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J. Bacteriol. doi:10.1128/JB.01080-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The thiol:disulfide oxidoreductase DsbB mediates the oxidizing effects of the toxic metalloid tellurite (TeO₃^2-) on the plasma membrane redox system of the facultative phototroph Rhodobacter capsulatus

Department of Biology, University of Bologna, Bologna Italy; Department of Biological Sciences, University of Calgary, Calgary Canada

^* To whom correspondence should be addressed. Email: davide.zannoni{at}unibo.it.

	Abstract

The highly toxic oxyanion tellurite (TeO₃^2-) is a well known pro-oxidant in mammalian and bacterial cells. This work examines the effects of tellurite on the redox state of the electron transport chain of the facultative phototroph Rhodobacter capsulatus, in relation with the role of the thiol:disulfide oxidoreductase DsbB. Under steady-state respiration, addition of tellurite (2.5 mM) to membrane fragments generated an extra-reduction of the cytochrome pool (c- and b-type hemes); further, in plasma membranes exposed to tellurite (0.25-2.5 mM) and subjected to a series of flashes of light, the rate of the QH₂:cyt c oxidoreductase activity was enhanced. The effect of tellurite was blocked by the antibiotics antimycin A and/or myxothiazol, specific inhibitors of the QH₂:cyt c oxidoreductase, and, most interestingly, the membrane-associated thiol:disulfide oxidoreductase DsbB was required to mediate the redox unbalance produced by the oxyanion; indeed, this phenomenon was absent from R. capsulatus MD22, a DsbB deficient mutant whereas the tellurite effect was present in membranes from MD22/pDsbB^WT in which the mutant gene was complemented to regain the wild type DsbB-phenotype. These findings were taken as evidence that the membrane bound thiol:disulfide oxidoreductase DsbB acts as "electron conduit" between the hydrophilic metalloid and the lipid-embedded Q-pool so that in habitats contaminated with sub-inhibitory amounts of Te^IV, the metalloid is likely to function as a disposal for the excess of reducing power at the Q-pool level of facultative phototrophic bacteria.