Enhancement of acetoin production from Bacillus licheniformis by 2,3-butanediol conversion strategy: Metabolic engineering and fermentation control

•Bacillus licheniformis was engineered to increase the production of acetoin.•The glycerol dehydrogenase GDH had high efficiency in conversion of 2,3-BD to AC.•The acetoin titer was further improved by fermentation control.•A highest acetoin titer reached 78.79 g L-1 in the engineered B. licheniformis.

Acetoin is a natural flavor with potential applications in food, pharmaceutical, and chemical industries. However, the titer of acetoin in fermentation production of this compound is still relatively low, which hinders its large-scale industrial production. In this work, fermentative production of acetoin by Bacillus licheniformis WX-02 was optimized through metabolic engineering and fermentation control to increase the titer of this compound. First, three single-gene mutants, deficient in genes of 2,3-butanediol dehydrogenase (budC), glycerol dehydrogenase (gdh), and acetoin dehydrogenase transcriptional activator (acoR) respectively, were compared. It was found that single deletion of budC or acoR significantly enhanced the acetoin production. Second, double genes mutant (WX-02ΔbudCΔacoR) and three genes mutant (WX-02ΔbudCΔgdhΔacoR) were evaluated, and the maximum acetoin titer reached 43.95 g L−1 in WX-02ΔbudCΔacoR. Finally, fermentation conditions were investigated for the mutant WX-02ΔbudCΔacoR, and moderate acidic and agitation conditions favored the acetoin production. Using three-stage agitation in fed-batch fermentation, 2,3-butanediol was accumulated to 110.04 g L−1, and then converted to acetoin. The maximum acetoin titer reached 78.79 g L−1, much higher than those of reported previously for the B. licheniformis strains. Collectively, this study reported an efficient approach producing acetoin by B. licheniformis strain through metabolic engineering and fermentation optimization.

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