Ferrous iron production mediated by tetrathionate hydrolase in tetrathionate-, sulfur-, and iron-grown Acidithiobacillus ferrooxidans ATCC 23270 cells

When tetrathionate-grown Acidithiobacillus ferrooxidans ATCC 23270 cells were incubated with ferric ions and tetrathionate at pH 3.0, ferrous ions were produced enzymatically. Fe³⁺-reductase, which catalyzes Fe ³⁺ reduction with tetrathionate, was purified to homogeneity not only from tetrathionate-grown, but also from sulfur-and iron-grown A. ferrooxidans ATCC 23270 cells. The results for apparent molecular weight measured by SDS-PAGE (52.3 kD) and the N-terminal amino acid sequences of the purified enzymes from iron-, sulfur, and tetrathionate-grown cells (AVAVPMDSTG) indicate that Fe ³⁺-reductase corresponds to tetrathionate hydrolase. The evidence that tetrathionate-grown A. ferrooxidans ATCC 23270 cells have high ironoxidizing activity at the early log phase, comparable to that of iron-grown ATCC 23270 cells, is supported by our finding that tetrathionate hydrolase produces Fe²⁺ from tetrathionate during growth on tetrathionate. This is the first report on ferric reductase activity associated with tetrathionate hydrolase.