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Surprising Form Of Bacteria Found In Yellowstone's Hot Spot Of Diversity

Bubbling hot springs and geysers spewing water hundreds of feet into the air draw millions of tourists annually to Yellowstone National Park. Scientists also come to the park to study the complex bacterial communities that live in the hot springs, which were once thought to be devoid of life due to above boiling temperatures and acidic or alkaline water. Scientists, however, have found a surprising variety of life in these extreme environments.

The latest discovery from Yellowstone's hot springs is a new bacterium that subsists by converting light into chemical energy, a process called phototrophy. The bacterium, Candidatus Chloracidobacterium thermophilum, belongs to a large biological grouping, or phylum, not previously known to contain phototrophic species.

The work was done by Donald Bryant of Penn State University, David M. Ward of Montana State University, and colleagues and the findings were published in the July 27, 2007 issue of Science.

The discovery of C. thermophilum is compelling for scientists because finding a new photosynthetic phylum is a relatively rare occurrence. Until this discovery, only five bacteria phyla were known to have members that produce pigments, known as chlorophylls, which are used by plants and some microscopic life to obtain energy from sunlight. In the last 100 years, only three new phototrophic groups have been discovered. C. thermophilum belongs to the Acidobacteria phylum, a poorly understood phylum of bacteria also found in soils.

"It is one of those wonderful discoveries that make you realize big discoveries are out there to be made, especially in the microbial world,” says Anna-Louise Reysenbach, a professor of microbial biology at Portland State University. Reysenbach studies the ecology of hot springs on land and on the seafloor.

The new bacterium originally was found in samples collected from Octopus Spring, about six miles from Old Faithful geyser. Octopus is a hot spring surrounded by layers of bacterial communities, or bacterial mats. Octopus' bacteria have been studied for over 30 years.

The bacteria that live in these mats interest scientists because they thrive in conditions too extreme for other life. Another Yellowstone hot spring bacterium, Thermus aquaticus, revolutionized DNA processing. In a process known as polymerase chain reaction, proteins from T. aquaticus enable DNA replication to occur rapidly at high temperatures. Large amounts of DNA are necessary for genetic tests. C. thermophilum may have advantages too.

The phototrophic nature of the new bacteria may provide useful applications, Bryant explains. "We feel that these microbial communities that are gathering light energy and converting it into essentially a fixed carbon biomass can be used, say, for biofuel production.”

The use of bacterial communities instead of a single species for production of biofuels, such as ethanol, could greatly increase the scale of production. Increased productivity in a smaller growing area could lead to cheaper ethanol. These possibilities have not been explored yet with hot spring bacteria. The scientific value of the new discovery is being investigated.

New research methods are allowing scientists to probe into smaller ecosystems with results indicating previously unimagined diversity. Although individual species cannot be differentiated with the naked eye, bacterial mats can contain many species living together. To study the bacterial community, a sample of the DNA from the mat community is processed and compared to a computer database to look for unknown species. The method is known as metagenomics. The previously used method involved culturing each species separately. Only about one percent of bacteria species from a sample grow in the lab, leaving a large gap in the knowledge of what exists in nature.

"Here was an organism that represented close to ten percent of the total biomass in the mat that had gone undetected for fifty years,” explains Bryant. "So I think the potential for finding new things in places like this is much greater than we can even imagine. Because even in the best studied systems we are still finding many new things that are actually quite abundant.”

"That is the thing about discoveries in science,” says Reysenbach. "You never quite know what applications they have.”

Beth Martin is a graduate student in the department of Earth and Spaces Sciences at the University of Washington.


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