Promethearchaeum

Promethearchaeum is a genus of archaea discovered from the deep-sea sediments of the Pacific Ocean at the coast of Japan. Described in 2020 as a single species, "Candidatus Prometheoarchaeum syntrophicum", it took 12 years for the archeal samples to be successfully cultured (grown in laboratory). Named after the Greek mythological god, Prometheus, the correct scientific name became Promethearchaeum (dropping the "o" according to the rules of the International Code of Nomenclature of Prokaryotes) and the species, Promethearchaeum syntrophicum.

Discovered by a team of Japanese biologists led by Hiroyuki Imachi and Masaru Konishi Nobu, the archaea were found to constitute a distinct group from other recognised groups so that a new kingdom Promethearchaeati was created. Another archaeon "Ca. Lokiarchaeum", which was described in 2015 and originally assigned to the phylum "Lokiarchaeota", was reassigned to the kingdom Promethearchaeati alongside P. syntrophicum. P. syntrophicum became the first successfully laboratory-cultured Asgard archaea.

For its simple cellular structure and function, and dependency on other organisms by symbiosis, P. syntrophicum is described (by the discoverer Hiroyuki Imachi) as "the least complete living thing ever found." With its symbiotic lifestyle with other archaea and bacteria, P. syntrophicum is taken as an example of syntrophic process of symbiogenesis in the early stages of eukaryogenesis and evolutionary root of eukaryotes. The discovery was lauded as "moon landing for microbial ecology."