title: Modifying the product pattern of Clostridium acetobutylicum: physiological effects of disrupting the acetate and acetone formation pathways.
abstract: Clostridial acetone-butanol-ethanol (ABE) fermentation is a natural source for microbial n-butanol production and regained much interest in academia and industry in the past years. Due to the difficult genetic accessibility of Clostridium acetobutylicum and other solventogenic clostridia, successful metabolic engineering approaches are still rare. In this study, a set of five knock-out mutants with defects in the central fermentative metabolism were generated using the ClosTron technology, including the construction of targeted double knock-out mutants of C. acetobtuylicum ATCC 824. While disruption of the acetate biosynthetic pathway had no significant impact on the metabolite distribution, mutants with defects in the acetone pathway, including both acetoacetate decarboxylase (Adc)-negative and acetoacetyl-CoA:acyl-CoA transferase (CtfAB)-negative mutants, exhibited high amounts of acetate in the fermentation broth. Distinct butyrate increase and decrease patterns during the course of fermentations provided experimental evidence that butyrate, but not acetate, is re-assimilated via an Adc/CtfAB-independent pathway in C. acetobutylicum. Interestingly, combining the adc and ctfA mutations with a knock-out of the phosphotransacetylase (Pta)-encoding gene, acetate production was drastically reduced, resulting in an increased flux towards butyrate. Except for the Pta-negative single mutant, all mutants exhibited a significantly reduced solvent production.
authors.affiliation: Abteilung Mikrobiologie, Institut für Biowissenschaften, Universität Rostock, Albert-Einstein-Str. 3, 18059 Rostock, Germany.
authors.forename: Dörte
authors.initials: D
authors.lastname: Lehmann
authors.forename: Daniel
authors.initials: D
authors.lastname: Hönicke
authors.forename: Armin
authors.initials: A
authors.lastname: Ehrenreich
authors.forename: Michael
authors.initials: M
authors.lastname: Schmidt
authors.forename: Dirk
authors.initials: D
authors.lastname: Weuster-Botz
authors.forename: Hubert
authors.initials: H
authors.lastname: Bahl
authors.forename: Tina
authors.initials: T
authors.lastname: Lütke-Eversloh
mesh_terms: D000085:Acetates / Q000378:metabolism*; D000096:Acetone / Q000378:metabolism*; D002087:Butyrates / Q000378:metabolism; D046969:Clostridium acetobutylicum / Q000235:genetics* / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D017353:Gene Deletion; D060847:Metabolic Engineering / Q000379:methods*; D053858:Metabolic Networks and Pathways / Q000235:genetics
chemical_list: D000085:Acetates; D002087:Butyrates; D000096:Acetone; D000431:Ethanol