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Abstract

Chromium occurs widely in most soils, but generally in trace amounts. Actinomycetes, one of the important components of the microbial population in soils interact with a variety of metals including chromium. This study was aimed to evaluate the tolerance of soil actinomycetes to Cr6+, other metals and antibiotics. Thirty-two actinomycete isolates were screened for their tolerance to Cr6+on tryptone yeast extract agar medium supplemented with Cr6+at concentrations ranging from 100 to 2000 µg ml–1. Thirteen Cr-tolerant isolates were selected on the basis of their growth at the highest concentration, but their performance was not satisfactory in Cr6+containing liquid salts medium. Resistance of these isolates to other metals and antibiotics was assessed using agar-cup assay and disc diffusion technique, respectively. The sequence of metal toxicity for the actinomycete isolates was in the order Hg2+≯ Ni2+≯ Cu2+≯ Co2+≯ Cd2+, but the Cr6+resistance of the isolates could not be correlated with their antibiotic-resistance profile.