Lokiarchaeon is hydrogen dependent

Abstract

The nature of the host that acquired the mitochondrion at the eukaryote origin is an important microbial evolutionary issue. Modern phylogenetics indicates that the host was an archaeon. The metagenome sequence of Candidatus Lokiarchaeon has identified it as being the closest relative of the host yet known. Here, we report comparative genomic evidence indicating that Lokiarchaeon is hydrogen dependent, as one theory for the eukaryote origin-the hydrogen hypothesis-predicts for the host lineage.

Peculiarities within peculiarities – dinoflagellates and their mitochondrial genomes

“…Mitochondria are two-membrane-bounded cellular 'powerhouses' that evolved, very likely, as a result of syntrophy between a Rickettsia-like a-proteobacterium and a hydrogendependent archaeon around two billions years ago (Martin & M€ uller 1998;Martin et al 2015;Wang & Wu 2015;Sousa et al 2016). Their symbiosis triggered one of the most important transitions in the history of life, namely the transformation of prokaryotes into eukaryotes (Lane & Martin 2010).…”

Symbiogenesis, gradualism, and mitochondrial energy in eukaryote origin

“…That the host should turn out to be an archaeon is precisely the prediction made by some archaeal host models for the origin of mitochondria (7,41,55,56). But in the same breath one should say that concerns have recently come to the fore about the data underlying the phylogenies of the new archaeal lineages (59), in that one of the proteins in the archaeal metagenomic data set might be eukaryotic, not archaeal (59) and might be influencing the phylogenetic signal.…”

“…Clearly, ATP export from the mitochondrion also did come into play at some point in mitochondrial evolution (49,53,54). Yet from the physiological perspective, the proposition of H 2 -based syntrophy as the initial benefit linking mitochondrion and host (41) is of particular interest because of the widespread occurrence of H 2 -dependence among modern archaeal lineages that appear related to the host (55,56), the widespread existence of anaerobic syntrophy among modern prokaryotes (57) and especially because of the widespread occurrence of hydrogenosomes and H 2 -producing mitochondria among eukaryotic anaerobes (41, 58).…”

“…e) An amitochondriate eukaryote arises via a symbiosis involving the origin of peroxisomes (30,85,154). f) A eukaryote having mitochondria, a nucleus, an endomembrane system, meiosis, and sex arises from a symbiotic association of an archeaon (the host) and a bacterium (the common ancestor of mitochondria and hydrogenosomes) without additional symbiotic partners (7,10,22,23,41,54,55,58,116 (116)). symbiont ( Fig.…”

The role of archaea in the origin of eukaryotes

“…В работах В. Мартина и др. [57,58] представлена обновленная версия «водородной» гипотезы, в которой суммированы аргументы, позволя-ющие рассматривать родственную Lokiarchaeum линию в качестве эволюционного мостика от определенной филогенетической ветви архей к LECA. Такая предко-вая архея была анаэробной, H 2 -зависимой, содержа-щей эукариотподобные гены, а протомитохондриальным предшественником служила факультативно-анаэробная бактерия, ставшая эндосимбионтом уже на раннем эта-пе эукариогенеза.…”