ELECTRON PROBE MICROANALYSIS OF METAL BINDING TO ACTIVE AND INACTIVATED CELLS OF MUCOR ROUXII
|I. Cano-Aguilera(1), J.L. Gardea-Torresdey(1), and N.E. Pingitore(2), (1)Chemistry Department, and (2)Geological Sciences Department, University of Texas at El Paso, El Paso, TX. 79968||
Microorganisms present many mechanisms of metal tolerance. These include: a) extracellular polymer-metal interaction; b) exclusion, by alterations of membrane or cell wall structures that prevent metal entry; c) metal transformation and volatilization; d) intracellular accumulation; and e) internal sequestration. This last process may involve sequestration by the cell wall, vacuoles, polyphosphate bodies, or protein complexes.
The important role played by fungi in biogeochemical cycles make them suitable candidates for performing studies of metal-microbe interactions. A better understanding of the factors for metal resistance may help in the application of fungal biomass for the treatment of metal-contaminated water, and also in enrichment or recycling of valuable metals. After repeated culturing in progressively higher concentrations of copper sulfate, a copper-tolerant Mucor rouxii strain was obtained. The copper-tolerant strain differed from the sensitive parental strain with respect to shape and size. Copper binding studies conducted with atomic absorption spectroscopy revealed that the copper-tolerant strain grown at higher copper levels bound large amounts of this metal. Freeze-dried active and inactivated cells of Mucor rouxii were used in this study.
Using Energy Dispersion Spectroscopy (EDS) and Wavelength Dispersion Spectroscopy (WDS) on the electron microprobe, we investigated: a) metal content, b) the chemical groups associated with the metal binding, and c) metal localization in the fungal cell, Mucor rouxii. By probing cell sectors, it was determined that the copper is taken up and sequestered by cell components. The copper signal was enhanced in the tolerant strain and showed a low but statistically significant correlation with the sulfur signal. In tungsten-treated cells, the phosphorous signal showed high correlation with the presence of this metal but not with copper. These results suggest that there are some mechanisms of detoxification in the cells, since the copper is present probably inside and outside of the cells of Mucor rouxii.
Key words: x-ray microanalysis, metal binding, fungi
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