Characterization of heterotrophic iron and sulfur-oxidizing bacteria from acid mine drainage in Sarcheshmeh copper mine Iran

Acid mine drainage (AMD) is an environmental pollution that is generated from the oxidation of sulfide minerals that exist in the mine dumps. AMD causes pollution of surface and underground waters and lead to distribution of heavy metals into the environment. The aim of this research is isolation and identification of heterotrophic iron and sulfur-oxidizing bacteria from AMD of Sarcheshmeh copper mine. The mine samples were collected from six different locations of the mine. Iron and sulfur-oxidizing heterotrophic bacteria were quantified with serial dilution and most probable number methods. Heterotrophic oxidizing bacteria were screened by three methods: decrease in pH, sulfate ion production activity and growth rate. Most efficient heterotrophic oxidizing bacteria were identified by molecular method. The results of this research show that the maximum quantity of these bacteria in Sarcheshmeh copper mine relate to dumps number 32 and 17 with value 8 x 10 and 5.9 x 10, respectively. Thirty two strains were isolated from six different locations of this copper mine and after screening tests 15 effective strains were selected and 8 strains were identified by molecular method. The results of the molecular identification showed that eight strains belong to: Bacillus thuringiensis strain DP26-1, Bacillus sp. strain DP-15-4, Pseudochrobactrum sp., Brevundimonas sp., Brevibacillus formosus, Sphingomonas ginsenosidimutans, Pseudomonas brassicacearum, Sphingomonas paucimobilis. Most efficient heterotrophic oxidizing bacteria related to DP-17-3 and DP-30-1 strains that produce high percentage of sulfate ion (270 and 223 ppm) also decrease dramatically the pH (4.2 and 4.9). Application of these bacteria in bioleaching process can enhanced efficiency of metal extraction in this copper mine.