Biosynthesis of enantiopure (S)-3-hydroxybutyrate from glucose through the inverted fatty acid β-oxidation pathway by metabolically engineered Escherichia coli

- E. coli was engineered to synthesise 3-hydroxybutyrate (3-HB) from glucose via inverted fatty acid β-oxidation.
- Enantioselective biosynthesis of (S)-form of 3-HB through engineered pathway was proved.
- 9.58 g/L of enantiopure (S)-3-HB was produced with yield of 66% of theoretical maximum.

Enantiomers of 3-hydroxybutyric acid (3-HB) can be used as the chiral precursors for the production of various optically active fine chemicals, including drugs, perfumes, and pheromones. In this study, Escherichia coli was engineered to produce (S)-3-HB from glucose through the inverted reactions of the native aerobic fatty acid β-oxidation pathway. Expression of only specific genes encoding enzymes responsible for the conversion of acetyl-CoA to acetoacetyl-CoA, reduction of acetoacetyl-CoA to 3-hydroxybutyryl-CoA and subsequent hydrolysis of 3-hydroxybutyryl-CoA to 3-HB was directly upregulated in an engineered strain. The operation of multiple turns of the inverted fatty acid β-oxidation was precluded by the deletion of gene encoding enzyme that catalyse the terminal stage of the respective cycle. While the overexpression of the C-acetyltransferase gene enabled 3-HB biosynthesis through the inverted fatty acid β-oxidation, the efficient conversion of glucose to the target product was achieved resulting from the additional overexpression of the gene encoding appropriate termination thioesterase II. The engineered strain synthesised the (S)-stereoisomer of 3-HB with an enantiomeric excess of more than 99%. Under microaerobic conditions, up to 9.58 g/L of enantiopure (S)-3-HB was produced from glucose, with a yield of 66% of the theoretical maximum.