title: Product Diversity Linked to Substrate Usage in Chain Elongation by Mixed-Culture Fermentation.
abstract: Acetate and ethanol can be converted to caproic acid by microorganisms through reverse β-oxidation. There is limited insight into the versatility of chain elongation in view of different starting substrates, including even- and odd-carbon carboxylates and alcohols other than ethanol. Thermodynamic analyses show that most elongation pathways are energetically feasible. Through incubations of microbial communities with different substrate-pair combinations, we established that ethanol and propanol were both highly suitable for chain elongation. As an electron acceptor, acetate, propionate, and butyrate readily elongated with ethanol, whereas an adaptation period was necessary for formate. Isobutyrate and longer-chained fatty acids above butyrate were not elongated. The microbial communities converged, and consistent enrichment of Clostridium spp. was observed, independent of the supplied alcohol or carboxylate, with a strain related to Clostridium kluyveri dominating the enrichments. Community analysis also showed phylotypes related to Bacteroidaceae and Microbacteriaceae families in all tests that are capable of converting the base substrates to useful intermediates. These organisms were mainly enriched with methanol or formate. Our overall conclusion is thus that multiple substrates can be used for chain elongation and that this process is carried out by highly similar organisms for direct chain elongation irrespective of the substrate.
authors.affiliation: Center for Microbial Ecology and Technology, Ghent University , Coupure Links 653, 9000 Ghent, Belgium.
authors.forename: Marta
authors.initials: M
authors.lastname: Coma
authors.affiliation: Center for Microbial Ecology and Technology, Ghent University , Coupure Links 653, 9000 Ghent, Belgium.
authors.forename: Ramiro
authors.initials: R
authors.lastname: Vilchez-Vargas
authors.affiliation: Center for Microbial Ecology and Technology, Ghent University , Coupure Links 653, 9000 Ghent, Belgium.
authors.forename: Hugo
authors.initials: H
authors.lastname: Roume
authors.affiliation: Microbial Interactions and Processes Group, Department of Molecular Infection Biology, Helmholtz Centre for Infection Research , Inhoffenstraße 7, D-38124 Braunschweig, Germany.
authors.forename: Ruy
authors.initials: R
authors.lastname: Jauregui
authors.affiliation: Microbial Interactions and Processes Group, Department of Molecular Infection Biology, Helmholtz Centre for Infection Research , Inhoffenstraße 7, D-38124 Braunschweig, Germany.
authors.forename: Dietmar H
authors.initials: DH
authors.lastname: Pieper
authors.affiliation: Center for Microbial Ecology and Technology, Ghent University , Coupure Links 653, 9000 Ghent, Belgium.
authors.forename: Korneel
authors.initials: K
authors.lastname: Rabaey
mesh_terms: D000085:Acetates / Q000378:metabolism; D002087:Butyrates / Q000378:metabolism; D003013:Clostridium / Q000378:metabolism; D000431:Ethanol / Q000737:chemistry*; D005285:Fermentation
chemical_list: D000085:Acetates; D002087:Butyrates; D000431:Ethanol