Research on Nitrogen Transformation Pathways of a Thermophilic Heterotrophic Nitrifying Bacterial Consortium GW7

Yongqi Ma¹Jiali Wang¹Yindi Zhang¹wenping guan¹wenrui qi¹Xisheng Tai²Dong Lin³Rong He⁴Likun Sun^1*Aiwen Zhang^5*

• ¹College of Animal Science and Technology, Gansu Agricultural University, Lanzhou, China
• ²College of Urban Environment,, Lanzhou City University, Lanzhou, Gansu, China
• ³College of Pratacultural, Gansu Agricultural University, Lanzhou, China
• ⁴Yuzhong Modern Agricultural Investment Development Co., Ltd., Lanzhou, Gansu Province, China
• ⁵Gansu Provincial Animal Husbandry Technology Promotion Station, Lanzhou, China

Abstract: High-temperature heterotrophic nitrifying bacteria can effectively convert reduced ammonia sources during the thermophilic phase in aerobic composting, reducing ammonia emissions and contributing to nitrogen fixation, thus exhibiting high application potential. In this study, an excellent high-temperature-tolerant heterotrophic nitrifying bacterial consortium, designated GW7, was enriched from compost samples at elevated temperatures. At 55°C, consortium GW7 demostrated utilization efficiency of 79.97% for ammonia nitrogen (NH₄⁺-N) (400 mg/L) and 21.18% for nitrate nitrogen (NO₃⁻-N) (400 mg/L). Response surface methodology experiments revealed that the optimal cultivation conditions for consortium GW7 as follows: sodium succinate the carbon source, a C/N of 15:1, temperature of 53℃, initial pH of 6, and rotation speed of 200 r/min. Under these optimized conditions, the NH₄⁺-N utilization efficiency reached 87.80%. Furthermore, enzymatic assays indicated high specific activities for for glutamine synthetase (GS), glutamate dehydrogenase (GDH) and glutamate synthetase (GOGAT) were 0.392 U/mg, 0.926 U/mg, and 0.195 U/mg, respectively. Notably, the specific activities of ammonia monooxygenase (AMO) and hydroxylamine oxidoreductase (HAO) enzymes were 1.459 U/mg and 0.701 U/mg, respectively. Based on GW7's utilization of various nitrogen sources, three nitrogen conversion pathways—ammonia assimilation, heterotrophic nitrification, and assimilatory nitrate reduction—were proposed. In summary, this composite bacterial consortium demonstrates exceptional nitrogen transformation capabilities and holds promise for mitigating nitrogen losses during aerobic composting processes.