Ancient Asgard archaea may have used oxygen long before it was abundant

A genomic survey of marine sediments found genes linked to oxygen use in Asgard archaea, including Heimdallarchaeia, suggesting these microbes may have tolerated or used oxygen earlier than previously thought.

Researchers report that Asgard archaea carry genes linked to oxygen use, based on a large genomic survey of marine sediments. The study, published Feb. 18 in Nature, analyzed about 15 terabytes of environmental DNA and reconstructed more than 13,000 microbial genomes. Asgard archaea were first identified in 2015 and are regarded as the closest microbial relatives of eukaryotes. Scientists have debated how an archaeal host and an oxygen-using bacterium could have come together to give rise to complex cells. Key findings: - The team recovered hundreds of Asgard genetic sequences from samples collected in the Bohai Sea and the Guaymas Basin. - The researchers analyzed roughly 15 terabytes of environmental DNA and reconstructed more than 13,000 microbial genomes. - Many Heimdallarchaeia genomes include genes associated with electron transport and oxygen-based energy generation, plus enzymes that manage reactive oxygen byproducts. - Some Asgards most closely related to eukaryotes were found in oxygenated environments such as shallow coastal sediments and the water column, while many other Asgards have been observed in low-oxygen settings. - The study used AlphaFold2 to predict protein structures and strengthen the interpretation that the detected genes could function in oxygen handling. Summary: The study suggests that the archaeal lineage related to eukaryotes may have carried oxygen-handling pathways before atmospheric oxygen was widespread, which could make models of eukaryote origins easier to picture. Undetermined at this time.