Bacteria builders

Science World, March 31, 2008 by David B. Williams

Yellowstone National Park has long fascinated geologists. The area's geothermal activity produces shooting geysers, stinky sulfur emissions, and gurgling mud pots. But a new discovery reveals that heat rising from deep within Earth isn't the only thing that creates the park's unique features. The stone terraces at the famous Mammoth Hot Springs appear to have formed with the help of bacteria.

The terraces are made from a type of limestone, called travertine. For more than a hundred years, geologists had thought that the travertine steps developed when a chemical reaction caused the compound calcium carbonate to precipitate (separate solids from a liquid) out of the mineral-rich springs.

Researchers from the University of Illinois at Urbana-Champaign, however, recently reported that thermophile bacteria that thrive in hot springs are necessary for travertine production. The heat-loving bacteria turn nitrogen into ammonia, a compound that makes the water less acidic. That makes it easier for calcium carbonate to form. In fact, two-and-a-half times more of the mineral crystallized when bacteria were present than when scientists filtered them out of the spring water.

This new discovery excites biologists as well as geologists. That's because it could help them understand whether microbes affect mineral formation in other extreme environments, like caves and even Mars.

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