Marine particulate matter serves as a hotspot for enriching pathogenic bacteria and disseminating antibiotic...

In coastal ecosystems, free-living (FLB) and particle-attached bacteria (PAB) occupy distinct niches, but their pathogenic and antibiotic resistance gene (ARG) reservoirs are lacking. Using molecular approaches, we compared the composition, pathogenic diversity, ARGs abundance, and microbial interactions of FLB and PAB communities from the Bohai Sea. We found PAB had higher diversity, heterogeneity, and network complexity than FLB. PAB hosted 233 potential pathogenic taxa (vs. 169 in FLB), with Escherichia spp., Staphylococcus spp., and Vibrio spp. dominant. Parallel qPCR analysis confirmed that the abundance of Escherichia coli, Vibrio spp., and Pseudomonas aeruginosa were significantly higher in PAB communities, whereas Staphylococcus aureus was more abundant in FLB communities. Among the ten targeted ARGs, eight were significantly more abundant in PAB communities, with sul1, NDM-1, and qacEΔ1-01 being the most dominant subtypes in the study region. Importantly, a significant positive correlation between the total abundances of ARGs and mobile genetic elements was observed exclusively in PAB communities, suggesting that particle surfaces serve as hotspots for horizontal gene transfer (HGT). Our results not only reinforce the role of HGT as a key mechanism for ARG dissemination in marine bacteria, but also highlights that such transfer likely occurred across the interface between FLB and PAB communities, forming a dynamic, interconnected network for ARG exchange. Collectively, this study highlights the critical role of marine particles in structuring microbial communities, enriching pathogens, and facilitating antibiotic resistance propagation, offering important insights for assessing ecological and public health risks in coastal waters.