Singlet molecular oxygen triggers the soxRS regulon of Escherichia coli

The electronically excited molecular oxygen (singlet oxygen, 1O2) can be detrimental to cells in several ways, although recent reports indicate that it may play a role as an intercellular signal in eukaryotes. Here we present evidence that 1O2, generated by thermodissociation of disodium 3,3'-(1,4-naphthylidene) diproprionate endoperoxide, activates transcription of genes of the soxRS regulon, and that this induction is paralleled by induction of a soxS'::lacZ operon fusion. The inductions were dependent on a functional soxR gene. These data imply that protective responses, such as induction of the soxRS regulon, may be triggered by diverse environmental oxidative stresses, and that 1O2 may also function as a signal molecule in prokaryotes.