Heavy metal stress alters soil microbial structure and diversity in the BBN industrial corridor, Himachal Pradesh, India.

Soil microorganisms are essential to ecosystem functioning, yet their communities are highly susceptible to environmental disturbances such as heavy metal contamination from industrial activities. This study investigates the impact of heavy metal pollution on soil bacterial and fungal communities in the Baddi-Barotiwala-Nalagarh (BBN) Industrial Corridor, Himachal Pradesh, India. Soil samples were analyzed for physicochemical properties and heavy metal content, i.e., cadmium (Cd), iron (Fe), copper (Cu), arsenic (As), lead (Pb), chromium (Cr), zinc (Zn), and manganese (Mn), followed by the isolation and characterization of culturable bacterial and fungal communities. Microbial profiling indicated significant variations in community composition, diversity, and abundance across industrial sites. Firmicutes (Bacillota) and Proteobacteria emerged as dominant bacterial phyla, while the fungal communities were predominantly composed of Ascomycota. Although overall microbial richness and diversity declined with increasing heavy metal concentrations, several isolates exhibited key plant growth-promoting (PGP) traits, including phosphate solubilization, siderophore production, indole-3-acetic acid (IAA) synthesis, ammonia production, and nitrate reduction. Pearson correlation analysis demonstrated a relation between microbial community structure and multiple environmental variables, including heavy metals and key soil physicochemical properties. The findings highlight the dual role of soil microbes as indicators of environmental stress and as potential agents for microbe-assisted bioremediation.