Abstract:

Objective To achieve efficient nitrogen retention during the aerobic composting of Chinese medicinal herbal residues (CMHRs), this study is aimed to isolate and identify microorganisms with high nitrification capacity and to elucidate their nitrification-denitrification characteristics, thereby providing potential microbial resources and a theoretical basis for developing nitrogen-conserving microbial agents. Method Pure strains were obtained from CMHRs compost using the enrichment culture, spread plate, and streak plate methods. Screening based on heterotrophic nitrification capability led to the selection of the high-efficiency strain. Identification of the strain was performed based on morphological characteristics and 16S rDNA gene sequencing. The effects of environmental factors on strain growth and nitrification capacity were investigated by adjusting six cultivation conditions: carbon source, carbon to nitrogen ratio (C/N), initial ammonium nitrogen concentration, pH, temperature, and rotational speed. The denitrification capability of strain YF-5 was examined by culturing it in media with nitrite nitrogen or nitrate nitrogen as the sole nitrogen source. Result A highly efficient nitrifying bacterium was isolated from the compost and named YF-5, which was identified as Alcaligenes aquatilis by morphological observation and molecular biology. Optimization experiments determined that the optimal nitrification conditions for this strain included a carbon source of sodium succinate, a C/N of 20, an initial ammonium nitrogen concentration of 100 mg/L, a pH of 7.0, a temperature of 35 ℃, and a rotation speed of 160 r/min. Analysis of nitrified products indicated that strain YF-5 performed heterotrophic nitrification with the accumulation of nitrite nitrogen. Denitrification experiments confirmed that strain YF-5 was incapable of employing nitrite or nitrate nitrogen as substrates for denitrification. Conclusion Strain YF-5 converts ammonium nitrogen into stable nitrite nitrogen under optimized conditions and lacks denitrification capability. This characteristic enables it to reduce both ammonia volatilization and denitrification through targeted nitrogen conversion during CMHRs composting, thereby minimizing nitrogen loss and demonstrating promising application potential.

Key words: Alcaligenes, nitrifying bacteria, heterotrophic nitrification, Chinese medicinal herbal residues, aerobic composting, denitrification, nitrogen conservation