Characterization of indigenous copper-resistant Streptomycetes from chickpea (Cicer arietinum L.) fields

A total of 432 morphotypes of Streptomycetes were isolated from rhizospheric and non-rhizospheric soils of chickpea (Cicer arietinum L.) which showed significant variation in population count. The generation time at different Cu2+ concentrations (0.5, 0.75 and 1.0 mM), were recorded for S160 as (1.2, 6.0 and 14.4 h), S161 (7.2, 12.0 and 24.0 h), and S164 (4.8, 7.2 and 16.8 h), respectively. Qualitative results showed 100, 62 and 8% of non-rhizospheric isolates tolerated 0.075, 0.264 and 0.628 mM of Cu2+, respectively, while rhizospheric isolates showed tolerance of 0.264 mM CuSO4. Semi-quantitative assay showed that the rhizospheric strain S160 has the ability to withstand 3.14 mM, while non-rhizospheric isolates S161 and S164 were able to tolerate up to 3.14 and 1.88 mM CuSO4, respectively. Acid-digested pellet of S160 strain indicated 68% reduction in copper residual concentration, confirming copper accumulation capacity in Streptomyces. The ability of growth of these strains in the presence of Cu2+ was co-induced by the presence of 3.1, 2.8 and 2.1 kb plasmid, respectively. Plasmids transformation into wild strain resulted in changes in metal resistance ability along with appreciable changes in resistance to antibiotics. Cultures were identified by 16S rDNA sequencing as Streptomyces sp. (S160 and S161) and Streptomyces hygroscopicus (S164), respectively.