Nosema bombycis (Microsporidia) suppresses apoptosis in BmN cells (Bombyx mori)

The gut commensal bacterium Enterococcus faecalis LX10 contributes to defending against Nosema bombycis infection in Bombyx mori

BACKGROUND

Microsporidia, a group of obligate intracellular fungal-related parasites, have been used as efficient biocontrol agents for agriculture and forestry pests due to their host specificity and transovarial transmission. They mainly infect insect pests through the intestinal tract, but the interactions between microsporidia and the gut microbiota of the host have not been well demonstrated.

RESULTS

Based on the microsporidia-Bombyx mori model, we report that the susceptibility of silkworms to exposure to the microsporidium Nosema bombycis was both dose and time dependent. Comparative analyses of the silkworm gut microbiome revealed substantially increased abundance of Enterococcus belonging to Firmicutes after N. bombycis infection. Furthermore, a bacterial strain (LX10) was obtained from the gut of B. mori and identified as Enterococcus faecalis based on 16S rRNA sequence analysis. E. faecalis LX10 reduced the N. bombycis spore germination rate and the infection efficiency in vitro and in vivo, as confirmed by bioassay tests and histopathological analyses. In addition, after simultaneous oral feeding with E. faecalis LX10 and N. bombycis, gene (Akirin, Cecropin A, Mesh, Ssk, DUOX and NOS) expression, hydrogen peroxide and nitric oxide levels, and glutathione S-transferase (GST) activity showed different degrees of recovery and correction compared with those under N. bombycis infection alone. Finally, the enterococcin LX protein was identified from sterile LX10 fermentation liquid based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis.

CONCLUSION

Altogether, the results revealed that E. faecalis LX10 with anti-N. bombycis activity might play an important role in protecting silkworms from microsporidia. Removal of these specific commensal bacteria with antibiotics and utilization of transgenic symbiotic systems may effectively improve the biocontrol value of microsporidia. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Protists in the Insect Rearing Industry: Benign Passengers or Potential Risk?

Simple Summary

As human populations grow and the climate crisis deepens, humans will need to look to alternative sustainable sources of protein. The insect rearing industry is now rapidly growing to generate more sustainable sources of food and feed, and, as it does so, there will be an urgent need to better understand the role that microorganisms play in both maintaining insect health and generating disease. Protists are microbes that are neither viral, bacterial nor fungal and, therefore, are sometimes overlooked when considering microbial fauna. In this paper, we review the literature on protists that have been uncovered within insects that are being considered for rearing as food and feed. We discuss what is known about how they interact with hosts, how they may affect industrially reared insects in the future and which tools now need to be developed to better study them.

Abstract

As the insects for food and feed industry grows, a new understanding of the industrially reared insect microbiome is needed to better comprehend the role that it plays in both maintaining insect health and generating disease. While many microbiome projects focus on bacteria, fungi or viruses, protists (including microsporidia) can also make up an important part of these assemblages. Past experiences with intensive invertebrate rearing indicate that these parasites, whilst often benign, can rapidly sweep through populations, causing extensive damage. Here, we review the diversity of microsporidia and protist species that are found in reared insect hosts and describe the current understanding of their host spectra, life cycles and the nature of their interactions with hosts. Major entomopathogenic parasite groups with the potential to infect insects currently being reared for food and feed include the Amoebozoa, Apicomplexa, Ciliates, Chlorophyta, Euglenozoa, Ichtyosporea and Microsporidia. However, key gaps exist in the understanding of how many of these entomopathogens affect host biology. In addition, for many of them, there are very limited or even no molecular data, preventing the implementation of molecular detection methods. There is now a pressing need to develop and use novel molecular tools, coupled with standard molecular diagnostic methods, to help unlock their biology and predict the effects of these poorly studied protist parasites in intensive insect rearing systems.

