EVALUATION OF NATIVE HEAVY METAL TOLERANT BACTERIA FROM THE MUNICIPAL WASTE DISPOSAL SITE OF THE BARAK RIVER, SOUTH ASSAM

Abstract

This study examined the physico-chemical parameters and heavy metal tolerant bacterial isolates from the municipal waste disposal site of the Barak River. These isolates displayed different degrees of metal tolerance. The water was slightly alkaline (pH 7.78 ± 0.32) with moderate dissolved oxygen (6.0 ± 0.45 mg/L), while high microbial loads were detected. A total of 7 heavy metal resistant bacteria were isolated and evaluated for tolerance to Ni, Cd, Co, and Cu at concentrations ranging from 0.1 to 4.0 mM. In Ni assays, isolate Br(3) showed the highest tolerance (50.44% at 4.0 mM), whereas Br(6) was highly sensitive. Under Cd stress, Br(3) again exhibited the greatest tolerance (40% at 4.0 mM), while Br(1) showed marked inhibition. For Co, all isolates maintained >88% relative growth at 0.1–0.5 mM, but growth dropped sharply at higher concentrations. In Cu assays, most isolates sustained >60% relative growth at lower concentrations; Br(6) tolerated 45.37% at 2.0 mM, and Br(2) retained the highest relative growth (24.36%) at 4.0 mM. These findings confirm the presence of multi-metal tolerant bacteria in the municipal waste disposal site of the Barak River. Such isolates represent promising candidates for bioremediation of heavy metal contaminated aquatic ecosystems.