Protein synthesis patterns reveal a complex regulatory response to singlet oxygen in Rhodobacter

Singlet oxygen (O-1(2)) is a stress factor and signal in the facultative phototrophic bacterium Rhodobacter sphaeroides. In vivo protein labeling with L-[S-35]-methionine and analysis by two-dimensional gel electrophoresis revealed that the synthesis of 61 proteins was changed in response to O-1(2). After O-1(2) treatment, protein synthesis patterns were distinct from those after H2O2 treatment but similar to those after high light exposure. This indicates regulatory mechanisms selective for different reactive oxygen species (ROS) and a response to light partly mediated by O-1(2). Analysis of mutant strains support that the response to O-1(2) is regulated mainly by rpoE (sigma(E)), but also a modulation of the sigma(E) dependent response by other factors and the existence of sigma(E) independent responses. The involvement of the RNA chaperon Hfq in the O-1(2) response implies a role of small regulatory RNAs.