AFM & EFM study on attachment of acidophilic leaching organisms

Bioleaching is the dissolution of metal sulfides by bacterial oxidation processes such as pyrite (FeS2) and chalcopyrite (CuFeS2). It is well known that attachment of leaching bacteria to the mineral surface enhances the metal sulfide dissolution. On one hand, leaching organisms oxidize different sulfidic ores, resulting in a type of water pollution called acid mine drainage (AMD). On the other hand, bioleaching processes are used in biotechnology due to their significant economic impact on heavy metal recovery such as gold, copper or zinc winning from sulfide ores. To prevent AMD or to optimize bioleaching processes for industrial use, attachment and the accompanying leaching efficiency of microorganisms have to be positively or negatively controlled. Therefore, not only the physiology of pure cultures has to be understood, but also the ecology and interactions of mixed cultures has to be studied.In this study a combination of Atomic Force Microscope (AFM) with Epifluorescence Microscope (EFM) are used to get “new insights” for a better understanding of attachment of leaching microorganisms to metal sulfides. The combination of AFM with EFM demonstrated by the use of DAPI staining and FISH probes that attached cells on pyrite coupons can be identified and assigned to a particular organism. During this study it was shown that L. ferriphilum causes aggregate formation and increased attachment of cells to pyrite coupons. Furthermore, it became obvious that mixed cultures of L. ferriphilum and A. caldus attach better than pure cultures. Moreover, A. caldus cannot attach to pyrite grains on its own, but needs a precolonization by L. ferriphilum for attachment. In such mixed cultures L. ferriphilum is the pivotal organism for biofilm formation.

Research highlights
► Combination of AFM and EFM is a useful tool for investigations on cell morphologys, spatial arrangement and aggregate formation.
► The combination of AFM and EFM demonstrated by the use of DAPI staining and FISH probes that an identification of organisms is possible.
► In mixed cultures L.ferriphilum is the pivotal organism for biofilm formation.