Tellurite effects on Rhodobacter capsulatus cell viability and superoxide dismutase activity under oxidative stress conditions

Cells of the facultative photosynthetic bacterium Rhodobacter capsulatus (MT1131 strain) incubated with 10 mu g ml(-1) of the toxic oxyan- ion tellurite (TeO32-) exhibited an increase in superoxide dismutase activity. The latter effect was also seen upon incubation with sublethal amounts of paraquat, a cytosolic generator of superoxide anions (O-2(-)), in parallel with a strong increase in tellurite resistance (Te-R). A mutant strain (CW10) deficient in SenC, a protein with similarities to peroxiredoxin/thiol: disulfide oxidoreductases and a homologue of mitochondrial Sco proteins, was constructed by interposon mutagenesis via the gene transfer agent system. Notably, the absence of SenC affected R. capsulatus resistance to periplasmic O-2(-) generated by xanthine/xanthine oxidase but not to cytosolic O-2(-) produced by paraquat. Further, 2 the absence of SenC did not affect R. capsulatus tellurite resistance. We conclude that: (1) cytosolic-generated O-2(-) enhances TeR of this 2 bacteria] species; (2) small amounts of tellurite increase SOD activity so as to mimic the early cell response to oxidative stress; (3) SenC protein is required in protection of R. capsulatus against periplasmic oxidative stress; and finally, (4) SenC protein is not involved in TeR, possibly because tellurite does not generate O-2(-) at the pedplasmic space level. (c) 2005 Elsevier SAS. All rights reserved.