Bioremediation potential of lead and cadmium tolerant bacteria isolated from industrial (tannery) effluents.

Heavy metal pollution from tannery industries presents significant environmental and public health concerns due to the toxicity and persistence of metals such as Pb2+ and Cd2+. This study aimed to isolate and characterize indigenous Pb2+ and Cd2+-tolerant bacteria from tannery effluents and contaminated soils of highly polluted areas in Dhaka for potential bioremediation applications. A total of 72 Pb2+-tolerant and 52 Cd2+-tolerant bacterial isolates were obtained using metal-supplemented LB agar. The minimum inhibitory concentrations (MICs) recorded were 4000 ppm for Pb2+ and 250 ppm for Cd2+. Quantitative analysis demonstrated removal efficiencies of 93.91% for Pb2+ and 89.66% for Cd2+. All isolates exhibited plant growth-promoting traits, including phosphate solubilization, ammonia production, indole-3-acetic acid (IAA) production, and cellulase activity. Most isolates were antibiotic-sensitive, though some showed multidrug resistance, emphasizing the need for biosafety evaluation. The most promising isolates were partially identified as Enterobacter spp. and K. pneumoniae. Protein expression profiling by SDS-PAGE revealed metal-responsive proteins ranging from 25 to 75 kDa under selective Pb2+ and Cd2+ stress. Genomic and proteomic analyses further indicated the involvement of efflux pump-associated genes in metal resistance, where cusR was identified as a common resistance gene among the dominant strains. Overall, these findings suggest that the indigenous K. pneumoniae possesses strong potential for Pb2+ and Cd2+ removal, along with plant growth-promoting capabilities, making them promising candidate for bioremediation and phytoremediation strategies.