Attachment to metal sulfide surfaces is a prerequisite of bioleaching activity via the contact mode [Rohwerder et al.: Appl. Microbiol. Biotechnol. Vol. 63 (2003), p. 239]. Until now, the mechanisms and possible variations of this attachment process among leaching bacteria is not well understood. Therefore, we are studying the diversity in the attachment behaviour of different strains of the genus Acidithiobacillus, which is one of the main bacterial group involved in the bioleaching of metal sulfides. Among the species At. ferrooxidans, cells of the type strain (ATCC 23270) were found to attach the least. Whereas bacterial cells of strains A2 and R1 attached the most. Other strains that were investigated in this study included At. ferrooxidans D-26 and R7. Highly likely, these strains exhibit different attachment behaviour due to specific variations in their extracellular polymeric substance (EPS) composition as loss of part of the EPS has previously been observed to have a negative effect on attachment and bioleaching activities. Differences in several EPS parameters such as the amount of complexed Fe(III) ions and the sugar composition are possible reasons for the observed strain-specific attachment behaviour. In addition to attachment assays and microscopic studies (AFM and epifluorescence), leaching activities of the strains were comparatively investigated by short-term as well as growth experiments.