Identification of low-temperature oligotrophic and heterotrophic nitrifying bacteria and safety tests with ICR mice

Five strains of heterotrophic nitrifying bacteria were isolated from Songhua River in northern China in winter. Through ammonia degradation experiment, the strain Y7 demonstrates the ability to convert ammonium to nitrogen under oligotrophic conditions at low temperature. The average ammonium removal rate was approximately 0.075±0.007 mg NH₄ ⁺-N/L h during the 48-hour observation period and 66.70±3.06% of ammonium removal was achieved in the end. The morphological and physiological characteristics and 16S rDNA sequence of strains were analyzed. The results showed that strain Y7 was belonging to Acinetobacter bacteria. Acute and chronic toxicity tests and Ames bacterial mutagenecity experiment were also conducted. No mortality occurred and none of the mice exhibited any clinical sign on cage-side observation. Blood and blood biochemical indicators of liver, kidney, spleen changed after contamination showed that various organs were not damaged and indicated that the strain Y7 is safe for animals. This study provided more information for the construction of nitrogen flora in the low-temperature oligotrophic environment.