Amine-Tolerant <i>E. coli</i> Strains Generated <i>via</i> Adaptive Evolution for Sustainable Synthesis of Chiral Amines

The biocatalytic synthesis of chiral amines from carbonyl compounds and ammonia is a major advance in sustainable synthetic chemistry. Using whole cells for bioamination reactions is advantageous given their low preparation cost and direct applicability; however, amine toxicity limits the reaction when living cells are used. Herein, we adapted Escherichia coli BL21(DE3) cells to grow in the presence of 100 mM hexan-2-amine via directed evolution in continuous culture, obtaining six times more tolerant strains than the wild-type. The adapted strains also displayed superior tolerance for structurally different amines. Coexpression of genes encoding for amine dehydrogenase (AmDH) and formate dehydrogenase activities in the adapted strains enabled the stereoselective bioamination (ee > 99%) of different prochiral ketones with up to 80% conversion at high substrate loading (up to 200 mM) without exogenous cofactor addition. The adapted cells displayed longer survival and higher population density during the reactions. The present biotechnological E. coli system contributes to the development of more robust biocatalysis for amine production.