The hydrogen hypothesis is a model proposed by William F. Martin and Miklós Müller in 1998 that describes a possible way in which the mitochondrion arose as an endosymbiont within a prokaryotic host in the archaea, giving rise to a symbiotic association of two cells from which the first eukaryotic cell could have arisen (symbiogenesis).
Hydrogenosomes are anaerobic mitochondria that produce ATP by, as a rule, converting pyruvate into hydrogen, carbon dioxide and acetate.
The hypothesis provides a straightforward explanation for the observation that eukaryotes are genetic chimeras with genes of archaeal and eubacterial ancestry.
In the 15 years following the publication of the hydrogen hypothesis, this specific prediction has been tested many times and found to be in agreement with observation.
[1][2][3][4][5] In 2015, the discovery and placement of the Lokiarchaeota (an archaeal lineage possessing an expanded genetic repertoire including genes involved in membrane remodeling and actin cytoskeletal structure) as the sister group to eukaryotes called into question particular tenets of the hydrogen hypothesis, as Lokiarchaeota appear to lack methanogenesis.