NM Tech Researchers Study Deep-subsurface Microbes

by George Zamora

SOCORRO, N.M., November 27, 2001 -- New Mexico Tech graduate student Sean McCuddy recently returned from field research conducted deep beneath the surface of the Earth, having spent most of his summer in the labyrinthine tunnels of several of the world's deepest gold mines -- many of them situated more than two miles below the South African plains.

Though he is pursuing a master of science degree in geology at New Mexico Tech, McCuddy's most recent field assignment did not involve gathering gold samples, but rather had him retrieving a variety of unusual microorganisms found at such extreme depths, many of which had never before been named or identified.

These deep-dwelling bacteria, known as thermophiles for their affinity for heat, survive and grow within rocks that have ambient temperatures that sometimes exceed 140 degrees Fahrenheit, and often do so without oxygen.

"One of the techniques we've employed in this research project is to sample pristine -- that is, uncontaminated by the mining process -- pore or fracture water that is typically found inside these types of rocks," explains New Mexico Tech microbiologist Tom Kieft, the principal investigator of the project. "However, this is not a trivial thing to do. It's hard to get a representative sample of water that will also have the viable subsurface microorganisms we're looking for."

From the fracture water reclaimed from the deep-subsurface rocks, Kieft and his research colleagues use bacteria-culturing methods to grow colonies of a few of these subterranean microbes right in the lab.

"However, many of these microbes cannot be cultivated through normal means," Kieft says, "so we've turned to sequencing their DNA."

Kieft, himself, has been down into the South African gold mines twice now in pursuit of microorganisms, and describes the environment as ". . . not for someone who's claustrophobic."

Even for McCuddy, who spent four months going down into the depths of the mines on average of two or three times a week, it was never something he could get used to doing.

"The steel cages of the mine's elevator system would be filled up with anywhere from 30 to 50 miners, besides myself," McCuddy relates, "and then we'd go down about a mile, where we'd walk over to another steel-cage elevator that would take us down another mile."

Once he reached bottom, McCuddy and other members of the research team would then walk another mile or two from the main shaft through the mine's vast network of tunnels to visit various sites, where they would either hoist down sampling cartridges into pre-existing bore holes or retrieve the ones they had left there two or three weeks prior.

"We wanted to take samples at different depths of these prospecting holes which had been drilled by the mining companies to see what types of microorganisms we could find at different levels," McCuddy says.

"There's even some hint in some of the mines of groundwater having come up from deeper, hotter zones," Kieft says, "and some microorganisms may have come up along with it.

"However, outside of any natural environment they might be found in, microorganisms are typically difficult to cultivate," he adds. "Nevertheless, we try to grow them in culture, or, if we have to, to characterize them through indirect means."

In the first two years of their five-year study, Kieft and his graduate students have been successful in growing several strains of sulfate-reducing bacteria, methanogenic (methane- generating) and methanotropic (methane-"eating") bacteria, and metal-reducing bacteria that cause formation of iron and manganese minerals.

"We also found a metal-reducing thermophile in the first sample we collected that we've discovered is extremely efficient in reducing iron, manganese, sulfur, nitrates, uranium, chromium, cobalt, and technetium," Kieft says. "We're calling this one Thermophillus multireducens, but that's still unofficial since the name hasn't been accepted in the literature, yet."

Kieft points out that the deep-subsurface microbiology research program -- a collaborative effort with Princeton University geoscientist Tullis Onstott -- is continually generating new data about the unique microbes, resulting in mutual benefits for all the parties involved in the research.

"There are potential benefits to the mining companies in South Africa in that they might be able to use some of the information about where these microbes are found to improve extraction of minerals in subsurface environments," he says. "As for us, it helps us better understand the limits of life, and extends our knowledge of bio-geochemistry."

NASA, who along with the National Science Foundation, is co- funding the study, is interested in applying what Kieft and his colleagues learn about subsurface environments to their planned missions to Mars, since there is speculation that microbial life may exist below that planet's surface, as well.

In the meantime, Kieft is planning on conducting a research workshop for minority undergraduates -- particularly African American and Black South African students -- which will give them first-hand experiences with collecting and studying subsurface microorganisms. The workshop will be held the week of December 16 - 21, in South Africa.