title: New insights into the butyric acid metabolism of Clostridium acetobutylicum.
abstract: Biosynthesis of acetone and n-butanol is naturally restricted to the group of solventogenic clostridia with Clostridium acetobutylicum being the model organism for acetone-butanol-ethanol (ABE) fermentation. According to limited genetic tools, only a few rational metabolic engineering approaches were conducted in the past to improve the production of butanol, an advanced biofuel. In this study, a phosphotransbutyrylase-(Ptb) negative mutant, C. acetobutylicum ptb::int(87), was generated using the ClosTron methodology for targeted gene knock-out and resulted in a distinct butyrate-negative phenotype. The major end products of fermentation experiments without pH control were acetate (3.2 g/l), lactate (4.0 g/l), and butanol (3.4 g/l). The product pattern of the ptb mutant was altered to high ethanol (12.1 g/l) and butanol (8.0 g/l) titers in pH ≥ 5.0-regulated fermentations. Glucose fed-batch cultivation elevated the ethanol concentration to 32.4 g/l, yielding a more than fourfold increased alcohol to acetone ratio as compared to the wildtype. Although butyrate was never detected in cultures of C. acetobutylicum ptb::int(87), the mutant was still capable to take up butyrate when externally added during the late exponential growth phase. These findings suggest that alternative pathways of butyrate re-assimilation exist in C. acetobutylicum, supposably mediated by acetoacetyl-CoA:acyl-CoA transferase and acetoacetate decarboxylase, as well as reverse reactions of butyrate kinase and Ptb with respect to previous studies.
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: Nadine
authors.initials: N
authors.lastname: Radomski
authors.forename: Tina
authors.initials: T
authors.lastname: Lütke-Eversloh
mesh_terms: D020001:1-Butanol / Q000378:metabolism; D000085:Acetates / Q000378:metabolism; D000096:Acetone / Q000378:metabolism; D020148:Butyric Acid / Q000378:metabolism*; D046969:Clostridium acetobutylicum / Q000378:metabolism*; D003470:Culture Media / Q000737:chemistry; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D017353:Gene Deletion; D055786:Gene Knockout Techniques; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000378:metabolism; D060847:Metabolic Engineering; D053858:Metabolic Networks and Pathways / Q000235:genetics; D010709:Phosphate Acetyltransferase / Q000235:genetics
chemical_list: D000085:Acetates; D003470:Culture Media; D020148:Butyric Acid; D000096:Acetone; D019344:Lactic Acid; D000431:Ethanol; D020001:1-Butanol; D010709:Phosphate Acetyltransferase; D005947:Glucose