Dynamic features of biochemical property and microbial succession of black soldier fly larvae (Hermetia illucens L) vermicompost during secondary composting

Abstract:

[Objective] The dynamic trends of biochemical property of black soldier fly (Hermetia illucens L., BSF) larvae vermicompost during the subsequent secondary composting was observed through the culture experiment, and the associated succession of microbial ecology of the BSF vermicompost and the stabilization mechanisms were also discussed. [Methods] Dynamic incubation experiment was conducted in which drums containing BSF vermicompost were buried into a full-scale biomass composting heap, and periodic sampling was conducted at intervals of 7 days during the 49-day testing period. 16S rRNA high-throughput sequencing was used to analyze the bacterial diversity, community structure and metabolic function of BSF vermicompost. [Results] After two weeks of rapid rising to 68.7℃, the temperature of BSF vermicompost gradually decreased to 37.7℃ on the 49th day. When the experiment ended, the total organic carbon, dissolved organic matter (DOM) and pH value reached 67.3%, 18.4 g/kg and 8.0, respectively. The bacterial diversity of Shannon index, Simpson index and Chao1 index increased rapidly with the process of composting, and then decreased slowly to 7.45, 0.98 and 985 at the end. 16S rRNA sequencing shows that dominant phyla included Bacteroidetes, Firmicutes, Proteobacteria and Actinobacteria among the microbial communities. Meanwhile, Corynebacteriaceae decreased from 35.7% at the beginning to 6.5% at the end, Flavobacteriaceae gradually increased from 3.22% to 12.6%, and Porphyromonadaceae increased rapidly to 11.5% and then slowly decreased to 5.1% at the same level as the initial level. PICRUSt predicted that the average relative abundances of amino acid sugar and nucleotide sugar metabolism, carbon fixation pathway, and methane metabolism remained strong throughout the whole secondary composting process of BSF vermicompost, and all of them peaked at the middle stage of composting (day 15-35) then declined. The average relative abundances of fatty acid metabolism, unsaturated fatty acid biosynthesis metabolism, polycyclic aromatic hydrocarbon degradation and sulfur metabolism were shown as decreasing first with following of rising again. [Conclusion] During the secondary composting of BSF vermicompost, the biochemical features of materials and their microbial ecology have significantly changed along with apparent reductions of moisture, DOM, and total organic matters, thus promoting the rapid maturation and stabilization of BSF vermicompost, which is conducive to the farmland reuse of BSF vermicompost as a novel organic fertilizer.