Progress in vitamin C biosynthesis related dehydrogenases / 生物工程学报

Vitamin C is an essential vitamin for human beings. It has a huge market in the fields of food and pharmaceuticals. 2-keto-L-gulonic acid is an important precursor to produce vitamin C by microbial fermentation in industrial. In microbial fermentations, the L-sorbose pathway and the D-gluconate pathway have been the focus of research because of high yield. This article aims at stating recent research progress in dehydrogenases related to biosynthesis of vitamin C in the L-sorbose pathway and the D-gluconate pathway. The properties of dehydrogenase in terms of localization, substrate specificity, cofactors, and electron transport carrier are elaborated. And then, the main problems and strategies are reviewed in the L-sorbose pathway and in the D-gluconate pathway. Finally, future research on the dehydrogenases in the biosynthesis of vitamin C through L-sorbose pathway and D-gluconate pathway is discussed.

A plate method for rapid screening of Ketogulonicigenium vulgare mutants for enhanced 2-keto-l-gulonic acid production

Abstract A new plate method was developed for rapid screening of Ketogulonicigenium vulgare mutants overproducing 2-keto-l-gulonic acid (2-KLG). The screening methodology took the advantage of the acidity caused by 2-KLG, which changes the color of bromothymol blue (pH indicator) from blue to yellow. Using the proposed method, a mutant, K. vulgare 65, was selected from 20,000 colonies produced by a strain subjected to spaceflight mutagenesis. When co-cultured with Bacillus megaterium 2980 in 20-L fermenters, K. vulgare 65 showed a high conversion rate (94.45%) of l-sorbose to 2-KLG. In contrast to the traditional screening method, this one significantly improved the frequency of obtaining positive mutants. The proposed plate screening method is cost-effective and easy to run and is thus useful for the isolation and screening of K. vulgare mutants overproducing 2-KLG.

THE TECHNOLOGICAL CONDITIONS OF PRODUCING 2-KETO-LGULONIC ACID FROM D-GLUCOSE BY DIRECT FERMENTATION / 微生物学通报

2-Keto-L-gulonic acid (2-KLG), the precurcor of L-ascorbic acid synthesis, was prepared directly from D-glucose by tandem fermentation. In the first step fermentation Erwinia sp. SCB 247 translated D-glucose to 2,5-diketo-D-gluconate (2,5-DKG), which accumenlated 180 mg 2,5-DKG per ml in the broth. In the second step fermentation Corynebacterium sp. SCB 3058 reduced 2,5-DKG to 2-KLG, which accumulated 35 mg 2-KLG per ml in the broth. This reductive fermentation was obtained under aerobic conditions by adding a hydrogen donor such as glucose.The average yield of five batches fermentation was 56.3 mol%, from D-glucose to 2-KLG in 10 L fermentor.