title: Co-occurrence of methanogenesis and N2 fixation in oil sands tailings.
abstract: Oil sands tailings ponds in northern Alberta, Canada have been producing biogenic gases via microbial metabolism of hydrocarbons for decades. Persistent methanogenic activity in tailings ponds without any known replenishment of nutrients such as fixed nitrogen (N) persuaded us to investigate whether N2 fixation or polyacrylamide (PAM; used as a tailings flocculant) could serve as N sources. Cultures comprising mature fine tailings (MFT) plus methanogenic medium supplemented with or deficient in fixed N were incubated under an N2 headspace. Some cultures were further amended with citrate, which is used in oil sands processing, as a relevant carbon source, and/or with PAM. After an initial delay, N-deficient cultures with or without PAM produced methane (CH4) at the same rate as N-containing cultures, indicating a mechanism of overcoming apparent N-deficiency. Acetylene reduction and (15)N2 incorporation in all N-deficient cultures (with or without PAM) suggested active N2 fixation concurrently with methanogenesis but inability to use PAM as a N source. 16S rRNA gene pyrosequencing revealed little difference between archaeal populations regardless of N content. However, bacterial sequences in N-deficient cultures showed enrichment of Hyphomicrobiaceae and Clostridium members that might contain N2-fixing species. The results are important in understanding long-term production of biogenic greenhouse gases in oil sands tailings.
authors.affiliation: Department of Renewable Resources, University of Alberta, Edmonton, AB T6G 2G7, Canada.
authors.forename: C E Victoria
authors.initials: CEV
authors.lastname: Collins
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada.
authors.forename: Julia M
authors.initials: JM
authors.lastname: Foght
authors.affiliation: Department of Renewable Resources, University of Alberta, Edmonton, AB T6G 2G7, Canada. Electronic address: tariq.siddique@ualberta.ca.
authors.forename: Tariq
authors.initials: T
authors.lastname: Siddique
mesh_terms: D000416:Alberta; D001673:Biodegradation, Environmental; D004784:Environmental Monitoring; D000074382:Greenhouse Gases / Q000378:metabolism*; D008772:Methylococcaceae / Q000378:metabolism*; D009586:Nitrogen Fixation / Q000502:physiology*; D061329:Oil and Gas Fields; D061005:Ponds / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000378:metabolism*
chemical_list: D000074382:Greenhouse Gases; D014874:Water Pollutants, Chemical
keywords: 16S rRNA gene pyrosequencing; Citrate metabolism; Methanogenesis; N(2) fixation; Oil sands tailings