Etching of {111} and {210} synthetic pyrite surfaces by two archaeal strains, Metallosphaera sedula and Sulfolobus metallicus

To improve our understanding of microbially mediated pyrite dissolution, the influence of different archaeal metabolisms and crystallographic orientations of pyrite surfaces was studied. Therefore, synthetic pyrite surfaces of different orientations, including octahedral {111} and pentagondodecahedral {210} faces, were etched by Metallosphaera sedula and Sulfolobus metallicus during a time period of up to 16 days. A ferrozine assay was used in order to determine the concentration of iron ions in the solution as result of pyrite oxidation. It revealed that M. sedula produces more ferric iron in the solution than S. metallicus, indicating M. sedula as the more active organism. Epifluorescence microscopy observations showed that cells of both strains partly attach to the mineral surface whereas the rest remains planktonic, suggesting that both organisms might act through both, the 'contact' and 'non-contact' mechanisms of the indirect biooxidation mechanisms for the dissolution of pyrite. Studies with Scanning Electron Microscopy (SEM) showed cell attachment and etching effects during the whole time period. Surface alteration forms features depending on surface crystallography up to 30 mu m in size in 16 days of etching, while the shape of the features varies with face-symmetry. (C) 2008 Elsevier B.V. All rights reserved.