WSH-004 was isolated that produced 2.5 g/L 2-KLG, and through adaptive evolution engineering, the strain G. oxydans MMC3 could tolerate 300 g/L D-sorbitol. This study verified that the sndh-sdh gene cluster encoded two key dehydrogenases for the 2-KLG biosynthesis pathway in this strain. Then G. oxydans MMC3 further evolved through adaptive evolution to G. oxydans 2-KLG5, which can tolerate high concentrations of D-sorbitol and 2-KLG. Finally, by increasing the gene expression levels of the sndh-sdh and terminal oxidase cyoBACD in G. oxydans 2-KLG5, the 2-KLG accumulation in the 5-L fermenter increased to 45.14 g/L by batch fermentation. The results showed that combined evolutionary and metabolic engineering efficiently improved the direct production of 2-KLG from D-sorbitol in G. oxydans.