Long-Term Incubation Reveals Methanogenic Biodegradation of C5 and C6 iso-Alkanes in Oil Sands Tailings.

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...