Metabolic engineering of Escherichia coli for the production of butyric acid at high titer and productivity

Background Several anaerobic bacteria produce butyric acid, a commodity chemical with use in chemical, pharmaceutical, food and feed industries, using complex media with acetate as a co-product. Butyrate titer of various recombinant Escherichia coli did not exceed 10 g l −1 in batch fermentations in any of the media tested. Results A recombinant E. coli (strain LW393) that produced butyrate as the major fermentation product was constructed with genes from E. coli , Clostridium acetobutylicum and Treponema denticola . Strain LW393 produced 323 ± 6 mM (28.4 ± 0.4 g l −1 ) butyric acid in batch fermentations in mineral salt medium with glucose as C source at a yield of 0.37 ± 0.01 g (g glucose consumed) −1 . Butyrate accounted for 90% of the total products produced by the culture. Supplementing this medium with yeast extract further increased butyric acid titer to 375 ± 4 mM. Average volumetric productivity of butyrate with xylose as C source was 0.89 ± 0.07 g l −1 h −1 . Conclusions The butyrate titer reported in this study is about 2.5–3-times higher than the values reported for other recombinant E. coli and this is achieved in mineral salt medium with an expectation of lower purification and production cost of butyrate.