Hopanoids as functional analogues of cholesterol in bacterial membranes

The function of the cell membrane as a barrier and a matrix for biochemical activity relies on the properties imparted by lipids. In eukaryotes, sterols are crucial for modulating the molecular order of membranes. Sterol ordering provides the basis for membrane lateral segregation and promotes a fluid, mechanically robust plasma membrane. How do organisms that lack sterols determine membrane order? Hopanoids are bacterial membrane lipids that have been demonstrated to have sterol-like properties in vitro. We now explore the distribution of hopanoids and their effect on membranes in Methylobacterium extorquens. We find that hopanoids determine bacterial outer membrane order in a manner analogous to sterol ordering in the eukaryotic plasma membrane, and that their deletion impairs energy-dependent multidrug efflux.