Arsenic and PAHs impose environmental stress on soil microorganisms, yet their compound effects remain poorly understood. While soil microorganisms possess the ability to metabolize As and PAHs, the mechanisms of microbial response are not fully elucidated. In our study, we established two simulated soil systems using soil collected from Xixi Wetland Park grassland, Hangzhou, China. The As-600 Group was contaminated with 600 mg/kg sodium arsenite, while the As-600-PAHs-30 Group received both 600 mg/kg sodium arsenite and 30 mg/ kg PAHs (phenanthrene:fluoranthene:benzo[a]pyrene = 1:1:1). These systems were operated continuously for 270 days, and microbial responses were assessed using high-throughput sequencing and metagenomic analysis. Our findings revealed that compound contamination significantly promoted the abundance of microbial defenserelated genes, with general defense genes increasing by 11.07 % 74.23 % and specific defense genes increasing by 44.13 % 55.74%. The dominate species Rhodococcus adopts these general and specific defense mechanisms to resist compound pollution stress and gain ecological niche advantages, making it a candidate strain for soil remediation. Our study contributes to the assessment of ecological damage caused by As and PAHs from a microbial perspective and provides valuable insights for soil remediation.

Arsenic (As) and polycyclic aromatic hydrocarbons (PAHs) are highly toxic, carcinogenic and teratogenic, and are commonly found in soils of industrial sites such as coking plants. They exert environmental stresses on soil microorganisms, but their compounding effects have not been systematically studied. Exploring the effects of compound contamination on microbial communities, species and genes is important for revealing the ecological damage caused by compound contamination and offering scientific insights into soil remediation strategies. In this study, we selected soil samples from 0 to 100 cm depth of a coking site with As, PAHs and compound contamination. We investigated the compound effects of As and PAHs on microbial communities by combining high-throughput sequencing, metagenomic sequencing and genome assembly. Compared with single contamination, compound contamination reduced the microbial community diversity by 10.68%-12.07% and reduced the community richness by 8.39%-18.61%. The compound contamination decreased 32.41%-46.02% of microbial PAHs metabolic gene abundance, 11.36%-19.25% of cell membrane transport gene abundance and 12.62%-57.77% of cell motility gene abundance. Xanthobacteraceae, , the biomarker for compound contaminated soils, harbors arsenic reduction genes and PAHs degradation pathways of naphthalene, benzo [a]pyrene, fluorene, anthracene, and phenanthrene. Its broad metabolic capabilities, encompassing sulfur metabolism and quorum sensing, facilitate the acquisition of energy and nutrients, thereby conferring ecological niche advantages in compound contaminated environments. This study underscores the significant impacts of As and PAHs on the composition and function of microbial communities, thereby enriching our understanding of their combined effects and providing insights for the remediation of compound contaminated sites.