Sukchawalit Rojana, Prapagdee Benjaphorn, Charoenlap Nisanart, Vattanaviboon Paiboon, Mongkolsuk Skorn
Laboratory of Biotechnology, Chulabhorn Research Institute, Lak Si, Bangkok 10210, Thailand.
Res Microbiol. 2005 Jan-Feb;156(1):30-4. doi: 10.1016/j.resmic.2004.07.005.
Arsenic has been shown to mediate its toxicity through induced generation of reactive oxygen species. Here, we examined the role of oxidative stress-inducible genes (katA, ahpC and ohr) and their regulators (oxyR and ohrR) in the response to arsenic treatment in a plant pathogenic bacterium, Xanthomonas campestris pv. phaseoli (Xp). Overproduction of peroxide-scavenging enzymes (KatA, AhpCF and Ohr) did not enhance arsenic tolerance in wild-type Xp. Furthermore, inactivation of katA, ahpC, ohr, and ohrR genes had no effect on the level of arsenic resistance. By contrast, an oxyR mutant (Xp oxyR) showed increased sensitivity to both pentavalent arsenate and, to a greater extent, trivalent arsenite. The resistance of cells to arsenite treatment was significantly affected by the level of iron. Cells were 10-fold more sensitive to arsenite killing in the presence of excess iron, while removal of iron by an iron chelator (2,2'-dipyridyl) protected Xanthomonas from arsenite toxicity. The arsenite-sensitive phenotype of Xp oxyR could be complemented by the expression of functional OxyR from a plasmid vector, but not by the expression of other known OxyR-regulated peroxide-scavenging enzymes such as KatA and AhpCF, Ohr and OhrR. The data suggested that as yet unidentified, OxyR-regulated gene(s) are involved in conferring arsenic resistance in Xp. To our knowledge, this is the first report showing that the peroxide-sensing regulator OxyR is involved in arsenic resistance.
已证明砷通过诱导活性氧的产生来介导其毒性。在此，我们研究了氧化应激诱导基因（katA、ahpC和ohr）及其调节因子（oxyR和ohrR）在植物病原菌野油菜黄单胞菌菜豆致病变种（Xp）对砷处理反应中的作用。过氧化物清除酶（KatA、AhpCF和Ohr）的过量产生并未增强野生型Xp对砷的耐受性。此外，katA、ahpC、ohr和ohrR基因的失活对砷抗性水平没有影响。相比之下，oxyR突变体（Xp oxyR）对五价砷酸盐以及在更大程度上对三价亚砷酸盐表现出更高的敏感性。细胞对亚砷酸盐处理的抗性受到铁水平的显著影响。在存在过量铁的情况下，细胞对亚砷酸盐杀伤的敏感性高出10倍，而通过铁螯合剂（2,2'-联吡啶）去除铁可保护野油菜黄单胞菌免受亚砷酸盐毒性的影响。Xp oxyR对亚砷酸盐敏感的表型可通过质粒载体表达功能性OxyR来互补，但不能通过表达其他已知的OxyR调节的过氧化物清除酶（如KatA和AhpCF、Ohr和OhrR）来互补。数据表明，尚未鉴定的OxyR调节基因参与赋予Xp砷抗性。据我们所知，这是第一份表明过氧化物感应调节因子OxyR参与砷抗性的报告。
