title: Biotransformation and volatilization of arsenic by three photosynthetic cyanobacteria.
abstract: Arsenic (As) is a pervasive and ubiquitous environmental toxin that has created worldwide human health problems. However, there are few studies about how organisms detoxify As. 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 As biotransformation in three cyanobacterial species (Microcystis sp. PCC7806, Nostoc sp. PCC7120, and Synechocystis sp. PCC6803). Each accumulated large amounts of As, up to 0.39 g kg(-1) dry weight, 0.45 g kg(-1) dry weight, and 0.38 g kg(-1) dry weight when treated with 100 μM sodium arsenite for 14 d, respectively. Inorganic arsenate and arsenite were the predominant species, with arsenate making up >80% of total As; methylated arsenicals were detected following exposure to higher As concentrations. When treated with arsenate for 6 weeks, cells of each cyanobacterium produced volatile arsenicals. The genes encoding the As(III) S-adenosylmethionine methyltransferase (ArsM) were cloned from these three cyanobacteria. When expressed in an As-hypersensitive strain of Escherichia coli, each conferred resistance to arsenite. Two of the ArsM homologs (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 homologs are widespread in cyanobacteria, we propose that they play an important role in As biogeochemistry.
authors.affiliation: Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China.
authors.forename: Xi-Xiang
authors.initials: XX
authors.lastname: Yin
authors.forename: Jian
authors.initials: J
authors.lastname: Chen
authors.forename: Jie
authors.initials: J
authors.lastname: Qin
authors.forename: Guo-Xin
authors.initials: GX
authors.lastname: Sun
authors.forename: Barry P
authors.initials: BP
authors.lastname: Rosen
authors.forename: Yong-Guan
authors.initials: YG
authors.lastname: Zhu
mesh_terms: D000595:Amino Acid Sequence; D001151:Arsenic / Q000378:metabolism* / Q000633:toxicity; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics; D001711:Biotransformation / Q000187:drug effects; D003001:Cloning, Molecular; D000458:Cyanobacteria / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D005798:Genes, Bacterial / Q000235:genetics; D006801:Humans; D008745:Methylation / Q000187:drug effects; D008969:Molecular Sequence Data; D010788:Photosynthesis / Q000187:drug effects; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic / Q000187:drug effects; D014835:Volatilization / Q000187:drug effects
chemical_list: D001426:Bacterial Proteins; D001151:Arsenic