Characterization of a Lipase From the Silkworm Intestinal Bacterium Bacillus pumilus With Antiviral Activity Against Bombyx mori (Lepidoptera: Bombycidae) Nucleopolyhedrovirus In Vitro

Study on anti-BmNPV mechanism of branched-chain amino acid aminotransferases in silkworm

Bombyx mori nucleopolyhedrovirus (BmNPV) is the most important virus that threatens sericulture industry. At present, there is no effective treatment for BmNPV infection in silkworms, and lncRNA plays an important role in biological immune response and host-virus interaction, but there are relatively few studies in silkworms. In this study, the four midgut tissue samples of the resistance strain NB (NB) and susceptible strain 306 (306) and the NB and 306 continuously infected with BmNPV for 96 h are used for whole transcriptome sequencing to analyze the differences in the genetic background of NB and 306 and the differences after inoculation of BmNPV, and the significantly different mRNA, miRNA and lnRNA between NB and 306 after BmNPV inoculation were screened. By comparing NB and 306, 2651 significantly different mRNAs, 57 significantly different miRNAs and 198 significantly different lncRNAs were screened. By comparing NB and 306 after BmNPV inoculation, 2684 significantly different mRNAs, 39 significantly different miRNAs and 125 significantly different lncRNAs were screened. According to the significantly different mRNA, miRNA and lncRNA screened from NB and 306 and NB and 306 after virus inoculation, the mRNA-miRNA-lncRNA regulatory network was constructed before and after virus inoculation, and the BmBCAT-Bomo_chr7_8305-MSTRG.3236.2 regulatory axis was screened from them, and it was found that BmBCAT was not Bomo_chr7_8305 regulated in the genetic background, after viral infection, MSTRG.3236.2 competes for binding Bomo_chr7_8305 regulates BmBCAT. The whole transcriptome sequencing results were verified by qPCR and the time-series expression analysis was performed to prove the reliability of the regulatory network. The BmBCAT-Bomo_chr7_8305-MSTRG.3236.2 regulatory axis may play a potential role in the interaction between silkworms and BmNPV. These results provide new insights into the interaction mechanism between silkworms and BmNPV.

Comparative analysis of the intestinal flora of BmNPV-resistant and BmNPV-sensitive silkworm varieties

Bombyx mori nucleopolyhedrovirus (BmNPV) is a very common and infectious virus that affects silkworms and hinders silk production. To investigate the intestinal flora of BmNPV-resistant and BmNPV-sensitive silkworm varieties, 16 S rDNA high-throughput sequencing was performed. The results of the cluster analysis showed that the intestinal flora of the resistant silkworm variety was more abundant than that of the sensitive silkworm variety. This was found even when infection with BmNPV caused a sharp decline in the number of intestinal floral species in both resistant and sensitive silkworm varieties. The abundances of the intestinal flora, including Aureimonas, Ileibacterium, Peptostreptococcus, Pseudomonas, Enterococcus, and Halomonas, in the resistant variety were considerably greater after infection with BmNPV than those in the sensitive variety. After infection with BmNPV, four kinds of important intestinal bacteria, namely, f_Saccharimonadaceae, Peptostreptococcus, Aureirmonas, and f_Rhizobiaceae, were found in the resistant silkworm variety. In the sensitive silkworm variety, only Faecalibaculum was an important intestinal bacterium. The differential or important bacteria mentioned above might be involved in immunoreaction or antiviral activities, especially in the intestines of BmNPV-resistant silkworms. By conducting a functional enrichment analysis, we found that BmNPV infection did not change the abundance of important functional components of the intestinal flora in resistant or sensitive silkworm varieties. However, some functional factors, such as the biosynthesis, transport, and catabolism of secondary metabolites (e.g., terpenoids and polyketides) and lipid transport and metabolism, were more important in the resistant silkworm variety than in the sensitive variety; thus, these factors may increase the resistance of the host to BmNPV. To summarize, we found significant differences in the composition, abundance, and function of the intestinal flora between resistant and sensitive silkworm varieties, especially after infection with BmNPV, which might be closely related to the resistance of resistant silkworm varieties to BmNPV.

