Vertical changes in water depth and environmental variables drove the antibiotics and antibiotic resistomes distribution, and microbial food web structures in the estuary and marine ecosystems.

The influence of vertical changes in water depth on emerging pollutants distribution and microbial food web remains elusive. We investigated the influence of vertical transition in water depth on the environmental variables, antibiotics and antibiotic resistomes, and microbial community structures in estuary and marine ecosystems (0-50 m). Stepwise multiple linear regression model showed that among investigated environmental variables, change in water salinity was the most influential factor dictating the fluoroquinolone and macrolides concentrations, while dissolved oxygen and turbidity were the key influencers of sulfonamides and beta-lactam concentrations, respectively. Bacterial and eukaryotic diversity and niche breadth significantly increased with the increasing water depth. Ecosystem food web structure at the bottom depths was more stable than at the middle and surface depths. At the surface depth, the top 5 keystone genera were Cryothecomonas, Syndiniales, Achromobacter, Pseudopirsonia, and Karlodinium. Whereas Eugregarinorida, Neptuniibacter, Mychonastes, Novel_Apicomplexa_Class_1, Aplanochytrium and Dietzia, Halodaphnea, Luminiphilus, Aplanochytrium, Maullinia dominated the top 5 genera at the middle and the bottom depth, respectively. Absolute abundance of antibiotic resistance genes (ARGs) was drastically increased at the surface depth compared with the middle and bottom depths. Abundance of the top 10 ARGs and mobile genetic elements (MGEs) detected including tnpA-05, aadA2-03, mexF, aadA1, intI-1(clinic), qacEdelta1-02, aadA-02, qacEdelta1-01, cmlA1-01, and aadA-01 were amplified at the surface depth. This study demonstrated that ARGs abundance was disproportionate to bacterial diversity, and anthropogenic disturbances, confinement, MGEs, and ecosystem stability play primary roles in the fate of ARGs. The findings of this study also implicate that vertical changes in the water depth on environmental conditions can influence antibiotic concentrations and microbial community dramatically.