Abstract: The phylogeny and denitrifying characteristics of a newly isolated strain Y-9 were clarified. The psychrotrophic and aerobic nitrite-bacterium, strain Y-9, was successfully identified based on the analysis of its morphology, phospholipid fatty acid and 16SrRNA gene sequence analysis. Additionally, factors such as temperature, shaking speed, pH, incubation quantity, carbon source and nitrite content affecting the aerobic denitrification ability of Y-9 strain were investigated. Results showed that the Y-9 was identified as Pseudomonas putida which combined with three methods to identify the newly isolated strain could offer taxonomic assignment with higher confidence. A psychrotrophic and aerobic nitrite-denitrifying strain Pseudomonas putida Y-9 exhibited high removal efficiency of nitrite and total nitrogen. The nitrite and total nitrogen removal efficiency was up to 100% and 77.13% with 100 r/min shaking speed at 15℃. The optimal conditions of culture were determined, including temperature 15℃, shaking speed 100 r/min, pH 7, inoculated quantity 1 mL（OD₆₀₀, 0.5）bacterial suspension within 100 mL denitrification broth medium and carbon source sodium citrate. Low concentration of nitrite nitrogen could be beneficial for the strain Y-9 to perform denitrification at 15℃. Strain Y-9 was a psychrotrophic nitrite-denitrifying bacterium with optimum temperature of 15℃ and strain Y-9 could tolerate high concentration of nitrite nitrogen, which has a great potential for removing nitrogen from aquaculture water environment, especially in the cold circumstance.

Key words: Nitrite nitrogen, Pseudomonas putida, aquaculture, aerobic