Given the global concern over heavy metal contamination in agricultural soil, comprehensive and in-depth investigations into the microbial ecological impacts of different agricultural practices on soil heavy metals and their biotransformation processes are both urgent and necessary. We employed metagenomic sequencing to investigate the impacts of integrated rice-fish farming on metal concentrations, metal resistance genes (MRGs), and microbial-mediated Fe, As, and Hg biotransformation processes within rice field. Our findings revealed that integrated rice-fish farming significantly reduced both the diversity and total abundance of MRGs. It also reduced the soil Al, Cd, Cu, Fe, Hg, Ni, Se, V, and Zn levels, with a marked correlation observed between metal concentration and MRGs profiles. Furthermore, integrated rice-fish farming markedly altered the microbial-mediated biotransformation processes for Fe, As, and Hg. It notably upregulated the abundance of Fe biotransformation genes, particularly those involved in the Fe gene regulation, oxidation, reduction, and storage. Biotransformation genes responsible for the As (III) oxidation and As methylation also exhibited increased abundances, along with mercury methylation and demethylation genes. Through metagenome assembled genomes (MAGs), we identified the Mycobacterium aubagnese from paddy soil which contained As oxidation genes and other multiple MRGs, exhibiting strong As remediation potential. Our findings demonstrated the potential of integrated rice-fish farming to reduce soil metal concentrations and mitigate soil metal pollution.