In silico modelling and virtual screening for identification of inhibitors for spore wall protein-5 in Nosema bombycis

Bombyx mori is an insect of economic importance in the production of silk. It often gets infected by Nosema bombycis, an intracellular parasite. The infection causes a fatal disease known as a Pebrine which affects the development of the worm. The infected larvae of silkworms are coated with brown spots and are unable to spin the silkworm thread. They lose appetite, become sluggish, opaque and ultimately die. The Spore Wall Protein 5 is an exospore protein in N. bombycis and interacts with the polar tube proteins PTP2 and PTP3, a part of the extrusion apparatus that facilitates infection of the host. SWP5 also plays an essential part in maintaining the structural integrity of the spore wall and could possibly regulate the route of the infection in N. bombycis. In the present study, the homology modelling of three protein structures SWP5, PTP2 and PTP3 were performed. The protein-protein interaction was studied and a complete complex of SWP5, PTP2 and PTP3 was generated to understand the discharge of the penetrating polar tube. Virtual screening and molecular dynamics simulation was performed and a potential lead-like molecule is identified.Communicated by Ramaswamy H. Sarma.

Nosema apis and N. ceranae Infection in Honey bees: A Model for Host-Pathogen Interactions in Insects

There has been increased focus on the role of microbial attack as a potential cause of recent declines in the health of the western honey bee, Apis mellifera. The Nosema species, N. apis and N. ceranae, are microsporidian parasites that are pathogenic to honey bees, and infection by these species has been implicated as a key factor in honey bee losses. Honey bees infected with both Nosema spp. display significant changes in their biology at the cellular, tissue, and organismal levels impacting host metabolism, immune function, physiology, and behavior. Infected individuals lead to colony dysfunction and can contribute to colony disease in some circumstances. The means through which parasite growth and tissue pathology in the midgut lead to the dramatic physiological and behavioral changes at the organismal level are only partially understood. In addition, we possess only a limited appreciation of the elements of the host environment that impact pathogen growth and development. Critical for answering these questions is a mechanistic understanding of the host and pathogen machinery responsible for host-pathogen interactions. A number of approaches are already being used to elucidate these mechanisms, and promising new tools may allow for gain- and loss-of-function experiments to accelerate future progress.

Functional analysis of a putative Bombyx mori cypovirus miRNA BmCPV-miR-10 and its effect on virus replication

Bombyx mori cypovirus (BmCPV) is an important pathogen of silkworm (B. mori), the economically beneficial insect. The mechanism of its interaction with host immune defence system in the process of infection is still not yet completely clear. Researches have demonstrated that virus-encoded microRNAs (miRNA) play a crucial role in regulating host-pathogen interaction, but few reports are available so far on miRNAs encoded by insect viruses, especially the RNA viruses. In this study, a putative miRNA encoded by the 10th segment of BmCPV genomic RNA, BmCPV-miR-10, was identified and functionally analysed. The expression of the putative BmCPV-miR-10 could be detected via stem-loop RT-PCR (reverse transcription-Polymerase Chain Reaction) in the midgut of silkworm larvae infected with BmCPV. BmCSDE1 (B. mori cold shock domain E1 protein) gene was predicted to be a candidate target gene for BmCPV-miR-10 with the miRNA binding site located in 3' untranslated region of its mRNA. The regulation effect of the putative BmCPV-miR-10 on BmCSDE1 was verified in HEK293 cells by lentiviral expression system, in BmN cells by transfecting BmCPV-miR-10 mimics. The qRT-PCR (quantitative real-time PCR) results showed that the putative BmCPV-miR-10 could suppress the expression of BmCSDE1. By injection of BmCPV-miR-10 mimics into the silkworm larvae infected with BmCPV, it was further proved that the putative BmCPV-miR-10 could suppress the expression of BmCSDE1 in vivo, then inhibit the expression of BmApaf-1 (B. mori apoptotic protease activating factor 1), while enhance the replication of BmCPV genomic RNAs to a certain extent. These results implied that the putative BmCPV-miR-10 could down-regulate the expression of BmCSDE1, then suppress the expression of BmApaf-1, thereby created a favourable intracellular environment for virus replication and proliferation.

UDP-Glucosyltransferases Induced by Nosema bombycis Provide Resistance to Microsporidia in Silkworm (Bombyx mori)

Simple Summary

Nosema bombycis (N. bombycis), an obligate intracellular eukaryotic parasite, is a virulent pathogen of the silkworm, that causes major economic losses. Although many studies have reported on B. mori host response to this pathogen, little is known about which genes are induced by N. bombycis. Our results showed that two B. mori uridine diphosphate-glucosyltransferases (UGTs) (BmUGT10295 and BmUGT8453) could be activated by N. bombycis and provide resistance to the microsporidia in silkworms. These results will contribute to our understanding of host stress reaction to pathogens and the two pathogen-induced resistant genes will provide a target for promoting pathogen resistance.

