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Biosensor-Mediated Adaptive Laboratory Evolution of Escherichia coli for L-Serine Overproduction from Glycerol

Abstract

In this study, adaptive laboratory evolution (ALE) combined with biosensor were employed to improving L-serine yield. First, serine-biosensor was constructed in E.coli based on the transcriptional regulator NCgl0581 of C. glutamicum, furthermore, the validity and sensitivity of the serinebiosensor was studied, and the results showed that serine-biosensor pDser from C. glutamicum was effective in E. coli and only cellular L-serine biosynthesized was monitored by serine-biosensor. Then E. coli 4W capable of producing 1.1 g/L L-serine from glycerol was used as a starting strain, and L-serine degradation pathway to glycine of 4W was deleted by CRISPR/ Cas9, resulting in strain 4WG, with L-serine titer of 2.01 g/L. 4WG was further evolved by using ALE combined with serine-biosensor, the evolved strain 4WGX was achieved and showed a yield of 0.41 g/g glycerol, and could produce 4.13 g/L L-serine, which was 105% and 275% higher than that of 4WG and 4W respectively, in addition, 4WGX showed better growth in the medium with 50 g/L L-serine addition, indicating its better L-serine tolerance. This work indicates that the serine-biosensor from C. glutamicum was useful in selecting serine over-producing E. coli, and this expanded the application of biosensor, and provided the more strategies for screening high performance strain.

Xiaomei Zhang, Dong Zhang, Yujie Gao, Xiaojuan Zhang, Guoqiang Xu, Hui Li, Jinsong Shi,Zhenghong Xu

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