Copper ions potentiate organic hydroperoxide and hydrogen peroxide toxicity through different mechanisms in Xanthomonas campestris pv. campestris

Copper (Cu)-based biocides are important chemical controls for both fungal and bacterial diseases in crop fields. Here, we showed that Cu ions at a concentration of 100 mu M enhanced t-butyl hydroperoxide (tBOOH) and hydrogen peroxide (H2O2) killing of Xanthomonas campestris pv. campestris through different mechanisms. The addition of an antilipid peroxidation agent (alpha-tocopherol) and hydroxyl radical scavengers (glycerol and dimethyl sulphoxide) partially protected the bacteria from the Cu-enhanced tBOOH and H2O2 killing, respectively. Inactivation of the alkyl hydroperoxide reductase gene rendered the mutant vulnerable to lethal doses of copper sulphate, which could be alleviated by the addition of an H2O2 scavenger (pyruvate) and alpha-tocopherol. Taken together, the data suggest that Cu ions influence the killing effect of tBOOH through the stimulation of lipid peroxidation, while hydroxyl radical production is the underlying mechanism responsible for the Cu-ion-enhanced H2O2 killing effects.