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 μg ml −1 of the toxic oxyanion tellurite (TeO 2− 3) 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, the absence of SenC did not affect R. capsulatus tellurite resistance. We conclude that: (1) cytosolic-generated O 2 ⋅ − enhances Te R of this bacterial 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 Te R, possibly because tellurite does not generate O ⋅− 2 at the periplasmic space level.