Evidence for a tellurite-dependent generation of reactive oxygen species and absence of a tellurite-mediated adaptive response to oxidative stress in cells of Pseudomonas pseudoalcaligenes KF707

Tellurite (TeO32-) is the most toxic and soluble oxyanion among tellurium (Te) compounds. The effects of the metalloid anion on the oxidative stress response of the obligate aerobe Pseudomonas pseudoalcaligenes KF707 were investigated. Cells treated with sub-lethal concentrations of TeO32- showed neither adaptation to it nor cross-protection against oxidants such as 1,1'-4,4'-bipyridinium dichloride (paraquat, PQ(2+)), diazenedicarboxylic acid bis-N,N-dimethylamide (diamide), tert-buthyl hydroperoxide (tBH) and hydrogen peroxide (H2O2). Notably, TeO32- exerted a synergic effect on the toxicity of these latter oxidants. Tellurite was shown to decrease the cellular content of reduced thiols (RSH) with a consequent increase in the production of reactive oxygen species (ROS) and stimulation of the superoxide dismutase (SOD) activity. However, since the time course of ROS production by TeO32 (t(1/2) > 30 min) was much slower than that with PQ(2+) and/or diamide (t(1/2) <= 10 min), in the former case the SOD activity was poorly activated. We conclude that in P. pseudoalcaligenes KF707 cells: (1) the TeO32- acts as a pro-oxidant by stimulating ROS production; (2) the release of superoxide oxyanions is directly linked to the mechanism of toxicity; (3) TeO32- is unable to induce an adaptive response to oxidative stress.