Characterisation of novel salt tolerant iron-oxidising bacteria

摘要

Three iron oxidising bacteria, A2-8, A19-22 and A20-24, previously shown to be capable of oxidising iron under saline conditions were physiologically and taxonomically characterised. All three strains were Gram positive rods (0.2-0.5 μm wide x 0.8-3 μm long) capable of mixotrophic growth on ferrous sulfate and yeast extract, and heterotrophic growth on yeast extract alone, over a range of 0.5-5% NaCl and pH 1.6-4.5. A20-25 was also able to grow at pH 6.0. The maximum temperature at which growth was observed was 44℃. Autotrophic growth on CO_2 and ferrous sulfate was not detected. These strains also required a reduced sulfur source for growth. The three strains could be distinguished on the basis of differences in utilisation of glucose, acetate, glutamic acid, thiosulfate, tetrathionate and elemental sulfur and efficacy of mineral oxidation. Leaching of pyrite, arsenopyrite, and mixed base metal sulfides was observed at 0.5-4% NaCl. Pyrite oxidation was maximal at 0.5-1% salt and declined with higher concentrations. Likewise Fe[Ⅱ] oxidation was optimal at 1% NaCl and doubling times increased threefold at 4% NaCl. Sequence analysis of the 16S rRNA gene in the three strains showed highest homology with Alicyclobacillus spp (90-94%). A20-24 also showed 98.2% homology with the unnamed bacterium GSM but was physiologically distinct from that organism which is a thermophile. A2-8 and A19-22 were 98.1% homologous. Despite phylogenetic similarities with Alicyclobacillus and GSM, and their physiological/morphological resemblance to Sulfobacillus and strains L15 and Rivl4 (1), the combination of salt tolerance, iron oxidation, and absence of thermotolerance, indicates that A2-8, A19-22 and A20-24 are novel organisms which may have potential application to bioleaching under saline conditions.