UMR7156 Génétique Moléculaire, Génomique et Microbiologie, CNRS Université de Strasbourg, 28 rue Goethe, 67000 Strasbourg, France.
BMC Microbiol. 2010 Feb 18;10:53. doi: 10.1186/1471-2180-10-53.
Both the speciation and toxicity of arsenic are affected by bacterial transformations, i.e. oxidation, reduction or methylation. These transformations have a major impact on environmental contamination and more particularly on arsenic contamination of drinking water. Herminiimonas arsenicoxydans has been isolated from an arsenic- contaminated environment and has developed various mechanisms for coping with arsenic, including the oxidation of As(III) to As(V) as a detoxification mechanism.
In the present study, a differential transcriptome analysis was used to identify genes, including arsenite oxidase encoding genes, involved in the response of H. arsenicoxydans to As(III). To get insight into the molecular mechanisms of this enzyme activity, a Tn5 transposon mutagenesis was performed. Transposon insertions resulting in a lack of arsenite oxidase activity disrupted aoxR and aoxS genes, showing that the aox operon transcription is regulated by the AoxRS two-component system. Remarkably, transposon insertions were also identified in rpoN coding for the alternative N sigma factor (sigma54) of RNA polymerase and in dnaJ coding for the Hsp70 co-chaperone. Western blotting with anti-AoxB antibodies and quantitative RT-PCR experiments allowed us to demonstrate that the rpoN and dnaJ gene products are involved in the control of arsenite oxidase gene expression. Finally, the transcriptional start site of the aoxAB operon was determined using rapid amplification of cDNA ends (RACE) and a putative -12/-24 sigma54-dependent promoter motif was identified upstream of aoxAB coding sequences.
These results reveal the existence of novel molecular regulatory processes governing arsenite oxidase expression in H. arsenicoxydans. These data are summarized in a model that functionally integrates arsenite oxidation in the adaptive response to As(III) in this microorganism.
砷的物种形成和毒性都受到细菌转化的影响，即氧化、还原或甲基化。这些转化对环境污染有重大影响，特别是对饮用水中的砷污染。Herminiimonas arsenicoxydans 已从砷污染环境中分离出来，并发展了多种应对砷的机制，包括将 As(III)氧化为 As(V)作为解毒机制。
在本研究中，采用差异转录组分析鉴定了参与 H. arsenicoxydans 对 As(III) 响应的基因，包括亚砷酸盐氧化酶编码基因。为了深入了解该酶活性的分子机制，进行了 Tn5 转座子诱变。导致缺乏亚砷酸盐氧化酶活性的转座子插入破坏了 aoxR 和 aoxS 基因，表明 aox 操纵子转录受 AoxRS 双组分系统调控。值得注意的是，转座子插入也发生在编码 RNA 聚合酶替代 N 西格玛因子 (sigma54) 的 rpoN 和编码 Hsp70 共伴侣的 dnaJ 基因中。用抗 AoxB 抗体进行 Western 印迹和定量 RT-PCR 实验证明，rpoN 和 dnaJ 基因产物参与了对亚砷酸盐氧化酶基因表达的控制。最后，使用快速扩增 cDNA 末端 (RACE) 确定了 aoxAB 操纵子的转录起始位点，并在 aoxAB 编码序列上游鉴定了一个推定的 -12/-24 sigma54 依赖性启动子模体。
这些结果揭示了在 H. arsenicoxydans 中控制亚砷酸盐氧化酶表达的新的分子调控过程的存在。这些数据总结在一个模型中，该模型功能上整合了该微生物中对 As(III)的适应性反应中的亚砷酸盐氧化。
