Title: Methanogenesis from Methanol at Low Temperatures by a Novel Psychrophilic Methanogen, “ <i>Methanolobus psychrophilus</i> ” sp. nov., Prevalent in Zoige Wetland of the Tibetan Plateau
Abstract: ABSTRACT The Zoige wetland of the Tibetan plateau is at permanent low temperatures and is a methane emission heartland of the plateau; however, cold-adaptive methanogens in the soil are poorly understood. In this study, a variety of methanogenic enrichments at 15°C and 30°C were obtained from the wetland soil. It was demonstrated that hydrogenotrophic methanogenesis was the most efficient type at 30°C, while methanol supported the highest methanogenesis rate at 15°C. Moreover, methanol was the only substrate to produce methane more efficiently at 15°C than at 30°C. A novel psychrophilic methanogen, strain R15, was isolated from the methanol enrichment at 15°C. Phylogenetic analysis placed strain R15 within the genus Methanolobus , loosely clustered with Methanolobus taylorii (96.7% 16S rRNA similarity). R15 produced methane from methanol, trimethylamine, and methyl sulfide and differed from other Methanolobus species by growing and producing methane optimally at 18°C (specific growth rate of 0.063 ± 0.001 h −1 ) and even at 0°C. Based on these characteristics, R15 was proposed to be a new species and named “ Methanolobus psychrophilus ” sp. nov. The K m and V max of R15 for methanol conversion were determined to be 87.5 ± 0.4 μM and 0.39 ± 0.04 mM h −1 at 18°C, respectively, indicating a high affinity and conversion efficiency for methanol. The proportion of R15 in the soil was determined by quantitative PCR, and it accounted for 17.2% ± 2.1% of the total archaea, enumerated as 10 7 per gram of soil; the proportion was increased to 42.4% ± 2.3% in the methanol enrichment at 15°C. This study suggests that the psychrophilic methanogens in the Zoige wetland are likely to be methylotrophic and to play a role in methane emission of the wetland.