Nitrogen removal characteristics and mechanism of the aerobic denitrifying bacterium Stutzerimonas stutzeri os3 isolated from shrimp aquaculture sediment

To overcome the limitations of denitrification under high dissolved oxygen conditions, an efficient aerobic denitrifier, Stutzerimonas stutzeri os3, was isolated from shrimp aquaculture sediment. The strain os3 achieved complete removal of nitrate without significant nitrite accumulation, when sodium citrate was used as the carbon source, with a C/N ratio of 5, and at a shaking speed of 50 r/min. Moreover, the strain os3 demonstrated a high TIN removal efficiency, reaching 98.29 % - 99.28 % under various nitrogen sources. Whole-genome sequencing revealed the presence of denitrification genes (napAB, nirS, norBC and nosZ) in the strain os3, which combined with nitrogen balance analysis, confirmed that the strain os3 primarily utilized aerobic denitrification for nitrate removal under aerobic conditions, as follows: ${\mathrm{NO}}_3^{-}-N\stackrel{\text{NapAB}}{\to }{\mathrm{NO}}_2^{-}-N\stackrel{\text{NirS}}{\to }\mathrm{NO}\stackrel{\text{NorBC}}{\to }{N}_{2}O\stackrel{\text{NosZ}}{\to }{N}_2$. Furthermore, the strain os3 significantly increased the removal efficiencies of TIN and NO₃⁻-N in shrimp aquaculture wastewater, reaching 90.20 % and 94.43 %, respectively. Therefore, the strain os3 contributes to enhancing aerobic denitrification, providing a biotechnological solution for improving nitrogen cycling in shrimp aquaculture water.