Fe/Mn superoxide dismutase-encoding gene in Paracoccus denitrificans is induced by azide and expressed independently of the FNR-type regulators.

Paracoccus denitrificans cells undergo changes in protein composition upon exposure to azide, a known activator of the fumarate-nitrate reduction (FNR)-type transcription factor NarR. One of the most prominent protein species inducible by azide is a Fe/Mn-family superoxide dismutase (SOD). Azide induces SOD at protein, mRNA transcript, and enzyme activity levels in the aerobically growing cells. Since SOD expression remains unaffected in the fnrP-, nnr-, and narR-mutant strains, we postulate a mechanism independent of the known FNR-type regulators but involving a redox signal arising from the respiratory chain.