Tetraether monosaccharide phospholipids (MPL) are the main phospholipids of Thermoplasma acidophilum. They contain a glycerophosphate and a gulosyl pyranoside monosaccharide linked via a tetraether chain. The MPL is largely responsible for T. acidophilum’s ability to survive in low pH (1-2) and high temperatures (55-59°C) and constitutes almost half of its total lipids.