Biotransformation of arsenic by algae
Arsenic is the most common toxic substance in the environment, ranking first on the US Superfund list of hazardous substances. It is introduced to the environment primarily from geologic sources and is acted on biologically, creating an arsenic biogeocycle. Geothermal environments are well known for their elevated arsenic content and thus provide an excellent setting in which to study microbe–arsenic interactions. So far, studies aimed at identifying the organisms participating in these and other arsenic transformations have focused almost entirely on microorganisms belonging to the domains Archaea and Bacteria. In contrast, comparatively little attention has been paid to the Eukarya that inhabit these extreme environments, much less their potential contribution to biogeochemical cycles in these extreme habitats. Now it would appear that algae play a significant role in arsenic cycling in the geothermal environment as also found in a range of marine and freshwater environments. These observations indicate that arsenic methylation forms an important component of the global arsenic biogeocycle.
Biotransformation of arsenic by a Yellowstone thermoacidophilic eukaryotic alga. PNAS USA March 10, 2009
Arsenic is the most common toxic substance in the environment, ranking first on the Superfund list of hazardous substances. It is introduced primarily from geochemical sources and is acted on biologically, creating an arsenic biogeocycle. Geothermal environments are known for their elevated arsenic content and thus provide an excellent setting in which to study microbial redox transformations of arsenic. To date, most studies of microbial communities in geothermal environments have focused on Bacteria and Archaea, with little attention to eukaryotic microorganisms. Here, we show the potential of an extremophilic eukaryotic alga of the order Cyanidiales to influence arsenic cycling at elevated temperatures. Cyanidioschyzon sp. isolate 5508 oxidized arsenite [As(III)] to arsenate [As(V)], reduced As(V) to As(III), and methylated As(III) to form trimethylarsine oxide (TMAO) and dimethylarsenate [DMAs(V)]. Two arsenic methyltransferase genes, CmarsM7 and CmarsM8, were cloned from this organism and demonstrated to confer resistance to As(III) in an arsenite hypersensitive strain of Escherichia coli. The two recombinant CmArsMs were purified and shown to transform As(III) into monomethylarsenite, DMAs(V), TMAO, and trimethylarsine gas, with a Topt of 60–70°C. These studies illustrate the importance of eukaryotic microorganisms to the biogeochemical cycling of arsenic in geothermal systems, offer a molecular explanation for how these algae tolerate arsenic in their environment, and provide the characterization of algal methyltransferases.
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Tags: Biology, Biotechnology, Environment, Microbiology, Science
