Anaerobic methane metabolism is solely conducted by Archaea, through a unique pathway with the key enzyme methyl-coenzyme M reductase (MCR) for methane activation/production. Recently, the MCR-based pathway was also found in propane and n-butane oxidation and related genes was also found actively expressed in natural environment. In this study, we then made a global metagenome-based survey of mcr containing archaeal genomes. Methane metabolizing archaea were found present in various environments such as lakes, hot springs, marine environments. In addition to the Euryarchaeota and Bathyarchaeota, MAGs (metagenome assembled genomes) harbouring mcr genes were found belonging to diverse archaeal lineages including such as the Korarchaeota, Hadesarchaeota, Verstraetearchaeota, Nezhaarchaeota (a new archaeal group named in this study using the Chinese mythological character "Nezha", who flies on the wind and fire wheels), far more diversified than ever recognized. The finding of anaerobic alkane metabolism in diverse archaeal phyla further indicates it as the most ancient biochemical process in the Archaea domain and even one of the earliest life attributes. Intriguingly, this study also found that anaerobic methane oxidation with sulfate reduction may co-occur within a single cell, although these two processes have only been found conducted by different cells co-ordinately at modern marine environment. It remains elusive why these two processes need to be separated in different cells.
It needs to be pointed that the metabolic functions of the MAGs need further verification, essentially by strain enrichment and cultivation. The collaborating team at Shanghai and Bremen are setting their goals to bring these alkane metabolizing bugs to the laboratory for further investigation.
Cartoon showing the expanding of archaea involved in alkane metabolism at a sequencing era. A Chinese mythological character "Nezha" who flies on the wind and fire wheels is shown, a newly found archaeal group was given the name of this Chinese beknown mythical figure---“Nezhaarchaeota”
McrA Phylogenetic tree. This key gene for anaerobic methane metabolism is found widespread in a range of different archaeal phyla, far more diversified than previously recognized.
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