Bacterial responses to photo-oxidative stress

Photo-oxidative stress is induced by the formation of the reactive oxygen species singlet oxygen, which is often caused by energy transfer from a light-excited donor to molecular oxygen.Carotenoids protect photosynthetic organisms such as Rhodobacter sphaeroides from the photo-oxidative damage that is caused by this energy transfer.The alternative σ-factor σE is the master regulator of the photo-oxidative stress response in R. sphaeroides.Some known σE target genes are found in many bacteria (forming the core σE regulon), whereas others are predicted to be part of the photo-oxidative stress response in only a subset of species (known as the extended σE regulon).The proposed core and extended σE regulons encode few proteins of known or predicted protective function, but how cells respond to photo-oxidative stress is largely unknown, as many target genes have no annotated function as yet.Conservation of the proposed core σE regulon suggests that the photo-oxidative stress response is broadly represented both in photosynthetic bacteria and in non-photosynthetic microorganisms that can generate singlet oxygen from light-dependent or light-independent processes.