Abstract

As a silkworm pathogen, the microsporidian N. bombycis can be transovarially transmitted from parent to offspring and seriously impedes sericulture industry development. Previous studies found that Uridine diphosphate (UDP)-glycosyltransferases (UGTs) are involved in regulating diverse cellular processes, such as detoxification, pigmentation, and odorant sensing. Our results showed that BmUGT10295 and BmUGT8453 genes were specifically induced in infected silkworms, but other BmUGTs were not. Tissue distribution analysis of the two BmUGTs showed that the transcriptions of the two BmUGTs were mainly activated in the midgut and Malpighian tubule of infected silkworms. Furthermore, there were significantly fewer microsporidia in over-expressed BmUGTs compared with the control, but there were significantly more microsporidia in RNA interference BmUGTs compared with the control. These findings indicate that the two BmUGTs were induced by N. bombycis and provided resistance to the microsporidia.

Transcriptome analysis reveals changes in silkworm energy metabolism during Nosema bombycis infection

Energy metabolism is important for the proliferation of microsporidia in infected host cells, but there is limited information on the host response. The energy metabolism response of silkworm (Bombyx mori) to microsporidia may help manage Nosema bombycis infections. We analyzed differentially expressed genes in the B.mori midgut transcriptome at two significant time points of microsporidia infection. A total of 1448 genes were up-regulated, while 315 genes were down-regulated. A high proportion of genes were involved in the phosphatidylinositol signaling system, protein processing in the endoplasmic reticulum, and glycerolipid metabolism at 48 h post infection (h p.i.), and a large number of genes were involved in the TCA cycle and protein processing at 120 h p.i. These results showed that the early stages of microsporidia infection affected the basic metabolism and biosynthesis processes of the silkworm. Knockout of Bm_nscaf2860_46 (Bombyx mori isocitrate dehydrogenase, BmIDH) and Bm_nscaf3027_062 (Bombyx mori hexokinase, BmHXK) reduced the production of ATP and inhibited microsporidia proliferation. Host fatty acid degradation, glycerol metabolism, glycolysis pathway, and TCA cycle response to microsporidia infection were also analyzed, and their importance to microsporidia proliferation was verified. These results increase our understanding of the molecular mechanisms involved in N. bombycis infection and provide new insights for research on microsporidia control. IMPORTANCE: Nosema bombycis can be vertically transmitted in silkworm eggs. The traditional prevention and control strategies for microsporidia are difficult and time-consuming, and this is a problem in silkworm culture. Research has mainly focused on host gene functions related to microsporidia infection and host immune responses after microsporidia infection. Little is known about the metabolic changes occurring in the host after infection. Understanding the metabolic changes in the silkworm host could aid in the recognition of host genes important for microsporidia infection and growth. We analyzed host metabolic changes and the main participating pathways at two time points after microsporidia infection and screened the microsporidia-dependent host energy metabolism genes BmIDH and BmHXK. The results revealed genes that are important for the proliferation of Nosema bombycis. These results illustrate how microsporidia hijack the host genome for their growth and reproduction.

Encephalitozoon cuniculi takes advantage of efferocytosis to evade the immune response

