Engineering Escherichia coli for High Selective Production of Butyric Acid

Butyric acid has many important applications in industry and is mainly produced by the petroleum-based process. The bio-based production method for butyrate is increasingly interesting because of a concern over global warming and fossil fuel shortage. Clostridium species have been long applied for the butyrate production. However, a mixture of butyrate and acetate is produced in the clostridial fermentation, which results in low selectivity of butyrate (ca. the butyrate/acetate (B/A) ratio within 10-14). To address this issue, Escherichia coli was engineered for the production of butyrate. This was carried out by pathway engineering of E. coli in a systematic way. First, the pathways leading to byproducts were removed to conserve NADH. Secondly, a heterologous pathway was constructed to direct acetyl-CoA to butyryl-CoA. Finally, endogenous atoDA was overexpressed for conversion of butyryl-CoA to butyrate at the expense of acetate. As a consequence, the resulting strain enabled production of 10 g/L butyrate from 20g/L glucose and 8 g/L acetate within 48 h. The result accounts for the B/A ratio of 143. It indicates that our approach is promising for production of butyrate in E. coli.