Journal of Bacteriology, January 2001, p. 101-108, Vol. 183, No. 1
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.1.101-108.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Departments of Chemistry3 and Microbiology1 and Center for Metalloenzyme Studies,2 University of Georgia, Athens, Georgia 30602, and Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada4
Received 15 June 2000/Accepted 11 October 2000
Evidence is presented for an alternative to the superoxide
dismutase (SOD)-catalase oxidative stress defense system in
Desulfovibrio vulgaris (strain Hildenborough). This
alternative system consists of the nonheme iron proteins, rubrerythrin
(Rbr) and rubredoxin oxidoreductase (Rbo), the product of the
rbo gene (also called desulfoferrodoxin). A
rbo strain of D. vulgaris was found to be
more sensitive to internal superoxide exposure than was the wild type.
Unlike Rbo, expression of plasmid-borne Rbr failed to restore the
aerobic growth of a SOD-deficient strain of Escherichia coli. Conversely, plasmid-borne expression of two different Rbrs from D. vulgaris increased the viability of a
catalase-deficient strain of E. coli that had been exposed
to hydrogen peroxide whereas Rbo actually decreased the viability. A
previously undescribed D. vulgaris gene was found to encode
a protein having 50% sequence identity to that of E. coli
Fe-SOD. This gene also encoded an extended N-terminal sequence with
high homologies to export signal peptides of periplasmic redox
proteins. The SOD activity of D. vulgaris is not affected
by the absence of Rbo and is concentrated in the periplasmic fraction
of cell extracts. These results are consistent with a superoxide
reductase rather than SOD activity of Rbo and with a peroxidase
activity of Rbr. A joint role for Rbo and Rbr as a novel cytoplasmic
oxidative stress protection system in D. vulgaris and other
anaerobic microorganisms is proposed.
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