The response of Xanthomonas campestris pv. campestris to sodium hypochlorite stressAnong Piwkam
( M.Sc. )
Xanthomonas campestris pv. campestris (Xcc) is a gram negative soil bacterium. This bacterium, which is a seed borne phytophatogen, is the causative agent of black rot disease of cruciferous crops worldwide. Most Xcc infection originates from planting infected seeds; treating the crucifer seeds with disinfectants such as sodium hypochlorite (NaOCl) solution is an effective strategy to eradicate contaminated Xcc from seeds before planting. However, it is still unclear how Xcc responds to NaOCl exposure and protect bacteria cell from its toxicity. Therefore, the purposes of this research were to evaluate the responses of Xcc to sublethal concentrations of NaOCl and also focus on the effect of NaOCl on oxidative stress protection of Xcc. Adaptive protection to NaOCl was observed in Xcc pretreated with 0.0625% w/v of NaOCl. Exposure of Xcc to sublethal concentrations of NaOCl solution induced the expression of antioxidant enzymes including ahpC, ohr, katA, katG, sodC, and sodA genes, indicating that the treated cells encounter oxidative stress. Pretreatment with oxidants viz. H2O2, BHP and MD induced cross-protection to NaOCl in an oxyR dependent manner. The NaOCl pretreated cells showed more resistant to H2O2. Flow cytometric analysis suggested accumulation of superoxide anion and particularly H2O2 in NaOCl-treated cells. The Xcc mutants devoid of OxyR, KatA catalase, KatG catalase, AhpC, and superoxide dismutases (SodC and SodA) were more vulnerable to NaOCl. Altogether, the results suggested that NaOCl toxicity is, in part, mediated by generation of reactive oxygen species and catalases, AhpC, and superoxide dismutases are primary scavengers responsible for protection of Xcc from NaOCl killing effects.