Going Down?

Microbiologist Jeff Gralnick and an interdisciplinary team of U of M researchers descend to the depths of the Soudan Mine to study unusual microbes that thrive without ever seeing the light of day.

Microbiologist Jeff Gralnick isn’t afraid of the dark, remote environments. That’s where the novel microorganisms hang out. So when E. Calvin Alexander, a geochemist in the U of M’s Department of Geology and Geophysics invited him to take a 2,341-foot trip to the lowest level (level 27) of Minnesota’s Soudan Mine to check out some microbial communities, Gralnick didn’t hesitate.

“This is a frontier of microbiology, an extreme environment where microbes live and even thrive despite the absence of light,” says Gralnick, a member of the University’s BioTechnology Institute and an assistant professor in the Microbiology Department. But it’s not just the novel environment that lures researchers deep underground. It’s the unusual properties of these darkness-dwelling microbes.

“Some of the bacteria that we are seeing are able to convert iron(II) into iron(III), essentially forming rust or iron oxide,” says Gralnick.  Typically, “Nobody knows how those bacteria do what they do.”

That first foray blossomed into an unusual collaboration across disciplines and campuses. The research team includes Gralnick and Alexander along with Dean Peterson, an adjunct geology professor at the University of Minnesota-Duluth. Gralnick describes Peterson as a “real rock geologist” who spent his career looking at the structure of the mine. The team also includes Brandy Toner in the Department of Soil, Water and Climate and Christine Salomon at the Center for Drug Design in the Academic Health Center. The project has gained momentum with the help of a $545,000 grant specifically targeting creative ideas from Minnesota’s Environment and Natural Resources Trust Fund. And the project has expanded beyond basic science research to include drug discovery, biotechnology and outreach. The team is already finding new microorganisms and will start sequencing them early next year with an eye to eventually looking at the environmental metagenomics of the site. “We knew there was biology there,” says Gralnick. “Now we can sequence the entire microbial community to help us understand how they live.”

The researchers are exploring sites where water is coming up from below the surface. The extremely salty brine contains lots of soluble iron and only mixes with oxygen once it reaches the surface. But unlike seawater, the salt content comes from calcium not sodium. The bacteria Gralnick has cultured so far are related to Marinobacter, a bacterial genus commonly found in oceans, some of which are able to accelerate rust formation with the help of oxygen. “We’re trying to get a feel for how organisms get to places and stay for a long time,” says Gralnick. But how does a marine microbe end up with a close cousin deep below the earth’s surface? And how are these bacteria thriving in this extreme environment? Another mystery: The age of the iron deposits in the mine.

“Formations like the Soudan Mine are seen all over the planet – most are around 2.4 billion years old, which is when oxygen became common in the atmosphere,” says Gralnick. The iron in the Soudan Mine is around 2.7 billion years old, well before oxygen that might cause the chemical reactions the researchers have observed. It’s a geological mystery, but one possibility does suggest itself to the researchers; the processes could be driven by biology. If that is the case, Gralnick and his colleagues may have hit a rich vein of new knowledge. “It’s a really different way to think about history and time in biology.”

Did the microbes arise slowly, where O2 reacted with ferrous iron resulting in rust and  banded iron formations such as the Soudan formation, or did they come on the scene rapidly, cataclysmically changing the chemistry of the atmosphere and oceans forever? Studying the Soudan Iron Mine may lend insight into this debate. “In some ways, the Soudan Iron Mine is not only a window into the deep subsurface,” says Gralnick, “but it is also a portal back in time.”

If the iron conversion process the researchers have observed is driven by biology rather than chemistry, the discovery holds great promise as the basis for biological solutions to some real-world problems such as the development of more effective microbial fuel cells. “If we can use biology on both sides of the equation [as opposed to biology on one side and chemistry on the other],” says Gralnick, “it opens up some interesting possibilities for using electricity to drive metabolism in organisms as a fuel source.” Ultimately, studying the microbes could also result in better anti-microbial and anti-cancer drugs, and improved toxic metal sequestration technology to name a few possible applications.

These bacteria aren’t easy to study, but their unusual properties keep the researchers coming back. Says Gralnick: “You never know what will pan out.”

– Stephanie Xenos