Microsporidia are recognized as opportunistic pathogens in individuals with immunodeficiencies, especially related to T cells. Although the activity of CD8+ T lymphocytes is essential to eliminate these pathogens, earlier studies have shown significant participation of macrophages at the beginning of the infection. Macrophages and other innate immunity cells play a critical role in activating the acquired immunity. After programmed cell death, the cell fragments or apoptotic bodies are cleared by phagocytic cells, a phenomenon known as efferocytosis. This process has been recognized as a way of evading immunity by intracellular pathogens. The present study evaluated the impact of efferocytosis of apoptotic cells either infected or not on macrophages and subsequently challenged with Encephalitozoon cuniculi microsporidia. Macrophages were obtained from the bone marrow monocytes from C57BL mice, pre-incubated with apoptotic Jurkat cells (ACs), and were further challenged with E. cuniculi spores. The same procedures were performed using the previously infected Jurkat cells (IACs) and challenged with E. cuniculi spores before macrophage pre-incubation. The average number of spores internalized by macrophages in phagocytosis was counted. Macrophage expression of CD40, CD206, CD80, CD86, and MHCII, as well as the cytokines released in the culture supernatants, was measured by flow cytometry. The ultrastructural study was performed to analyze the multiplication types of pathogens. Macrophages pre-incubated with ACs and challenged with E. cuniculi showed a higher percentage of phagocytosis and an average number of internalized spores. Moreover, the presence of stages of multiplication of the pathogen inside the macrophages, particularly after efferocytosis of infected apoptotic bodies, was observed. In addition, pre-incubation with ACs or IACs and/or challenge with the pathogen decreased the viability of macrophages, reflected as high percentages of apoptosis. The marked expression of CD206 and the release of large amounts of IL-10 and IL-6 indicated the polarization of macrophages to an M2 profile, compatible with efferocytosis and favorable for pathogen development. We concluded that the pathogen favored efferocytosis and polarized the macrophages to an M2 profile, allowing the survival and multiplication of E. cuniculi inside the macrophages and explaining the possibility of macrophages acting as Trojan horses in microsporidiosis.

Genetic bioengineering of overexpressed guanylate binding protein family BmAtlastin-n enhances silkworm resistance to Nosema bombycis

Microsporidia are obligate single-celled eukaryote parasites. Microsporidian infection can cause large economic losses to beneficial insects such as silkworms and honey bees. Identification of resistance biomacromolecules and breeding of transgenic lines resistant to the microsporidian Nosema bombycis are important for disease management. We previously used transcriptome analysis to identify a guanylate binding protein family BmAtlastin-n gene that was significantly upregulated after Nosema bombycis infection, and we determined that the molecule was highly expressed in resistance-related tissues such as the midgut, fat body and the epidermis. The transgenic silkworm line overexpressing BmAtlastin-n biomolecules had economic characters similar to those of non-transgenic lines. The transgenic OE-BmAtlastin-n lines had significantly improved survival after microspore infection. We used RT-PCR and H&E staining to show that the number of spores in the transgenic lines was significantly lower than in the control lines. In this study, we identified a BmAtlastin-n macromolecule with resistance to N. bombycis and developed a transgenic line. The results improved understanding of the GBP protein family and provided biomacromolecule material for the treatment and prevention of microsporidia.

The ins and outs of host-microsporidia interactions during invasion, proliferation and exit

Microsporidia are a large group of fungal-related obligate intracellular parasites. They are responsible for infections in humans as well as in agriculturally and environmentally important animals. Although microsporidia are abundant in nature, many of the molecular mechanisms employed during infection have remained enigmatic. In this review, we highlight recent work showing how microsporidia invade, proliferate and exit from host cells. During invasion, microsporidia use spore wall and polar tube proteins to interact with host receptors and adhere to the host cell surface. In turn, the host has multiple defence mechanisms to prevent and eliminate these infections. Microsporidia encode numerous transporters and steal host nutrients to facilitate proliferation within host cells. They also encode many secreted proteins which may modulate host metabolism and inhibit host cell defence mechanisms. Spores exit the host in a non-lytic manner that is dependent on host actin and endocytic recycling proteins. Together, this work provides a fuller picture of the mechanisms that these fascinating organisms use to infect their hosts.

Innate and Adaptive Immune Responses Against Microsporidia Infection in Mammals

Microsporidia are obligate intracellular and eukaryotic pathogens that can infect immunocompromised and immunocompetent mammals, including humans. Both innate and adaptive immune systems play important roles against microsporidian infection. The innate immune system can partially eliminate the infection by immune cells, such as gamma delta T cell, natural killer cells (NKs), macrophages and dendritic cells (DCs), and present the pathogens to lymphocytes. The innate immune cells can also prime and enhance the adaptive immune response via surface molecules and secreted cytokines. The adaptive immune system is critical to eliminate microsporidian infection by activating cytotoxic T lymphocyte (CTL) and humoral immune responses, and feedback regulation of the innate immune mechanism. In this review, we will discuss the cellular and molecular responses and functions of innate and adaptive immune systems against microsporidian infection.

