Bioremediation of enrofloxacin and modulation of nitrogen cycling in a simulated aquaculture system by the fungus Cladosporium cladosporioides 11.

While microbial bioremediation is a promising strategy for antibiotic removal, the potential of fungi in mitigating antibiotic contamination and its associated ecological impacts in aquaculture systems remains largely unexplored. This study evaluated the bioremediation efficacy of the fungus Cladosporium cladosporioides 11 (CC11) in a simulated aquaculture ecosystem. The introduction of CC11 significantly accelerated enrofloxacin (ENR) removal in the aquaculture system and mitigated ENR bioaccumulation in crucian carp. Meanwhile, CC11 application notably lowered the accumulation of total nitrogen and ammonium nitrogen in the water column. Metagenomic analysis revealed that CC11 helped maintain a more active nitrogen-cycling microbial community, sustaining higher abundances of key genes involved in nitrogen fixation (nifB/K/T/Z) and assimilatory nitrate reduction (nasA/C/E/B/D) under ENR stress. Furthermore, CC11 restored specific bacterial taxa correlated with these functional genes, including methylotrophs associated with nif genes and Comamonadaceae members linked to nas genes, thereby reinforcing the functional network for nitrogen transformation. These findings demonstrate that CC11 acts as a multifunctional bioremediation agent, capable of simultaneously enhancing antibiotic removal and regulating nitrogen dynamics, offering a sustainable strategy for managing ENR pollution in aquaculture environments.