Isolation and characterization of indigenous copper-resistant actinomycete strains

Fifty actinomycetes were isolated from copper contaminated and non-contaminated area. Primary qualitative screening assays showed that 100% of the isolated microorganisms of the contaminated area were resistant up to 80 mg L−1 of CuSO4. On the other hand, 100% of isolates from non-contaminated area grew at 16 mg L−1, 87.4% at 40 mg L−1 and only 19.4% of them were capable of growing at 80 mg L−1 of CuSO4. The semiquantitative assay showed that the isolated strains from the sediments of the contaminated site were resistant up to the highest concentration tested (1000 mg L−1) with the exception of AB2C strain; however, the strains isolated from non-contaminated sediments were sensitive to Cu2+ concentrations higher than 200 and 400 mg L−1, respectively. Microbial growth of AB0 strain in presence of 39 mg L−1 copper showed an inhibition of 32% after 6 days of incubation as compared to the control, and copper residual concentration indicated a reduction in the supernatant of 71.2% after 6 days of incubation: pellet acid digestion proved that copper was accumulated by the cells. 16S rDNA restriction digestion of 1300 bp amplicons with CfoI and HpaII showed only one restriction pattern for all the strains and it matched with the control, Streptomyces coelicolor.