The moderately thermophilic bacteriumAcidithiobacillus caldus is found in bacterial populations in many bioleaching operations throughout the world. This bac-terium oxidizes elemental sulfur and other reduced inor-ganic sulfur compounds as the sole source of energy. The purpose of this study was to purify and characterize the tetrathionate hydrolase of A. caldus. The enzyme was purified by one step chromatography using a SP Sepharose column. The purified enzyme resolved into a single band in 10% polyacrylamide gel, both under denaturing and native conditions. Its homogeneity was confirmed by N-terminal amino acid sequencing
