title: The FlxABCD-HdrABC proteins correspond to a novel NADH dehydrogenase/heterodisulfide reductase widespread in anaerobic bacteria and involved in ethanol metabolism in Desulfovibrio vulgaris Hildenborough.
abstract: Flavin-based electron bifurcation (FBEB) is an important mechanism for the energy metabolism of anaerobes. A new family of NADH dehydrogenases, the flavin oxidoreductase (FlxABCD, previously called FloxABCD), was proposed to perform FBEB in sulphate-reducing organisms coupled with heterodisulfide reductase (HdrABC). We found that the hdrABC-flxABCD gene cluster is widespread among anaerobic bacteria, pointing to a general and important role in their bioenergetics. In this work, we studied FlxABCD of Desulfovibrio vulgaris Hildenborough. The hdr-flx genes are part of the same transcriptional unit and are increased in transcription during growth in ethanol-sulfate, and to a less extent during pyruvate fermentation. Two mutant strains were generated: one where expression of the hdr-flx genes was interrupted and another lacking the flxA gene. Both strains were unable to grow with ethanol-sulfate, whereas growth was restored in a flxA-complemented strain. The mutant strains also produced very reduced amounts of ethanol compared with the wild type during pyruvate fermentation. Our results show that in D. vulgaris, the FlxABCD-HdrABC proteins are essential for NADH oxidation during growth on ethanol, probably involving a FBEB mechanism that leads to reduction of ferredoxin and the small protein DsrC, while in fermentation they operate in reverse, reducing NAD(+) for ethanol production.
authors.affiliation: Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Oeiras, 2780-157, Portugal.
authors.forename: Ana Raquel
authors.initials: AR
authors.lastname: Ramos
authors.affiliation: Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Oeiras, 2780-157, Portugal.
authors.forename: Fabian
authors.initials: F
authors.lastname: Grein
authors.affiliation: Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Oeiras, 2780-157, Portugal.
authors.forename: Gonçalo P
authors.initials: GP
authors.lastname: Oliveira
authors.affiliation: Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Oeiras, 2780-157, Portugal.
authors.forename: Sofia S
authors.initials: SS
authors.lastname: Venceslau
authors.affiliation: Biochemistry Department, University of Missouri, Columbia, MO, USA.|ENIGMA (Ecosystems and Networks Integrated with Genes and Molecular Assemblies), Berkeley, CA, USA.
authors.forename: Kimberly L
authors.initials: KL
authors.lastname: Keller
authors.affiliation: Biochemistry Department, University of Missouri, Columbia, MO, USA.|ENIGMA (Ecosystems and Networks Integrated with Genes and Molecular Assemblies), Berkeley, CA, USA.
authors.forename: Judy D
authors.initials: JD
authors.lastname: Wall
authors.affiliation: Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Oeiras, 2780-157, Portugal.
authors.forename: Inês A C
authors.identifier: http://orcid.org/0000-0003-3283-4520
authors.initials: IA
authors.lastname: Pereira
mesh_terms: D016969:Desulfovibrio vulgaris / Q000201:enzymology* / Q000235:genetics; D004583:Electrons; D004734:Energy Metabolism / Q000235:genetics / Q000502:physiology; D000431:Ethanol / Q000378:metabolism*; D038181:FMN Reductase / Q000378:metabolism*; D005288:Ferredoxins / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D009245:NADH Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D019289:Pyruvic Acid / Q000378:metabolism; D013431:Sulfates / Q000378:metabolism
chemical_list: D005288:Ferredoxins; D013431:Sulfates; D009243:NAD; D000431:Ethanol; D019289:Pyruvic Acid; D010088:Oxidoreductases; C087171:heterodisulfide reductase; D038181:FMN Reductase; D009245:NADH Dehydrogenase