A putative protease, its function overlaps that of the related putative proteases HtrA and HhoA. No induction by UV-B light. No effect in a single knockout, but growth is inhibited at high light (120 umol photons/m(2)/s) or at elevated temperature in a triple protease knockout mutant (hhoA, hhoB and htrA). Triple mutants are not phototactic. No effect on the PSII repair cycle, even in the triple protease knockout strain. Belongs to the peptidase S1C family.