Singlet molecular oxygen triggers the soxRS regulon of Escherichia coli

The electronically excited molecular oxygen (singlet oxygen, O-1(2)) 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 O-1(2), 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 O-1(2) may also function as a signal molecule in prokaryotes.