Renewable Fatty Acid Ester Production in Clostridium

Endproduct toxicity is a key bottleneck for biofuel/biochemical production. Biosynthesis of high-value derivatives that can easily separate would alleviate such toxicity and thus enhance bioproduction efficiency. As a proof of principle, biosynthesis (along with in-line extractive recovery) of fatty acid esters using clostridia was investigated in this study. We hypothesize that solventogenic clostridia are excellent platforms for ester production, because they co-produce acyl-CoAs (acetyl-CoA and butyryl-CoA), acids (acetate and butyrate), and alcohols (ethanol and butanol). Through rational screening for host strains and genes (encoding alcohol acyl transferases and lipase), systematic metabolic engineering, and elimination of putative prophages, we obtained strains that can produce 20.3 g/L butyl acetate and 1.6 g/L butyl butyrate respectively, which were both historically highest levels in microbial hosts. Our principle for engineering microorganisms to produce high-value and easy-recoverable endproducts is highly applicable to other bioprocesses, and could lead to breakthroughs in biofuel/biochemical production and general bioeconomy.