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

Abstract

Aims: Constructing a strain with high yield of O-succinyl-l-homoserine (OSH) and improving the titre through multilevel fermentation optimization.

Methods and results: OSH high-yielding strain was first 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 titre of OSH. The Box-Behnken response surface method was used to optimize the fermentation conditions. Through gene editing and medium optimization, the titre of OSH increased from 7·20 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 titre 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 and metabolic pathway analysis effectively improved the titre of OSH.

Significance and impact of the study: In this study, the titre of OSH reached the needs for industrial production and the metabolic pathway of OSH was demonstrated for further optimization.

Keywords: O-succinyl-l-homoserine; fed-batch strategy; fermentation optimization.