Methanogenesis in subglacial environments – biosignatures of extraterrestrial life
CfG staff: Mitchell, Andrew.
Key collaborators: Montana State University, Dr Mark Skidmore and Dr. Eric Boyd. Queens University, Canada: Dr. Melissa Lafrenière.
Evidence of liquid water in the basal zones of Polar ice sheets and the discovery of over 140 subglacial lakes in Antarctica suggests that these environments may not be the lifeless deserts they were once thought. Indeed, subglacial sediments, ice, and water have been shown to harbor a diversity of microorganisms. While the majority of organisms found in subglacial and polar environments have been those which live by respiring oxygen, it is quite likely that there is no oxygen in many subglacial environments, resulting from a lack of connectivity to the outside atmosphere, which suggests that many microorganisms which can live in oxygen free environments may be present. There is also the exciting possibility that in oxygen-free icy extra-terrestrial environments, including the icy Martian Poles, and the icy moons of Jupiter, similar forms of microbial life may also exist.
Methanogens are a major group of microorganisms which live and survive in oxygen-free environments, because instead of oxygen, they use carbon and hydrogen to respire, and produce methane, the well-known greenhouse gas, as a by-product of their activity. However, because of scientific limitations in detecting methanogens, we have until now known very little about the occurrence, diversity, abundance, and activity of methanogens in subglacial environments, despite the implications such data would have for our ability to identify biosignatures of life-sustaining processes on other planets.
In this NASA funded project, we for the first, present genetic, biochemical and geochemical evidence indicative of an active population of methanogens associated with subglacial sediments from Robertson Glacier (RG), Canadian Rockies. Porewater CH4 was quantified in two subglacial sediment cores at concentrations of 16 and 29 ppmv. Coenzyme M (CoM), a metabolic biomarker for methanogens, was detected at a concentration of 1.3 nmol g sediment−1 corresponding to ∼3 × 103 active cells g sediment−1. Genetic characterization of communities associated with subglacial sediments indicated the presence of several archaeal 16S rRNA and methyl CoM reductase subunit A (mcrA) gene phylotypes, all of which were affiliated with the euryarchaeal order Methanosarcinales. Further, CH4 was produced at 9–51 fmol g dry weight sediment−1 h−1 in enrichment cultures of RG sediments incubated at 4°C. Collectively, these results demonstrate active subglacial methanogenesis for the first time.
These results highlight the importance of anaerobic microbial processes in subglacial environments and suggest that they may have an important and previously overlooked role in global biogeochemical cycles both (i) at present, given the recent estimates of a subglacial biome of 104 to 106 cells km3, and (ii) at times in the past, especially when ice cover on the planet was greater than at present such as during the Quaternary glaciations and the long periods of pervasive low latitude glaciation (‘Snowball Earth’) in the Late Proterozoic.
Key publications:
Boyd, ES.; Skidmore, M.; Mitchell, AC.; Bakermans, C.; Peters, JW. (2010) Methanogenesis in subglacial sediments. Environmental Microbiology Reports. DOI: 10.1111/j.1758-2229.2010.00162.
Boyd, ES, Lange, RK, Mitchell, AC, Havig, JR, Hamilton, TR, Lafrenie, MJ, Shock, EL, Peters, JW, Skidmore, ML (2011) Diversity, Abundance, and Potential Activity of Nitrifying and Nitrate-Reducing Microbial Assemblages in a Subglacial Ecosystem. Applied and Environmental Microbiology, 77, 4778–4787.
Mitchell, AC, Lafrenière, MJ, Skidmore, ML, Boyd, ES (2013) Influence of bedrock mineral composition on microbial diversity in a subglacial environment. Geology 10.1130/g34194.1.
Funding: NASA EPSCoR Space Grant (2008-2009). Methanogenesis in subglacial environments – Implications for Quaternary deglaciation. PI: AC Mitchell.