This award in the Environmental Geochemistry and Biogeochemistry Program is jointly supported by the Divisions of Earth Sciences and Chemistry. Drs. Jillian F. Banfield, Geology Department, and Robert J. Hamers, Chemistry Department, of the University of Wisconsin-Madison will investigate effects of microbes on pyrite surfaces. Abundant organisms (bacteria and archaea) have been shown to attach to pyrite and to occur in the low pH solutions produced by pyrite dissolution. The mechanism of `direct` biological catalysis of pyrite dissolution involving attached organisms is poorly understood, however, as are the geochemical controls on the distribution of attached and non-attached Fe and S oxidizing organisms. In this research, the abundance and distribution of chemolithotrophs will be studied as a function of pH, ionic strength and geochemical conditions. Attachment sites for organisms will be correlated with surface morphology using precharacterized surfaces and cultured microbes as well as microbes in the natural environment. The polymeric binding layer whereby microbes attach to pyrite will be studied at low pH and the relationship to pyrite dissolution determined. The results will be compared to kinetic data from field studies of acid mine drainage generation. Experiments will be constrained by both molecular biological information about the relevant species at the site and physical and chemical details of the solid-liquid-organic interfaces. The role of bacteria in acid mine drainage is not well understood. Until recently, only chemical and geological factors were considered in models for dissolution of iron sulfides (pyrite) at locations such as Iron Mountain (Redding, California). The identify of some bacteria associated with iron pyrite dissolution was determined in previous work. Here the role of bacteria in dissolution of the metal sulfides will be determined. Factors such as how bacteria attach to mineral surfaces and how transport of metals is affected by that attachment will be explored
