Ulva fasciata litter decomposition fuels microbial restructuring and antibiotic resistance proliferation in mariculture sediment.

Antibiotic resistance genes (ARGs) pose a global public health threat, with marine environments acting as critical reservoirs for their dissemination. This study aimed to ascertain the nutrients release of Ulva (U.) fasciata litter and their effects on antibiotics resistance variation of maricultural sediment. Laboratory microcosms simulated decomposition under varying U. fasciata particle sizes (small, 5-6 mm; large, 2-3 cm) and biomass levels (2-10 g L-1) for 3 months. Results revealed that U. fasciata decomposition significantly increased nutrient concentrations, with total nitrogen and phosphors levels positively correlated with both the quantity and size of U. fasciata litter. Microbial richness and diversity were positively correlated with nutrient inputs, primarily driven by enrichment of Chloroflexota and Acidobacteriota. Notably, U. fasciata decomposition induced the total abundance of antibiotic resistance genes (∑ARGs) significant enrichment by 0.15-0.48% after 3-month operation, and more pronounced effect observed in the small-sized U. fasciata compared to controls, mainly due to resistance genes mexW, sul4, mexF, bacA, etc. ΣARGs showed stronger associations with mobile genetic elements and nutrient variables at the overall structural level, as revealed by Mantel test analysis, compared to its correspondence with the microbial community.