Metabolic engineering of Escherichia coli for efficient ectoine production

Ectoine is a high-value stabilizer and protective agent with various applications in enzyme industry, cosmetics, and biomedicine. In this study, rational engineering strategies have been implemented in Escherichia coli to efficiently produce ectoine. First, the synthetic pathway of ectoine was constructed in E. coli MG1655 by introducing an artificial thermal switch system harboring the ectABC cluster from Halomonas elongate, and the resulting strain produced 1.95 g/L ectoine. Second, crr encoding the glucose-specific enzyme II domain A of phosphotransferase system and iclR encoding the glyoxylate shunt transcriptional repressor were deleted in E. coli for enhancing the oxaloacetate supply, leading to the increasement of the ectoine titer to 9.09 g/L. Third, thrA encoding the bifunctional aspartokinase/homoserine dehydrogenase was removed from the genome to weaken the competitive pathway; simultaneously, an endogenous feedback-resistant lysC was overexpressed to complement the enzymatic activity deficiency of the aspartate kinase, leading to 30.36% increase of ectoine titer. Next, the expression of phosphoenolpyruvate carboxylase was modulated with varying gradient strength promoters to accelerate the biosynthesis efficiency of ectoine. Finally, aspDH encoding aspartate dehydrogenase from Pseudomonas aeruginosa PAO1 was overexpressed to further improve the biosynthesis of ectoine. The final strain MWZ003/pFT28-ectABC-EclysC*-aspDH-ppc3 produced 30.37 g/L ectoine after 36-h fed-batch fermentation with a yield of 0.132 g/g glucose and a productivity of 0.844 g/(L h).