Biosorption of aluminum by sulfate-reducing bacteria isolated from uranium mine tailings was examined. A top agar method with Alizarin Red S was used for initial screening of the isolates for aluminum tolerance and biosorption. Five strains of aluminumion-fixing sulfate-reducing bacteria and a strain designated UFZ B 406 isolated from another source were used in the experiments. The mechanism of aluminum biosorption was found to be a passive one. Freezing and thawing of the cells resulted in higher sorption of aluminum, whereas heat treatment or the uncoupler carbonyl-cyanide-m- chlorophenylhydrazone (CCCP) had no effect. The pH value had significant influence on the aluminum ion adsorption, the most absorbance being at pH 3 and 5, and the lowest at pH 7. Addition of magnesium and the presence of iron sulfide precipitates decreased aluminum sorption. The relationship between biomass and Al3+ ions accumulated was linear. Polyphosphate granules as possible site of aluminum accumulation were not found to be present. Fluorescence microscopy showed deposition of aluminum ions exclusively on the surface of the cell. Use of the isolates in bioremediation processes for removing aluminum from water is considered.
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