Training of Iron-oxidizing Bacteria Capable of Oxidizing Ferrous Ion at pH below 1

据信，自养铁氧化细菌氧化亚铁硫杆菌不能在pH低于1.4时生长。本项目的目的是培养能够在pH低于1.0的条件下氧化亚铁离子的细菌，并研究其对底物的氧化特性。为了培养耐酸铁氧化细菌，假设氧化硫硫杆菌（Thiobacillusthiooxidans）的可传递质粒可以传递到T. ferrooxidans和T.氧化亚铁酶可能具有质粒上编码的耐酸性。首先，以T. thiooxidans和T.以元素硫为能源反复继代培养氧化亚铁硫杆菌，使其在pH低于1.0时氧化硫。然后，在初始pH为0.6的条件下，以亚铁离子为能源培养微生物，观察到亚铁离子被氧化，离子氧化细菌生长。因此推测质粒的传递是从T. thiooxidans到T. ferrooxidans，因此，T. ferrooxidans的抗酸性。氧化硫杆菌在pH低于1.0时生长并氧化亚铁离子。然而，几个月后，当在初始pH 0.6下用亚铁离子培养上述耐酸离子氧化细菌时，在不向培养基中加入元素硫的情况下，离子氧化细菌显示出很少的生长，而在加入元素硫的情况下观察到活跃的生长和离子氧化。此外，在以元素硫或亚铁离子作为能量源富集培养的细菌在初始pH 0.6下用亚铁离子培养的实验中，如果向培养基中加入元素硫，则离子氧化细菌生长并氧化亚铁离子。因此，这表明元素硫本身直接参与T。氧化亚铁硫杆菌的耐酸性与氧化硫杆菌的质粒无关。

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.