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Background   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.    Results  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 Δ rhtA Δ ilvIH /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.    Conclusions  This novel metabolically tailored strain offers a promising approach to fulfill industrial requirements for production of  l -ABA.    Electronic supplementary material  The online version of this article (10.1186/s12934-019-1095-z) contains supplementary material, which is available to authorized users.

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