Use of epifluorescence microscopy for characterizing the activity of Thiobacillus Ferrooxidans on iron pyrite

The enumeration and characterization of microorganisms attached to solid surfaces have always presented significant difficulties. This is particularly true for micro organisms that are indigenous to coal mines and mineral deposits where metal sulfides are ubiquitous. The complications that arise are the result of the variety of inorganic compounds that are present in these environments, the harsh conditions under which the microorganisms proliferate, and the low cell densities to which they grow. The work presented here suggests that epifluorescence microscopy using acridine orange can be a useful probe to study acidophilic metal-leaching bacteria. Experiments involving the growth of Thiobacillus ferrooxidans on iron pyrite are described which indicate a relationship between cell fluorescence color and bacterial activity. Both attached and free-solution cell densities were determined throughout the course of the leaching process and considered along with changes in cell fluorescence color which might be associated with changes in intracellular pH. As such, epifluorescence microscopy, using acridine orange, can be used for assessing the activity of T. ferrooxidans on iron pyrite as well as resolving the controversy concerning the significance of attachment during the leaching process.