The FlxABCD-HdrABC proteins correspond to a novel NADH dehydrogenase/heterodisulfide reductase widespread in anaerobic bacteria and involved in ethanol metabolism in Desulfovibrio vulgarisHildenborough

• Published in: Environmental microbiology 2015-07, Vol.17 (7), p.2288-2305
• Main Authors: Ramos, Ana Raquel, Grein, Fabian, Oliveira, Gonçalo P, Venceslau, Sofia S, Keller, Kimberly L, Wall, Judy D, Pereira, Inês A C
• Format: Article
• Language: English
• Subjects: Bacteria; Bacteriology; Desulfovibrio; Ethanol; Fermentation; Metabolism
• ISSN: 1462-2912; 1462-2920
• DOI: 10.1111/1462-2920.12689

Summary 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 vulgarisHildenborough. 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.