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September 24, 2001
Life at the Extremes

Woods Hole, MA-Linda Amaral Zettler is finding life in a place few expected to find it: the blood-red, highly acidic, toxic waters of the Rio Tinto in southwest Spain. "People essentially assumed the river was dead," says Amaral Zettler, a year-round staff scientist in the Marine Biological Laboratory's Bay Paul Center. Instead, she's found an ecosystem where organisms endure despite conditions that are usually considered deadly. Amaral Zettler's job is to find out what organisms inhabit this 90km river and how they are able to survive. 

The ruddy color of the Rio Tinto arises from acidic water dissolving the rusty, oxidized iron that coats the river's glistening yellow riverbed and banks. Acid-tolerant plants border the river, but Amaral Zettler's interest lies in the diverse microscopic organisms that exist as blooms of algae covering the water and maintain the acidity of the Rio Tinto. Amaral Zettler first collects samples of the Rio Tinto's sediment, and biofilm, the slime composed of densely packed living and dead organisms that coats the surface of the river's water and rocks. She then probes these biologically rich layers using molecular technology. By examining the DNA extracted from the samples, Amaral Zettler can determine the types of organisms populating the river. 

Amaral Zettler's research is uncovering a self-contained ecosystem that is home to many new microscopic single-celled organisms. Some of the microbes are photosynthetic algae, capable of making their own food. Others are heterotrophic and eat the other organisms in the river to survive. She has not only identified but cultivated in her laboratory a diminutive creature called the Euglena mutabilis, which looks and moves like a worm when viewed under a microscope. This diversity in a river traditionally considered "dead" is exciting, says Amaral Zettler, and "there is no doubt we're finding new species." She just hasn't determined how many new genera or families of microorganisms have been discovered. To discern this, Amaral Zettler needs to raise and study more of the Rio Tinto's microorganisms in her lab. 

Once Amaral Zettler documents the scope of the Rio Tinto's diversity, research on how these organisms live in an acidic environment with toxic concentrations of metals will begin. With this information scientists can better understand how organisms survive in extreme environments here on earth, some of which may be similar to ecosystems in the severe climates of other planets. The ability of scientists to find and characterize the extent of microbial diversity in the universe may depend on the lessons Amaral Zettler's learned from a red river in Spain once considered uninhabitable.

Recent Publications

Amaral Zettler, L. A., Anderson, O. R., Nerad, T. A., & Sogin, M. L. 2001. The phylogenetic position of Comandonia operculata and its implications for the taxonomy of the genus Acanthamoeba. IXth International Meeting on the Biology and Pathogenicity of Free-Living Amoebae, Paris 8-14 July, John Libbey Eurotext, Paris. 235-242. 

Amaral Zettler, L. A., Nerad, T. A., O'Kelly, C. J., & Sogin, M. L. 2001. The Nucleariid Amoebae: More Protists at the Animal-Fungal Boundary. Journal of Eukaryotic Microbiology. 48(3) 293-297.

Amaral Zettler, L. A., Nerad, T. A., O'Kelly, C. J., Peglar, M. T., Gillevet, P. M., Silberman, J. D. & Sogin, M. L. 2000. A Molecular Reassessment of the Leptomyxid Amoebae.  Protist 151: 275-282.