Evaluation of metal tolerance of bacterial strain isolated from Hooghly River coast soil

The mangrove soils of the Sundarbans represent metal-rich, ecologically dynamic environments that support diverse microbial populations with potential applications in bioremediation. Heavy metal-tolerant bacteria from such habitats possess adaptive physiological mechanisms that enable survival under environmental stress. This study aimed to isolate and characterize bacterial strains capable of tolerating multiple heavy metals from mangrove soils of Sundarbans, West Bengal, India. Soil samples from five stations were processed using enrichment techniques to isolate Gram-positive and Gram-negative bacteria. Sixteen predominant and morphologically distinct isolates were selected for characterization. Heavy metal tolerance was evaluated against ZnSO₄, CuSO₄, MnSO₄, Pb, HgCl₂, CoCl₂, and K₂CrO₄ across increasing concentrations. Antibiotic susceptibility was evaluated, and the activities of stress-related enzymes such as catalase, peroxidase, polyphenol oxidase, ascorbate peroxidase, and ascorbic acid oxidase were assessed. The isolates exhibited varied tolerance profiles, sustaining 50–200 ppm of ZnSO₄, CuSO₄, MnSO₄, and Pb, but only 1–40 ppm of HgCl₂ and 5–100 ppm of CoCl₂. Strain MS-8 demonstrated the broadest tolerance range and was identified as Klebsiella aerogenes strain Ka37751. Most isolates were sensitive to tested antibiotics, except for resistance observed against Nystatin. The findings highlight diverse adaptive responses, reflected in differential enzyme activities and metal tolerance capacities. The study was limited by the number of isolates and lacked molecular investigation of resistance mechanisms. To identify metal-tolerant bacterial strains and evaluate their potential utility in bioremediation.