Study On The Effect And Mechanism Of Phage Lysis Of Hosts On The Humification Process Of Sludge Composting

Aerobic composting is a resource-recycling and environmentally friendly way to treat sludge.The composting process enables microorganisms to drive the conversion of organic matter into humus,producing a maturation product that can be used as a soil conditioner and fertilizer.Phages are almost ubiquitous in the biosphere,and their ecological functions have been proven to regulate microbial community structure and nutrient cycling in ecosystems by exerting top-down control over the host.However,the role and ecological function of the phage lysing host in compost humification are still unknown.In this thesis,we isolated the phage of the dominant thermophilic bacteria from municipal sludge thermophilic composting samples,studied their morphological structure,biological properties and genome,and mass-cultured the phage to obtain phage lysates.The linkage between "phage lysates" and "humic precursor material" was made.In the process of simulated composting experiments with phage lysates,three-dimensional fluorescence spectroscopy(3D-EEM),Fourier transform ion cyclotron resonance mass spectrometry(FTICR MS)and 16 S rRNA high-throughput sequencing were applied to characterize the transformation pattern of dissolved organic matter and structural changes of bacterial communities,to reveal the influence of phage lysates on compost humification process,and to explore the mechanism of phage lysates affecting humus formation.The mechanism of humus formation by phage lysates was investigated.The specific research contents and results are as follows:(1)Nine bacterial strains were isolated and purified from compost thermophilic phase samples,and Geobacillus subterraneus was screened as the host for phage GBS17,which has an icosahedral head and belongs to the order Caenorhabditis and family Mycobacteriophage.Biological characteristics showed that the optimal temperature of GBS17 was 50 ℃,the optimal pH was 9,and the optimal multiplicity of infection(MOI)was 0.1.The one-step growth curve showed that the incubation period of GBS17 infestation of Geobacillus subterraneus was 20 min,and the outbreak period was 30 min,followed by the plateau period.Genome-wide analysis showed that the gene structure of phage GBS17 was a double-stranded DNA with a GC content of about 42.5% and a total base number of 90.67 kb.57 ORFs were annotated to known functional genes,which were the four major categories of phage cleavage genes,phage replication assembly genes,phage metabolic function genes and phage structure genes.The genome-wide phylogenetic tree showed that GBS17 has high affinity with Geobacillus phage phi OH2.(2)Phage lysates promoted the composting humification process.At the end of the composting,the DOC and TN concentrations of Pro-vDOM treatment decreased by 69.6%and 90.1%,respectively,indicating that phage lysates were available to microorganisms.3D-EEM revealed that phage lysates brought more aromatic proteins and microbial metabolic by-products,and accelerated humus formation.Parallel factor analysis showed that its Fmax value of humic acid-like substances was 5948.27 a.u.,which was much higher than other treatments and controls.(3)The phage lysate regulated the succession of heterotrophic microbial community and enriched the core functional microorganisms in the compost.Analysis of microbial community structure under Pro-vDOM treatment showed that the abundance of Sphingobacterium,Geobacillus and Bacillus increased by 10%,4.5% and 4.5%,respectively.In the mesophilic phase,the abundance of Niabella and Paenibacillus increased by 5.6% and2.6%,respectively.These core microbes promote the formation of humus in the composting process.(4)Phage lysates provide an active carbon source(humic precursors)for humicification.FTICR MS results demonstrated that phage lysates brought abundant precursors such as proteins and carbohydrates to the Pro-vDOM treatment;these precursors were converted to aromatic oxygenates,resulting in an increase in the proportion of lignin/carboxy-rich alicyclic molecules with a molecular composition similar to that of humic substances by 14.8%.The results of network analysis showed that the enriched core microorganisms were connected to the phage lysate DOM and lignin,and may convert the proteins and lignin into amino acids and phenol precursors,which were involved in the formation of humus through the phenol-protein theory.This paper reveals the mechanism of phage lysis of hosts in regulating humus formation during sludge composting,which fills the gap of ecological functions of phages in composting and has important theoretical value for the development of sludge aerobic composting process.