Metabolic engineering combined with enzyme engineering for overproduction of ectoine in Escherichia coli

Abstract

Ectoine, a natural protective agent, is naturally synthesized at low titers by some extreme environment microorganisms that are usually difficult to culture. There is a need for an efficient and eco-friendly ectoine production process. In this study, Escherichia coli BL21(DE3) with the ectABC gene cluster from Halomonas venusta achieved 1.7 g/L ectoine. After optimizing the expression plasmid, 2.1 g/L ectoine was achieved. Besides, the aspartate kinase mutant LysC^T311I from Corynebacterium glutamicum and aspartate semialdehyde dehydrogenase from Halomonas elongata were overexpressed to increase precursors supply. Furthermore, the rate-limiting enzyme EctB was semirationally engineered, and the E407D mutation enhanced ectoine production by 13.8 %. To improve acetyl-CoA supply, the non-oxidative glycolysis pathway was introduced. Overall, the optimized strain ECT9-5 produced 67.1 g/L ectoine by fed-batch fermentation with a 0.3 g/g of glucose and the kinetic model resulted in a good fit.

Keywords: Ectoine; Enzyme engineering; Fed-batch fermentation; Kinetic model; Non-oxidative glycolysis.