The efficiency and mechanism of vermicompost in enhancing the composting of swine manure as an additive

Abstract Vermicompost was used as an additive in swine manure composting, and the expression of bacterial functional genes on biotransformation of nutrient was investigated. Results showed that vermicompost extended the thermophilic period to 12 days, decreased the NH4+ -N/NO3− -N ratio to 0.85 and increased GI value to 166%. With vermicompost addition, higher relative abundances of Firmicutes were observed in substrate at the beginning. The dominant phyla of Proteobacteria was decreased in thermophilic stage, as well as its pathogenic related genera Acinetobacter and Stenotrophomonas, while the potentially beneficial genera Actinomadura and Chryseolinea were increased. And the activities of primary functional genes associated with metabolisms of carbohydrate, amino acid and xenobiotics at the level 2 and fatty acid metabolism at the level 3 were enhanced during the thermophilic phase. Besides, most dominant genera showed strengthened correlations with NO3−-N and GI with vermicompost amendment, and they were the strongest environmental factors for bacterial communities. Network analysis showed dominant genera Pseudomonas, Acinetobacter, Stenotrophomonas Oceanobacter associated metabolic pathways increased from two to three with vermicompost added in substrate. These results indicated that vermicompost promoted the composting efficiency by increasing the potentially beneficial bacteria, decreasing pathogenic bacteria and enhancing the metabolic capacity of bacterial communities.