| Budget Amount *help |
¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 1987: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1986: ¥1,000,000 (Direct Cost: ¥1,000,000)
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| Research Abstract |
It's been believed that the autotrophic iron-oxidizing bacterium Thiobacillus ferrooxidans cannot grow at pH below 1.4. The objective of this project was to train bacteria capable of oxidizing ferrous ions at pH below 1.0 and to study its character for oxidation of the substrate. For training acid-resistant iron-oxidizing bacteria, it was assumed that the transmissible plasmid of Thiobacillus thiooxidans, a sulfur-oxidizing bacterium which can grow at pH as low as 0.5, could be transmitted to T. ferrooxidans , and T. ferrooxidans might assume the acid-resistance encoded on the plasmid. At first, a culture consisting mainly of T. thiooxidans and T. ferrooxidans was subcultured repeatedly with elemental sulfur as energy source so that it got to oxidize sulfur at pH below 1.0. Then, the microorganisms were cultured at initial pH 0.6 with ferrous ions as energy source, and it was observed that ferros ions were oxidized and ion-oxidizing bactera grew. There-fore, it was speculated that transmission of plasmid had occured from T. thiooxidans to T. ferrooxidans, and in consequence, T. ferrooxidans which had assumed the acid-resistance of T. thiooxidans had grown and oxidized the ferrous ions at pH below 1.0. Several months later, however,when the acid-resistant ion-oxidizing bacteria above were cultured with ferrous ions at initial pH 0.6, ion-oxidizing bacteria showed little growth in the case no elemental sulfur was added to the medium, while active growth and ion oxidation was observed with elemental sulfur added. Moreover, in experiments in which bacteria which were enrichment-cultured either with elemental sulfur or ferrous ions as energy source were cultured at initial pH 0.6 with ferrous ions, ion-oxidizing bacteria grew and oxidized the ferrous ions if elemental sulfur was added to the medium. Thus, it is suggested that elemental sulfur itself is engaged directly in T. ferrooxidans' assuming acid-resistance apart from plasmid of T.thiooxidans.
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