title: Engineering Bacillus licheniformis for the production of meso-2,3-butanediol.
abstract: BACKGROUND
  2,3-Butanediol (2,3-BD) can be used as a liquid fuel additive to replace petroleum oil, and as an important platform chemical in the pharmaceutical and plastic industries. Microbial production of 2,3-BD by Bacillus licheniformis presents potential advantages due to its GRAS status, but previous attempts to use this microorganism as a chassis strain resulted in the production of a mix of D-2,3-BD and meso-2,3-BD isomers.
  
  
  RESULTS
  The aim of this work was to develop an engineered strain of B. licheniformis suited to produce the high titers of the pure meso-2,3-BD isomer. Glycerol dehydrogenase (Gdh) was identified as the catalyst for D-2,3-BD biosynthesis from its precursor acetoin in B. licheniformis. The gdh gene was, therefore, deleted from the wild-type strain WX-02 to inhibit the flux of acetoin to D-2,3-BD biosynthesis. The acoR gene involved in acetoin degradation through AoDH ES was also deleted to provide adequate flux from acetoin towards meso-2,3-BD. By re-directing the carbon flux distribution, the double-deletion mutant WX-02ΔgdhΔacoR produced 28.2 g/L of meso-2,3-BD isomer with >99 % purity. The titer was 50 % higher than that of the wide type. A bench-scale fermentation by the double-deletion mutant was developed to further improve meso-2,3-BD production. In a fed-batch fermentation, meso-2,3-BD titer reached 98.0 g/L with a purity of >99.0 % and a productivity of 0.94 g/L-h.
  
  
  CONCLUSIONS
  This work demonstrates the potential of producing meso-2,3-BD with high titer and purity through metabolic engineering of B. licheniformis.
authors.affiliation: Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, College of Life Sciences, Hubei University, Wuhan, 430062 China ; Ministry-of-Education Key Laboratory for Green Preparation and Application of Functional Materials, School of Materials Science and Engineering, Hubei University, Wuhan, 430062 China.
authors.forename: Yimin
authors.initials: Y
authors.lastname: Qiu
authors.affiliation: State Key Laboratory of Agricultural Microbiology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, 430070 China.
authors.forename: Jinyan
authors.initials: J
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Agricultural Microbiology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, 430070 China.
authors.forename: Lu
authors.initials: L
authors.lastname: Li
authors.affiliation: College of Food Science and Technology, Huazhong Agricultural University, Wuhan, 430070 China ; Department of Food Science and Human Nutrition, Iowa State University, Ames, IA 50011 USA.
authors.forename: Zhiyou
authors.initials: Z
authors.lastname: Wen
authors.affiliation: Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, College of Life Sciences, Hubei University, Wuhan, 430062 China ; Department of Chemistry, The State University of New York College of Environmental Science and Forestry (SUNY ESF), Syracuse, NY 13210 USA.
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Nomura
authors.affiliation: Ministry-of-Education Key Laboratory for Green Preparation and Application of Functional Materials, School of Materials Science and Engineering, Hubei University, Wuhan, 430062 China.
authors.forename: Shuilin
authors.initials: S
authors.lastname: Wu
authors.affiliation: Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, College of Life Sciences, Hubei University, Wuhan, 430062 China.
authors.forename: Shouwen
authors.initials: S
authors.lastname: Chen
keywords: 3-Butanediol; Bacillus licheniformis; Meso-2; Metabolic engineering; gdh Gene