Requirements for FisB-mediated membrane fission during sporulation

Little is known about mechanisms of membrane fission in bacteria despite their requirement for cytokinesis. The only known dedicated membrane fission machinery in bacteria, FisB, is expressed during sporulation in Bacillus subtilis and is required at the last stage of engulfment to release the developing spore into the mother cell cytoplasm. Here we characterize the requirements for FisB-mediated fission. FisB forms mobile clusters of [~]12 molecules that give way to an immobile cluster at the engulfment pole containing [~]40 proteins at the time of membrane fission. Reducing FisB to [~]6 copies at the pole slowed but did not eliminate fission. Function mutants revealed that binding to acidic lipids and homo-oligomerization are both critical for targeting FisB to the engulfment pole and membrane fission. Finally, a distant FisB homolog from Clostridium perfringens was functional in B. subtilis suggesting FisB catalyzes fission without protein partners. Our results suggest that FisB is a robust and unusual membrane fission protein that likely relies on homo-oligomerization, lipid-binding and the unique membrane topology generated during engulfment for localization and membrane scission.