Diversity and functional characteristics of culturable bacterial endosymbionts from cassava whitefly biotype Asia II-5, Bemisia tabaci

Whitefly Bemisia tabaci, a carrier of cassava mosaic disease (CMD), poses a significant threat to cassava crops. Investigating culturable bacteria and their impact on whiteflies is crucial due to their vital role in whitefly fitness and survival. The whitefly biotype associated with cassava and transmitting CMD in India has been identified as Asia II 5 through partial mitochondrial cytochrome oxidase I gene sequencing. In this study, bacteria associated with adult B. tabaci feeding on cassava were extracted using seven different media. Nutrient Agar (NA), Soyabean Casein Digest Medium (SCDM), Luria Bertani agar (LBA), and Reasoner's 2A agar (R2A) media resulted in 19, 6, 4, and 4 isolates, respectively, producing a total of 33 distinct bacterial isolates. Species identification through 16SrRNA gene sequencing revealed that all isolates belonged to the Bacillota and Pseudomonadota phyla, encompassing 11 genera: Bacillus, Cytobacillus, Exiguobacterium, Terribacillus, Brevibacillus, Enterococcus, Staphylococcus, Brucella, Novosphingobium, Lysobacter, and Pseudomonas. All bacterial isolates were tested for chitinase, protease, siderophore activity, and antibiotic sensitivity. Nine isolates exhibited chitinase activity, 28 showed protease activity, and 23 displayed siderophore activity. Most isolates were sensitive to antibiotics such as Vancomycin, Streptomycin, Erythromycin, Kanamycin, Doxycycline, Tetracycline, and Ciprofloxacin, while they demonstrated resistance to Bacitracin and Colistin. Understanding the culturable bacteria associated with cassava whitefly and their functional significance could contribute to developing effective cassava whitefly and CMD control in agriculture.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-03949-0.

Dietary exposure of copper and zinc oxides nanoparticles affect the fitness, enzyme activity, and microbial community of the model insect, silkworm Bombyx mori

Copper and Zinc oxides nanoparticles (CuO and ZnO NPs, respectively) are among the most produced and commonly used engineered nanomaterials. They can be released into the environment, thereby causing health concerns and risks to biodiversity that indicate a need to evaluate their toxicological effects in a complex situation. Here, we used the insect model organism silkworm Bombyx mori to address the concerns about the biological effects associated with dietary exposure of CuO and ZnO NPs. ICP-MS analysis revealed significant accumulation of Cu and Zn (the latter being more accumulated) in silkworms' tissues (gut, fat body, silk gland, and malpighian tubule), and some elimination through feces in the respective NPs-exposed groups. NPs-exposures led to a decrease in larval body mass, survivorship, and cocoon production, where the effects of ZnO NPs were more pronounced. We also found that NPs-exposure induced gene expression changes (Attacin, lysozyme, SOD, and Dronc) and altered the activities of antioxidant enzymes (SOD, GST, and CAT), as well as impaired nutrient metabolism (alpha-amylase). Given their antibacterial property, CuO and ZnO NPs decreased species richness and diversity of the gut bacterial community and shifted their configuration to overt microbiome i.e., decreased abundance of probiotics (e.g., Acetobacter) and increased pathobionts (e.g., Pseudomonas, Bacillus, Escherichia, Enterococcus, Ralstonia, etc.) proportions. Overall, this integrated study revealed the unintended negative effects of CuO and ZnO NPs on silkworms and highlighted the potential to inevitably affect all living things due to intensive and possible mishandling of nanomaterials.

Genome-wide identification of lipases in silkworm (Bombyx mori) and their spatio-temporal expression in larval midgut

Lipases play crucial roles in food digestion by degrading dietary lipids into free fatty acids and glycerols. The domesticated silkworm (Bombyx mori) has been widely used as an important Lepidopteran model for decades. However, little is known about the lipase gene family in the silkworm, especially their hydrolytic activities as digestive enzymes. In this study, a total of 38 lipase genes were identified in the silkworm genome. Phylogenetic analysis indicated that they were divided into three major groups. Twelve lipases were confirmed to be expressed in the midgut at both transcriptional and translational levels. They were grouped into the same gene cluster, suggesting that they could have similar physiological functions. Quantitative real-time PCR (qRT-PCR) analyses indicated that lipases were mainly expressed in anterior and middle midgut regions, and their expression levels varied greatly along the length of midgut. A majority of lipases were down-regulated in the midgut when larvae stopped feeding. However, a unique lipase gene (Bmlip10583) showed low expression level during feeding stage, but it was significantly up-regulated during the larvae-pupae transition. These results demonstrated that expression of silkworm lipases was spatially and temporally regulated in the midgut during larval development. Taken together, our results provide a fundamental research of the lipase gene family in the silkworm.

