Searching for Answers about an Ancient Organism

July 25, 2014 | by the Office of Marketing and Communications

Hot springs in the remote northwestern reaches of Wyoming’s Yellowstone National Park put on uncanny displays of color, their peculiar chemistry producing prisms of jeweled tints at the water’s edge.

Tamara Marsh, a professor of biology at Elmhurst, has spent parts of the past four summers in this astonishing corner of Yellowstone, but she doesn’t visit for the natural beauty. She’s interested in the ancient microorganisms that thrive in the low oxygen and high temperatures of the seemingly inhospitable springs.

Some scientists believe that these single-celled organisms, called archaea, may have been the first living things on earth. Many such microorganisms still make themselves at home in extreme environments, like deep-sea thermal vents, salt lakes and acid-laden streams. Conditions in some of these environments may approximate those generally found on Earth 3.6 billion years ago, when archaea are believed to have first appeared.

Marsh is investigating whether some kinds of archaea from springs at Yellowstone use heavy metals such as chromium 6—which can be toxic to humans at certain levels—to create energy. What she learns may provide clues about the evolution of simple life forms, about which science knows surprisingly little. According to some estimates, less than one percent of all microbial species have been described.

“This is a chance to fill in some blanks about early evolution and to learn more about microbial life,” Marsh said.

Archaea, though their name comes from a Greek word meaning “ancient things,” were discovered only in the 1970s. Marsh’s research focuses on those archaea that produce methane as a byproduct of energy-producing processes—so-called methanogens. Marsh suspects that methanogenic archaea may be able to create energy in other ways besides making methane.

Her hunch is based on recent gene-sequencing work that has shown that methanogenic archaea are genetically encoded to be resistant to heavy metals. That discovery raised questions for Marsh.

“Methanogens have always been thought to do just one thing for energy—they make methane or they die,” she said. “So why do they carry this genetic code? Why would an organism have this extra equipment if it didn’t use it in some way?”

Marsh’s search for answers begins in the Lower Geyser Basin area of Yellowstone, where each summer she trawls the waters of a half-dozen springs, on a kind of microbial fishing expedition. She works under a permit from the National Park Service, which requires her to do her microbe collecting out of the public view. So her work takes her to some of the less accessible, less traveled parts of the park—hot springs with evocative names like Queen’s Laundry, Narrow Gauge and Octopus Springs. Marsh and a field assistant—Elmhurst undergraduates have assisted her on several of her expeditions—hike about four miles from the nearest road to the springs, lugging about 20 pounds of gear. They bring cameras to record the conditions around the springs, heat guns to measure water temperatures, even hand warmers repurposed to keep their heat-loving samples of archaea warm. The microbes thrive in water temperatures of 50 degrees Celsius or warmer.

Marsh’s journey to the springs takes her over meadows and along ridges, through fields scattered with bison remains, past elk and the occasional bear.

Even for a scientist like Marsh, focused on finding much smaller creatures, the beauty of Yellowstone can be stunning. “The quiet is amazing. You sometimes feel like you are the only two people on earth,” she said. “There are definitely worse places to work than in Yellowstone.”

At the springs, Marsh begins by cataloging any changes to the landscape since her last visit. Then, like an experienced angler, she looks for telltale signs of the presence of the microorganisms. Bubbling water is one such clue. So are floating microbial mats, multicolored layer cakes of bacteria and other microorganisms.

“You can find hundreds of layers of microbes in biomat, so there’s a good chance that I’ll find what I’m looking for there,” Marsh said.

She casts into the water with a long pole and a dipper to collect archaea-laden water from the springs. She also takes samples from the soil at the water’s edge. It all goes into collection vessels, to be kept warm during the overnight trip to Elmhurst’s campus, where the samples can be stored in incubators.

For all of Yellowstone’s wonders, it is back at Elmhurst that Marsh can really begin looking for answers about archaea.

“I’m really excited about what happens in the lab,” she said.

In her lab, she creates a slurry of water, sediment and biomaterial from each spring. By manipulating the temperatures of the samples, or adjusting the concentrations of sediments, or inoculating the samples with various chemical inhibitors, she hopes to create conditions in which archaea are likely to use chromium 6 to create energy. Her hypothesis is that as the microorganisms deplete chromium levels in their environment over time, they begin to produce methane as an alternative means of creating energy. On one wall of her office, she has created what she calls her “dream graph.” It shows two lines: One represents chromium levels sinking; the other, methane production beginning when chromium levels reach a low point. Her aim is to create in the lab the processes depicted in the graph.

“We haven’t gotten to that dream graph yet,” Marsh says. But she has seen evidence that methanogenic archaea do play a part in chromium reduction. She is at work on two papers that she plans to submit to journals this year.

Marsh began working with other anaerobic microbes while in graduate school at the University of Oklahoma. Later, she took a National Science Foundation–funded short course on the geochemistry and microbiology of Yellowstone. She was intrigued by what she found there.

“It offers a close replicate of early Earth,” Marsh said. She began looking more closely at the microorganisms found in the hot springs there. Could archaea like the ones thriving at Yellowstone be the long-sought last universal common ancestor (sometimes called LUCA), the great-grandparent of all living things?

“That’s one of the blank spaces on the family tree that still need to be filled in,” Marsh said. She hopes some answers about the beginnings of life on Earth can be found in the steaming and bubbling waters of Yellowstone’s hot springs. At first glance, those hot springs, which struck 19th-century explorers as “infernal,” may seem like unlikely places to find insights into the evolution of life on Earth. But conditions there make it an ideal place for Marsh to learn more about a most important form of early life.

“These springs are teeming with life,” Marsh said. “It just happens to be very tiny.”

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