Arsenic is one of the most widespread environmental carcinogens and has created devastating human health problems worldwide, yet little is known about mechanisms of biotransformation in contaminated regions. Methylarsonic acid [MAs(V)], extensively utilized as an herbicide, is largely demethylated to more toxic inorganic arsenite, which causes environmental problems. To understand the process of demethylation of methylarsenicals, soil samples commonly used on Florida golf courses were studied. Several soil extracts were found to demethylate MAs(V) to inorganic arsenite [As(III)]. From these extracts, a bacterial isolate was capable of reducing MAs(V) to MAs(III) but not of demethylating to As(III). A second bacterial isolate was capable of demethylating MAs(III) to As(III) but not of reducing MAs(V). A mixed culture could carry out the complete process of reduction and demethylation, demonstrating that demethylation of MAs(V) to As(III) is a two-step process. Analysis of the 16S ribosomal DNA sequences of the two organisms identified the MAs(V)-reducing and the MAs(III)-demethylating isolates as belong to Burkholderia and Streptomyces species respectively. This is the first report of a novel pathway of degradation of a methylarsenical herbicide by sequential reduction and demethylation in a microbial soil community, which we propose plays a significant role in the arsenic biogeocycle.

中文翻译：

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微生物群落对甲基胂酸的去甲基化作用。

砷是最普遍的环境致癌物之一，在世界范围内造成了毁灭性的人类健康问题，但对受污染地区的生物转化机制知之甚少。广泛用作除草剂的甲基胂酸 [MAs(V)] 在很大程度上脱甲基化为毒性更大的无机亚砷酸盐，这会导致环境问题。为了了解甲基砷的去甲基化过程，研究了佛罗里达高尔夫球场常用的土壤样品。发现几种土壤提取物将 MAs(V) 去甲基化为无机亚砷酸盐 [As(III)]。从这些提取物中，细菌分离物能够将 MAs(V) 还原为 MAs(III)，但不能去甲基化为 As(III)。第二种细菌分离物能够将 MAs(III) 去甲基化为 As(III)，但不能还原 MAs(V)。混合培养可以进行完整的还原和去甲基化过程，证明 MAs(V) 到 As(III) 的去甲基化是一个两步过程。对这两种生物的 16S 核糖体 DNA 序列的分析确定了 MAs(V)-reducing 和 MAs(III)-demethylating 分离物分别属于伯克霍尔德菌属和链霉菌属物种。这是通过在微生物土壤群落中顺序还原和去甲基化降解甲基砷除草剂的新途径的第一份报告，我们认为该途径在砷生物地球循环中起着重要作用。对这两种生物的 16S 核糖体 DNA 序列的分析确定了 MAs(V)-reducing 和 MAs(III)-demethylating 分离物分别属于伯克霍尔德菌属和链霉菌属物种。这是通过在微生物土壤群落中顺序还原和去甲基化降解甲基砷除草剂的新途径的第一份报告，我们认为该途径在砷生物地球循环中起着重要作用。对这两种生物的 16S 核糖体 DNA 序列的分析确定了 MAs(V)-reducing 和 MAs(III)-demethylating 分离物分别属于伯克霍尔德菌属和链霉菌属物种。这是通过在微生物土壤群落中顺序还原和去甲基化降解甲基砷除草剂的新途径的第一份报告，我们认为该途径在砷生物地球循环中起着重要作用。