Responses of bacterial and fungal communities to cadmium contamination in paddy soils of Western Thailand

Abstract

Cadmium (Cd) contamination poses a significant threat to agricultural soils near mining areas by altering soil microbial communities and ecosystem functions. This study investigated the effects of different Cd contamination levels on bacterial and fungal communities in paddy soils from a long-term abandoned zinc mining area in Mae Sot, western Thailand, using high-throughput amplicon sequencing. Bacterial diversity remained relatively stable across contamination levels, whereas fungal richness and diversity declined significantly under high Cd conditions, indicating greater fungal sensitivity to metal stress. Community analyses revealed a reduction in core bacterial and fungal taxa with increasing Cd contamination, suggesting strong environmental filtering. Nevertheless, several bacterial genera, including Streptomyces, Nocardioides, Bacillus, and Nitrospira, persisted across all contamination levels, indicating high Cd tolerance. Anaeromyxobacter was identified as a key biomarker associated with highly contaminated soils. Functional predictions indicated enrichment of pathways related to glutathione metabolism, oxidative stress response, and heavy-metal efflux systems, reflecting microbial adaptation to long-term Cd exposure. These findings demonstrate that prolonged Cd contamination selectively reshapes soil microbiomes by reducing sensitive taxa while enriching metal-tolerant microorganisms. The persistence of Cd-resistant bacterial taxa and detoxification-related functions highlights their potential as bioindicators of soil health and promising candidates for the development of microbially assisted bioremediation strategies in Cd-contaminated agricultural soils.