Microbial interactions with mineral surfaces influence the bioavailability of both nutrients and contaminants in the environment, impacting such diverse environmental processes as the fate and transport of heavy metals, biodegradation of environmental contaminants, and effective use of agrochemicals. Yet, as critical as microbe-mineral interactions are, in terms of research, "minerals and microbes might as well be night and day," says Virginia Tech geochemist Michael Hochella.
"We know that the earth communicates with water and air, that microorganisms alter the physical and chemical properties of minerals, and that the diversity and distribution of microorganism on earth is at least in part due to the dynamic geochemistry of mineral surfaces," says Hochella. "Thousands of minerals with enormous variability in surface chemistry and structure interact with any of an unimaginable number of microbial species; yet, despite the vast amount of work in geochemistry and microbiology, microbe-mineral interactions remain largely unexplored."
He decided to change that and in 1996 launched the university's Microbe-Mineral Group with microbial ecologist Duane Berry and environmental engineer John Little.
After three years of weekly meetings to learn each other's science, study of a model microbe-mineral interaction, and cross-training of graduate students, the Virginia Tech group has received a three-year, $386,202 grant from the Department of Energy, effective Sept. 15, 1999.
"The intent is to discover and define the conditions under which microbes cause the release of nutrients or contaminants from mineral surfaces," says Hochella. The model the researchers are studying are microbes that, in a glucose environment, release phosphorus from goethite -- the most common iron oxide in soils worldwide. In the glucose environment, microbes alter their metabolism to produce glucolipids, and even reduce their cell size, so they can 'digest' and absorb phosphorus from the mineral-oxide surface. Many other degrees and types of interactions take place as well.
In addition to being a nutrient for the microbes, phosphorus can be a plant nutrient or a water contaminant. "Confidence that phosphorus--and other minerals--are safely bound may be misplaced," says group member and soil scientist Duane Berry. "Understanding the nutrient requirements of microorganisms and knowing what conditions enable microbes to interact with minerals will help us use and enhance them in bioremediation, and control unwanted release. But this is basic reseaerch," he emphasizes. "We need to have a better handle on bioavailability of phosphorus."
Microbes may also be unleashing substances more dangerous than phosphorus, says Hochella. "Microbe-mineral interactions impact or play a role in the fate and transport of energy-related contaminants, such as contaminants generated during the production of nuclear fuels and bombs, including tritium, cesium, strontium, and technetium."
He also is concerned about other contaminants that make their way through rocks and soils via groundwater, such as from leaking landfills, dumping or draining of industrial waste, leaking underground gasoline storage tanks, various agricultural practices, and septic tanks. "The contaminants cover a huge range of organic and inorganic compounds. Examples of particularly toxic organic wastes are benzene, xylene, and toluene; and inorganic wastes are arsenic, chromium, lead, mercury, and nitrate," says Hochella.
"Mineral-microbe interactions have a great deal to do with the transport of these contaminants in the subsurface -- mostly still not understood. Understanding this is so critical because we derive a major portion of our fresh water worldwide from wells that, of course, tap into this priceless and precious subsurface water supply. There is far more fresh water in the subsurface than in all of the rivers and lakes in the world."
The central goal of the VT microbe-mineral group's research is to gain entirely new insights into direct and indirect interactions between microbes and mineral surfaces that are responsible for increasing the bioavailability (releasing) and ultimately impacting the fate of nutrients and contaminants from minerals. Objectives include:
* recognizing and characterizing the strategies and or chemical micro-environments that microbes use to obtain nutrients strongly bound to mineral surfaces;
* refining surface sensitive imaging and characterization techniques, which will advance the study of other interactions.
Members of the Microbe-Mineral Group are Duane Berry and Matthew Eick of crop and soil environmental sciences, Malcolm Potts from biochemistry, John Little from civil and environmental engineering, postdoc Chris Tadanier, and two of Hochella's Ph.D. students, Steven Lower and Treavor Kendall. "Chris, Steve, and Treavor belong to the next generation of cross disciplinary scientists--who will be snapped up by universities and companies," says Hochella. "That excites me the most. We're training the best of the best. Thanks to seed money from the university research division and the three colleges, I see the group growing in terms of students, post docs, and research for the rest our careers at Virginia Tech."
The research project, although funded by the DOE grant for three years, is a major, long-term interdisciplinary program--certainly more than a decade, says Hochella.
The above story is based on materials provided by Virginia Tech. Note: Materials may be edited for content and length.
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