Urbanization cast a shadow over bacterial community in river sediment: Insights from community diversity, assembly processes and network interactions.

Rivers reflect natural-anthropogenic interactions, yet how urbanization affects riverine bacterial communities along rural-urban gradients is poorly understood. This study examined bacterial diversity and assembly mechanisms along such a gradient of river sediments. Results showed that bacterial diversity significantly decreased with increasing urban influence. Community assembly shifted from stochastic processes dominating in rural zones to environmental selection prevailing in urban zones. The rural-urban transition caused bacterial network instability, potentially reducing resilience. The participation of prevalent taxa decreased but the rare taxa related to chitinolysis and nitrate/nitrite denitrification were selectively enriched along with rural-urban gradient, suggesting rapid functional recruitment to exploit dissolved organic nitrogen and nitrate pulses typical of urban runoff. Our findings underscore that urbanization's influence on bacterial communities is more pronounced than the river's inherent natural characteristics. These insights highlight the profound ecological consequences of urbanization on river microbiomes, informing protection and restoration strategies.