Biosynthesis of butenoic acid through fatty acid biosynthesis pathway in Escherichia coli.

Butenoic acid is a C4 short-chain unsaturated fatty acid mainly used in the preparation of resins, pharmaceuticals, and fine chemicals. However, butenoic acid derived from petroleum is costly and unfriendly to the environment. Here, we report a novel biosynthetic strategy to produce butenoic acid by utilizing the intermediate of fatty acid biosynthesis pathway in engineered Escherichia coli. A thioesterase gene (B. thetaiotaomicron thioesterase (bTE)) from Bacteroides thetaiotaomicron was heterologously expressed in E. coli to specifically convert butenoyl-acyl carrier protein (ACP), a fatty acid biosynthesis intermediate, to butenoic acid. The titer of butenoic acid ranged from 0.07 to 11.4 mg/L in four different E. coli strains with varied expressing vectors. Deletion of endogenous fadD gene (encoding acyl-CoA synthetase) to block fatty acid oxidation improved the butenoic acid production in all strains to some extent. The highest butenoic acid accumulation of 18.7 mg/L was obtained in strain XP-2 (BL21-∆fadD/pET28a-bTE). Moreover, partially inhibiting the enoyl-ACP reductase (FabI) of strain XP-2 by triclosan increased butenoic acid production by threefold, and the butenoic acid titer was further increased to 161.4 mg/L by supplying glucose and tryptone in the M9 medium. Fed-batch fermentation of this strain further enhanced butenoic acid production to 4.0 g/L within 48 h. The butenoic acid tolerance assay revealed that this strain could tolerate 15-20 g/L of butenoic acid.