Volatile Arsenic Species Released from Escherichia coli Expressing the AsIII S-adenosylmethionine Methyltransferase Gene

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• 作者：Chungang Yuan ; Xiufen Lu ; Jie Qin ; Barry P. Rosen ; X. Chris Le
• 刊名：Environmental Science & Technology
• 出版年：2008
• 出版时间：May 1, 2008
• 年：2008
• 卷：42
• 期：9
• 页码：3201 - 3206
• 全文大小：558K
• 年卷期：v.42,no.9(May 1, 2008)
• ISSN：1520-5851

文摘

Biological systems, ranging from bacteria and fungi to humans, can methylate arsenic. Recent studies have suggested that the AsIII S-adenosylmethionine methyltransferase (arsM) gene in bacteria was responsible for the removal of arsenic as the volatile arsines from the bacteria. However, there has been no direct measure of the arsines released from bacteria cultures. We describe here an integrated system incorporating the bacterial incubation and volatile arsenic species analysis, and we demonstrate its application to the identification of the volatile arsines produced in bacterial cultures. The headspace of the bacterial cultures was purged with helium, and the volatile arsenic species were trapped in a chromatographic column immersed in liquid nitrogen. The cryogenically trapped arsines [AsH₃, (CH₃)AsH₂, (CH₃)₂AsH, and (CH₃)₃As] were separated by gas chromatography and were detected by inductively coupled plasma mass spectrometry. A hydride generation system was coupled to the bacterial culture system, allowing for spiking standards and for generating calibration arsines necessary for quantitative analysis. Both bacteria containing the arsM gene or its variant arsMC2 gene were able to produce 400–500 ng of trimethylarsine. No trimethylarsine was detectable in bacteria lacking the arsM gene (containing the vector plasmid as negative control). These results confirm that arsM is responsible for releasing arsenic as volatile species from the arsenic-resistant bacteria. Our results also show traces of AsH₃, CH₃AsH₂, and (CH₃)₂AsH in cultures of bacteria expressing arsM. The method detection limits for AsH₃, CH₃AsH₂, (CH₃)₂AsH, and (CH₃)₃As were 0.5, 0.5, 0.7, and 0.6 pg, respectively. The ability to quantify trace levels of these volatile arsenic species makes it possible to study the biotransformation and biochemical roles of the evolution of these volatile arsenic species by biological systems.