Exobiology and Evolutionary Biology

Methane cycling in subglacial sediments

PI: Mark Skidmore

We propose to examine biological methane production and oxidation in situ in anaerobic subglacial sediments at ambient temperatures ~ 0-1ºC. Archaeal methanogens and methanotrophs catalyze the interconversion of C1 and C2 substrates to CH4; reactions which are considered to result in free energy near the thermodynamic limit for supporting life. Data on CH4 cycling in cold environments on Earth is currently limited to permafrost and cold marine sediments. To the best of our knowledge, no data exist on the CH4 cycle in subglacial environments with the exception of the data presented here, despite the size of this biome (~ 10 million cubic km). Thus, subglacial methanogenesis could represent an important and overlooked component of the global carbon cycle. Indeed, a recent global carbon cycle modeling study notes that “the presence of Archaea and rates of methanogenesis have yet to be demonstrated in subglacial sediments”.

Our preliminary data from subglacial sediments from Robertson Glacier (RG), Canada demonstrate: 1) Subglacial sediment porewater CH4 at concentrations 10-15 times greater than present-day atmospheric concentration, 2) Archaeal GDGT lipids, 3) 16S rRNA and mcrA gene sequences that cluster phylogenetically with archaeal methanogens and archaeal methanotrophs, and 4) Coenyzme M at a concentration of 1.3 pmol per g sediment, corresponding to ~3000 archaeal methanogen and/or methanotroph cells per g sediment. Whilst none of these biochemical signatures directly reflect in situ methanogenesis, the combined data strongly point toward an active population of archaeal methanogens and perhaps methanotrophs in these sediments. Given the presence of CH4 production, a logical progression is to understand the cycling of methane in the subglacial sediments and the flux to the atmosphere.

A combination of biochemical, isotopic, and geochemical techniques will be employed to investigate the abundance and activity of archaea and bacteria involved in methane cycling in subglacial sediments collected from RG. Specifically, this research is directed at defining the activities of specific functional classes of archaeal methanogens/methanotrophs and bacterial methanotrophs in the CH4 cycle in anoxic and permanently cold (0-1ºC) sediments. The research team will utilize the youthful energy of two young investigators, PI Skidmore and NAI-post doc and Co-I Boyd in combination with experienced senior personnel, NAI director and Co-I Peters and collaborator Shock, thereby creating a truly cross-disciplinary effort that harnesses new bioanalytical tools for a cutting edge view of anaerobic subglacial processes. Graduate and undergraduate researchers are also a key component of the team and through their involvement we strive to train the next generation of (NASA) scientists.

With particular relevance to NASA, an increased awareness of the tenacity of life on Earth has fueled speculation that sub-ice extraterrestrial environments such as on Europa or Mars may also be habitable by microbes due to the availability of liquid water in these systems. The cold, anoxic sub-glacial terrestrial environment on present day Earth provides a potential model analog for these extraterrestrial systems that are also likely to have very low to no oxygen. Therefore, this proposal directly addresses the research topic 1. Planetary Conditions for Life (NRA: NNH07ZDA001N-EXOB) since “Studies of sites thought to be analogues to other planetary environments that might potentially harbor life will be considered as part of NASA’s broader interest in the search for life in the Universe.” In addition, the research is timely given the high level of interest in CH4 cycling on Mars and how it relates to the existence or past existence of life on Mars. Further, this research has implications for defining the limits for life on other icy, non-Earth based bodies.