The phylogenetic positions of 60 bacterial strains isolated from three tailing piles were determined by analyzing their partial 16S rRNA gene sequences. These strains were divided into three phylogenetically distinct groups of Arthrobacter and likely represented several non-described species. The physiological diversities of these phylogenetically and geographically distinct populations were evaluated based on their resistance to five heavy metals (Zn, Pb, Cd, Cu and Co) and four antibiotics (Kan, Rif, Str and Amp), and differences in utilization of 49 carbon sources. Genetic differentiations were demonstrated with randomly amplified polymorphic DNA (RAPD) analysis. These biological parameters were significantly different among three phylogenetically distinct groups. Notably, detectable differences were also observed among three geographically distinct subdivisions with similar taxonomic position. These results indicate that mine tailings are an ideal site for investigating the differentiation of natural bacterial populations in response to extreme metal contamination. Additionally, these environments appear to harbor many previously not characterized bacterial species, which are potentially important candidates for application in bioremediation due to their remarkable resistance to multiple metals.

Six samples containing extremely high concentration of Pb, Zn, and Cd were obtained from the layers of 5−10 cm and 25−30 cm three tailing piles, with ages of about 10, 20 and more than 80 years, respectively. Then, 48 bacterial strains were obtained from these samples, and subsequently their phylogenetic positions were determined by analysis on the partial sequence of 16S rRNA gene (fragment length ranging from 474 to 708 bp). These isolates were members of the Arthrobacter genus, phylogenetically close to A. keyseri and A. ureafaciens, with sequence ranging from 99.1% to 100%. Furthermore, genetic variation between subpopulations from different samples was revealed by analysis on their randomly amplified polymorphic DNA profile. Nei genetic distance showed that the greatest differentiation occurred between subpopulation A and C. Notably, either genetic distance between subpopulations from the layers of 5−10 cm and 25−30 cm of each tailing pile or between same layers of different tailing pile increased with the history of tailings. Moreover, correlation analysis showed that soluble Pb has a significantly negative relationship with Nei' gene diversity of subpopulation. It was assumed that soluble Pb may be responsible for the reduced genetic diversity of the Arthrobacter population. Our data provided evidence that genetic differentiation of microbial populations was consistent with the changes of environmental factors, particularly heavy metals.