Some Like It Hot, Some Like It Cold
Microbial Life in Hot Springs and Antarctic Lakes

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"Imagine diving into a refreshingly cool swimming pool. Now think instead of plowing into water that is boiling or near freezing." These images, provided by Dr. Michael Madigan and Dr. Barry Marrs in the arcticle "Extremophiles" published in 1997 in Scientific American ">http://www.sciam.com/0497issue/0497marrs.html"> http://www.sciam.com/0497issue/0497marrs.html , has me asking why would any organism plunge into freezing or boiling waters? And how could they survive? Are there organisms that live in these kinds of environments? I worked for six weeks in the Dry Valleys in Antarctica, studying a bacterium that survived in a permanently ice-covered lake, as well as, assisted in the isolation of an organism living in a hot spring in Yellowstone National Park! What are the known temperature limitations for living things on our planet?

It was long believed that no organism could survive in the desolate, cold Dry Valleys of Antarctica or in the areas of the Earth where geothermal activity is evident. Psychrophiles are organisms that live in cold environments. Living at temperatures between 1^oC and 15^oC, these organisms include algae, diatoms, and bacteria. Because they grow so slowly, these organisms are much more difficult to culture. In Lake Bonney, a lake permanently covered with 4 meters of ice, biologic activity is found between 12 and 20 meters. Below this suboxic region, little bacterial activity is evident.

Thermophiles are organisms that have optimal growth temperatures above 50^oC. These bacteria have been isolated from hot springs, where oxygen is limited and in hydrothermal vents in deep oceans where life is dependent on organisms that use chemicals instead of sunlight for primary production.

What are the temperature ranges for the growth of common bacteria, such as Eshcerichia coli and Pseudomonas aeruginosa? Do either of these organisms withstand extremes of heat or cold? What kinds of bacteria are found in these unfriendly environments? In this activity, students will have the opportunity to witness the fragile nature of these organisms, with regard to temperature. Students will understand the role of temperature in determining what kinds of organisms are found in these unforgiving environments.

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