Addition of Thermotolerant Nitrifying Bacteria During Pig Manure Composting Enhanced Nitrogen Retention and Modified Microbial Composition

Preventing loss of nitrogen during aerobic manure composting is a critical challenge, and introducing microbial agents with specific functions offers a promising solution. This study aimed to explore how <i>Bacillus subtilis</i> F2 (a thermotolerant nitrifying bacterium) affects nitrogen conservation, microbial dynamics, and nitrogen conversion-associated gene abundance during pig manure composting. Relative to the uninoculated controls, adding F2 markedly raised the germination index, nitrate content, and total nitrogen in the final compost, resulting in reduced nitrogen loss. The inoculation led to a distinct succession of bacterial communities, enriching microorganisms associated with fermentation and hydrocarbon degradation, while the fungal communities did not change significantly between the control and treated compost. Furthermore, inoculation markedly increased <i>amoA</i> gene levels and decreased <i>nirK</i> abundance during the cooling and maturation phases. Significant relationships were detected between nitrogen content, microbial composition, and nitrogen conversion genes in correlation analyses. In summary, the addition of F2 is recommended for bolstering nitrogen retention in the context of composting.