BIOMINERALIZATION OF COPPER: SOLUTIONS FOR WASTE REMEDIATION AND BIOMINING
|C.R. Ashby, S.A. Thompson, and T.C. Crusberg, Worcester Polytechnic Institute, Department of Biology and Biotechnology, 100 Institute Road, Worcester, MA 01609||
Spores of the fungus Penicillium ochro-chloron from a two-week old culture were transferred into glucose minimal salts (GMS) medium containing Tween-80. In a shake flask P. ochro-chloron propagated into fungal mycelial beads 3-4 mm in diameter. These four-day-old fungal beads were transferred into another glucose salts maintenance medium (NMM) and challenged with 200 mg/L Cu2+.
As the fungal mycelial beads incubated in the copper solution they acquired a blue-green color. The fungal mycelial beads were removed from the solution, cut in half and rapidly frozen by immersion in petroleum ether at -70°C and then lyophilized in a Virtis freeze drier. The fungal beads were mounted onto carbon-coated aluminum stubs with a graphite adhesive. Some were coated with Au/Pd (60:40) in a Fullam sputter coater, or carbon coated in a Varian 860 vacuum evaporator.
Using a Jeol JSM 5600 scanning electron microscope, we discovered small spheres (20-40(m dia.) embedded within the fungal mycelial beads. Through energy dispersive x-ray (EDX) analysis, we found two different types of spheres, that we call mineralspheres, with distinct textures. One mineralsphere showed the presence of both copper and phosphorous (presumably insoluble copper phosphate) and appeared to have a spongy, rough exterior.
The other mineralsphere also showed the presence of copper but lacked the characteristic phosphorous signal. Both mineralspheres had the same size and shape, but the mineralsphere without phosphorous exhibited a smooth exterior. The absence of phosphorous may indicate that an insoluble oxalate salt precipitate had possibly formed.
Both mineralspheres were embedded in hyphae and were most often found towards the center of the fungal bead. This ability of the fungus, and perhaps other fungi as well, to immobilize heavy metals in the soil may be a natural process by which divalent metal ions are kept in the soil as trace elements for use by other members of the ecosystem.
The applications for this biomineralization process may be useful in the development of innovative technologies for biosorption, bioremediation, and biomining operations in which heavy metals must be removed from wastewaters. The conditions in this experiment were comparable to those existing in the Berkeley Pit copper mine in Butte, Montana. P. ochro-chloron may provide a suitable technology to recover metals from that water source.
Key words: biomineralization, biomining, copper, penicillium
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