Autochthonous microorganisms of a soil contaminated by polycyclic aromatic hydrocarbons: allies or silent threats?

Soil harbours complex microbial communities that provide essential ecosystem functions. Industrial activities and fossil fuel combustion have resulted in widespread polyaromatic hydrocarbon (PAH) contamination, which severely compromises soil quality. Several microorganisms are capable of degrading PAHs, however, the structure and functional roles of these communities are strongly influenced by the degree of contamination and soil features. Previous research focused either on isolated strains under controlled conditions or on a single component of the microbiota, leaving gaps in our understanding of indigenous microbial communities in contaminated environments. The objective of this study was to comprehensively investigate the diversity of microbial communities in a PAH-contaminated urban garden in Torino (Italy), primarily polluted by benzo(a)pyrene, benzo(g, h,i)perylene, fluoranthene, and phenanthrene. Investigating the microbial communities in PAH-contaminated soils is crucial to designing effective bioremediation strategies and elucidating the potential impact of PAHs on the emergence of antimicrobial resistance. By integrating culture-dependent and culture-independent approaches, we obtained 379 microbial isolates (181 fungi, mainly Ascomycota, and 198 bacteria, mainly Proteobacteria and Bacillota) and characterized the unculturable diversity to broaden our understanding of the entire microbial community in a degraded soil. Furthermore, we assessed the potential association between the ability to survive in a PAH-polluted environment and antimicrobial resistance, revealing a concerning positive correlation. These findings demonstrate that microbial populations isolated from PAH-contaminated soils not only exhibit a heightened ability to survive in the presence of these pollutants, but also display an increased prevalence of antimicrobial resistance, indicating that environmental contamination may actively contribute to the selection and spread of antibiotic-resistant microorganisms.