Characterization of arsenic resistant and arsenopyrite oxidizing Acidithiobacillus ferrooxidans from Hutti gold leachate and effluents

Four arsenic resistant ferrous oxidizers were isolated from Hutti Gold Mine Ltd. (HGML) samples. Characterization of these isolates was done using conventional microbiological, biochemical and molecular methods. The ferrous oxidation rates with these isolates were 16, 48, 34 and 34 mg L−1 h−1 and 15, 47, 34 and 32 mg L−1 h−1 in absence and presence of 20 mM of arsenite (As3+) respectively. Except isolate HGM 8, other three isolates showed 2.9–6.3% inhibition due to the presence of 20 mM arsenite. Isolate HGM 8 was able to grow in presence of 14.7 g L−1 of arsenite, with 25.77 mg L−1 h−1 ferrous oxidation rate. All the four isolates were able to oxidize iron and arsenopyrite from 20 g L−1 and 40 g L−1 refractory gold ore and 20 g L−1 refractory gold concentrate. Once the growth was established pH adjustment was not needed inspite of ferrous oxidation, which could be due to concurrent oxidation of pyrite. Isolate HGM 8 showed the final cell count of as high as 1.12 × 108 cells mL−1 in 40 g L−1 refractory gold ore. The isolates were grouped into one haplotypes by amplified ribosomal DNA restriction analysis (ARDRA). The phylogenetic position of HGM 8 was determined by 16S rDNA sequencing. It was identified as Acidithiobacillus ferrooxidans and strain name was given as SRHGM 1.