Thiobacillus thiooxidansによる鉄酸化

The iron-oxidizing activity of Thiobacillus thiooxidans cultured in the ONM medium was very weak. When the bacteria were successively cultured in the 9K medium containing sulfur, whose content was decreased step by step, the activity of iron-oxidation adaptically increased to 25-fold as much as that of the non-acclimatized organism. However, this activity was only about 5% of that of Thiobacillus ferrooxidans. The optimum pH value of the ferrous iron-oxidation of the acclimatized organism was very low. As the pH of the reaction mixtures was decreased down to 1.2, the activities gradually increased. The non-acclimatized bacteria contained B-, C- and A-type cytochromes, but B-type cytochrome could not be detected in the acclimatized organism. When ferrous iron was added to the cell-free extracts of both bacteria, C- and A-type cytochromes were reduced, but the reduction of B-type cytochrome could not be observed. The iron-oxidizing activity of the non-acclimatized bacteria was found in the particulate fraction. On the other hand, the activity of the acclimatized organism was found neither the particulate fraction, nor in the soluble fraction. However, the activity was recovered to the same level as the cell-free extracts when both fractions were combined. From these results it is postulated that the iron-oxidizing system of acclimatized T. thiooxidans was modified to a system which is similar to those of T. ferrooxidans.