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FALL 2006
New Hypothesis on the Evolution of Hot Springs Microorganisms
by Sam Fahmy

Since their discovery in the late 1970s, microorganisms known as archaea have fascinated scientists with their ability to thrive in conditions that are extremely hot, acidic or salty.

In the 1990s, however, scientists discovered that archaea occur widely in more mundane, low-temperature environments such as oceans and lakes. Now, researchers from the University of Georgia and Harvard University have found evidence that these low-temperature archaea might have evolved from a moderate-temperature environment rather than from their high-temperature counterparts — as most scientists had believed. The results appeared in the June 2006 Applied and Environmental Microbiology.

“Archaea represent one of the three domains of life on Earth,” said Chuanlun Zhang, lead author of the study and professor of marine sciences at UGA. “Understanding their evolution may shed light on how all life forms evolve and interact with the environment through geological history.”

Zhang and his colleagues examined a common group of archaea known as Crenarchaeota, whose low-temperature success may involve the unique molecule crenarchaeol. This molecule enables an organism’s cell membrane to remain flexible in cooler environments.

Previously, most scientists viewed crenarchaeol as a relatively new feature by evolutionary standards — evolving 112 million years ago, or about the same time that dinosaurs became extinct.

By analyzing 17 samples from springs in California, Nevada and Thailand, as well as examining data published by other researchers in different environments, Zhang and his colleagues found that crenarchaeol was most commonly found at temperatures of approximately 104 degrees Fahrenheit — well above even the warmest sea surface temperatures during the Cretaceous period. Zhang and his team concluded that the Crenarchaeota evolved much earlier than previously thought — about 3.5 billion years ago, shortly after life began to emerge on Earth.

Understanding these ancient organisms is important to the planet’s future, Zhang said. Most scientists believe that Crenarchaeota play an important role in helping sequester greenhouse gases from the atmosphere. Having a better understanding of how abundant Crenarchaeota are and how much carbon they remove from the ecosystem can help scientists more accurately model the effects of global warming.

For more information, email Chuanlun Zhang at zhang@srel.edu.