Dicer regulates Nosema ceranae proliferation in honeybees

Nosema ceranae is a microsporidian parasite that infects the honeybee midgut epithelium. The protein-coding gene Dicer is lost in most microsporidian genomes but is present in N. ceranae. By feeding infected honeybees with small interfering RNA targeting the N. ceranae gene coding Dicer (siRNA-Dicer), we found that N. ceranae spore loads were significantly reduced. In addition, over 10% of total parasite protein-coding genes showed significantly divergent expression profiles after siRNA-Dicer treatment. Parasite genes for cell proliferation, ABC transporters and hexokinase were downregulated at 3 days postinfection, a key point in the middle of parasite replication cycles. In addition, genes involved in metabolic pathways of honeybees and N. ceranae showed significant co-expression. Furthermore, the siRNA-Dicer treatment partly reversed the expression patterns of honeybee genes. The honeybee gene mucin-2-like showed significantly upregulation in the siRNA-Dicer group compared with the infection group continually at 4, 5 and 6 days postinfection, suggesting that the siRNA-Dicer feeding promoted the strength of the mucus barrier resulted from interrupted parasite proliferation. As the gene Dicer broadly regulates N. ceranae proliferation and honeybee metabolism, our data suggest the RNA interference pathway is an important infection strategy for N. ceranae.

Interaction of Phthorimaea operculella granulovirus with a Nosema sp. microsporidium in larvae of Phthorimaea operculella

An antagonistic effect of a microsporidium (Nosema sp.) infection on the virulence of Phthorimaea operculella granulovirus (PhopGV) was recorded in potato tuber moth (Phthorimaea operculella) larvae with mixed infections. When the P. operculella colony was infected at a high rate (42.8-100%) with the microsporidium, it was less susceptible to the isolate PhopGV-GR1.1. A virus concentration 1.89 × 10⁵ higher was necessary to cause the same level of mortality produced in the P. operculella colony when it was uninfected or had a low level of infection with the microsporidium (0-30%). This antagonistic effect was driven by a Nosema isolate (termed Nosema sp. Phop) that was purified from microsporidian-infected P. operculella individuals. The purified microsporidium was characterised by morphological features, including size, filament coils and different developmental stages using transmission electron microscopy (TEM). On the molecular level, the partial cistron rDNA information of the small ribosomal subunit (SSU), internal transcribed spacer (ITS), and the large ribosomal subunit (LSU) were identified. Phylogenetic analyses revealed that the newly described microsporidium belongs to the "true Nosema" clade. Partial sequence information of the RNA polymerase II largest subunit (RPB1) suggested that Nosema bombycis is the closest relative (98% identity). The morphological and phylogenetic characteristics suggest that it is an isolate of N. bombycis. Interactions of microsporidia and betabaculoviruses are rarely described in the literature, although mixed infections of different pathogens seem to be rather common events, ranging from antagonistic to mutualistic interactions. The observed antagonistic relationship between the Nosema sp. and PhopGV-GR1.1 showed that pathogen interactions need to be considered when single pathogens are applied to insect populations in the context of biological control of insect pests.

Encephalitozoon cuniculi and Vittaforma corneae (Phylum Microsporidia) inhibit staurosporine-induced apoptosis in human THP-1 macrophages in vitro

Obligately intracellular microsporidia regulate their host cell life cycles, including apoptosis, but this has not been evaluated in phagocytic host cells such as macrophages that can facilitate infection but also can be activated to kill microsporidia. We examined two biologically dissimilar human-infecting microsporidia species, Encephalitozoon cuniculi and Vittaforma corneae, for their effects on staurosporine-induced apoptosis in the human macrophage-differentiated cell line, THP1. Apoptosis was measured after exposure of THP-1 cells to live and dead mature organisms via direct fluorometric measurement of Caspase 3, colorimetric and fluorometric TUNEL assays, and mRNA gene expression profiles using Apoptosis RT2 Profiler PCR Array. Both species of microsporidia modulated the intrinsic apoptosis pathway. In particular, live E. cuniculi spores inhibited staurosporine-induced apoptosis as well as suppressed pro-apoptosis genes and upregulated anti-apoptosis genes more broadly than V. corneae. Exposure to dead spores induced an opposite effect. Vittaforma corneae, however, also induced inflammasome activation via Caspases 1 and 4. Of the 84 apoptosis-related genes assayed, 42 (i.e. 23 pro-apoptosis, nine anti-apoptosis, and 10 regulatory) genes were more affected including those encoding members of the Bcl2 family, caspases and their regulators, and members of the tumour necrosis factor (TNF)/TNF receptor R superfamily.

