title: Switching Clostridium acetobutylicum to an ethanol producer by disruption of the butyrate/butanol fermentative pathway.
abstract: Solventogenic clostridia are well-known since almost a century due to their unique capability to biosynthesize the solvents acetone and butanol. Based on recently developed genetic engineering tools, a targeted 3-hydroxybutyryl-CoA dehydrogenase (Hbd)-negative mutant of Clostridium acetobutylicum was generated. Interestingly, the entire butyrate/butanol (C(4)) metabolic pathway of C. acetobutylicum could be inactivated without a severe growth limitation and indicated the general feasibility to manipulate the central fermentative metabolism for product pattern alteration. Cell extracts of the mutant C. acetobutylicum hbd::int(69) revealed clearly reduced thiolase, Hbd and crotonase but increased NADH-dependent alcohol dehydrogenase enzyme activities as compared to the wildtype strain. Neither butyrate nor butanol were detected in cultures of C. acetobutylicum hbd::int(69), and the formation of molecular hydrogen was significantly reduced. Instead up to 16 and 20g/l ethanol were produced in glucose and xylose batch cultures, respectively. Further sugar addition in glucose fed-batch fermentations increased the ethanol production to a final titer of 33g/l, resulting in an ethanol to glucose yield of 0.38g/g.
authors.affiliation: Department of Microbiology, Institute of Biological Sciences, University of Rostock, Albert-Einstein-Strasse 3, Rostock, Germany.
authors.forename: Dörte
authors.initials: D
authors.lastname: Lehmann
authors.forename: Tina
authors.initials: T
authors.lastname: Lütke-Eversloh
mesh_terms: D015094:3-Hydroxyacyl CoA Dehydrogenases / Q000096:biosynthesis / Q000235:genetics; D000426:Alcohol Dehydrogenase / Q000096:biosynthesis* / Q000235:genetics; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D000440:Butanols / Q000378:metabolism; D002087:Butyrates / Q000378:metabolism; D046969:Clostridium acetobutylicum / Q000235:genetics / Q000378:metabolism*; D003470:Culture Media / Q000494:pharmacology; D004746:Enoyl-CoA Hydratase / Q000096:biosynthesis / Q000235:genetics; D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation; D055785:Gene Knockdown Techniques; D005798:Genes, Bacterial; D005947:Glucose / Q000494:pharmacology; D009154:Mutation; D014994:Xylose / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D000440:Butanols; D002087:Butyrates; D003470:Culture Media; D000431:Ethanol; D014994:Xylose; D015094:3-Hydroxyacyl CoA Dehydrogenases; D000426:Alcohol Dehydrogenase; C021388:3-hydroxybutyryl-CoA dehydrogenase; D004746:Enoyl-CoA Hydratase; D005947:Glucose