Enhancement of free fatty acid production in Saccharomyces cerevisiae by control of fatty acyl-CoA metabolism

Production of biofuels derived from microbial fatty acids has attracted great attention in recent years owing to their potential to replace petroleum-derived fuels. To be cost competitive with current petroleum fuel, flux toward the direct precursor fatty acids needs to be enhanced to approach high yields. Herein, fatty acyl-CoA metabolism in Saccharomyces cerevisiae was engineered to accumulate more free fatty acids (FFA). For this purpose, firstly, haploid S. cerevisiae double deletion strain ^Δfaa1 ^Δfaa4 was constructed, in which the genes FAA1 and FAA4 encoding two acyl-CoA synthetases were deleted. Then the truncated version of acyl-CoA thioesterase ACOT5 (Acot5s) encoding Mus musculus peroxisomal acyl-CoA thioesterase 5 was expressed in the cytoplasm of the strain ^Δfaa1^Δfaa4. The resulting strain ^Δfaa1^Δfaa4 [Acot5s] accumulated more extracellular FFA with higher unsaturated fatty acid (UFA) ratio as compared to the wild-type strain and double deletion strain ^Δfaa1 ^Δfaa4. The extracellular total fatty acids (TFA) in the strain ^Δfaa1^Δfaa4 [Acot5s] increased to 6.43-fold as compared to the wild-type strain during the stationary phase. UFA accounted for 42 % of TFA in the strain ^Δfaa1^Δfaa4 [Acot5s], while no UFA was detected in the wild-type strain. In addition, the expression of Acot5s in ^Δfaa1^Δfaa4 restored the growth, which indicates that FFA may not be the reason for growth inhibition in the strain ^Δfaa1^Δfaa4. RT-PCR results demonstrated that the de-repression of fatty acid synthesis genes led to the increase of extracellular fatty acids. The study presented here showed that through control of the acyl-CoA metabolism by deleting acyl-CoA synthetase and expressing thioesterase, more FFA could be produced in S. cerevisiae, demonstrating great potential for exploitation in the platform of microbial fatty acid-derived biofuels.