Sterols are key components of eukaryotic cellular membranes that are synthesized by multi-enzyme pathways that require molecular oxygen. Because prokaryotes fundamentally lack sterols, it is unclear how the vast diversity of bacterivorous eukaryotes that inhabit hypoxic environments obtain, or synthesize, sterols. Here we show that tetrahymanol, a triterpenoid that does not require molecular oxygen for its biosynthesis, likely functions as a surrogate of sterol in eukaryotes inhabiting oxygen-poor environments. Genes encoding the tetrahymanol synthesizing enzyme squalene-tetrahymanol cyclase were found from several phylogenetically diverged eukaryotes that live in oxygen-poor environments and appear to have been laterally transferred among such eukaryotes.Reviewers: This article was reviewed by Eric Bapteste and Eugene Koonin.
Bibliographical noteFunding Information:
We thank Dr. G. Tanifuji (Dalhousie University) for his technical assistance. This work was funded by a Canadian Institutes for Health Research Grant MOP-62809 awarded to AJR. MML is supported by the National Research Fund, Luxembourg. EK is supported by Tula Foundation.
- Lateral gene transfer