Metabolic Engineering of P. Freudenrichii for Enhanced Propionic Acid Production

Propionic acid is widely used as a chemical intermediate in various manufacturing processes, and its salts are common food preservatives. It is mainly produced via petrochemicals, but there is increasing interest in its production by fermentation these days. Unfortunately, fermentative production provides low yields due to the formation of other organic acids, mainly acetic, as byproducts. In addition, the accumulation of propionic acid in the medium is inhibitory to cells. In this work, the effect of up-regulating some genes in the propionate biosynthesis pathway to shift the carbon flux towards propionate was studied. Higher propionate yields from sugar fermented were obtained. Surprisingly, acetate yields increased assumingly to provide more NADH to support propionate formation. Consequently, up-regulating the propionate pathway is better accompanied by down-regulating the acetate pathway. We anticipate that such approach in combination with process engineering can facilitate the development of a fermentation process for the economic production of propionic acid from sugars and other renewable feedstocks.