Sensitivity of Iron-Oxidizing Bacteria, Thiobacillus ferrooxidans and Leptospirillum ferrooxidans , to Bisulfite Ion

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Abstract
When grown on iron-salt medium supplemented with the bisulfite ion, Leptospirillum ferrooxidans was much more sensitive to the ion than was Thiobacillus ferrooxidans . The causes of the sensitivity of L. ferrooxidans to the bisulfite ion were studied. The bisulfite ion completely inhibited the iron-oxidizing activities of L. ferrooxidans and T. ferrooxidans at 0.02 and 0.2 mM, respectively. A trapping reagent for the bisulfite ion, formaldehyde, completely reversed the inhibition. The treatment of intact cells with 1.0 mM bisulfite ion for 1 h and washing the bisulfite ion from the cells had no harmful effects on the iron-oxidizing activity of T. ferrooxidans . However, the treatment of L. ferrooxidans with 0.1 mM bisulfite ion for 1 h completely destroyed the iron-oxidizing activity. T. ferrooxidans had sulfite:ferric ion oxidoreductase activity. In contrast, a quite low level of sulfite:ferric ion oxidoreductase activity was found in L. ferrooxidans , suggesting that it is much more difficult for L. ferrooxidans to oxidize the bisulfite ion to the less harmful sulfate than it is for T. ferrooxidans . These results suggest that the sensitivity of L. ferrooxidans to the bisulfite ion is due to a lack of an active sulfite:ferric ion oxidoreductase and the sensitivity of its iron oxidase to bisulfite ion.