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

一般认为自养氧化铁细菌氧化亚铁硫杆菌在pH值低于1.4时不能生长。该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，并研究其氧化底物的特性。为了培养耐酸氧化铁细菌，假设硫氧化硫杆菌（Thiobacillus thioooxidans）的可传递质粒可以在pH低至0.5的环境下生长，并且T. ferrooxidans可能具有编码在质粒上的耐酸能力。首先以氧化T.硫代菌和氧化T.铁代菌为主的培养物，以单质硫为能量源反复培养，使其在pH低于1.0的条件下氧化硫。然后，在初始pH为0.6的条件下，以亚铁离子为能量源培养微生物，观察到亚铁离子被氧化，并生长出离子氧化细菌。因此，推测质粒是由T. thiooxidans向T. ferrooxidans传播的，因此，承担T. thiooxidans耐酸能力的T. ferrooxidans在pH低于1.0的条件下生长并氧化亚铁离子。然而，几个月后，在初始pH为0.6的条件下，将上述抗酸离子氧化菌与亚铁离子一起培养时，在培养基中不添加单质硫的情况下，离子氧化菌几乎没有生长，而在添加单质硫的情况下，离子氧化菌有活性生长和离子氧化。此外，在以单质硫或亚铁离子为能量源的富集培养细菌的实验中，在初始pH为0.6的条件下，用亚铁离子培养细菌，如果在培养基中加入单质硫，则离子氧化细菌生长并氧化亚铁离子。因此，认为单质硫除了直接参与氧化亚铁铁菌的质粒外，还直接参与了氧化亚铁铁菌的耐酸作用。

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.