Specific activities of TetH in the cell extracts of different strains grown in 9K-S4O62− medium. WT, ΔtetH mutant, WT (pMSD1), and WT (pMSD1-tac-tetH) represent the wild type, ΔtetH mutant, wild type carrying plasmid pMSD1, and tetH overexpression strain of A. ferrooxidans ATCC 23270, respectively.