Fig. 1: Engineering of solventogenic clostridia for fatty acid ester production.

Top: Five strains out of four representative clostridial species were selected and evaluated as the host to be engineered for ester production in this study. We hypothesized that the different metabolic fluxes within different strains would make a big difference for the desirable ester production. The metabolic pathways of the four different species were represented in four different colors. Bottom: Fatty acid esters could be synthesized through two primary biological pathways: one is through the esterification of fatty acid and alcohol catalyzed by lipases, and the other is through the condensation of acyl-CoA and alcohol catalyzed by alcohol acyl transferases (AATs). Key genes in the pathway: pta phosphotransacetylase, ack acetate kinase, thl thiolase, hbd beta-hydroxybutyryl-CoA dehydrogenase, crt crotonase, bcd butyryl-CoA dehydrogenase, adh alcohol dehydrogenase, adhE aldehyde-alcohol dehydrogenase, adc acetoacetate decarboxylase, ctfAB CoA transferase, ptb phosphotransbutyrylase, buk butyrate kinase, ald aldehyde dehydrogenase. EA: ethyl acetate, EB: ethyl butyrate, BA: butyl acetate, BB: butyl butyrate.