EN
The course of thiosulphate oxidation by selected strains of autotrophic bacteria Thiobacillus thiooxidans and Thiobacillus ferrooxidans as well as mixotrophic bacteria Sulfobacillus sp. and Siderocapsa sp. was analysed. Hexathionate and trithionate were found to be main intermediate compounds in iron-free solutions containing T. ferrooxidans, Sulfobacillus sp. or Siderocapsa sp., whereas tetrathionate was found in systems with T. thiooxidans. Tetrathionates were commonly present in iron-containing solutions inoculated with all tested strains. Chemical and biochemical processes, occurring within tested solutions, are discussed. Ferrous ion concentration > 0.02 g/dm3 was found to have inhibiting effect on the rate of biotic oxidation of thiosulphate.