Regulatory locus soxRS partially protects Escherichia coli against ozone.

Ozone is one of the major city air pollutants. Since it is known to induce the overexpression of superoxide-dismutase in various models, and is also a powerful oxidant, we tested if ozone can induce the expression of the soxRS regulon of Escherichia coli, which is activated by superoxide and nitric oxide. A sub-lethal exposure to ozone was unable to activate the expression of soxS'::lacZ transcriptional fusions. However, cells lacking the soxRS locus were more susceptible than wild-type to ozone-mediated killing. Constitutive expression of the soxRS regulon did not increase the resistance to ozone. Ozone might be exerting a selective pressure upon oxidative-stress defense mechanisms in airborne bacteria.