Metal resistance in Pseudomonas strains isolated from soil treated with industrial wastewater

Heavy metal concentrations in soil treated with industrial wastewater of Al igarh City (U.P.), India were determined. The analysis of test samples reve aled high levels of Fe, Zn, Ni and Cu. A total of 45 Pseudomonas spp. were isolated from soil and were characterized on the basis of morphological, cu ltural and biochemical characteristics. MICs of Hg2+, Cd2+, Cu2+, Cr3+, and Zn2+ for each isolate were determined. Eighty percent of the strains isola ted from soil harboured resistance to copper, whereas 73.3% of the isolates exhibited resistance to cadmium, 71.1% to chromium and zinc and 48.8% to m ercury. A maximum MIC of 200 mu g/ml for mercury and 1600 mu g/ml for other metals was observed. Metal resistance was found to be plasmid mediated as evidenced by transformation studies. Further, the transmissible nature of c hromium resistance was confirmed by conjugation. Agarose gel electrophoresi s using the miniprep method for plasmid isolation revealed that these isola tes harboured plasmids of molecular weights (45 & 47 kb) using EcoRI and Hi ndIII digests of lambda DNA and undigested lambda DNA as standard markers.