Responses of soil bacterial communities and PAH-degrading genes to PAHs during soil self-purification: Evidence from a microcosm experiment

Polycyclic aromatic hydrocarbons (PAHs) are persistent environmental pollutants threatening soil ecosystems and human health. While soil microbial communities possess intrinsic PAH degradation potential, the dynamics of bacterial populations and degradation-associated genes during natural attenuation remain poorly understood. This study investigated the self-purification capacity of PAH-contaminated soil through a 32-day microcosm experiment using three model PAHs: naphthalene (NAP), phenanthrene (PHE), and pyrene (PYR). Results demonstrated high PAH dissipation rates (94.36 %, 72.60 %, and 47.70 % for NAP, PHE, and PYR, respectively). High-throughput sequencing revealed that PAH exposure (10–100 mg kg⁻¹) shifted bacterial community structure, enriching Actinobacterial taxa (Mycobacterium, Rhodococcus, Nocardioides) linked to PAH degradation and strengthening bacterial interactions. Quantitative PCR further indicated substrate-specific gene responses: Actinobacteria harboring nahAC preferentially degraded NAP, while nidA and phe genes were upregulated under PHE/PYR stress. These findings highlight Actinobacteria as keystone degraders and propose leveraging microbial community assembly strategies to optimize bioremediation of PAH-contaminated soils.