Biodegradation potential of Air Pollutants by Phyllosphere Microbiome in Milan urban Area (Italy)

Urban plants and their associated phyllosphere microbiomes hold potential for the biodegradation of airborne pollutants such as polycyclic aromatic hydrocarbons (PAHs) and alkanes, which originate mainly from anthropogenic sources and accumulate on leaf surfaces. Although phyllosphere microbes are known to degrade such compounds, the ecological factors shaping their composition and functional capabilities remain insufficiently explored. In this study, we investigated microbial communities from the leaves of four plant species and from bioaerosols, sampled across three locations in Milan (urban traffic area, peri-urban park, and extra-urban park) and four seasons. Amplicon sequencing of the 16S rRNA gene and ITS1 region was performed to assess microbial diversity. These data were then analyzed in relation to environmental variables, including concentrations of PM10 and PAHs. To estimate biodegradation potential, relative abundances of bacterial genera were combined with functional coefficients (ranging from 0 to 1), calculated based on the proportion of genomes in the GTDB database containing hydrocarbon-degrading genes, as identified using Hidden Markov Models (HMMs). Microbial community composition was significantly influenced by plant species, season, and location, including interactions among these factors. Several bacterial genera with potential to degrade long-chain alkanes and aromatic hydrocarbons were detected. Overall, the results highlight the combined influence of ecological and environmental factors in structuring phyllosphere microbial communities and shaping their biodegradation potential. This study supports the role of phyllosphere microbes as contributors to urban air pollutant degradation and lays the groundwork for future strategies in microbiome-informed phytoremediation.