砷（As）是一種無處不在的有毒元素，砷污染問題已成為當前世界環境研究的熱點之一。藍藻廣泛分布在土壤和各種水生環境中。由于它們的環境適應力強，生長速度快，因此是引起水華的主要物種。目前有關藍藻對砷響應機制的研究還鮮有報道。

*城市環境研究所城市環境與健康重點實驗室朱永官組研究揭示了藍藻砷甲基化的分子機制。該研究發現微囊藻（Microcystis sp. PCC7806）、念珠藻（Nostoc sp. PCC7120）和集胞藻（Synechocysis sp. PCC6803）都能將無機砷轉化為甲基砷。將三種藍藻的砷甲基轉移酶基因（arsM）克隆，并表達在對砷高度敏感的大腸桿菌突變株AW3110（ΔarsRBC）中，它們都能賦予細胞對As（III）的抗性。兩種純化的蛋白質SsArsM （Synechocystis ArsM）和NsArsM（Nostoc ArsM）在體外能夠將As（III）轉化為甲基砷，并生成一定量的揮發砷。鑒于藍藻具有較強的砷轉化能力及其在環境中的廣泛存在，它在砷的生物地球化學循環中起到了重要的作用。

此項研究由*和國家自然科學基金委資助。博士生尹西翔為*作者，朱永官博士為文章通訊作者。相關論文在《植物生理學》（Plant Physiology）雜志在線發表（Biotransformation and volatilization of arsenic by three photosynthetic cyanobacteria, doi:10.1104/pp. 111.178947）

原文出處：

Plant Physiology DOI：10.1104/pp.111.178947

Biotransformation and volatilization of arsenic by three photosynthetic cyanobacteria

Xixiang Yin, Jian Chen, Jie Qin, Guoxin Sun, Barry Rosen and Yongguan Zhu

Arsenic （As） is a pervasive and ubiquitous environmental toxin that has created world-wide human health problems. However, there are few studies about how organisms detoxify arsenic. Cyanobacteria are capable of both photolithotrophic growth in the light and heterotrophic growth in the dark and are ubiquitous in soils, aquatic systems and wetlands. In this study, we investigated arsenic biotransformation in three cyanobacterial species （Microcystis sp. PCC7806, Nostoc sp. PCC7120 and Synechocystis sp. PCC6803）. Each accumulated large amounts of arsenic, up to 0.39 g kg-1 dry weight （DW）, 0.45 g kg-1 DW, and 0.38 g kg-1 DW when treated with 100 μM sodium arsenite for 14 days, respectively. Inorganic arsenate and arsenite were the predominant species, with arsenate making up more than 80% of total arsenic; methylated arsenicals were detected following exposure to higher arsenic concentrations. When treated with arsenate for six weeks, cells of each cyanobacteria produced volatile arsenicals. The genes encoding the ArsM （As（III） S-adenosylmethionine methyltransferase） were cloned from these three cyanobacteria. When expressed in an arsenic-hypersensitive strain of Escherichia coli, each conferred resistance to arsenite. Two of ArsM homologues （SsArsM from Synechocystis sp. PCC6803 and NsArsM from Nostoc sp. PCC7120） were purified, and were shown to methylate arsenite in vitro with trimethylarsine as the end product. Given that ArsM homologues are widespread in cyanobacteria, we propose that they play an important role in arsenic biogeochemistry.