Adhesion to metal sulfide surfaces by cells of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans

Attachment of four strains of Acidithiobacillus ferrooxidans to pyrite, chalcopyrite, galena, sphalerite or quartz was found to be mineral-selective. The bacterial extracellular polymeric substances (EPS) are responsible for mediating this process. Attachment of cells of A. ferrooxidans as well as of Acidithiobacillus thiooxidans was diminished, when depleted of their EPS. After 5 days of cultivation cells of A. ferrooxidans cover mineral surfaces with a dense biofilm, as visualised by fluorescence microscopy and AFM. Primary attachment was restricted to surface sites with visible defects.Chemical analyses of EPS of A. ferrooxidans, A. thiooxidans and Leptospirillum ferrooxidans indicated neutral sugars, fatty acids and uronic acids. The composition differed with the strain and the growth substrate. IronIII ions were only detectable in EPS of ironII ion- and pyrite-grown cells, but not in EPS of sulfur grown cells. Pyrite oxidation rates correlated with the amount of EPS-complexed ironIII ions in the case of A. ferrooxidans and L. ferrooxidans. Furthermore, pyrite oxidation rates of L. ferrooxidans were correlated with the genetic affiliation of the strains. The data for A. ferrooxidans seem to indicate a similar correlation, however, the results were not as clear-cut as those obtained for L. ferrooxidans. Sulfur oxidation rates of A. thiooxidans did not require EPS complexed ironIII ions.