INVESTIGATING HEAVY METAL-INDUCED STRESS ON MICROBIAL POPULATIONS AND THEIR RESPONSE TO ADAPTIONS AND GROWTH

Shambhavi C B , Ashrith Kumar A , Ann Irene. D

Heavy metal contamination, bacterial tolerance, lead acetate, mercury chloride, bioremediation.

Heavy metal contamination is a significant environmental issue. Toxic metals like lead (Pb) and mercury (Hg) do not break down and build up in living organisms. They disrupt how microbes function and can affect ecosystems, even in small amounts. This study looked at how stress from heavy metals impacts bacterial populations isolated from industrial soil samples. We also assessed their tolerance and growth responses to lead acetate (Pb(C?H?O?)?) and mercury chloride (HgCl?). Soil samples were collected from two industrial sites in Bengaluru. We obtained bacterial isolates using serial dilution and culture methods. Pure isolates underwent disc diffusion assays, heavy metal-supplemented sub-culturing, and broth exposure experiments to examine their responses based on metal type and concentration. The disc diffusion assay showed that mercury chloride had strong bacteriostatic activity. It created large zones of inhibition at all tested concentrations (5 mg, 10 mg, and 15 mg) and completely stopped bacterial growth. In contrast, lead acetate created smaller inhibition zones, with bacteria continuing to grow at all concentrations. This indicates partial tolerance and suggests adaptive mechanisms like efflux, sequestration, or biosorption. Broth culture experiments confirmed that the inhibition was dependent on concentration with lead exposure. However, there was no growth in mercury-supplemented broth. Luria broth did not support bacterial growth for either heavy metal, and we consistently observed precipitation, likely due to chemical interactions reducing nutrient availability. Screening on Eosin Methylene Blue agar showed no growth, suggesting that the isolates were non-lactose fermenters. Gram staining confirmed the presence of Gram-positive cocci and bacilli, indicating a diverse bacterial community. Overall, the results showed that bacterial tolerance to heavy metals varies by metal type and concentration. Isolates were more sensitive to mercury but showed greater tolerance to lead. These findings shed light on how microbes adapt to heavy metal stress and underline the potential use of lead-tolerant bacterial strains in bioremediation efforts for contaminated environments. There is a need for more molecular characterization and resistance gene profiling to better understand adaptive mechanisms and improve microbial applications for environmental restoration

Volume 13 Issue 8, August-2025

Pages : g840-g850