Nitrogen Transformation Characteristics and Mechanisms of the High-Temperature-Tolerant Heterotrophic Nitrifying Bacterium Aeribacillus pallidus sp. GW-E

High-temperature heterotrophic nitrifying bacteria grow stably at elevated temperatures and exhibit effective nitrification capabilities. These bacteria exhibit remarkable environmental adaptability and have significant potential for practical applications in nitrogen transformation. In this study, the high-temperature-tolerant heterotrophic nitrifying bacterium, Aeribacillus pallidus sp. GW-E, was isolated from a high-temperature aerobic composting pile. The nitrification performance of this strain was evaluated based on its ability to utilize different types of inorganic nitrogen sources. The nitrogen transformation characteristics and mechanisms of strain GW-E were elucidated using nitrogen balance assessments, enzyme-specific activity analysis, and whole-genome sequencing. The results indicated that the utilization rates of NH ₄ ⁺ -N (416.31 mg/L), NO ₃ ^- -N (409.68 mg/L), and NO ₂ ^- -N (415.71 mg/L) were 3.79 mg/L/h, 0.71 mg/L/h, and 2.24 mg/L/h, respectively. Whole-genome analysis identified several genes associated with nitrogen metabolism, including amt, npd, nirA, gdhA, glnA, and gltBD . Through this analysis, three nitrogen transformation pathways related to ammonia assimilation, heterotrophic nitrification, and assimilatory nitrate reduction were identified. At the optimal cultural conditions of A. pallidus sp. GW-E, the NH ₄ ⁺ -N utilization rate reached 4.33 mg/L/h when the carbon-to-nitrogen (C/N) ratio was 15:1, the temperature was 54°C, and the pH was 8. These results indicate that A. pallidus sp. GW-E exhibits exceptional nitrification performance, ammonia assimilation capacity, and the ability to reduce assimilatory nitrate. This study provides reliable strain resources and scientific evidence for the application of high-temperature heterotrophic nitrifying bacteria.