Evolution of Dicer and Argonaute orthologs in microsporidian parasites

Microsporidia are a group of intracellular parasites which infect animal hosts. The infection can broadly influence the hosts' metabolism, growth as well as immune responses. Recently, a functional RNAi pathway was suggested from the microsporidia parasite Nosema ceranae, whereby the gene Dicer showed strong impact on spore proliferation. Based on sequenced microsporidian species, the RNAi gene orthologs have only been annotated for a few species. In order to study the selection of RNAi gene Dicer and Argonaute orthologs from microsporidian genomes, a phylogenetic analysis was performed based on single copy orthologs of 21 microsporidian parasite species. Of the 21 studied parasite species, 11 parasite species maintained Dicer and Argonaute orthologs, which were further used to build the gene trees. The gene Dicer and Argonaute orthologs were either both maintained or both lost. The topology structures between the phylogenetic Dicer, Argonaute and species trees were consistent. The results suggest that the gene Dicer and Argonaute were selected as a unit, which were selectively maintained/lost during the lineage divergence. The study provides general insights on the selection of RNAi pathway in microsporidian parasites and the evolution of parasitism.

Interactions Among Host-Parasite MicroRNAs During Nosema ceranae Proliferation in Apis mellifera

We previously identified microRNA (miRNA) from Nosema ceranae and found that knockdowns of transcripts for the parasite protein Dicer greatly reduce parasite reproduction. In order to study parasitic miRNA functions and identify candidate target genes, we fed honey bees infected with N. ceranae with small interfering RNA (siRNA) targeting the N. ceranae gene Dicer. We then deep-sequenced honey bee and N. ceranae miRNAs daily across a full 6-day proliferation cycle. We found seven honey bee and five N. ceranae miRNAs that were significantly differently expressed between the infection and siRNA-Dicer groups. N. ceranae miRNA showed potentially strong impacts on the N. ceranae transcriptome, where over 79% of the total protein coding genes were significantly correlated with one or more miRNAs. N. ceranae miRNAs also can regulate honey bee metabolism and immune response, given parasitic miRNAs were secreted into the cytoplasm. Our results suggest that N. ceranae miRNAs regulate both parasite and host gene expression, providing new insights for microsporidia parasitism evolution.

Molecular characterization and expression analysis of Turtle protein in silkworm that is associated with Nosema bombycis infection

In this report, we describe the cloning and characterization of a member of the immunoglobulin superfamily (IgSF); i.e., Turtle. The cDNA of Turtle was cloned from the silkworm Bombyx mori using the rapid amplification of cDNA ends (RACE) technique. Three isoforms of Bombyx Turtle were obtained, including Bmtutl-464, Bmtutl-519, and Bmtutl-810. The three isoforms had identical 27-amino acid signal peptides and four extracellular immunoglobulin (Ig) domains (IgI-IgIV). Sequence similarity and phylogenic analysis indicated that Bmtutl-810 belongs to the group of insect Turtle isoforms and shares 76.2% identity with Drosophila Turtle. Quantitative real-time PCR analysis revealed that the Bombyx Turtle isoforms were expressed throughout the entire development period, the highest levels of expression of Bmtutl-464 and Bmtutl-519 were observed at the second instar larvae stage, whereas that of Bmtutl-810 peaked at the embryonic stage. The ubiquitous expression of Bmtutl-464, Bmtutl-519, and Bmtutl-810 were observed in all studied tissues, except for Bmtutl-519 in the silk gland. The expression level of Bmtutl-464 was highest in the ovary, whereas that of Bmtutl-519 and Bmtutl-810 was highest in the hemolymph. Bmtutl-519 was upregulated in BmN cells infected by Nosema bombycis, We speculated that Bombyx Turtle was not only involved in neural development in silkworm, as well as Drosophila Turtle, but was also involved in the regulation of other biological functions. For example, Bmtutl-519 might be involved in N. bombycis infection and may play an important role in the immune response of silkworms to N. bombycis infection.

