Isolation and characterization of heavy metal resistant bacteria from Barak River contaminated with pulp paper mill effluent, South Assam.

A group of 15 heavy metal resistant bacteria were isolated from Barak River contaminated with paper and pulp effluents. These isolates displayed different degrees of chromium tolerance. Four isolates showed 34 %-49 % of growth at a concentration of 4.0 mM of Cr(6+) and subjected to chromium reduction assay under aerobic condition. The isolate E (4) showed highest reduction (34.38 %) followed by E (3) and K(6)PA6, both showed 28.75 % reduction and then D (2) (27.5 %) after 72 h of incubation. These 4 isolates also showed different degrees of resistance to other heavy metals like Ni, Cu, Co and Cd. Antibiotic sensitivity profile of these selected bacterial strains was determined against 10 different antibiotics. Isolate E (4) appeared to be most susceptible being inhibited by eight antibiotics and resistant to penicillin G and ampicillin. The isolate E (3) was resistant to as many as five antibiotics and showed susceptible responses to the rest of the antibiotics. Both the isolates K(6)PA6 and D (2) were resistant to four antibiotics and showed intermediate to susceptible responses to the rest of the antibiotics.