title: Long-Term Incubation Reveals Methanogenic Biodegradation of C5 and C6 iso-Alkanes in Oil Sands Tailings.
abstract: iso-Alkanes are major components of petroleum and have been considered recalcitrant to biodegradation under methanogenic conditions. However, indigenous microbes in oil sands tailings ponds exposed to solvents rich in 2-methylbutane, 2-methylpentane, 3-methylpentane, n-pentane, and n-hexane produce methane in situ. We incubated defined mixtures of iso- or n-alkanes with mature fine tailings from two tailings ponds of different ages historically exposed to different solvents: one, ~10 years old, receiving C5-C6 paraffins and the other, ~35 years old, receiving naphtha. A lengthy incubation (>6 years) revealed iso-alkane biodegradation after lag phases of 900-1800 and ~280 days, respectively, before the onset of methanogenesis, although lag phases were shorter with n-alkanes (~650-1675 and ~170 days, respectively). 2-Methylpentane and both n-alkanes were completely depleted during ~2400 days of incubation, whereas 2-methylbutane and 3-methylpentane were partially depleted only during active degradation of 2-methylpentane, suggesting co-metabolism. In both cases, pyrotag sequencing of 16S rRNA genes showed codominance of Peptococcaceae with acetoclastic (Methanosaeta) and hydrogenotrophic (Methanoregula and Methanolinea) methanogens. These observations are important for predicting long-term greenhouse-gas emissions from oil sands tailings ponds and extend the known range of hydrocarbons susceptible to methanogenic biodegradation in petroleum-impacted anaerobic environments.
authors.affiliation: Department of Renewable Resources, University of Alberta , Edmonton, AB T6G 2G7, Canada.
authors.forename: Tariq
authors.initials: T
authors.lastname: Siddique
authors.affiliation: Department of Renewable Resources, University of Alberta , Edmonton, AB T6G 2G7, Canada.
authors.forename: Mohd Faidz
authors.initials: MF
authors.lastname: Mohamad Shahimin
authors.affiliation: Department of Renewable Resources, University of Alberta , Edmonton, AB T6G 2G7, Canada.
authors.forename: Saima
authors.initials: S
authors.lastname: Zamir
authors.affiliation: Department of Biological Sciences, University of Alberta , Edmonton, AB T6G 2E9, Canada.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Semple
authors.affiliation: Department of Biological Sciences, University of Alberta , Edmonton, AB T6G 2E9, Canada.
authors.forename: Carmen
authors.initials: C
authors.lastname: Li
authors.affiliation: Department of Biological Sciences, University of Alberta , Edmonton, AB T6G 2E9, Canada.
authors.forename: Julia M
authors.initials: JM
authors.lastname: Foght
mesh_terms: D000473:Alkanes / Q000737:chemistry / Q000378:metabolism*; D001673:Biodegradation, Environmental; D006586:Hexanes / Q000378:metabolism; D008697:Methane / Q000378:metabolism; D017019:Methanosarcinaceae / Q000235:genetics / Q000378:metabolism; D059013:Microbial Consortia / Q000235:genetics / Q000502:physiology*; D061329:Oil and Gas Fields / Q000382:microbiology*; D010420:Pentanes / Q000378:metabolism; D010459:Peptococcaceae / Q000235:genetics / Q000378:metabolism; D010578:Petroleum / Q000378:metabolism; D012336:RNA, Ribosomal, 16S / Q000235:genetics
chemical_list: D000473:Alkanes; D006586:Hexanes; D010420:Pentanes; D010578:Petroleum; D012336:RNA, Ribosomal, 16S; C026385:n-hexane; C094659:2-methylpentane; C033353:pentane; C004544:naphtha; D008697:Methane; C087331:3-methylpentane; C067038:isopentane