Microbe may be a key to mine pollution

A newfound microbe that eats iron and lives in acid-drenched conditions has been identified as a chief suspect in the environmental damage caused by metal ore mining.

Writing in the Friday, March 10, edition of the journal Science, a team of university scientists report the discovery in an old mine of an archaeon that thrives when metal sulfide ores are exposed to air and water, conditions that mimic hot battery acid. The microbe, the scientists say, is present in such abundance that it is believed to be a key mediator of the process of acid mine drainage, the primary environmental problem associated with the extraction of metal ores from the earth.

More information: Acid Mine Drainage Page

The microbe shows an ability to transform the sulfide found in metal ores to sulfuric acid, the chemical pollutant that contaminates mining sites and drains into nearby rivers, streams and groundwater.

“We think this new archaeon might be one of the more important players in catalyzing these reactions,” says Katrina J. Edwards, the lead author of the Science article.

Microbial archaea, a branch of life with ancient roots, have different basic characteristics than other microscopic organisms such as bacteria.

Edwards is a geomicrobiologist at the Woods Holes Oceanographic Institute, Woods Hole, Mass. The work, funded largely by the National Science Foundation, was conducted as part of her doctoral thesis at UW–Madison in the lab of Jillian Banfield, a professor of geology and geophysics and a co-author of the study.

The discovery of the new microbe is important because it helps explain how the natural cycle of the conversion of sulfide to sulfuric acid is greatly accelerated around mines. Moreover, the physiological character of the archaeon is of great interest because it has no cell wall, defying the idea that microorganisms tough it out in nasty environments with the help of durable external walls to shield themselves from extreme conditions.

It is possible, according to Edwards, that the microbe found in such abundance at the Iron Mountain Mine near Redding, Calif., is ubiquitous in nature, living off ore bodies exposed naturally to air and water and geochemically impacting iron and sulfur cycles.

But under the conditions created by the mining of metal ores, where many tons or ores and tailings are exposed, the organism thrives and revs up the production of sulfuric acid.

“It speeds up environmental damage,” says Banfield, an authority on the relationship between microbes and minerals. “The organism’s metabolism greatly accelerates the acid mine drainage process” by converting the solid sulfide mineral to sulfuric acid, a corrosive liquid that leaches from mining sites into the surrounding environment. The process has caused billions of dollars in damage to the environment worldwide.

“This is a process that takes place all over the Earth’s crust, but mining exacerbates the problem by exposing metal to air and water,” she says.

Banfield’s group has been working at the Iron Mountain Mine for nearly five years, and has gained significant insight into an environment that is extremely hostile to any form of life, an environment that is acidic, hot and full of toxic metals.

“The mine has a fairly simple ecology and this seems to be the major player,” say Banfield. “It oxidizes irons and forms slimes and grows on pyrite sediments.”

The new archaeon, dubbed Ferroplasma acidarmanus, is one of about a dozen microbes found in the mine, Banfield says. Her group determined the newfound microbe was among the most active and numerous in the mine by sampling during the summer when the sediment solutions in the mine are concentrated.

The biology of Ferroplasma acidarmanus is sure to be of interest in part because of the peculiar fact that it has no cell wall. “It turns out to be a bit of an irony that the most abundant organisms in the mine might be considered to be rather fragile since they lack cell walls,” say Edwards. “It’s cytoplasm is surrounded only by a single, peripheral membrane.”

How the microbe endures the heat, acid and high metal concentrations of its own environment is unknown. But the fact that it does, say Banfield, is certain to be of interest to people studying the origins of life on Earth and the possibility that microbial life may exist beyond the confines of Earth.

It could be, say Banfield, that the organism’s seemingly fragile cytoplasmic membrane confers an advantage that is yet unknown to science.

Research on the new microbe and its remarkable abilities will continue at UW–Madison in collaboration with Brian Fox, a professor of biochemistry, and Charles Kaspar, an environmental toxicologist and professor of food microbiology and toxicology.