Abstract
Background2,3-Butanediol (2,3-BD) with low toxicity to microbes, could be a promising alternative for biofuel production. However, most of the 2,3-BD producers are opportunistic pathogens that are not suitable for industrial-scale fermentation. In our previous study, wild-type Bacillus subtilis 168, as a class I microorganism, was first found to generate only d-(−)-2,3-BD (purity >99 %) under low oxygen conditions.ResultsIn this work, B. subtilis was engineered to produce chiral pure meso-2,3-BD. First, d-(−)-2,3-BD production was abolished by deleting d-(−)-2,3-BD dehydrogenase coding gene bdhA, and acoA gene was knocked out to prevent the degradation of acetoin (AC), the immediate precursor of 2,3-BD. Next, both pta and ldh gene were deleted to decrease the accumulation of the byproducts, acetate and l-lactate. We further introduced the meso-2,3-BD dehydrogenase coding gene budC from Klebsiellapneumoniae CICC10011, as well as overexpressed alsSD in the tetra-mutant (ΔacoAΔbdhAΔptaΔldh) to achieve the efficient production of chiral meso-2,3-BD. Finally, the pool of NADH availability was further increased to facilitate the conversion of meso-2,3-BD from AC by overexpressing udhA gene (coding a soluble transhydrogenase) and low dissolved oxygen control during the cultivation. Under microaerobic oxygen conditions, the best strain BSF9 produced 103.7 g/L meso-2,3-BD with a yield of 0.487 g/g glucose in the 5-L batch fermenter, and the titer of the main byproduct AC was no more than 1.1 g/L.ConclusionThis work offered a novel strategy for the production of chiral pure meso-2,3-BD in B. subtilis. To our knowledge, this is the first report indicating that metabolic engineered B. subtilis could produce chiral meso-2,3-BD with high purity under limited oxygen conditions. These results further demonstrated that B. subtilis as a class I microorganism is a competitive industrial-level meso-2,3-BD producer.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0502-5) contains supplementary material, which is available to authorized users.
Highlights
By analysis of extracellular metabolites by HPLC, we found that acetate was the main product of the oxidative dissimilation of AC in B. subtilis, which is consistent with Lopez et al.’s study on the direct oxidative cleavage of AC [40]
This study provided a deep understanding of chiral 2,3-BD metabolism in B. subtilis, and a strategy for enhancing the chiral pure 2,3-BD production through genetic modification
Deletion of ldh and introduction of udhA, low Dissolved oxygen (DO) control, and additional reducing substrates further enhanced meso2,3-BD production, which indicated that the key factor for meso-2,3-BD production in B. subtilis was transformation of AC to 2,3-BD
Summary
D-(−)-2,3-BD production was abolished by deleting d-(−)-2,3-BD dehydrogenase coding gene bdhA, and acoA gene was knocked out to prevent the degradation of acetoin (AC), the immediate precursor of 2,3-BD. Both pta and ldh gene were deleted to decrease the accumulation of the byproducts, acetate and l-lactate. We further introduced the meso-2,3-BD dehydrogenase coding gene budC from Klebsiella pneumoniae CICC10011, as well as overexpressed alsSD in the tetra-mutant (ΔacoAΔbdhAΔptaΔldh) to achieve the efficient production of chiral meso-2,3-BD. The pool of NADH availability was further increased to facilitate the conversion of meso-2,3-BD from AC by overexpressing udhA gene (coding a soluble transhydrogenase) and low dissolved oxygen control during the cultivation. The best strain BSF9 produced 103.7 g/L meso-2,3-BD with a yield of 0.487 g/g glucose in the 5-L batch fermenter, and the titer of the main byproduct AC was no more than 1.1 g/L
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