Bacteria and geochemistry in a former uranium open pit mine - mobilization of trace metals

Abstract: In mining areas around the world, chemical and biotic processes have lead to the release of toxic substances, e.g. metals. Microbial processes influence metal speciation, while the chemical environment shapes and controls microbial populations. This thesis has two parts and the papers cover various aspects of metal-to-microbe links in a former uranium mine at Ranstad, Sweden.The first part of the thesis examines bacteria-induced metal mobilization by the cultivation of Pseudomonas fluorescens with ore and minerals from the Ranstad mine. The presence of a mineral source stimulated bacterial growth. Pyoverdine-type siderophores typical for P. fluorescens were produced, but also other types of siderophores. The bacterial mobilization of metals is implied by the agreement in concentrations of Fe-pyoverdine complex and soluble Fe, and by the concentrations of Ni and Co in solution.  U was mobilized from the ore as a result of bacterial growth raising pH.The second part of the thesis focus on the partitioning of metals and their links to the microbial communities in the water of the former open pit mine, Lake Tranebärssjön. The lake was pH-neutral to alkaline, highly stratified, and had an anoxic hypolimnion with high concentrations of metals and SO42-. Size fractionation showed the dissolved fraction dominating for most metals, while the particulate and colloidal fractions dominated for Fe. Chemical equilibrium models agreed reasonably well with these results. In the pyrosequencing study of the bacterial community, depth-related changes in water chemistry corresponded to a distinct shift in the microbial community, indicating a chemical control. The presence of metal- and SO42--reducing bacteria suggests a possible microbe – chemistry connection.The findings of this thesis could be used for the restoration and remediation of mining sites, and provides information on factors governing the establishment and control of bacterial populations in freshwaters.