Analysis of Bacterial Diversity and Safety Evaluation of the Recycled Manure Solids

【Objective】 To evaluate the safety of recycled manure solids(RMS)treated by bedding recovery unit(BRU)in the hope of providing theoretical basis and reference for safe and reasonable application RMS on breeding farms. 【Methods】 Bacterial cultivation methods were used to detect the counts of the total bacteria, Escherichia coli, Salmonella, Staphylococcus aureus and parasitic eggs in RMS before and after the treatments by BRU. Besides, those detecting items in samples of the BRU treated by RMS that were stacked for a month were also determined and high-throughput sequencing method was used to detect the composition and diversity of pathogenic bacteria. 【Results】 After 16-18 h of aerobically fermentation, the counts of total bacterial and Escherichia coli in manure samples were decreased tenfold compared with fresh manure, but the counts of Staphylococcus aureus and parasitic eggs were not significantly changed (P>0.05). The counts of total bacterial number and Escherichia coli were significantly increased (P<0.05), but the counts of parasitic eggs were on the contrary (P<0.01). The pathogenic bacteria were only detected in manure samples untreated by BRU and they were divided into 4 genera: Aerococcus (1.40%±0.8%), Facklamia (20.73%±3.97%), Paeniclostridium (7.20%±2.35%) and Carnobacterium (0.27%±0.15%). Bacterial alpha-diversity indexes presented an significant decreasing trend after BRU treatment (P<0.01), mainly in terms of the bacterial OTU numbers, the bacterial richness (ACE index), and the Shannon-Weiner diversity index decreased 57.73%, 57.47% and 81.63%, respectively. While, the Shannon-Weiner diversity index of samples in RMS stacked for a month was significantly increased (21.76%) compared with the index in RMS treated by BRU. Furthermore, the bacterial beta-diversity analysis showed that the bacterial community structures were significantly changed after BRU treatment, and its communities were significantly increased in RMS stacked for a month (P<0.01). After 16-18 h of aerobically fermentation, the counts of total bacterial number, bacterial diversity and community structures were significantly changed. However, its killing effect on most pathogenic bacteria (apart from Escherichia coli) and parasitic eggs were still weak. 【Conclusion】 When RMS is treated with BRU system for 16-18 h, bovine manure can significantly reduce bacterial diversity and change community composition, but its killing effect on pathogenic bacteria and parasite eggs other than Escherichia coli is limited. Therefore, the risk can be reduced by prolonging stacking time.