Coupled nitrogen and phosphorus cycles mediated by coordinated variations of functional microbes in industrial recirculating aquaculture system

Industrial Recirculating Aquaculture Systems (IRAS) represent a sustainable and efficient approach to aquaculture, offering significant benefits in water conservation and environmental management. A comprehensive understanding of nitrogen (N) and phosphorus (P) cycling is essential for optimizing system design and operational strategies, enabling the maintenance of a balanced ecosystem within IRAS.Here, water microbial communities in the shrimp aquaculture pond (AP) and nitrification tank (NT) of the IRAS were investigated using a metagenomics-based approach to explore the mechanisms of N and P coupling cycles. Results showed that (1) N and P cycling genes were more abundant in AP water than in NT, with higher potentials for degrading organic N and P compounds, nitrate reduction, denitrification, and phosphate uptake in AP; and their hosts (functional bacteria) were identified as Marivivens for nitrate reduction, Polaribacter and Erythobacter for organophosphorus hydrolysis, and Fluviibacter and Sediminibacterium for phosphate uptake; (2) the coupling of N and P cycles was observed through the abundance of functional genes, likely mediated by coordinated variations in host composition, with nitrite content as a key factor influencing this variation; several bacterial species possessing both N and P cycling genes were identified, primarily engaged in the degradation of organic N and P compounds, denitrification, and phosphate uptake.This study highlights the coupling of N and P cycling in IRAS and the important role of functional bacteria in maintaining water quality. The results also have important implications for the management and improvement of IRAS for more effective aquaculture activities.