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Infect. Immun., Mar 1995, 794-798, Vol 63, No. 3
T Nunoshiba, T DeRojas-Walker, SR Tannenbaum and B Demple
Nitric oxide (NO.) is produced as a cytotoxic free radical through
enzymatic oxidation of L-arginine in activated macrophages. Pure NO. gas
was previously found to induce the Escherichia coli soxRS oxidative stress
regulon, which is readily monitored by using a soxS'::lac fusion. The soxRS
system includes antioxidant defenses, such as a superoxide dismutase and a
DNA repair enzyme for oxidative damage, and protects E. coli from the
cytotoxicity of NO.-generating macrophages. Previous experiments involved
exposing E. coli to a bolus of NO. rather than the steadily generated gas
expected of activated macrophages. We show here detectable induction of
soxS transcription by NO. delivered at rates as low as 25 microM/h. Maximal
induction was observed at 25 microM NO. per h under anaerobic conditions
but at 125 microM/h aerobically. After incubation with murine macrophages,
soxS expression was induced in the phagocytosed bacteria up to
approximately 30-fold after an 8-h exposure. This in vivo induction was
almost completely eliminated by the NO. synthase inhibitor
NG-monomethyl-L-arginine. The inhibitor increased the survival of a delta
soxRS strain but not that of wild-type E. coli after phagocytosis, which
suggests that induction of the soxRS regulon by NO. can counteract most of
the cytotoxic effects of NO. production by the macrophages. We show that
the soxRS- regulated enzyme glucose-6-phosphate dehydrogenase is an
important element of the defense against macrophages.
Copyright © 1995, American Society for Microbiology
Roles of nitric oxide in inducible resistance of Escherichia coli to activated murine macrophages
Department of Molecular and Cellular Toxicology, Harvard School of Public Health, Boston, Massachusetts 02115.
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