蓝藻砷甲基化分子机制

砷（As）是一种无处不在的有毒元素，砷污染问题已成为当前世界环境研究的热点之一。蓝藻广泛分布在土壤和各种水生环境中。由于它们的环境适应力强，生长速度快，因此是引起水华的主要物种。目前有关蓝藻对砷响应机制的研究还鲜有报道。

*城市环境研究所城市环境与健康重点实验室朱永官组研究揭示了蓝藻砷甲基化的分子机制。该研究发现微囊藻（Microcystis sp. PCC7806）、念珠藻（Nostoc sp. PCC7120）和集胞藻（Synechocysis sp. PCC6803）都能将无机砷转化为甲基砷。将三种蓝藻的砷甲基转移酶基因（arsM）克隆，并表达在对砷高度敏感的大肠杆菌突变株AW3110（ΔarsRBC）中，它们都能赋予细胞对As（III）的抗性。两种纯化的蛋白质SsArsM （Synechocystis ArsM）和NsArsM（Nostoc ArsM）在体外能够将As（III）转化为甲基砷，并生成一定量的挥发砷。鉴于蓝藻具有较强的砷转化能力及其在环境中的广泛存在，它在砷的生物地球化学循环中起到了重要的作用。

此项研究由*和国家自然科学基金委资助。博士生尹西翔为*作者，朱永官博士为文章通讯作者。相关论文在《植物生理学》（Plant Physiology）杂志在线发表（Biotransformation and volatilization of arsenic by three photosynthetic cyanobacteria, doi:10.1104/pp. 111.178947）

原文出处：

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.