Microbes (from canada), (non-biological) methane, and implication for life on Mars
A group of American and Canadian scientists (primarily based at McGill) published a paper recently in the journal of the International Society of Microbial Ecology (ISME) that offers insight into the possibility of life on Mars. The paper is entitled “Microbial characterization of a subzero, hypersaline, methane seep in the Canadian High Arctic”, and you can read the abstract here. The researchers found a spring that is below freezing, but liquid due to the high salinity (24%, for comparison the ocean is about 3.5%). They found methane seeping out of this spring. Methane seeps like this are extremely rare in the terrestrial world, but have been relatively well studied in the ocean.
In their words : “Here we report on the first microbiological and geochemical characterization of the only known terrestrial methane seep in a cryo-environment on Earth in the form of the hypersaline subzero spring, which arises through thick extensive permafrost in an area with an average annual air temperature of -15 °C and with air temperatures below -40 °C common during the winter months. This site provides a model of how a methane seem can form in a hypersaline cryo-environment and can support a viable microbial community where methane itself may behave as an energy and carbon source for sustaining anaerobic oxidation of methane.”
Typically when methane is being produced it is either through biological or geological processes. The recent discovery of methane plumes on Mars was exciting for this reason… it implied that either there was some unknown geologic activity on Mars (it is assumed to be inactive below the surface) or there was a community of microbes producing methane on Mars. That is a maybe bit of an oversimplification, but I am not a planetary geologist. Anyhow, folks in the astrobiology world have been proposing that we might be looking at evidence of methane producing microbes (methanogens) on Mars. Other astrobiologists disagree with this contention because while there is water on Mars, it is very saline… so saline that some think life is impossible (technically it is the water activity and not the salinity that make the planet so inhospitable, but sanity is a good way to thing about it). Two of the things that make this recent paper so cool is that it finds a location on Earth that could be analogous to the hyper-saline methane seeps on Mars, and that it provides evidence for an alternate scenario to methanogens being what we should expect to find if there is life on Mars.
The methane in the spring in this study is not likely to be produced biologically. The difference between the carbon isotopes in the methane and the carbon dioxide indicate that it is not biological in origin (organisms preferentially use certain isotopes, and therefore leave an isotopic “signature” in the carbon that indicates when methane was formed biologically). However, the scientists found a community of organisms living in this ultra-extreme environment. The organisms they found (both bacteria and archaea) seem to be using the methane as energy and a carbon source, rather than producing it. These metabolisms might be coupled with sulfur oxidation like it is at deep-sea hydrothermal vents and methane seeps. Microbes that “eat” methane are interesting from a climate change point of view because methane is one of the major greenhouse gasses aside from carbon dioxide.
The archaea found in this study are related to those found in hypersaline deep-sea methane seep sediments, while the bacteria seemed to be related to those found in terrestrial Arctic and Antarctic environments. Another cool thing about this paper is that the authors were able to culture 8 different types of bacteria from these samples. This is exciting because more than 99% of all bacteria have not yet been cultured, and scientists can learn a great deal more about an organims once they are able to grow it in a lab.
The authors also suggest that this site might be a location where ancient DNA could be preserved. This is because high salt tends to keep DNA from degrading over long periods of time.
In summary this study is very cool because…
- It characterizes life from an extreme environment that has not been studied previously (terrestrial hypersaline methane seep).
- It offers insight into what type of life we might expect to find in similar environments on Mars (not necessarily what we expected).
- The authors were able to extract DNA from difficult samples, and was able to culture organisms from this extreme environment.
- It suggests that this site might offer more cool discoveries in the future (like ancient DNA).
- It draws a connection between the microbial ecology of the hot deep sea and the frigid Arctic.