Souradip Mallick, National Institute of Technology, Rourkela
The anaerobic oxidation of methane (AOM) plays an important role in the emission of greenhouse gas and represents a primary production pathway that helps in the mobilization of carbon, sulfur, and nitrogen on a global scale. AOM at marine methane seeps has been estimated to consume more or less about 80% of subsurface methane. At the seafloor methane leaks slowly and moves upwards toward the open ocean and the microbial communities consume those majorities of methane before it escapes into the atmosphere.
The study published in Proceedings of the National Academy of Sciences states that methane-eating microbes are present within the carbonate rocks. The microbes present within the carbonate rocks is acting like methane biofilter by consuming all of the methane before it escapes the ocean. Seafloor carbonate rocks are unusual chimney-like structures of about 12 to 60 inches in height and are found in groups along the seafloor. The carbonate rocks are porous which help the methane-consuming microbes to live in higher densities. The microbes living in the carbonate rocks consume methane 50 times faster than microbes in the sediment. The microbes transformed methane into bicarbonate, which can precipitate out of the seawater as carbonate rock.
In order to understand the exact mechanisms of microbes, an experiment was conducted by maintaining the carbonates into high-pressure reactors. The methane was isotopically labeled with Carbon-14 or Deuterium (H-2) in order to track methane production and consumption. Also, the structure, electrical conductivity, fluid flow, and dense microbial community of the different carbonate rocks were studied.
Though rock-hosted habitat varies from the laboratory set up it is widely accepted that microbial communities play a vital role in methane consumption in marine environments. After studying the geological ocean floor and continental-scale it has been concluded that endolithic AOM is the most common phenomenon. The rate of methane consumption by the microbial communities within the carbonate rocks often exceeds those associated with sediments. These carbonate rocks are chimney-like structures present on the seafloor and it is porous that helps the microbes to be present within those rock structures. Thus when the methane leaks from the seafloor then the microbes present within the carbonate rock consume it and prevent it from escaping into the atmosphere. The several factors, including cell abundance, mineral composition, kinetic parameters, and the presence of specific microbial lineages were studied to understand the mechanism of methane consumption and also to understand the elevated endolithic AOM rates. The carbonate rocks at methane seeps may constitute a major marine methane sink. Since methane is a strong greenhouse gas, thus it can control the temperature of the Earth. The microbes consuming methane prevents global warming and hence the temperature of the Earth can also be controlled. Thus it can be concluded that methane-eating microbes can regulate the temperature of the Earth and maintain the global climate.
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Source: Marlow, J. J., Hoer, D., Jungbluth, S. P., Reynard, L. M., Gartman, A., Chavez, M. S., & Girguis, P. R. (2021). Carbonate-hosted microbial communities are prolific and pervasive methane oxidizers at geologically diverse marine methane seep sites. Proceedings of the National Academy of Sciences, 118(25) https://doi.org/10.1073/pnas.2006857118.
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