Hopanoids are polycyclic triterpenoids that occur in some Bacteria. They are structurally similar to sterols, and have been hypothesized to play a similar role in the cell - i.e. modulating membrane fluidity or forming lipid rafts.
Genomic evidence suggests that the last common ancestor of all Bacterial life was hopanoid-producing, but yet only an estimated 5 percent of Bacteria contain hopanoids today. We have used genetic techniques to perturb the hopanoid profile of hopanoid-producing bacteria in the laboratory, to observe how they change physiologically