OAK RIDGE, Tenn. -- Novel bacteria that produce magnetic material and could remove heavy metals from contaminated soils and groundwater have been discovered by microbiologists from the Department of Energy's (DOE's) Oak Ridge National Laboratory (ORNL).
Living on hydrogen in mud, these newly discovered bacteria produce tiny particles of magnetic iron oxides, as shown under a scanning electron microscope.
The bacteria were discovered by Tommy Phelps of ORNL's Environmental Sciences Division. He worked with samples extracted in 1993 by Texaco engineers drilling for oil and gas deposits near the Chesapeake Bay as part of a collaborative arrangement between Texaco and DOE's Office of Health and Environmental Research. In a trailer near a derrick, Phelps studied samples extracted by Texaco from a depth of 2800 meters (9100 feet). He and his colleagues observed that metallic compounds had been chemically altered by microbes at a temperature of 70 degrees Celsius (158 degrees Fahrenheit), even though the subsurface samples had been geologically isolated for some 100 to140 million years.
"In 1994," Phelps says, "we determined that these microbes from the Taylorsville Triassic Rift Basin near Fredericksburg, Va., have an interesting capability. They produce magnetic material. We isolated micron-sized bacteria and found that these microorganisms produced nanometer-scale magnetic iron precipitates." A micron is a millionth of a meter, and a nanometer is a billionth of a meter.
"We also found evidence that the microbes can remediate groundwater containing chlorocarbon compounds, such as trichloroethylene and tetrachloroethylene, and heavy metals."
The researchers found similar bacteria at the Naval Oil Shale Reserve at the Piceance Basin in Colorado. Both the Taylorsville and Piceance basins, although separated geographically and formed at different times, contain deep subsurface formations heated by compression and burial to high temperatures.
These thermophilic (heat-loving) bacteria feed on compounds containing carbon, hydrogen, and oxygen, such as acetate and lactate (an ingredient of sour milk). The Piceance Basin bacteria, which also metabolize hydrogen and pyruvate, were found in groundwater and drilling mud; the Taylorsville bacteria were present in subsurface shale and sandstones.
The anaerobic bacteria convert food to energy and waste through an electron transfer process typical of respiration, rather than fermentation. Just as humans get rid of electrons by forming and exhaling carbon dioxide, these bacteria dump electrons on nearby electron-accepting metals, such as iron. In the process, they reduce iron hydroxide to magnetic iron.
These magnetite particles serve as catalysts, easing the breakdown of chlorocarbon compounds. The bacteria can also reduce other electron-accepting heavy metals such as chromium, cobalt, and uranium. In this way, the bacteria are potentially useful for bioremediation of soil and groundwater contaminated with mixed waste if the contaminated zone is sufficiently heated.
Potential biotechnological applications of these bacteria include production of magnetic fluids for brakes and lubricants for high-speed turbines.
"The bacteria," Phelps says, "also are of interest to researchers studying the evolution of the atmosphere, the banded iron formations responsible for the earth's magnetic field, and respiration in organisms."
The research was supported by DOE, Office of Health and Environmental Research.
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