Iron Oxidation by Thiobacillus thiooxidans

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.T.thiooxidansの鉄酸化について検討し,以下の結果を得た. 1)T.thiooxidansをイオウを含む9K培地で培養を続けると,添加イオウの減少に伴い菌体量も減少し,無添加の段階では生育は認められず,鉄の酸化エネルギーを生育に利用することはできなかった. しかし,添加イオウ0.5%の段階までは,鉄は85%以上酸化され,この菌の鉄酸化能の適応的増大がみられた. 2)適応菌の鉄酸化活性は,非適応菌の25借に増加したが,イオウ酸化活性は減少した. 3)適応菌のチトクロム組成は,非適応菌のもの(B型,C型,A型チトクロム)とは異なり,C型とA型チトクロムのみであり,その両者がFe2+によって還元された. 4)適応菌による鉄酸化の至適pHは,この菌の生育環境のPHとよく一致し,1.2まではpHが低い程,活性が高かった. 5)鉄酸化活性は,可溶性画分あるいは顆粒画分のみではほとんど認められず,両者の混合によってはじめて現われた