Carbon-negative bio-production of short-chain carboxylic acids (SCCAs) from syngas via the sequential two-stage bioprocess by Moorella thermoacetica and metabolically engineered Escherichia coli

Syngas can be efficiently converted to acetate and is environmentally friendly using Moorella thermoacetica under anaerobic conditions. Coupled with acetate production from syngas, using acetate to synthesize value-added compounds such as short-chain carboxylic acids (SCCAs) become a negative-carbon process. Escherichia coli is engineered to utilize acetate as the sole carbon source to produce SCCAs. By knocking out some acetyltransferase genes, combined with introducing exogenous pathway and additional cofactor engineering, the strains can synthesize 3.79 g/L of 3-hydroxypropionic acid (3-HP), 1.83 g/L of (R)-3-hydroxybutyric acid (R-3HB), and 2.31 g/L of butyrate. We used M. thermoacetica to produce acetate from syngas, subsequently, all engineered E. coli strains were able to produce SCCAs from syngas-derived acetate. The titer of 3-HP, R-3HB, and butyrate is 3.75, 1.68, and 2.04 g/L, with carbon sequestration rates of 51.1, 26.3, and 38.1 %, respectively. This coupled bioprocess has great potential for producing other value-added chemicals from syngas.