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Researchers Find Alga that Influence Arsenic Cycling in Hot Springs


Arsenic is the most common toxic substance in the environment, ranking first on the Superfund list of hazardous substances. Geothermal environments are known for their elevated arsenic content and thus provide an excellent setting in which to study microbial redox transformations of arsenic species. Such places are also known for the presence of archaic organisms withstanding the extreme living conditions.  Up to now, most studies of microbial communities in geothermal environments have focused on Bacteria and Archaea, with little attention to eukaryotic microorganisms.

The new study:
The alga and how it transforms arsenic species are described in a paper posted the week of March 9 in the online edition of Proceedings of the National Academy of Sciences, or PNAS. Lead authors are McDermott, professor in the Department of Land Resources and Environmental Sciences at Montana State University and Barry Rosen of Florida International University. Among the four co-authors is Corinne Lehr, who formerly worked with McDermott as a postdoctoral scientist at MSU and is now a faculty member at California Polytechnic State University.

According to McDermott, arsenic is very common in the hot, acidic waters of Yellowstone and presents real challenges for microorganisms living in these conditions. Indeed, there are challenges for the researchers. McDermott said the acid in the soil and water is strong enough that it sometimes eats holes through his jeans when he kneels to collect samples.

The alga investigated -- a simple one-celled algae called Cyanidioschyzon -- withstands such extremely harsh conditions and is able to chemically modify arsenic species occurring naturally around hot springs, said Tim McDermott.

McDermott has worked in Yellowstone for more than a decade and travels year-round to the Norris Geyser Basin to study the microbial mats that grow in acidic springs. Over the years, he noticed thick algae mats that were so lush and green in December that they looked like Astro-Turf, however by June, they were practically gone. While investigating the change, McDermott and his collaborators learned about the Cyanidiales alga and its ability to modify toxic arsenic species into less dangerous forms.

The alga thrives in water up to 135 degrees Fahrenheit (too hot to shower) with a very acidic pH factor ranging from 0.5 to 3.5. Creeks are considered acidic if their pH factor is less than 7.

The scientists cloned genes from the alga, and then studied the enzymes to figure out how they changed arsenic speciation. They learned that the alga oxidizes, reduces, and converts arsenic to several forms, such as monomethylarsenite, dimethylarsenate and trimethylarsine oxide that are less toxic than the original inorganic arsenic.

One of the species formed is arsine, a gas that can evaporate, especially at the high temperatures of the Yellowstone springs. Rosen explained, that such evaporation allows life to exist in otherwise "really deadly concentrations of arsenic".

McDermott said the scientists conducted basic research that may have implications someday for acid mine drainage and acid rock drainage remediation efforts.

Molecular evidence suggests that the algae in these springs are comprised of two different population groups, McDermott said. One flourishes in the winter and the other in the summer. The algae that dominate in the summer can tolerate high levels of ultraviolet rays.

Source: adapted from MSU news

The original study

Jie Qin, Corinne R. Lehr, Chungang Yuan, X. Chris Le, Timothy R. McDermott, Barry P. Rosen, Biotransformation of arsenic by a Yellowstone thermoacidophilic eukaryotic alga, Proc. Natl. Acad. Sci. U.S.A. , Published online before print March 10, 2009, DOI: 10.1073/pnas.0900238106

Related studies (newest first)

Ferdi L. Hellweger, Dynamics of arsenic speciation in surface waters: As(III) production by algae, Appl. Organomet. Chem., 19/6 (2005) 727-735. DOI: 10.1002/Aoac.894

Toshikazu Kaise, Shoko Fujiwara, Mikio Tsuzuki, Teruaki Sakurai, Tohru Saitoh, Chiyo Mastubara, Accumulation of arsenic in a unicellular alga Chlamydomonas reinhardtii, Appl. Organomet. Chem., 13/2 (1999) 107-111. DOI: 10.1002/(SICI)1099-0739(199902)13:2<107::AID-AOC824>3.0.CO;2-9

T. Kuroiwa, A. Ohki, K. Naka, S. Maeda, Biomethylation and biotransformation of arsenic in a freshwater food chain: Green alga (Chlorella vulgaris) -> Shrimp (Neocaridina denticulata) -> Killifish (Oryzias latipes), Appl. Organomet. Chem., 8/4 (1994) 325-333. DOI: 10.1002/aoc.590080407

William R. Cullen, H. Li, S.A. Pergantis, G.K. Eigendorf, L.G. Harrison, The Methylation of Arsenate by a Marine Alga Polyphysa peniculus in the Presence of L-methionine-methyl-d3, Chemosphere, 28 (1994) 1009-1019.

S. Maeda, K. Kusadone, H. Arima, A. Ohki, K. Naka, Biomethylation of arsenic and its excretion by the alga Chlorella vulgaris, Appl. Organomet. Chem., 6/4 (1992) 407-413.  DOI: 10.1002/aoc.590060416

S. Maeda, H. Wada, K. Kumeda, M. Onoue, A. Ohki, S. Higashi, T. Takeshita, Methylation of inorganic arsenic by arsenic-tolerant freshwater algae, Appl. Organomet. Chem., 1/5 (1987) 465-472. DOI: 10.1002/aoc.590010512

M.D. Baker, P.T.S. Wong, Y.K. Chau, C.I. Mayfield, W.E. Inniss, Methylation of arsenic by freshwater green algae, Can. J. Fish Aquat. Sci., 40 (1983) 1254-1257. DOI: 10.1139/f83-142

Meinrat O. Andreae, D. Klumpp, Biosynthesis and release of organoarsenic compounds by marine algae, Environ. Sci. Technol., 13/6 (1979) 738-741. DOI: 10.1021/ES60154A001

Kurt J. Irgolic, E.A. Woolson, R.A. Stockton, R.D. Newman, N.R. Bottino, R.A. Zingaro, P.C. Kearney, R.A. Pyles, S. Maeda, W.J. McShane, E.R. Cox, Characterization of arsenic compounds formed by Daphnia magna and Tetraselmis chuii from inorganic arsenate, Environ. Health Perspect., 19 (1977) 61-66. DOI: 10.1289/ehp.771961

Related EVISA Resources

Journal Database: Proceedings of the National Academy of Sciences of the USA
Link database: Arsenic environmental pollution
Link database: Toxicity of arsenic species

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last time modified: March 17, 2009


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