by Cliff Bueno de Mesquita
The microbe of this month is the phylum Verstraetearchaeota. Verstraetearchaeota is in the domain Archaea, one of the three domains of life along with the Bacteria and Eukarya. Archaea can be identified with the commonly used 16S gene, although they are often overlooked as 16S studies often focus only on the Bacteria. One of the most important biogeochemical cycles that is dominated by archaea is the methane cycle. Methane is produced by archaea in a process known as methanogenesis which occurs during the decomposition of organic matter in anaerobic (low oxygen) environments. Verstraetearchaeota, along with Euryarchaeota and Bathyarchaeota are the three phyla that contain organisms performing methanogenesis. However, the Verstraetearchaeota were only recently described in 2016 (Vanwonterghem et al., 2016)!
Methane (CH4) is a greenhouse gas with a global warming potential 25-35X that of CO2 over a 100-year time span. Methane is produced naturally by methanogenesis in anaerobic environments such as wetlands. It is also produced in the earth’s crust in fossil fuel deposits (i.e. natural gas) and in the guts of some animals known as ruminants (e.g. cows). It is also produced during coal combustion. Human activities and industries have vastly increased the amount of methane released to the atmosphere via landfills and the fossil fuel and animal agriculture industries. Globally, anthropogenic sources contribute about 430 teragrams (1012 grams) of methane while natural sources produce only 215 Tg of methane (Schlesinger & Bernhardt, 2013). This is not surprising when you think about there being over a billion cows on Earth today and they’re all belching methane! And this is one reason, among others, that anyone reading this post should seriously consider going vegan (like two members of our lab!) or at least cut beef and dairy consumption out of their diets! Atmospheric methane levels have risen from around 625 ppb (parts per billion) in the 1700s to 1760 ppb in 2010 (Figure 1). It’s also notable that atmospheric methane levels have never risen above 800 ppb in the last 800,000 years (Schlesinger & Bernhardt, 2013)!
Anyways, back to the Verstraetearchaeota. This phylum is cool because its members can perform methylotrophic methanogenesis (production of methane from methyl-containing compounds like methanol), which is one of the three main methanogenesis pathways. The other two are known as acetoclastic methanogenesis (splits acetate into methane and carbon dioxide) and hydrogenotrophic methanogenesis (producing methane and water from carbon dioxide and hydrogen). Acetoclastic and hydrogenotrophic methanogenesis were thought to produce most of the world’s methane, but recently methylotrophic methanogenesis has been shown to be a primary source of methane in some ecosystems, most notably salty environments such as ocean sediments, salt ponds, and coastal wetlands (Conrad, 2020; Zhuang et al., 2016, 2018). Genomic studies have confirmed the presence of genes in Verstraetearchaeota that perform methylotrophic methanogenesis (Vanwonterghem et al., 2016).
Conrad, R. (2020). Importance of hydrogenotrophic, aceticlastic and methylotrophic methanogenesis for methane production in terrestrial, aquatic and other anoxic environments: A mini review. Pedosphere, 30(1), 25–39. https://doi.org/10.1016/S1002-0160(18)60052-9
Schlesinger, W. H., & Bernhardt, E. S. (2013). Biogeochemistry: An analysis of global change (3rd Edition). Academic Press.
Vanwonterghem, I., Evans, P. N., Parks, D. H., Jensen, P. D., Woodcroft, B. J., Hugenholtz, P., & Tyson, G. W. (2016). Methylotrophic methanogenesis discovered in the archaeal phylum Verstraetearchaeota. Nature Microbiology, 1(12), 1–9. https://doi.org/10.1038/nmicrobiol.2016.170
Zhuang, G.-C., Elling, F. J., Nigro, L. M., Samarkin, V., Joye, S. B., Teske, A., & Hinrichs, K.-U. (2016). Multiple evidence for methylotrophic methanogenesis as the dominant methanogenic pathway in hypersaline sediments from the Orca Basin, Gulf of Mexico. Geochimica et Cosmochimica Acta, 187, 1–20. https://doi.org/10.1016/j.gca.2016.05.005
Zhuang, G.-C., Heuer, V. B., Lazar, C. S., Goldhammer, T., Wendt, J., Samarkin, V. A., Elvert, M., Teske, A. P., Joye, S. B., & Hinrichs, K.-U. (2018). Relative importance of methylotrophic methanogenesis in sediments of the Western Mediterranean Sea. Geochimica et Cosmochimica Acta, 224, 171–186. https://doi.org/10.1016/j.gca.2017.12.024
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