title: Methanogenic paraffin degradation proceeds via alkane addition to fumarate by 'Smithella' spp. mediated by a syntrophic coupling with hydrogenotrophic methanogens.
abstract: Anaerobic microbial biodegradation of recalcitrant, water-insoluble substrates, such as paraffins, presents unique metabolic challenges. To elucidate this process, a methanogenic consortium capable of mineralizing long-chain n-paraffins (C28 -C50 ) was enriched from San Diego Bay sediment. Analysis of 16S rRNA genes indicated the dominance of Syntrophobacterales (43%) and Methanomicrobiales (26%). Metagenomic sequencing allowed draft genome assembly of dominant uncultivated community members belonging to the bacterial genus Smithella and the archaeal genera Methanoculleus and Methanosaeta. Five contigs encoding homologs of the catalytic subunit of alkylsuccinate synthase (assA) were detected. Additionally, mRNA transcripts for these genes, including a homolog binned within the 'Smithella' sp. SDB genome scaffold, were detected via RT-PCR, implying that paraffins are activated via 'fumarate addition'. Metabolic reconstruction and comparison with genome scaffolds of uncultivated n-alkane degrading 'Smithella' spp. are consistent with the hypothesis that syntrophically growing 'Smithella' spp. may achieve reverse electron transfer by coupling the reoxidation of ETFred to a membrane-bound FeS oxidoreductase functioning as an ETF:menaquinone oxidoreductase. Subsequent electron transfer could proceed via a periplasmic formate dehydrogenase and/or hydrogenase, allowing energetic coupling to hydrogenotrophic methanogens such as Methanoculleus. Ultimately, these data provide fundamental insight into the energy conservation mechanisms that dictate interspecies interactions salient to methanogenic alkane mineralization.
authors.affiliation: Department of Microbiology and Plant Biology, University of Oklahoma, George Lynn Cross Hall, 770 Van Vleet Oval, Norman, OK, 73019, USA.
authors.forename: Boris
authors.initials: B
authors.lastname: Wawrik
authors.affiliation: Department of Microbiology and Plant Biology, University of Oklahoma, George Lynn Cross Hall, 770 Van Vleet Oval, Norman, OK, 73019, USA.|Institute for Energy and the Environment, University of Oklahoma, 100 East Boyd Street, Norman, OK, 73019, USA.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Marks
authors.affiliation: Department of Microbiology and Plant Biology, University of Oklahoma, George Lynn Cross Hall, 770 Van Vleet Oval, Norman, OK, 73019, USA.|Institute for Energy and the Environment, University of Oklahoma, 100 East Boyd Street, Norman, OK, 73019, USA.
authors.forename: Irene A
authors.initials: IA
authors.lastname: Davidova
authors.affiliation: Department of Microbiology and Plant Biology, University of Oklahoma, George Lynn Cross Hall, 770 Van Vleet Oval, Norman, OK, 73019, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McInerney
authors.affiliation: Department of Microbiology and Plant Biology, University of Oklahoma, George Lynn Cross Hall, 770 Van Vleet Oval, Norman, OK, 73019, USA.|Development and Alumni Relations, Oglethorpe University, 4484 Peachtree Road, NE, Atlanta, GA, 30319, USA.
authors.forename: Shane
authors.initials: S
authors.lastname: Pruitt
authors.affiliation: Department of Microbiology and Plant Biology, University of Oklahoma, George Lynn Cross Hall, 770 Van Vleet Oval, Norman, OK, 73019, USA.|Institute for Energy and the Environment, University of Oklahoma, 100 East Boyd Street, Norman, OK, 73019, USA.
authors.forename: Kathleen E
authors.initials: KE
authors.lastname: Duncan
authors.affiliation: Department of Microbiology and Plant Biology, University of Oklahoma, George Lynn Cross Hall, 770 Van Vleet Oval, Norman, OK, 73019, USA.|Institute for Energy and the Environment, University of Oklahoma, 100 East Boyd Street, Norman, OK, 73019, USA.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Suflita
authors.affiliation: Department of Microbiology and Plant Biology, University of Oklahoma, George Lynn Cross Hall, 770 Van Vleet Oval, Norman, OK, 73019, USA.
authors.forename: Amy V
authors.initials: AV
authors.lastname: Callaghan
mesh_terms: D000473:Alkanes / Q000378:metabolism*; D001673:Biodegradation, Environmental; D020564:Deltaproteobacteria / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D004734:Energy Metabolism / Q000502:physiology; D005650:Fumarates / Q000378:metabolism*; D020745:Genome, Archaeal / Q000235:genetics; D016680:Genome, Bacterial / Q000235:genetics; D056186:Metagenomics; D017018:Methanomicrobiales / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010232:Paraffin / Q000378:metabolism*; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics
chemical_list: D000473:Alkanes; D005650:Fumarates; D012336:RNA, Ribosomal, 16S; D010232:Paraffin; D010088:Oxidoreductases