Evaluation of the genetic basis of heavy metal resistance in an isolate from electronic industry effluent

Halomonas BVR 1 isolated from an electronic industry effluent had high level of resistance to heavy metals like cadmium, lead, zinc and to various antibiotics. Minimum Inhibitory Concentration (MIC) of the strain toward cadmium and lead was found to be 200 mg L−1 and 400 mg L−1 respectively, while it could tolerate zinc up to 250 mg L−1 and chromium up to 150 mg L−1. The present study proved the genetic contribution of heavy metal resistance in this strain to be plasmid mediated. Isolation of the plasmid from Halomonas BVR 1 and its subsequent linearization with Bam H1 confirmed the presence of a plasmid of size >10 kb. Plasmid curing experiments affirmed plasmid mediated heavy metal resistance. Additionally, genetic transformation of a non metal resistant lab strain Escherichia coli and the cured strain of Halomonas BVR 1 with the isolated plasmid increased their metal tolerance level by 50% confirming the genetic determinant to be present in the plasmid.