The isolation of heavy-metal resistant culturable bacteria and resistance determinants from a heavy-metal-contaminated site

In this study we performed a phylogenetic analysis of a culturable bacterial community isolated from heavymetal-contaminated soil from southwest Slovakia using 16S rRNA (16S rDNA) and heavy-metal resistance genes. The soil sample contained high concentrations of nickel (2,109 mg/kg), cobalt (355 mg/kg) and zinc (177 mg/kg), smaller concentrations of iron (35.75 mg/kg) and copper (32.2 mg/kg), and a trace amount of cadmium (<0.25 mg/kg). A total of 100 isolates were grown on rich (Nutrient agar No. 2) or minimal (soil-extract agar medium) medium. The isolates were identified by phylogenetic analysis using partial sequences of their 16S rRNA (16S rDNA) genes. Representatives of two broad taxonomic groups, Firmicutes and Proteobacteria, were found on rich medium, whereas four taxonomic groups, Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria, were represented on minimal medium. Forty-two isolates grown on rich medium were assigned to 20 bacterial species, while 58 bacteria grown on minimal medium belonged to 49 species. Twenty-three isolates carried czcA- and/or nccA-like heavy-metal-resistance determinants. The heavy-metalresistance genes of nine isolates were identified by phylogenetic analysis of their protein sequences.