Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous priority pollutants that cause great damage to the natural environment and health.Average genome size in a community is critical for shedding light on microbiome\'s functional response to pollution stress within an environment.Here,microcosms under different concentrations were performed to eval-uate the selection of PAHs stress on the average genome size in a community.We found the distinct communities of significantly larger genome size with the increase of PAHs con-centration gradients in soils,and consistent trends were discovered in soils at different lat-itudes.The abundance of Proteobacteria and Deinococcus-Thermus with relatively larger genomes increased along with PAHs stress and well adapted to polluted environments.In contrast,the abundance of Patescibacteria with a highly streamlined and smaller genome decreased,implying complex interactions between environmental selection and functional fitness resulted in bacteria with larger genomes becoming more abundant.Moreover,we confirmed the increased capacity for horizontal transfer of degrading genes between com-munities by showing an increased connection number per node positively related to the nidA gene along the concentration gradients in the co-occurrence network.Our findings suggest PAHs tend to select bacterial taxa with larger genome sizes,with significant consequences for community stability and potential biodegradation strategies.