Pathways and mechanisms for efficient nitrogen utilization in the high-temperature tolerant heterotrophic nitrifying bacterium Aeribacillus pallidus sp. GW-E.

This study isolated a novel thermophilic heterotrophic nitrifying bacterium, Aeribacillus pallidus sp. GW-E, from aerobic composting. Under conditions of 55 °C, the utilization efficiency of NH₄⁺-N, NO₃⁻-N, and NO₂⁻-N were 87.42%, 21.44%, and 51.68%, respectively. Whole-genome analysis identified key nitrogen metabolism genes (amt, npd, nirA, gdhA, glnA, and gltBD) as well as heat stress-related genes (GRPE, hslO, groES, groEL). Response surface optimization revealed that under conditions of a C/N ratio of 15, a temperature of 54 °C, and a pH of 8, the NH₄⁺-N utilization efficiency reached 100%. Enzyme activity assays indicated that the activities of three enzymes in the ammonia assimilation pathway were GS 1.014 ± 0.030 U/mg, GDH 1.114 ± 0.090 U/mg, and GOGAT 11.611 ± 0.061 U/mg, which were significantly higher than those of other pathways (P < 0.05). Nitrogen balance analysis confirmed that approximately 40.04% of the nitrogen was assimilated. In conclusion, the bacterium primarily utilizes ammonia assimilation, with additional assimilated nitrate reduction and nitrification pathways for nitrogen transformation. This strain represents a valuable microbial resource and provides a theoretical basis for nitrogen retention in high-temperature composting systems.