Nitrogen metabolism potential in biofilm microbial communities: potential applications in the mariculture wastewater treatment

Marine aquaculture wastewater is one of the major sources of nitrogen pollution in coastal areas, and excessive discharge poses a threat to human health and the marine ecosystem. In order to investigate the nitrogen metabolism potential of microorganisms in marine aquaculture water, metagenomic sequencing was conducted, and microbial communities involved in nitrogen metabolism on composite filler biofilms and their contributions to nitrogen metabolism functions were analyzed based on KEGG annotation. Metagenomic analysis revealed that nitrogen metabolism microorganisms were primarily composed of Proteobacteria, Planctomycetota, Bacteroidota, and Firmicutes. KEGG results indicated the presence of complete nitrogen metabolism pathways within the biofilm. Analysis of nitrogen metabolism modules and relative enzyme abundance showed that the nitrification module was much less abundant compared to denitrification. Denitrification, dissimilatory nitrate reduction, and ammonia conversion to amino acids were the major modules of nitrogen metabolism in the biofilm, reflecting the main nitrogen transformation pathways. The study systematically revealed key driving taxa in the nitrogen cycle within the biofilm. Proteobacteria, Planctomycetota, Bacteroidota, and Verrucomicrobia were identified as the major executors of nitrogen metabolism pathway modules and enzyme functions in the biofilm. This research underscores the diverse microbial communities cooperate to maintain the potential nitrogen removal capacity of the biofilm. This study provide new insights into the critical driving factors of nitrogen cycling in marine aquaculture wastewater, which can serve as a scientific basis for the efficient purification of aquaculture wastewater.