Evaluation of the role hydroxyl radicals and iron play in hydrogen peroxide killing ofXanthomonas campestrispv.phaseoli

Hydroxyl radical, a product of H2O2 metabolism in the Fenton reaction, is a major reactive oxygen species involved in H2O2 killing of Xanthomonas campestris pv. phaseoli ( Xp ). Compounds which absorbed hydroxyl radicals protected Xanthomonas from H2O2 killing, but not from killing by a superoxide generator or an organic peroxide. Addition of iron potentiated H2O2 killing. On the other hand, pre-treatment of Xp with an iron chelator showed no protective effects and H2O2 killing was actually enhanced. Unexpectedly, resuspension of Xp in either water or phosphate buffer induced high-level resistance to H2O2 killing. The unknown protection mechanism was independent of new protein synthesis.