Cadmium-driven restructuring of soil nematode gut microbiota: Coordinated response of reduced diversity and enhanced...

Soil heavy metal pollution poses a significant threat to soil biodiversity. While extensive research has examined heavy metal impacts on soil communities and organismal health, their effects on soil fauna gut microbiota remain less explored. Here, we characterize gut microbial communities of soil nematodes across heavy metal gradients using high-throughput sequencing. The gut microbiota of soil nematodes was predominantly composed of Proteobacteria (75.97 %), Firmicutes (6.62 %), Actinobacteriota (3.79 %), etc. Remarkably, core microbial taxa (shared ASVs) represented 89.77 % of total sequences, indicating high compositional similarity across nematodes. Heavy metal pollution significantly reduced gut microbiota diversity and compositional stability (p < 0.05). RDA analysis identified cadmium (Cd), copper (Cu), chromium (Cr), soil properties (TN, TP, TOC), and soil bacterial diversity as key determinants of community structure, with Cd emerging as the primary driver through Mantel tests and random forest analysis. A significant negative correlation existed between Cd levels and microbial diversity (p < 0.05). Structural equation model further delineated that Cd impacts nematode gut microbiota via both direct and indirect pathways mediated by soil properties and bacterial diversity. Network analysis demonstrated increasing complexity (interactions) and stability under pollution escalation, evidenced by rising network density (0.053→0.093→0.100) and declining modularity (0.579→0.480→0.464). Core microbiota in heavily polluted soils exhibited enhanced disturbance resistance, underscoring their role in maintaining stability under metal stress. Collectively, heavy metals drive a dual response: diminishing diversity and stability while simultaneously selecting for adaptive microbial network restructuring. This study elucidates the variations in nematode gut microbiota under heavy metal stress, advancing understanding over adaptive response of gut microbiota to contaminated environments.