Preprint Hypothesis Version 1 This version is not peer-reviewed

The Eukaryotic Last Common Ancestor Was Bifunctional for Hopanoid and Sterol Production

Version 1 : Received: 9 April 2020 / Approved: 12 April 2020 / Online: 12 April 2020 (08:47:26 CEST)

How to cite: Francis, W. The Eukaryotic Last Common Ancestor Was Bifunctional for Hopanoid and Sterol Production. Preprints 2020, 2020040186 (doi: 10.20944/preprints202004.0186.v1). Francis, W. The Eukaryotic Last Common Ancestor Was Bifunctional for Hopanoid and Sterol Production. Preprints 2020, 2020040186 (doi: 10.20944/preprints202004.0186.v1).

Abstract

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

Subject Areas

sterol; hopanoid; proterozoic; biosynthesis; squalene

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