title: Metabolic engineering of Clostridium acetobutylicum for enhanced production of butyric acid.
abstract: Clostridium acetobutylicum has been considered as an attractive platform host for biorefinery due to its metabolic diversity. Considering its capability to overproduce butanol through butyrate, it was thought that butyric acid can also be efficiently produced by this bacterium through metabolic engineering. The pta-ctfB-deficient C. acetobutylicum CEKW, in which genes encoding phosphotransacetylase and CoA-transferase were knocked out, was assessed for its potential as a butyric acid producer in fermentations with four controlled pH values at 5.0, 5.5, 6.0, and 6.4. Butyric acid could be best produced by fermentation of the CEKW at pH 6.0, resulting in the highest titer of 26.6 g/l, which is 6.4 times higher than that obtained with the wild type. However, due to the remaining solventogenic ability of the CEKW, 3.6 g/l solvents were also produced. Thus, the CEKW was further engineered by knocking out the adhE1-encoding aldehyde/alcohol dehydrogenase to prevent solvent production. Batch fermentation of the resulting C. acetobutylicum HCEKW at pH 6.0 showed increased butyric acid production to 30.8 g/l with a ratio of butyric-to-acetic acid (BA/AA) of 6.6 g/g and a productivity of 0.72 g/l/h from 86.9 g/l glucose, while negligible solvent (0.8 g/l ethanol only) was produced. The butyric acid titer, BA/AA ratio, and productivity obtained in this study were the highest values reported for C. acetobutylicum, and the BA/AA ratio and productivity were also comparable to those of native butyric acid producer Clostridium tyrobutyricum. These results suggested that the simultaneous deletion of the pta-ctfB-adhE1 in C. acetobutylicum resulted in metabolic switch from biphasic to acidogenic fermentation, which enhanced butyric acid production.
authors.affiliation: Metabolic and Biomolecular Engineering National Research Laboratory, Department of Chemical and Biomolecular Engineering, BioProcess Engineering Research Center, Center for Systems and Synthetic Biotechnology, Institute for the BioCentury, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon, 305-701, Republic of Korea.
authors.forename: Yu-Sin
authors.initials: YS
authors.lastname: Jang
authors.forename: Hee Moon
authors.initials: HM
authors.lastname: Woo
authors.forename: Jung Ae
authors.initials: JA
authors.lastname: Im
authors.forename: In Ho
authors.initials: IH
authors.lastname: Kim
authors.forename: Sang Yup
authors.initials: SY
authors.lastname: Lee
mesh_terms: D020148:Butyric Acid / Q000378:metabolism*; D046969:Clostridium acetobutylicum / Q000235:genetics* / Q000378:metabolism*; D048014:Clostridium tyrobutyricum / Q000378:metabolism; D000431:Ethanol / Q000378:metabolism; D055786:Gene Knockout Techniques; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D060847:Metabolic Engineering; D053858:Metabolic Networks and Pathways / Q000235:genetics
chemical_list: D020148:Butyric Acid; D000431:Ethanol; D005947:Glucose