Chlamydial contribution to anaerobic metabolism during eukaryotic evolution

Courtney W. Stairs, Jennah E. Dharamshi, Daniel Tamarit, Laura Eme, Steffen L. Jørgensen, Anja Spang, Thijs J.G. Ettema*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

11 Citations (Scopus)


The origin of eukaryotes is a major open question in evolutionary biology. Multiple hypotheses posit that eukaryotes likely evolved from a syntrophic relationship between an archaeon and an alphaproteobacterium based on H2 exchange. However, there are no strong indications that modern eukaryotic H2 metabolism originated from archaea or alphaproteobacteria. Here, we present evidence for the origin of H2 metabolism genes in eukaryotes from an ancestor of the Anoxychlamydiales-a group of anaerobic chlamydiae, newly described here, from marine sediments. Among Chlamydiae, these bacteria uniquely encode genes for H2 metabolism and other anaerobiosis-associated pathways. Phylogenetic analyses of several components of H2 metabolism reveal that Anoxychlamydiales homologs are the closest relatives to eukaryotic sequences. We propose that an ancestor of the Anoxychlamydiales contributed these key genes during the evolution of eukaryotes, supporting a mosaic evolutionary origin of eukaryotic metabolism.

Original languageEnglish
Article numbereabb7258
JournalScience Advances
Issue number35
Publication statusPublished - 26 Aug 2020


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