Quantitative Proteomic Analysis of Germination of Nosema bombycis Spores under Extremely Alkaline Conditions

The microsporidian Nosema bombycis is an obligate intracellular pathogen of the silkworm Bombyx mori, causing the epidemic disease Pebrine and extensive economic losses in sericulture. Although N. bombycis forms spores with rigid spore walls that protect against various environmental pressures, ingested spores germinate immediately under the extremely alkaline host gut condition (Lepidoptera gut pH > 10.5), which is a key developmental turning point from dormant state to infected state. However, to date this process remains poorly understood due to the complexity of the animal digestive tract and the lack of genetic tools for microsporidia. Here we show, using an in vitro spore germination model, how the proteome of N. bombycis changes during germination, analyse specific metabolic pathways employed in detail, and validate key functional proteins in vivo in silkworms. By a label-free quantitative proteomics approach that is directly based on high-resolution mass spectrometry (MS) data, a total of 1136 proteins were identified with high confidence, with 127 proteins being significantly changed in comparison to non-germinated spores. Among them, structural proteins including polar tube protein 1 and 3 and spore wall protein (SWP) 4 and 30 were found to be significantly down-regulated, but SWP9 significantly up-regulated. Some nucleases like polynucleotide kinase/phosphatase and flap endonucleases 1, together with a panel of hydrolases involved in protein degradation and RNA cleavage were overrepresented too upon germination, which implied that they might play important roles during spore germination. The differentially regulated trends of these genes were validated, respectively, by quantitative RT-PCR and 3 proteins of interest were confirmed by Western blotting analyses in vitro and in vivo. Furthermore, the pathway analysis showed that abundant up- and down-regulations appear involved in the glycolysis, pentose phosphate pathway, purine, and pyrimidine metabolism, suggesting preparations of energy generation and substance synthesis for the following invasion and proliferation inside the host. This report, to our knowledge, provides the first proteomic landscape of N. bombycis spores, and also a stepping stone on the way to further study of the unique infection mode of this economically important pathogen and other microsporidia in general.

Molecular and immune response characterizations of a novel AIF and cytochrome c in Litopenaeus vannamei defending against WSSV infection

Apoptosis inducing factor (AIF) and cytochrome c (CYC) are two mitochondrial apoptogenic factors. In the present study, the cDNA sequences of AIF (LvAIF) and CYC (LvCYC) were cloned from Pacific white shrimp, Litopenaeus vannamei. The LvAIF was 1664 bp, including a 5'-terminal untranslated region (UTR) of 154 bp, an open reading frame (ORF) of 1323 bp encoding a polypeptide of 440 amino acids (aa) and a 3' UTR of 187 bp. The LvCYC was 582 bp, including a 50 bp 5' UTR, a 315 bp ORF encoding for 104 aa, and a 217 bp 3' UTR. The deduced protein of LvAIF contained a conserved Pyr_redox and AIF_C domain at the N-terminal and the predicted LvCYC included a conservative cytochrome_C domain, respectively. Phylogenetic analysis revealed that LvAIF belonged to AIF1 subfamily and showed a close relationship with AIF1 from vertebrates and LvCYC showed the closest relationship with its counterparts from shrimp Marsupenaeus japonicus. Tissue expression profiles showed that both LvAIF and LvCYC existed in most tissues, with the most predominant expression of LvAIF in intestine, then followed muscle and the weakest expression in gill. The highest expression of LvCYC was detected in muscle, and the weakest expression was in hemocytes. Additionally, after white spot syndrome virus (WSSV) infection, the significant up-regulation of LvAIF, LvCYC and caspase 3 transcripts and the increase of pro-caspase 3 and active-caspase 3 protein were detected at most time points (P < 0.05). However, all of the three genes down-regulated in hemocytes in the early stage after WSSV infection. WSSV proliferation and shrimp mortality showed a time-dependent manner and the production of ROS in hemocytes were significantly increased at 6 and 24 h after infection. Our results showed that the apoptotic genes AIF, CYC and caspase 3 might play crucial roles in hepatopancreas, however, the production of ROS in hemocytes might be important in shrimp defense against WSSV infection.