Synthesis of Pure meso-2,3-Butanediol from Crude Glycerol Using an Engineered Metabolic Pathway in Escherichia coli

Abstract

meso-2,3-Butanediol (meso-2,3-BDO) is essential for the synthesis of various economically valuable biosynthetic products; however, the production of meso-2,3-BDO from expensive carbon sources is an obstacle for industrial applications. In this study, genes involved in the synthesis of 2,3-BDO in Klebsiella pneumoniae were identified and used to genetically modify Escherichia coli for meso-2,3-BDO production. Two 2,3-BDO biosynthesis genes-budA, encoding acetolactate, and meso-budC, encoding meso-SADH-from K. pneumoniae were cloned into the pUC18 plasmid and introduced into E. coli. In 2 l batch culture, the SGSB03 E. coli strain yielded meso-2,3-BDO at 0.31 g/g(glucose) (with a maximum of 15.7 g/l(culture) after 48 h) and 0.21 g/g(crude glycerol) (with a maximum of 6.9 g/l(culture) after 48 h). Batch cultures were grown under optimized conditions (aerobic, 6% carbon source, 37 A degrees C, and initial pH 7). To find the optimal culture conditions for meso-2,3-BDO production, we evaluated the enzyme activity of meso-SADH and the whole cell conversion yield (meso-2,3-BDO/acetoin) of the E. coli SGSB02, which contains pSB02. meso-SADH showed high enzyme activity at 30-37 A degrees C and pH 7 (30.5-41.5 U/mg of protein), and the conversion yield of SGSB02 E. coli was highest at 37-42 A degrees C and a pH of 7 (0.25-0.28 g (meso-2,3-BDO)/g(acetoin)).