| The ex situ fermentation system（EFS）can efficiently treat livestock and poultry manure by fermenting of microorganisms under high temperature and aerobic conditions to reduce environmental pollution and realize the resource utilization of agricultural waste.Driven by functional microorganisms,organic matter in feces and urine can gradually decompose,and nitrogen-containing compounds can also complete the transformation of various forms.Previous studies have found that the ex situ fermentation system has excellent performance in removing ammonia and storing nitrogen.In order to reduce nitrogen loss and improve the quality of fermentation products,it is important to clarify the mechanism of nitrogen conversion driven by functional microorganisms in ex situ fermentation system.The environmental characteristics during the operation of EFS were determined in this study,and the nitrogen conversion rate and the copy number changes of key functional genes at different fermentation stages were explored using stable isotope labeling technology and fluorescent quantitative PCR technology.Microorganisms and functional genes related to nitrogen metabolism were annotated by using metagenomics technology.By revealing the correlation between microorganisms and environmental characteristics,functional genes and environmental characteristics,and microbes and functional genes,the nitrogen cycle network of EFS was initially established,and the nitrogen conversion mechanism of EFS was discussed.The environmental characteristics of EFS are high temperature,alkalinity,and high nitrogen,and the water content is basically maintained between 45%and 65%.In EFS,bacteria are mainly composed of Firmicutes,Bacteroidetes,Proteobacteria and Actinobacteria.The most abundant bacterial genus is Bacillus.Temperature is the main factor driving the variation of bacterial communities.Fungi are mainly composed of Ascomycota,Basidiomycota,Mucoromycota and Chytridiomycota.The most abundant fungal genus is Batrachochytrium.The main factors driving the variation of fungal community are nitrogen content and temperature.The 109high-quality MAGs recombined by binning belong to the bacterial kingdom.Under the action of microorganisms,the metabolism of EFS is vigorous.The continuous addition of livestock and poultry manure supplements the nitrogen in the system,and the nitrogen metabolism in EFS is strong.The maximum rate of total nitrogen mineralization promoted by bacteria carrying ure A/B/C,ans B,asn B genes,such as Bacillus,Microbacterium,Halomonas,can reach 136.60μg N g-1 d-1.Autotrophic nitrification is the main way for the production of nitrate nitrogen,which is related to high ammonia nitrogen content.The abundance of amo A gene is higher than other genes,and the abundance of hao,nar G,nir K,and nos Z genes all decrease in the later stage,which helps reduce N2O emissions.Truepera and Deinococcus are not only involved in denitrification,but also potential hosts for hao and gdh＿K00261.The nos Z gene can be used as a characterizing gene of EFS denitrification.Gemmatimonas and Gemmatirosa may simultaneously play important roles in the three processes of anammox,denitrification,and mineralization in the nitrogen metabolism of EFS.Nitrogen fixation is mainly performed by Enterobacter spp.,Pantoea spp.and Lelliottia spp.carrying nif D/H/K/W genes.This study clarified the environmental characteristics and nitrogen transformation characteristics of EFS,and initially revealed that the nitrogen migration process driven by EFS functional microorganisms under the catalysis of the relevant enzymes encoded by functional genes.This is of great significance for reducing nitrogen loss and suppressing greenhouse gas emissions in the process of EFS processing livestock and poultry waste. |
