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

*城市環(huán)境研究所城市環(huán)境與健康重點(diǎn)實(shí)驗(yàn)室朱永官組研究揭示了藍(lán)藻砷甲基化的分子機(jī)制。該研究發(fā)現(xiàn)微囊藻（Microcystis sp. PCC7806）、念珠藻（Nostoc sp. PCC7120）和集胞藻（Synechocysis sp. PCC6803）都能將無機(jī)砷轉(zhuǎn)化為甲基砷。將三種藍(lán)藻的砷甲基轉(zhuǎn)移酶基因（arsM）克隆，并表達(dá)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(xì)胞對As（III）的抗性。兩種純化的蛋白質(zhì)SsArsM （Synechocystis ArsM）和NsArsM（Nostoc ArsM）在體外能夠?qū)s（III）轉(zhuǎn)化為甲基砷，并生成一定量的揮發(fā)砷。鑒于藍(lán)藻具有較強(qiáng)的砷轉(zhuǎn)化能力及其在環(huán)境中的廣泛存在，它在砷的生物地球化學(xué)循環(huán)中起到了重要的作用。

此項(xiàng)研究由*和國家自然科學(xué)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(guān)論文在《植物生理學(xué)》（Plant Physiology）雜志在線發(fā)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.