摘要
Arsenic-contaminated water is a serious hazard for human health. Plankton plays a critical role in the fate and toxicity of arsenic in water by accumulation and biotransformation.Spirulina platensis（S. platensis）, a typical plankton, is often used as a supplement or feed for pharmacy and aquiculture, and may introduce arsenic into the food chain, resulting in a risk to human health. However, there are few studies about how S. platensis biotransforms arsenic. In this study, we investigated arsenic biotransformation by S. platensis. When exposed to arsenite（As（Ⅲ））, S. platensis accumulated arsenic up to 4.1 mg/kg dry weight.After exposure to As（Ⅲ）, arsenate（As（Ⅴ）） was the predominant species making up 64% to86% of the total arsenic. Monomethylarsenate（MMA（Ⅴ）） and dimethylarsenate（DMA（Ⅴ））were also detected. An arsenite S-adenosylmethionine methyltransferase from S. platensis（Sp Ars M） was identified and characterized. Sp Ars M showed low identity with other reported Ars M enzymes. The Escherichia coli AW3110 bearing Spars M gene resulted in As（Ⅲ） methylation and conferring resistance to As（Ⅲ）. The in vitro assay showed that Sp Ars M exhibited As（Ⅲ） methylation activity. DMA（Ⅴ） and a small amount of MMA（Ⅴ） were detected in the reaction system within 0.5 hr. A truncated Sp Ars M derivative lacking the last 34 residues still had the ability to methylate As（Ⅲ）. The three single mutants of Sp Ars M（C59S, C186 S, and C238S） abolished the capability of As（Ⅲ） methylation, suggesting the three cysteine residues are involved in catalysis. We propose that Sp Ars M is responsible for As methylation and detoxification of As（Ⅲ） and may contribute to As biogeochemistry.
Arsenic-contaminated water is a serious hazard for human health. Plankton plays a critical role in the fate and toxicity of arsenic in water by accumulation and biotransformation.Spirulina platensis（S. platensis）, a typical plankton, is often used as a supplement or feed for pharmacy and aquiculture, and may introduce arsenic into the food chain, resulting in a risk to human health. However, there are few studies about how S. platensis biotransforms arsenic. In this study, we investigated arsenic biotransformation by S. platensis. When exposed to arsenite（As（Ⅲ））, S. platensis accumulated arsenic up to 4.1 mg/kg dry weight.After exposure to As（Ⅲ）, arsenate（As（Ⅴ）） was the predominant species making up 64% to86% of the total arsenic. Monomethylarsenate（MMA（Ⅴ）） and dimethylarsenate（DMA（Ⅴ））were also detected. An arsenite S-adenosylmethionine methyltransferase from S. platensis（Sp Ars M） was identified and characterized. Sp Ars M showed low identity with other reported Ars M enzymes. The Escherichia coli AW3110 bearing Spars M gene resulted in As（Ⅲ） methylation and conferring resistance to As（Ⅲ）. The in vitro assay showed that Sp Ars M exhibited As（Ⅲ） methylation activity. DMA（Ⅴ） and a small amount of MMA（Ⅴ） were detected in the reaction system within 0.5 hr. A truncated Sp Ars M derivative lacking the last 34 residues still had the ability to methylate As（Ⅲ）. The three single mutants of Sp Ars M（C59S, C186 S, and C238S） abolished the capability of As（Ⅲ） methylation, suggesting the three cysteine residues are involved in catalysis. We propose that Sp Ars M is responsible for As methylation and detoxification of As（Ⅲ） and may contribute to As biogeochemistry.
基金
supported by the Natural Science Foundation of Fujian Province (No. 2014J01141)
the National Natural Science Foundation of China (No. 31270161)
the Fujian-Taiwan Joint Innovative Center for Germplasm Resources and Cultivation of Crop (No. Fujian 2011 Program, [2015]75)
