BPS2026 – Evolution of lipid membrane adaptation to oxygen-free environments

Cell membranes are essential for cellular function, acting as barriers and platforms for processes such as signaling, transport, and protein activity. Their properties, such as fluidity, thickness, and phase behavior, are shaped by lipid composition, particularly sterols and glycerophospholipids. In eukaryotes, however, the synthesis of both sterols and unsaturated phospholipid tails requires oxygen, raising the question of how membrane properties are maintained under oxygen-limited conditions. Here, we used Schizosaccharomyces japonicus , a eukaryotic unicellular yeast that thrives in both normoxic and anoxic conditions. Under anoxia, this organism remodels its lipidome by replacing unsaturated phospholipid acyl chains with asymmetric saturated chains, thereby preserving bilayer fluidity without desaturation. In parallel, it substitutes sterols with diplopterol, a hopanoid that mimics the structure of sterols. Together, these modifications maintain critical membrane biophysical parameters despite the metabolic block on oxygen-dependent lipid synthesis. These two adaptations co-evolve to maintain membrane function in the absence of oxygen. Finally, we discuss the limitations of these strategies and why eukaryotic evolution favored sterols over hopanoids.