Roles of microbial generalists-specialists and dissolved organic matter components in regulating heavy metal(loid)s occurrence in the Yangtze River.

Heavy metal(loid)s (HMs) solid-liquid partitioning is crucial for ecological risk assessment in large-scale rivers. However, the roles of microbial communities (generalists vs. specialists) and dissolved organic matter (DOM) composition in regulating HMs dynamics remain unclear. We investigated 77 aquatic sites across the Yangtze River (>1000 km), analyzed HMs distributions and DOM composition, as well as elucidated the mechanisms of HMs solid-liquid partitioning driven by microbial generalist-specialist. HMs primarily originated from natural sources, with limited anthropogenic influence. Community structures, diversity, and metabolic characteristics of bacteria and eukaryotes differed substantially between water and sediments. Bacterial specialists and eukaryotic generalists dominated their respective community formation. From sediments to water, changes in metabolic abundance of bacteria and eukaryotes are key drivers of HMs dynamics and DOM composition, and different taxa influence HMs distribution via distinct pathways. Bacterial specialists indirectly promote HMs retention in sediments through the mediation of protein-like substances. In contrast, eukaryotic generalists directly drive HMs migration into water. Although ecological risks in water were relatively low, most HMs still pose a migration risk from sediments to water, especially As, Cd, and Hg. This study highlights the key roles of microbes and DOM in regulating HMs dynamics, advancing riverine HMs fate understanding.