Sterols 4. Hopanoids and Related Lipids

Bacteria and other prokaryotic organisms such as blue-green algae do not in general contain any of the conventional sterols found in plants and animals, but rather many species have related molecules, i.e. pentacyclic triterpenoids, based on a hopane skeleton with a cyclopentane E-ring and termed ‘hopanoids’ (from the plant genus Hopea, from which they were isolated as components of the resin (dammar resin)). The more complex forms are sometimes termed ‘bacteriohopanepolyols’. They were first discovered in 1973 as the compounds responsible for the alignment of the cellulose microfibrils secreted by Acetobacter xylinum.