title: Copper chloride induces antioxidant gene expression but reduces ability to mediate H2O2 toxicity in Xanthomonas campestris.
abstract: Copper (Cu)-based biocides are currently used as control measures for both fungal and bacterial diseases in agricultural fields. In this communication, we show that exposure of the bacterial plant pathogen Xanthomonas campestris to nonlethal concentrations of Cu(2+) ions (75 µM) enhanced expression of genes in OxyR, OhrR and IscR regulons. High levels of catalase, Ohr peroxidase and superoxide dismutase diminished Cu(2+)-induced gene expression, suggesting that the production of hydrogen peroxide (H2O2) and organic hydroperoxides is responsible for Cu(2+)-induced gene expression. Despite high expression of antioxidant genes, the CuCl2-treated cells were more susceptible to H2O2 killing treatment than the uninduced cells. This phenotype arose from lowered catalase activity in the CuCl2-pretreated cells. Thus, exposure to a nonlethal dose of Cu(2+) renders X. campestris vulnerable to H2O2, even when various genes for peroxide-metabolizing enzymes are highly expressed. Moreover, CuCl2-pretreated cells are sensitive to treatment with the redox cycling drug, menadione. No physiological cross-protection response was observed in CuCl2-treated cells in a subsequent challenge with killing concentrations of an organic hydroperoxide. As H2O2 production is an important initial plant immune response, defects in H2O2 protection are likely to reduce bacterial survival in plant hosts and enhance the usefulness of copper biocides in controlling bacterial pathogens.
authors.affiliation: Program in Applied Biological Sciences: Environmental Health, Chulabhorn Graduate Institute, Bangkok 10210, Thailand.
authors.forename: Phornphan
authors.initials: P
authors.lastname: Sornchuer
authors.affiliation: Laboratory of Biotechnology, Chulabhorn Research Institute, Bangkok 10210, Thailand.
authors.forename: Poommaree
authors.initials: P
authors.lastname: Namchaiw
authors.affiliation: Department of Biotechnology, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.
authors.forename: Jarunee
authors.initials: J
authors.lastname: Kerdwong
authors.affiliation: Laboratory of Biotechnology, Chulabhorn Research Institute, Bangkok 10210, Thailand.
authors.forename: Nisanart
authors.initials: N
authors.lastname: Charoenlap
authors.affiliation: Center of Excellence on Environmental Health and Toxicology, Bangkok, Thailand.|Department of Biotechnology, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.|Laboratory of Biotechnology, Chulabhorn Research Institute, Bangkok 10210, Thailand.
authors.forename: Skorn
authors.initials: S
authors.lastname: Mongkolsuk
authors.affiliation: Center of Excellence on Environmental Health and Toxicology, Bangkok, Thailand.|Laboratory of Biotechnology, Chulabhorn Research Institute, Bangkok 10210, Thailand.|Program in Applied Biological Sciences: Environmental Health, Chulabhorn Graduate Institute, Bangkok 10210, Thailand.
authors.forename: Paiboon
authors.initials: P
authors.lastname: Vattanaviboon
mesh_terms: D000900:Anti-Bacterial Agents / Q000633:toxicity*; D000975:Antioxidants / Q000378:metabolism*; D003300:Copper / Q000633:toxicity*; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D006861:Hydrogen Peroxide / Q000633:toxicity*; D008826:Microbial Sensitivity Tests; D018384:Oxidative Stress; D016959:Xanthomonas campestris / Q000187:drug effects* / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D000975:Antioxidants; D003300:Copper; D006861:Hydrogen Peroxide; C029892:cupric chloride