title: Disruption of the acetate kinase (ack) gene of Clostridium acetobutylicum results in delayed acetate production.
abstract: In microorganisms, the enzyme acetate kinase (AK) catalyses the formation of ATP from ADP by de-phosphorylation of acetyl phosphate into acetic acid. A mutant strain of Clostridium acetobutylicum lacking acetate kinase activity is expected to have reduced acetate and acetone production compared to the wild type. In this work, a C. acetobutylicum mutant strain with a selectively disrupted ack gene, encoding AK, was constructed and genetically and physiologically characterized. The ack                         (-) strain showed a reduction in acetate kinase activity of more than 97% compared to the wild type. The fermentation profiles of the ack                         (-) and wild-type strain were compared using two different fermentation media, CGM and CM1. The latter contains acetate and has a higher iron and magnesium content than CGM. In general, fermentations by the mutant strain showed a clear shift in the timing of peak acetate production relative to butyrate and had increased acid uptake after the onset of solvent formation. Specifically, in acetate containing CM1 medium, acetate production was reduced by more than 80% compared to the wild type under the same conditions, but both strains produced similar final amounts of solvents. Fermentations in CGM showed similar peak acetate and butyrate levels, but increased acetoin (60%), ethanol (63%) and butanol (16%) production and reduced lactate (-50%) formation by the mutant compared to the wild type. These findings are in agreement with the proposed regulatory function of butyryl phosphate as opposed to acetyl phosphate in the metabolic switch of solventogenic clostridia.
authors.affiliation: Bioprocess Engineering Group, Wageningen University and Research Centre, Bomenweg 2, 6703 HD Wageningen, the Netherlands. wouter.kuit@gmail.com
authors.forename: Wouter
authors.initials: W
authors.lastname: Kuit
authors.forename: Nigel P
authors.initials: NP
authors.lastname: Minton
authors.forename: Ana M
authors.initials: AM
authors.lastname: López-Contreras
authors.forename: Gerrit
authors.initials: G
authors.lastname: Eggink
mesh_terms: D000084:Acetate Kinase / Q000235:genetics* / Q000378:metabolism*; D019342:Acetic Acid / Q000378:metabolism*; D000093:Acetoin / Q000378:metabolism; D000440:Butanols / Q000378:metabolism; D002087:Butyrates / Q000378:metabolism; D046969:Clostridium acetobutylicum / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism; D003470:Culture Media / Q000737:chemistry; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation; D055786:Gene Knockout Techniques
chemical_list: D000440:Butanols; D002087:Butyrates; D003470:Culture Media; D000431:Ethanol; D000093:Acetoin; D000084:Acetate Kinase; D019342:Acetic Acid