Comparative Study Of The Composition And Type Of Dominant Intestinal Microflora In Silkworm Reared With Different Forages

Silkworm is an important economic lepidopteron, and sericulture has made a significant contribution to our national income.But the issue of low leaf-silk effect is still with us in the silk-producing process. The major reasons of this problem are occurrence rate of disease and deficiency of mulberry leaves in the process of rearing silkworms. Thus, we can improve the utilization rate of mulberry leaves and reduce the occurrence of disease through multiple channels to resolve the urgent problem of low the leaf-silk effect. Besides genetic improvement of variety and rearing management, the regulation and improvement on microenvironment of intestine of silkworm is another important ways.So, we should pay more attention to study of the influence of intestinal microflora. their metabolic product on silkworms, the role of resistance to pathogenic microorganism, the relationship of the intestinal microflora of lepidopteran insects with host growth, development and disease resistance and the influence of these changes of dominant intestinal strains from lepidopteran insects reared with different forages on host. We also should do some research on the interaction of these microorganisms in order to explore the role and function of the intestinal microflora of lepidopteran insects with host.We reared silkworm larvae with tricuspid cudrania leaves and mulberry leaves (both belong to the family Moraceae) respectively, used methods of pure culture isolation,16S rDNA sequence determination and phylogenetic analysis to investigate the gut microorganisms in fourth and fifth instar silkworm in order to find the composition changes of the microbial community that induced by forages.In addition, we made preliminary studies on the relationship among different dominant intestinal strains of the silkworm larvae that reared with tricuspid cudrania and mulberry leaves respectively.The results are as followings:1.A total of 56 dominant strains were isolated from intestine of silkworm larvae.There were 29 dominant strains isolated from silkworm larvae reared with tricuspid cudrania leaves, while 27 dominant strains isolated from silkworm larvae reared with mulberry leaves. These dominant strains were classified into twelve different genera according to the characteristics of colonial morphology, mycelial, physiological-biochemical identification and 16S rDNA phylogeny. These twelve genera are respectively:Brevundimonas, Stenotrophomonas, Enterobacter, Staphylococcus, Pseudomonas, Agrobacterium,Aeromonas, Brevibacterium,Citrobacter, Escherichia, Klebsiella and Bacillus.2.Only four genera of these dominant strains (Brevundimonas, Stenotrophomonas. Enterobacter and Staphylococcus) were common existence in the intestine of silkworm larvae reared with tricuspid cudrania and mulberry leaves. Besides, five genera of these dominant strains (Aeromonas, Brevibacterium,Citrobacter, Escherichia and Klebsiella) were detected in the intestine of the silkworm larvae which reared with mulberry leaves, while only two genera (Pseudomonas and Agrobacterium) were presented in the intestine of the silkworm larvae reared with tricuspid cudrania leaves.While Bacillus were only isolated from intestines of the two kinds of silkworms at fourth instar. The composition of dominant intestinal microflora had shown significant difference between two kinds of silkworm larvae that reared with different forages.While the silkworm larvae were reared with tricuspid cudrania leaves, it was notable that the diversity of dominant intestinal microflora was considerably lower than that of silkworm larvae which reared with mulberry leaves.3.The certain dominant intestinal strains from silkworm larvae that reared with two different leaves mentioned above were combined together as microbial additive to feed silkworm larvae. Taking 3 independent experiments for each combination, we found that the silkworm larvae got sickness induced by some combinations with the symptoms such as spitting yellow liquid, head shaking and finally led to death within 24 hours.These results suggested that there could be substantial change on intestinal microflora of silkworm larvae, possibly the gut microbial community structure changes, induced by different forages. The composition changes of intestinal microflora were qualitatively differed from the changes of that along with the inter-instar changes of silkworm larvae reared with the same forage. According to the studies, we speculated that the community structure changes and lower diversity of dominant microflora in intestine of silkworm larvae reared with tricuspid cudrania leaves might be related to their retarded growth and susceptibility to Bombyx mori nuclear polyhedrosis virus (BmNPV). We are interested in the symptom and start to study pathogenesis of BmNPV from many angle and all-round direction.