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J. Bacteriol., Dec 1996, 6736-6742, Vol 178, No. 23
MJ Pianzzola, M Soubes and D Touati
In an attempt to isolate the superoxide dismutase (SOD) gene from the
anaerobic sulfate-reducing bacterium Desulfoarculus baarsii, a DNA fragment
was isolated which functionally complemented an Escherichia coli mutant
(sodA sodB) deficient in cytoplasmic SODs. This region carries two open
reading frames with sequences which are very similar to that of the rbo-rub
operon from Desulfovibrio vulgaris. Independent expression of the rbo and
rub genes from ptac showed that expression of rbo was responsible for the
observed phenotype. rbo overexpression suppressed all deleterious effects
of SOD deficiency in E. coli, including inactivation by superoxide of
enzymes containing 4Fe-4S clusters and DNA damage produced via the
superoxide-enhanced Fenton reaction. Thus, rbo restored to the sodA sodB
mutant the ability to grow on minimal medium without the addition of
branched amino acids, and growth on gluconate and succinate carbon sources
was no longer impaired. The spontaneous mutation rate, which is elevated in
SOD- deficient mutants, returned to the wild-type level in the presence of
Rbo, which also restored aerobic viability of sodA sodB recA mutants. Rbo
from Desulfovibrio vulgaris, but not Desulfovibrio gigas desulforedoxin,
which corresponds to the NH2-terminal domain of Rbo, complemented sod
mutants. The physiological role of Rbo in sulfate- reducing bacteria is
unknown. In E. coli, Rbo may permit the bacterium to avoid superoxide
stress by maintaining functional (reduced) superoxide sensitive 4Fe-4S
clusters. It would thereby restore enzyme activities and prevent the
release of iron that occurs after cluster degradation and presumably leads
to DNA damage.
Copyright © 1996, American Society for Microbiology
Overproduction of the rbo gene product from Desulfovibrio species suppresses all deleterious effects of lack of superoxide dismutase in Escherichia coli
Facultad de Quimica, Catedra de Microbiologia, Montevideo, Uruguay.
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