Eleven pure bacteria cultures, able to oxidize thiosulfate during growth at pH 7.0-9.4, were isolated from surface layers of Yavoriv sulfur deposit open pit waters. Two cultures proved to be obligate aerobes, but nine cultures performed anaerobic respiration using nitrite, N2O (5 cultures) or only nitrite (4 cultures) as terminal electron acceptors. The growth of all cultures at 22 and 28 degrees C and growth absence at 35, 42 and 55 degrees C was established. All the bacteria are obligate chemolithoauthotrophs, because after cultivation with thiosulfate in the presence ofbiotin, yeast extract, formiate, succinate, arabinose, glucose, fructose and sucrose no growth stimulation was observed, heterothropic growth of any culture was not shown. As to their morphology the cells were bacillary, cytoplasmic membrane was surrounded by three-layer cell wall typical of gram negative bacteria intracellular inclusions, nucleoid, ribosomes and polysomes were also available. On the basis of obtained physiological and morphological characteristics the isolated bacteria cultures were referred to a group of neutrophiles, representatives of genus Thiobacillus, in particular to obligate chemolithoauthotrophs.