RESUMO
A thiosulfate-oxidizing bacterium TX was isolated from polysulfide wastewater treatment system.It was preliminarily identified as Halothiobacillus sp.according to its morphological,physiological proper-ties and similarity analysis of 16S rRNA gene sequence(GenBank accession No.EU871645).This bacte-rium was an obligate chemolithoautotrophic sulfur-oxidizing bacterium since it could utilize thiosulfate,elemental sulfur,tetrathionate,sulfide or sulfite as sole energy source but did not show growth on the me-dium with glucose,sucrose,fructose,lactose,mannose or yeast extract as sole carbon source.The optimal growth condition for thiosulfate oxidation was 30?C~35?C and pH 3.0~5.0 respectively.Significant reduc-tion in medium pH from 4.0 to 1.2 was observed due to oxidation of thiosulfate to sulfate during the batch culture incubation period.During the course of thiosulfate oxidation accumulation of tetrathionate was ob-served either in synthetic medium or in the mixed liquor from aeration tank of the polysulfide wastewater treatment system.This indicates that the "S4 intermediate(S4I)" pathway was responsible for thiosulfate oxidation in this bacterium.