Mechanism of 2,3-butanediol stereoisomers formation in a newly isolated Serratia sp. T241.

Serratia sp. T241, a newly isolated xylose-utilizing strain, produced three 2,3-butanediol (2,3-BD) stereoisomers. In this study, three 2,3-butanediol dehydrogenases (BDH1-3) and one glycerol dehydrogenase (GDH) involved in 2,3-BD isomers formation by Serratia sp. T241 were identified. In vitro conversion showed BDH1 and BDH2 could catalyzed (3S)-acetoin and (3R)-acetoin into (2S,3S)-2,3-BD and meso-2,3-BD, while BDH3 and GDH exhibited the activities from (3S)-acetoin and (3R)-acetoin to meso-2,3-BD and (2R,3R)-2,3-BD. Four encoding genes were assembled into E. coli with budA (acetolactate decarboxylase) and budB (acetolactate synthase), responsible for converting pyruvate into acetoin. E. coli expressing budAB-bdh1/2 produced meso-2,3-BD and (2S,3S)-2,3-BD. Correspondingly, (2R,3R)-2,3-BD and meso-2,3-BD were obtained by E. coli expressing budAB-bdh3/gdh. These results suggested four enzymes might contribute to 2,3-BD isomers formation. Mutants of four genes were developed in Serratia sp. T241. Δbdh1 led to reduced concentration of meso-2,3-BD and (2S,3S)-2,3-BD by 97.7% and 87.9%. (2R,3R)-2,3-BD with a loss of 73.3% was produced by Δbdh3. Enzyme activity assays showed the decrease of 98.4% and 22.4% by Δbdh1 and Δbdh3 compared with the wild strain. It suggested BDH1 and BDH3 played important roles in 2,3-BD formation, BDH2 and GDH have small effects on 2,3-BD production by Serratia sp. T241.