Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China.
Ecotoxicol Environ Saf. 2024 Apr 15;275:116258. doi: 10.1016/j.ecoenv.2024.116258. Epub 2024 Mar 28.
Biomethylation is an effective means of arsenic detoxification by organisms living in aquatic environments. Ciliated protozoa (including Tetrahymena species) play an important role in the biochemical cycles of aquatic ecosystems and have a potential application in arsenic biotransformation. This study compared arsenic tolerance, accumulation, methylation, and efflux in 11 Tetrahymena species. Nineteen arsenite (As(III)) S-adenosylmethionine (SAM) methyltransferase (arsM) genes, of which 12 are new discoveries, were identified, and protein sequences were studied. We then constructed recombinant cell lines based on the Tetrahymena thermophila (T. thermophila) wild-type SB210 strain and expressed each of the 19 arsM genes under the control of the metal-responsive the MTT1 promoter. In the presence of Cd and As(V), expression of the arsM genes in the recombinant cell lines was much higher than in the donor species. Evaluation of the recombinant cell line identified one with ultra-high arsenic methylation enzyme activity, significantly higher arsenic methylation capacity and much faster methylation rate than other reported arsenic methylated organisms, which methylated 89% of arsenic within 6.5 h. It also had an excellent capacity for the arsenic detoxification of lake water containing As(V), 56% of arsenic was methylated at 250 μg/L As(V) in 48 h. This study has made a significant contribution to our knowledge on arsenic metabolism in protozoa and demonstrates the great potential to use Tetrahymena species in the arsenic biotransformation of aquatic environments.
生物甲基化是水生环境中生物解毒砷的有效手段。纤毛原生动物（包括四膜虫属物种）在水生生态系统的生化循环中发挥着重要作用，并且在砷的生物转化方面具有潜在的应用价值。本研究比较了 11 种四膜虫属物种对砷的耐受性、积累、甲基化和外排。鉴定了 19 种砷代腺苷蛋氨酸（SAM）甲基转移酶（arsM）基因，其中 12 种是新发现的，并对其蛋白质序列进行了研究。然后，我们基于嗜热四膜虫（T. thermophila）野生型 SB210 菌株构建了重组细胞系，并在金属响应 MTT1 启动子的控制下表达了 19 种 arsM 基因中的每一种。在 Cd 和 As(V)存在的情况下，重组细胞系中 arsM 基因的表达水平远高于供体物种。对重组细胞系的评估鉴定出一种具有超高砷甲基化酶活性的细胞系，其砷甲基化能力明显高于其他已报道的砷甲基化生物，在 6.5 小时内可将 89%的砷甲基化。它还具有极好的湖泊水中 As(V)解毒能力，在 250μg/L As(V)浓度下 48 小时内可将 56%的砷甲基化。本研究为我们对原生动物砷代谢的认识做出了重要贡献，并展示了使用四膜虫属物种进行水生环境中砷的生物转化的巨大潜力。
