Isolation and characterization of Pseudomonas sp. QX11 with high-efficiency aerobic denitrification for eutrophication control in aquaculture

Eutrophication of aquatic ecosystems, primarily induced by the excessive accumulation of nitrogen compounds from aquaculture activities, poses significant environmental challenges. To address this issue through biological denitrification, a total of 17 strains with aerobic denitrification activity were isolated from river prawn pond using selective media. Among these isolates, strain QX11 exhibited the highest denitrification activity and was consequently selected for further investigation. Phylogenetic analysis identified strain QX11 as showing highest homology (98.32 %) with Pseudomonas mendocina, with optimal growth and denitrification performance observed at a C/N ratio of 10, salinity of 5, temperature of 30 °C and rotational speed of 150 rpm. Under these optimized conditions, QX11 exhibited remarkable nitrogen removal efficiencies: achieving 98.06 % NH₄⁺-N removal when NH₄Cl served as the sole nitrogen source; 97.9 % NO₃⁻-N removal with KNO₃ as the sole nitrogen source, and simultaneous removal rates of 98.96 % NH₄⁺-N and 96.5 % NO₃⁻-N in mixed nitrogen sources (NH₄Cl and KNO₃), while accumulating only negligible amounts of NO₂⁻-N regardless of nitrogen source composition. The biosafety assessment revealed that QX11 demonstrated sensitivity to most tested antibiotics and exhibited no hemolytic activity. Experimental trials with river shrimp showed no significant difference (P > 0.05) in mortality rates between QX11-treated and control groups. In simulated aquaculture effluent treatment systems, QX11 exhibited exceptional bioremediation performance, achieving removal efficiencies of 99.74 % for NH₄⁺-N, 97.98 % for NO₃⁻-N, 99.63 % for NO₂⁻-N, and 97.44 % for COD. Notably, QX11 inoculation significantly altered the microbial community composition in the moving bed biofilm reactor (MBBR), particularly affecting the relative abundance of dominant phyla and genera. These comprehensive results demonstrate that QX11 represents an efficient and environmentally safe aerobic denitrifying bacteria, providing a promising biological solution for mitigating water eutrophication in aquaculture and treating various types of nitrogen-contaminated wastewater.