Study On Efficient Degradation Of Cellulose From Silkworm Excrement By Housely Fly Larvae And Its Microecological Mechanism

China’s sericulture industry has a large scale,with cocoon and silk production accounting for about 80% of the world’s total.It produces approximately 4.5 million tons of silkworm excrement annually,resulting in a huge resource output.At present,the environmental pollution caused by silkworm excrement is becoming increasingly prominent,with low utilization rate of silkworm excrement resources.Traditional composting is still the most common method for harmless and resource utilization of silkworm excrement,but due to the high content of difficult to degrade cellulose in silkworm excrement,it has problems such as long cycle,high odor,and low fertilizer efficiency.As a green and safe means of waste pollution treatment and reuse,housely fly larvae biotransformation technology has the advantages of short treatment cycle,low cost and high resource utilization rate,and has great development potential.This study takes the biotransformation of the organic matter in the silkworm excrement as the research goal.First,build an efficient and stable biotransformation system of the silkworm excrement,transform the silkworm excrement into high-quality organic fertilizer and silkworm excrement protein,and analyze its main nutrients and physical and chemical properties.Cellulose degrading bacteria were screened from the biotransformation silkworm excrement of housefly fly larvae,and the mechanism of interaction between housefly fly larvae and cellulose degrading bacteria to accelerate cellulose degradation in silkworm excrement was studied by using high-throughput sequencing analysis of microbial diversity.The research results will provide a theoretical basis for the efficient utilization of silkworm sand resources,and are of great significance for promoting the healthy and sustainable development of the sericulture industry.The main research findings are as follows:The organic matter system of biotransformation of silkworm excrement by maggots was constructed,and the cellulose content of silkworm excrement in the process of biotransformation by maggots was quantitatively analyzed.The results showed that the experimental group added housely fly larvae had a 58.9% decrease in cellulose content in the silkworm excrement within 6 days,significantly higher than the 11.5% of the control group without housely fly larvae added,indicating that housely fly larvae can accelerate the degradation of cellulose in the silkworm excrement matrix.The results of the study on the changes of physical and chemical properties of silkworm excrement matrix in the process of biotransformation of housely fly larvae showed that housely fly larvae could not only affect the changes of p H and temperature in the silkworm excrement matrix,but also significantly increase the content of key nutrients in the silkworm excrement matrix.The content of nitrogen in the control group increased by 43.46%,and that in the experimental group increased by 16.88%;The phosphorus content in the experimental group increased by 52.02%,while in the control group,it increased by 34.98%;The potassium content in the experimental group increased by 70.8%,while in the control group,it increased by 50%.Three novel cellulose degrading bacteria named DC1,DC2 and DC3 were isolated from the biotransformation silkworm excrement substrate of housely fly larvae for the first time.Through morphological observation,physiological and biochemical characteristics and 16 S r DNA gene phylogenetic analysis,three cellulose degrading bacteria were Bacillus licheniformis,Bacillus amyloliquefaciens and Bacillus subtilis.The optimal conditions for producing cellulase from DC2 strain were optimized as follows: p H 6,culture temperature40 ℃,inoculation amount 1%,enzyme catalyzed reaction p H 5,and enzyme catalyzed reaction temperature 50 ℃.After optimizing the enzyme production conditions,the activity of CMCase increased from the initial 6.28 U/m L to 14.35 U/m L;The FPase activity increased from the initial 3.89 U/m L to 8.25 U/m L;CXase activity increased from the initial 4.88 U/m L to 12.73 U/m L.Using miseq high-throughput sequencing technology,the characteristics and changes of microbial community structure in silkworm excrement before and after biotransformation of housely fly larvae were studied.The results showed that there were significant differences in the microbial community structure and composition between the experimental group with added housely fly larvae and the control group without added housely fly larvae at the phylum and genus classification levels;Environmental impact factors such as temperature and p H can significantly increase the abundance of cellulose degrading bacteria such as Bacillus and Pseudomonas in silkworm excrement.The prediction of key enzyme functions shows that housely fly larvae can increase the abundance of cellulase in the silkworm excrement matrix.In summary,it can be seen that housely fly larvae affect environmental factors such as temperature and p H of the silkworm excrement matrix through their own activities.Environmental factors can significantly increase the abundance of cellulose degrading bacteria in the silkworm excrement,thereby increasing the abundance of cellulase and accelerating the degradation of cellulose in the silkworm excrement.