Superbug Survival is Basic

Sometimes the most extreme environment for life isn’t at the bottom of the ocean or inside a volcano. It’s just south of Chicago.

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"… some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity etc…", Charles Darwin, on the origins of life in tidal pools
Credit:Smithsonian

Illinois groundwater scientists have found microbial communities thriving in the slag dumps of the Lake Calumet region of southeast Chicago where the water can reach extraordinary alkalinity of pH 12.8. That’s comparable to caustic soda and floor strippers – far beyond known naturally occurring alkaline environments.

The closest known relatives of some of the microbes are in South Africa, Greenland and the alkaline waters of Mono Lake, California.

"Other alkaline communities have been found at pHs up to 11," says Illinois State Water Survey hydrogeologist George Roadcap. "That’s sort of the high end of known natural communities."

Roadcap and his colleagues at the University of Illinois Champaign Urbana came upon the microbes while studying contaminated groundwater created by more than a century of industrial iron slag dumping in southern Illinois and northern Indiana. Roadcap presented details of what appear to be the most alkaline-tolerant life known to date on Tuesday, Nov. 4 at the annual meeting of the Geological Society of America in Seattle, WA.

Genetic analyses at one site revealed bacteria related to Clostridium and Bacillus species. These are found in highly alkaline waters of Mono Lake, tufa columns in Greenland, and cement-contaminated groundwater in a deep gold mine in Africa. Some RNA sequences appeared most closely related to thermophilic, or "heat loving," bacteria found in other parts of the world. The temperatures of the slag dumps are not extraordinary at all, of course. In fact they get pretty cold in the winter, driving the pH even higher, says Roadcap.

At five other sites the dominant microbes belonged to the Proteobacteria class including a large number from the Comamonadacea family of the beta subclass. "In high-pH microcosms experiments, one of these microbes is closely related to a hydrogen oxidizer," said Roadcap. That means the bacteria exploits the hydrogen given off from the corrosion of metallic iron slag in water.

Just how the unusual bacteria got to the slag dumps is currently a mystery, says Roadcap. "I’d hate to hazard a guess," he said, regarding their origins. One possibility is that local bacteria adapted to the extreme environment over the last century. Another possibility is that they somehow got imported.

As for whether the unexpected microbial community has any effect on the extensive groundwater contamination problem in the slag dumps, "We have not come to any conclusion about that," says Roadcap. Among the possible harmful things microbes could do is collect and distribute hazardous materials to nearby lakes and wetlands. But so far that has not been documented.

Alkaline groundwater in the Lake Calumet region was created when steel slag was dumped and used to fill in wetlands and lakes. Water and air reacts with the slag to create lime (calcium hydroxide), driving up the pH. There is an estimated 21 trillion cubic feet of contaminated industrial fill dumped in southeast Illinois and northeast Indiana, about half of which is thought to be slag, Roadcap noted. The slag dumps where the microbial communities were found resembled filled wetlands and are often devoid of surface vegetation, he explained.

Microbial species are now known to occupy almost the entire range of pH from 1.4 (extremely acid) to rear 13 (extremely alkaline). Life also thrives in extreme temperatures, with some species showing growth up to 114 degrees C (thermal springs at Vulcano, Italy and deep sea vents) and other species surviving down to -15 degrees C (brine films in Siberian permafrost). Life also occupies an equally broad range of salinity, ranging from fresh water up to sodium chloride saturation (about 300 percent), where salt precipitates.


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