title: Metabolic engineering of Clostridium tyrobutyricum for enhanced butyric acid production from glucose and xylose.
abstract: Clostridium tyrobutyricum is a promising microorganism for butyric acid production. However, its ability to utilize xylose, the second most abundant sugar found in lignocellulosic biomass, is severely impaired by glucose-mediated carbon catabolite repression (CCR). In this study, CCR in C. tyrobutyricum was eliminated by overexpressing three heterologous xylose catabolism genes (xylT, xylA and xlyB) cloned from C. acetobutylicum. Compared to the parental strain, the engineered strain Ct-pTBA produced more butyric acid (37.8g/L vs. 19.4g/L) from glucose and xylose simultaneously, at a higher xylose utilization rate (1.28g/L·h vs. 0.16g/L·h) and efficiency (94.3% vs. 13.8%), resulting in a higher butyrate productivity (0.53g/L·h vs. 0.26g/L·h) and yield (0.32g/g vs. 0.28g/g). When the initial total sugar concentration was ~120g/L, both glucose and xylose utilization rates increased with increasing their respective concentration or ratio in the co-substrates but the total sugar utilization rate remained almost unchanged in the fermentation at pH 6.0. Decreasing the pH to 5.0 significantly decreased sugar utilization rates and butyrate productivity, but the effect was more pronounced for xylose than glucose. The addition of benzyl viologen (BV) as an artificial electron carrier facilitated the re-assimilation of acetate and increased butyrate production to a final titer of 46.4g/L, yield of 0.43g/g sugar consumed, productivity of 0.87g/L·h, and acid purity of 98.3% in free-cell batch fermentation, which were the highest ever reported for butyric acid fermentation. The engineered strain with BV addition thus can provide an economical process for butyric acid production from lignocellulosic biomass.
authors.affiliation: William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, 151 West Woodruff Avenue, Columbus, Ohio 43210, USA; School of Life Science and Biotechnology, Dalian University of Technology, Dalian 116024, China.
authors.forename: Hongxin
authors.initials: H
authors.lastname: Fu
authors.affiliation: William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, 151 West Woodruff Avenue, Columbus, Ohio 43210, USA.
authors.forename: Le
authors.initials: L
authors.lastname: Yu
authors.affiliation: Bioprocessing Innovative Company, 4734 Bridle Path Ct., Dublin, Ohio 43017, USA.
authors.forename: Meng
authors.initials: M
authors.lastname: Lin
authors.affiliation: School of Bioscience and Bioengineering, South China University of Technology, Guangzhou 510006, China.
authors.forename: Jufang
authors.initials: J
authors.lastname: Wang
authors.affiliation: School of Life Science and Biotechnology, Dalian University of Technology, Dalian 116024, China.
authors.forename: Zhilong
authors.initials: Z
authors.lastname: Xiu
authors.affiliation: William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, 151 West Woodruff Avenue, Columbus, Ohio 43210, USA. Electronic address: yang.15@osu.edu.
authors.forename: Shang-Tian
authors.initials: ST
authors.lastname: Yang
mesh_terms: D053898:Biosynthetic Pathways / Q000235:genetics; D020148:Butyric Acid / Q000302:isolation & purification / Q000378:metabolism*; D048014:Clostridium tyrobutyricum / Q000502:physiology*; D024861:Genetic Enhancement / Q000379:methods*; D005947:Glucose / Q000378:metabolism*; D060847:Metabolic Engineering / Q000379:methods*; D053858:Metabolic Networks and Pathways / Q000235:genetics; D014994:Xylose / Q000378:metabolism*
chemical_list: D020148:Butyric Acid; D014994:Xylose; D005947:Glucose
keywords: Butyric acid; Carbon catabolite repression; Clostridium tyrobutyricum; Metabolic engineering; Xylose