Fermentative production of the unnatural amino acid L-2-aminobutyric acid based on metabolic engineering

L-2-aminobutyric acid (L-ABA) is an unnatural amino acid that is a key intermediate for the synthesis of several important pharmaceuticals. To make the biosynthesis of L-ABA environmental friendly and more suitable for the industrial-scale production. We expand the nature metabolic network of Escherichia coli using metabolic engineering approach for the production of L-ABA. In this study, Escherichia coli THR strain with a modified pathway for threonine-hyperproduction was engineered via deletion of the rhtA gene from the chromosome. To redirect carbon flux from 2-ketobutyrate (2-KB) to L-ABA, the ilvIH gene was deleted to block the L-isoleucine pathway. Furthermore, the ilvA gene from Escherichia coli W3110 and the leuDH gene from Thermoactinomyces intermedius were amplified and co-overexpressed. The promoter was altered to regulate the expression strength of ilvA* and leuDH. The final engineered strain E. coli THR ΔrhtAΔilvIH/Gap-ilvA*-Pbs-leuDH was able to produce 9.33 g/L of L-ABA with a yield of 0.19 g/L/h by fed-batch fermentation in a 5 L bioreactor. This novel metabolically tailored strain offers a promising approach to fulfill industrial requirements for production of L-ABA.