Meet the Extremophiles | Miscellany | Chicago Reader

Meet the Extremophiles 

They live where few would dare. And they may help clean up acid rain.

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George Roadcap

Hydrogeologist

Illinois State Water Survey

In recent years scientists have found microbes in active volcanoes, antarctic lake floors, deep-sea thermal vents, sulfuric lakes--places previously thought too hot, cold, salty, high pressured, acidic, or alkaline to support life. As a group these organisms are called extremophiles. In 2001, while working on a groundwater pollution survey, hydrogeologist George Roadcap discovered what may be the world's most alkali-loving bacteria in a slag dump on the southeast side.

Harold Henderson: Where were you working?

George Roadcap: We took samples in the general Lake Calumet area, from the Bishop Ford Expressway on over to Hammond, Indiana. One sample we took was right on the state line; the others were on the Illinois side, in the city limits.

HH: What were you looking for?

GR: We started out looking at groundwater chemistry and contamination. The Water Survey has been studying that for years. I started in the early 1990s. We want to know what controls that chemistry--why some contaminants move and others don't, especially the metals in the slag. I don't want to give all slag a bad name. Iron slag left over from making pig iron is fairly innocuous. Steel slag is more reactive and contains more metals that are left over from making pig iron into steel. For instance, some steel slag can have as much as 2 percent chromium.

HH: What can bacteria do with that?

GR: If conditions are right they can consume metals and release them in forms that are soluble in water, thus potentially having a toxic effect on aquatic life. So I got interested in what bacteria might be growing there, if anything. The conventional wisdom was that little or no life could exist there because the pH is so high.

HH: I read that the pH in some of these slag dumps could be as high as 12.8 on a scale from 0 (very acid) to 14 (very alkali).

GR: Other alkaliphiles have been found on the coast of Greenland, in the Rift Valley in east Africa, and in Mono Lake in California. There the pH is around 11. Since it's measured on a logarithmic scale, 12.8 is almost 100 times more alkaline than what's found in those places. We did some simple culture tests. We put some water from the slag in a vial with nutrients, and bacteria started growing, so we knew there were plenty there.

HH: But you didn't know what kinds?

GR: You can't really identify bacteria by looking at them under a microscope. Instead we took samples back to the lab and started doing molecular work. We used a technique developed at the U. of I. where we take a particular section of the bacteria's DNA and compare it to others in the database of 20,000 to 30,000 other DNA sequences. It's a section of DNA that's shared by all bacteria, and by us--the one they use to determine the evolutionary tree of life.

At first we didn't have any good matches in the database with known alkaliphiles, but over the next couple of years researchers from California and Africa added new sequences, and we got some better matches. Some of the bacteria we found are related to Clostridium [e.g., tetanus] and Bacillus [e.g., anthrax] species, others are in the Proteobacteria class [a phylum that includes iron and sulfur bacteria].

HH: Do you get to name the new species in a situation like this?

GR: You first have to do a lot of testing and characterization to proclaim that you have a new species. I would include the Latin form of descriptors such as alkaline, slag, or Calumet.

HH: These bacteria are living in an environment that's as alkaline as ammonia or floor stripper. What do they eat?

GR: They'll eat carbon if they can find any. Otherwise it's hydrogen. If you corrode iron--it is a slag dump after all--it produces hydrogen that combines with oxygen in an energetically beneficial way.

HH: So they're basically eating rust?

GR: An early stage, yeah. But to survive they have to do more than eat. They also have to keep their insides at a pH between 7 and 9, while their surroundings may be as much as 100,000 times more alkaline than that.

HH: The reason you went looking for these bacteria was to see if they might be helping spread heavy-metal contamination in the groundwater. Any news on that?

GR: Actually, they may be playing a larger role in immobilizing the metals. Bacteria capable of reducing sulfate introduced into the system from external sources, such as acid rain, produce sulfide that can combine with the metals to form insoluble minerals.

HH: How did creatures like these show up here in the first place?

GR: Clearly some of them were imported from other places, because they're closely related to bacteria in the other alkali areas. Others we found are related to bacteria you'd find in any wetland. They may be local bacteria that have adapted.

HH: But these are wetlands where normal vegetation doesn't grow, right?

GR: Some places have no vegetation. But some of our real-high-pH ditches do have vegetation growing in them--phragmites [a tall reed generally considered an invasive pest].

HH: Do you know how much slag is in the southeast-side area overall?

GR: The U.S. Geological Survey has estimated it on the order of ten billion cubic feet. I always describe it as a square mile 350 feet high--700 feet high if you include all the fill. Once I did calculate how many Soldier Fields that much slag would fill, but with the new Soldier Field it wouldn't be the same.

HH: So you're not likely to run out of work to do?

GR: In the Calumet region people will be working on slag forever.

Art accompanying story in printed newspaper (not available in this archive): photo/Lloyd DeGrane.

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