Deciphering microbial dynamics in coastal ecosystems under polycyclic aromatic hydrocarbon stress: Community...

The significant toxicity and carcinogenicity of polycyclic aromatic hydrocarbons (PAHs) have raised increasing concern about their contamination, particularly in coastal regions with intensive human activities and urbanization. However, limited information exists on microbial response mechanisms across varying levels of PAHs contamination. In this study, sediment samples at 18 locations along the Yantai inland river and estuary were collected in October 2024 to examine the partitioning and spatial dispersal of PAHs, while microbial community assembly, interaction networks, and metabolic adaptations were analysed using metagenomics. Results showed that the average ∑PAHs concentration in the estuary (27.95 ± 2.91 ng/g) was significantly lower than that in the river (77.54 ± 43.39 ng/g), with a correspondingly higher ecological risk in the river. High-molecular-weight (HMW) PAHs dominated in both estuary and river sediments due to their high hydrophobicity and stability. Microbial community analysis revealed increased microbial diversity and a higher abundance of PAHs-degrading microbes (e.g., Ruegeria, known for degrading low-molecular-weight PAHs) under higher PAHs contamination. Co-occurrence network and topological analyses demonstrated dual regulatory effects of PAHs stress on microbial interactions, where elevated PAHs contamination intensified interspecies connectivity while simultaneously inducing destabilizing negative covariance patterns that weakened microbial network integrity. Additionally, neutral community model analysis indicated that stochastic processes dominated community assembly, with higher proportions of stochasticity observed in rivers under high PAHs stress. Notably, elevated PAHs concentrations significantly impaired energy metabolism and nitrogen metabolic pathways (p < 0.05), suggesting altered nitrogen biogeochemistry under PAHs contamination. This study advances the understanding of microbial population responses to different PAHs contamination levels in coastal regions.