Metabolic Engineering of Escherichia Coli for Ectoine Production with the Fermentation Strategy of Supplementing Amino Donor

Background: Ectoine, a compatible solute, has broad application prospects in food biotechnology, agriculture, medicine, and cosmetics because of its protective action on biological compounds. Industrially, ectoine is produced by halophilic bacteria in a complex process. Recently, various works focus on improving ectoine production by using engineered strains, but there are still problems of low yield and low ectoine production efficiency. Results: To overcome the drawback, a final metabolic engineered strain E. coli ET08 was constructed by eliminating lysine synthesis branch and by-product metabolic pathways, and ectoine production reached 10.2 g/L through culture medium optimization. Compared with nitrate, addition of ammonium salt contributed more to the ectoine synthesis. Furthermore, the ammonium sulphate boosted more ectoine titers than ammonium chloride and sodium glutamate. The analysis of transcriptional levels revealed that the ammonium sulfate enhanced ectoine biosynthesis by enhancing metabolic flux toward ectoine biosynthesis and providing affluent synthetic precursors. Ultimately, the ectoine production and yield of the E. coli ET08 reached 36.5 g/L and 0.3 g/g glucose with supplementing amino donor in a 7.5 L bioreactor. Conclusions: a novel potential metabolic engineered Escherichia coli for ectoine production was constructed. optimizing amino donor and analyzing the transcription levels conclude that ammonium sulfate, as the optimal amino donor, has a positive effect on ectoine synthesis. It is the first report about the effect of exogenous amino donor on ectoine fermentation by metabolic engineered strain. The maximum ectoine production and yield from glucose synthesized by E. coli were obtained by two-stage feeding fermentation with supplementing amino donor. It provides a novel strategy for the synthesis of ectoine by engineered strain in industry. This research provides the basis for an effective process for ectoine production, together with the further applications of ectoine in food and cosmetics, and could also be used to produce other high value amino acid derivative.