89 / 2021-06-30 20:55:13

Diversity characteristics of bacteria and fungi during the primary and secondary fermentation stages of biocompost inoculated with VT agent

Composting; Bacterial and fungal community; Primary and secondary fermentation

    Composting is an effective way for the harmless resource utilization of agricultural waste. The material changes and microbial changes during the primary fermentation and the secondary fermentation of compost are different. To explore the diversity of microbial communities in the primary fermentation and secondary fermentation during aerobic composting, and to understand the microbial flora that play a key role, this study used high-throughput sequencing to analyze the microbial community structure and composition in the primary and secondary fermentation stages of biocompost after inoculation with VT agent. The results showed that after 27 days of primary fermentation, the compost started secondary fermentation. After the second fermentation, the compost was mature and the quality was improved. The richness and diversity of bacteria and fungi showed a downward trend as a whole. Bacterial richness and diversity change consistently. However, fungal richness showed a downward trend in the first fermentation, and increased first and then decreased in the second fermentation; while the diversity showed an upward trend in the first fermentation process and a downward trend in the second fermentation process. Bacterial OTUs showed an overall downward trend, while the fungal OTUs at the beginning of the secondary fermentation was larger than the initial stage of composting. After composting entered the secondary fermentation, the bacterial community was highly stable, while the fungal community was different. The dominant taxa of bacteria and fungi in different composting stages were different. In the initial stage of composting, the relative abundance order of the dominant bacteria phyla was Proteobacteria> Firmicutes> Bacteroidetes> Actinobacteria. On Day13, Firmicutes increased to more than 90% and Bacteroidetes disappeared. On Day27, Firmicutes  became the most abundant bacteria phyla, and Actinomycetes showed an increasing trend. Ascomycota, Basidiomycota and Rhozellomycota were the main fungal dominant phyla. Ascomycota showed a trend of decreasing first and then increasing, reaching 90% at the end of the secondary fermentation. Basidiomycota showed a downward trend from Day3 to Day39. Weissalla and Lactobacillus are the dominant genus on Day1, and disappear on Day13. Bacillus appeared on Day3, and its relative abundance was the highest on Day13, and neither the cooling period nor the secondary fermentation period appeared. In the secondary fermentation stage, the main bacterial dominant genera were Oceanobacillus, Pusillimonas, Gracilibacillus, Pseudogracilibacillus, Sinibacillus, Nocardiopsis etc. On Day31, Nocardiopsis appeared, and its relative abundance increased. Guuehomyces and Candida disappeared at the end of the secondary fermentation. Microascus first increased and then decreased, and became the dominant genus at the early stage of secondary fermentation after the high temperature period. Acremonium showed a sharp upward trend from the start of the second fermentation, and became the dominant genus on Day39. Fusarium disappeared during the high temperature period of composting and the second fermentation period. Cryptococcus disappeared during the second fermentation. Aspergillus and Chrysosporium were present throughout the composting process. There was a significant positive correlation between physical-chemical factors and bacterial and fungal communities, which proved that changes in bacterial and fungal communities are the result of the interaction between microorganisms and environmental factors.