Arsenic is a ubiquitous carcinogen in the environment, threatening water and food supply in some regions of the world. Arsenic has many species in nature and the speciation determines its toxicity, mobility, and fate. Usually inorganic arsenicals (arsenite, arsenate) are more toxic than organic arsenicals. Organic arsenicals are often produced by biomethylation of inorganic arsenic, resulting in mono- and di-methylarsenate, even volatile, non-toxic trimethylarsenite. Thus it has provided a new theory for bioremediation of As-contaminated environments. The corresponding molecular mechanism has become a topic of interest in this field.
Arsenic biomethylation has been studied in bacteria, cyanobacteria, red alga, and humans, but little is known in protozoa, one important group of the aquatic eco-system. Professor Yong-Guan Zhu’s group in the Institute of Urban Environment, Chinese Academy of Sciences reported in 2011 that the protozoan Tetrahymena pyriformis has strong ability to methylate arsenic (Environ. Pollut，2011). Through the collaboration with Professor Wei Miao’s group in the Institute of Hydrobiology, they identified and characterized the first protozoan arsenic methyltransferase gene in this species. They verified the arsenic methylation function of this gene by knock-out of the gene in Tetrahymena and heterologous expression of this gene in hypersensitive E. coli. They found that the purified protein not only methylated inorganic arsenic to mono- and di- methylarsenate, but also had the novel property of producing trimethylarsenite and dimethylarsine gases. This work revealed the molecular mechanism of arsenic methylation in protozoa. It has enriched our knowledge of arsenic biomethylation and has provided insight for bioremediation of arsenic-contaminated environments by protozoa.
This work has been published in Aquatic Toxicology (149: 50-57, 2014), titled “Identification and characterization of the arsenite methyltransferase from a protozoan, Tetrahymena pyriformis” (http://dx.doi.org/10.1016/j.aquatox.2014.01.028).
