Diversity and characterization of the ammonia-oxidizing bacteria responsible for nitrification in tea field soils.

Ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and comammox Nitrospira have been considered to coexist in acidic soils, oxidizing ammonia within their respective niches. However, their relative contributions to soil nitrification, as well as their properties and ecological roles in acidic soils, remain poorly understood. This study focused on AOB in acidic tea field soils, investigating their ecology and physiology through metagenomic analysis and the genomic and physiological characterization of AOB isolates. β-AOB were significantly more abundant than γ-AOB and AOA in soil layers with the highest potential for nitrification activity, indicating that β-AOB play a key role in acidic tea soil. Diversity analysis of this dominant group identified Nitrosospira as the major genus present in tea fields, and four pure strains representing some of the main operational taxonomic units in this environment were isolated. Physiological and genetic characterization of these isolates revealed some distinct traits compared to other species of the genus and closely related taxa, suggesting adaptations that may contribute to niche differentiation and survival in acidic soils. These findings provide new insights into the ecological role of β-AOB in acidic soils and may inform strategies to manage soil nitrification and reduce nitrogen loss in agricultural ecosystems.