The digestive proteinase trypsin, alkaline A contributes to anti-BmNPV activity in silkworm (Bombyx mori)

Bombyx mori nucleopolyhedrovirus (BmNPV) is a serious pathogenic microorganism that causes tremendous loss to sericulture. Previous studies have found that some proteins of serine protease family in the digestive juice of B. mori larvae have anti-BmNPV activity. In our previous publication about proteome analysis of the digestive juice of B. mori larvae, the digestive enzyme trypsin, alkaline A (BmTA) was filtered as a differentially expressed protein possibly involved in BmNPV resistance. Here, the biological characteristics and anti-BmNPV functions of BmTA were comprehensively analysed. The cDNA sequence of BmTA had an ORF of 768 nucleotides encoding 255 amino acid residues. Domain architecture analysis showed that BmTA contained a signal peptide and a typical Tryp_SPc domain. Quantitative real-time PCR analysis showed that BmTA was highly expressed in the larval stages and specifically expressed in the midgut of B. mori larvae. The expression level of BmTA in BmNPV resistant strain A35 was higher than that in susceptible strain P50. After BmNPV infection, the expression of BmTA increased in both strains from 24 to 72 h. Virus amplification analysis showed that the relative levels of VP39 in B. mori larvae and BmN cells infected with the appropriate concentration of recombinant-BmTA-treated BmNPV were significantly lower than in the control groups. Moreover, overexpression of BmTA in BmN cells significantly inhibited the amplification of BmNPV. Taken together, the results of this study indicated that BmTA possessed anti-BmNPV activity in B. mori, which broadens the horizon for virus-resistant breeding of silkworms.

Interaction of Viruses with the Insect Intestine

In nature, insects face a constant threat of infection by numerous exogeneous viruses, and their intestinal tracts are the predominant ports of entry. Insects can acquire these viruses orally during either blood feeding by hematophagous insects or sap sucking and foliage feeding by insect herbivores. However, the insect intestinal tract forms several physical and immunological barriers to defend against viral invasion, including cell intrinsic antiviral immunity, the peritrophic matrix and the mucin layer, and local symbiotic microorganisms. Whether an infection can be successfully established in the intestinal tract depends on the complex interactions between viruses and those barriers. In this review, we summarize recent progress on virus-intestinal tract interplay in insects, in which various underlying mechanisms derived from nutritional status, dynamics of symbiotic microorganisms, and virus-encoded components play intricate roles in the regulation of virus invasion in the intestinal tract, either directly or indirectly. Expected final online publication date for the Annual Review of Virology, Volume 8 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Identification and Functional Analysis of BmNPV-Interacting Proteins From Bombyx mori (Lepidoptera) Larval Midgut Based on Subcellular Protein Levels

Bombyx mori nucleopolyhedrovirus (BmNPV) is a major pathogen causing severe economic loss. However, the molecular mechanism of silkworm resistance to BmNPV and the interactions of this virus with the host during infection remain largely unclear. To explore the virus-binding proteins of silkworms, the midgut subcellular component proteins that may interact with BmNPV were analyzed in vitro based on one- and two-dimensional electrophoresis and far-western blotting combined with mass spectrometry (MS). A total of 24 proteins were determined to be specifically bound to budded viruses (BVs) in two subcellular fractions (mitochondria and microsomes). These proteins were involved in viral transportation, energy metabolism, apoptosis and viral propagation, and they responded to BmNPV infection with different expression profiles in different resistant strains. In particular, almost all the identified proteins were downregulated in the A35 strain following BmNPV infection. Interestingly, there were no virus-binding proteins identified in the cytosolic fraction of the silkworm midgut. Two candidate proteins, RACK1 and VDAC2, interacted with BVs, as determined with far-western blotting and reverse far-western blotting. We speculated that the proteins interacting with the virus could either enhance or inhibit the infection of the virus. The data provide comprehensive useful information for further research on the interaction of the host with BmNPV.

A Novel Digestive Proteinase Lipase Member H-A in Bombyx mori Contributes to Digestive Juice Antiviral Activity Against B. mori Nucleopolyhedrovirus

Previous studies have revealed that some proteins in Bombyx mori larvae digestive juice show antiviral activity. Here, based on the label-free proteomics data, BmLipase member H-A (BmLHA) was identified as being involved in the response to BmNPV infection in B. mori larvae digestive juice. In the present study, a gene encoding the BmLHA protein in B. mori was characterized. The protein has an open reading fragment of 999 bp, encoding a predicted 332 amino acid residue-protein with a molecular weight of approximately 35.9 kDa. The phylogenetic analysis revealed that BmLHA shares a close genetic distance with Papilio xuthus Lipase member H-A. BmLHA was highly expressed in the middle part of the B. mori gut, and the expression level increased with instar rising in larvae. There was higher expression of BmLHA in A35 than in P50 strains, and it was upregulated in both A35 and P50 strains, following BmNPV infection. The expression level of VP39 decreased significantly in appropriate recombinant-BmLHA-treated groups compared with the PBS-treated group in B. mori larvae and BmN cells. Meanwhile, overexpression of BmLHA significantly reduced the infectivity of BmNPV in BmN cells. These results indicated that BmLHA did not have digestive function but had anti-BmNPV activity. Taken together, our work provides valuable data for the clarification of the molecular characterization BmLHA and supplements research on proteins of anti-BmNPV activity in B. mori.