Enhanced O-succinyl-L-homoserine production by recombinant Escherichia coli ΔIJBB*TrcmetL/pTrc-metAfbr -Trc-thrAfbr -yjeH via multilevel fermentation optimization.

AIMS Constructing a strain with high yield of O-succinyl-L-homoserine (OSH) and improving the titer through multilevel fermentation optimization. METHODS AND RESULTS OSH high-yielding strain was firstly constructed by deleting the thrB gene to block the threonine biosynthesis. Single-factor experiment was carried out, where a Plackett-Burman design was used to screen out three factors (glucose, yeast and threonine) from the original 11 factors that affected the titer of OSH. The Box-Behnken response surface method was used to optimize the fermentation conditions. Through gene editing and medium optimization, the titer of OSH increased from 7·20 g l-1 to 8·70 g l-1 in 500 ml flask. Furthermore, the fermentation process and fed-batch fermentation conditions including pH, temperature, feeding strategy and feeding medium were investigated and optimized. Under the optimal conditions, the titer of OSH reached 102·5 g l-1 , which is 5·6 times higher than before (15·6 g l-1 ). CONCLUSIONS O-succinyl-L-homoserine fermentation process was established and the combination of response surface methodology (RSM) and metabolic pathway analysis effectively improved the titer of OSH. SIGNIFICANCE AND IMPACT OF STUDY In this study, the titer of OSH reached the needs for industrial production and the metabolic pathway of OSH was demonstrated for further optimization.