Gene family analysis suggests new evolutionary scenario for sterol and hopanoid biomarkers

Steroid and hopanoid biomarkers can be found in ancient rocks may give a glimpse of what life was present at that time. Sterols hopanoids are produced by two related enzymes, though the evolutionary history this protein family is complicated losses horizontal gene transfers, appears to widely misinterpreted. Here, I have added sequences from additional species, re-analysis phylogeny SHC OSC indicates single origin both enzymes among eukaryotes. This pattern best explained endosymbiotic acquisition bacterial ancestor, followed widespread loss SHC, subsequent HGT events ferns ascomycetes. Thus, last common ancestor eukaryotes would been bifunctional for sterol production. Later enzymatic innovations allowed diversification sterols Contrary previous interpretations, eukaryotic (LECA) potentially able produce as substitute anaerobic conditions. Without invoking any other metabolic demand, LECA could facultative aerobe, living unstable conditions with respect oxygen level.