Optimization of carbon source and glucose feeding strategy for improvement of L-isoleucine production by Escherichia coli.

Fed-batch cultivations of L-isoleucine-producing Escherichia coli TRFP (SG(r), α-ABA(r), with a pTHR101 plasmid containing a thr operon and ilvA) were carried out on different carbon sources: glucose, sucrose, fructose, maltose and glycerol. The results indicated that sucrose was the best initial carbon source for L-isoleucine production and then sucrose concentration of 30 g·L(-1) was determined in the production medium. The results of different carbon sources feeding showed that the glucose solution was the most suitable feeding media. The dissolved oxygen (DO) of L-isoleucine fermentation was maintained at 5%, 15% and 30% with DO-stat feeding, respectively. The results indicated that when the DO level was maintained at 30%, the highest biomass and L-isoleucine production were obtained. The accumulation of acetate was decreased and the production of L-isoleucine was increased markedly, when the glucose concentration was maintained at 0.15 g·L(-1) by using glucose-stat feeding. Finally, the glucose concentration was maintained at 0.10 g·L(-1) and the DO level was controlled at approximately 30% during the whole fermentation period, using the combined feeding strategy of glucose-stat feeding and DO feedback feeding. The acetate accumulation was decreased to 7.23 g·L(-1), and biomass and production of L-isoleucine were increased to 46.8 and 11.95 g·L(-1), respectively.