Development of efficient microbial cell factory for whole-cell bioconversion of L-threonine to 2-hydroxybutyric acid

Production of 2-hydroxybutyric acid (2-HBA) was attempted in recombinant Escherichia coli W3110 Δtdh ΔilvIH (over)expressing a homologous and mutated threonine dehydratase (ilvA*) and a heterologous 2-ketobutyric acid (2-KBA) reductase from Alcaligenes eutrophus H16 (Ae_ldh). To prevent the degradation of 2-KBA, the aceE, poxB and pflB genes were deleted, and for blocking the 2-HBA degradation, the lldD and dld genes were disrupted. In addition, for efficient NADH regeneration/supply, a heterologous formate dehydrogenase from Candida boidinii (Cb_fdh) was overexpressed. Under anaerobic condition, E. coli W3110 Δtdh ΔilvIH ΔaceE ΔpoxB ΔlldD Δdld ΔpflB could produce > 400 mM 2-HBA in 33 h with the yield of ∼ 0.95 mol/mol. Furthermore, by enhancing the expression of a mutant Cb_fdh, the titer could be increased to ∼ 650 mM in 33 h. This study provides an efficient microbial cell factory for the bioconversion of threonine to 2-HBA with a high yield.