Invertebrate host responses to microsporidia infections

Emergence of genetic diversity of Enterocytozoon bieneusi from snakes in China

Enterocytozoon bieneusi belongs to the phylum Microsporidia, a parasite reported to infect various domestic animals, wildlife and humans, thereby causing an intestinal disease characterized by severe or chronic diarrhea and malabsorption. The typical mode of transmission is contaminated water and food. Few studies on E. bieneusi infections have been reported in reptiles, however, our report focuses on the molecular characterization of E. bieneusi infection in snakes in China. We collected a total of 603 fecal samples from snakes in China. The samples were tested for the presence of E. bieneusi through PCR amplification of the internal transcribed spacer (ITS) locus. Our analysis showed E. bieneusi overall prevalence rate of 15.59 %, the highest prevalence was recorded in Eastern rat snake (21.99 %), followed by Corn snake (19.63 %) while the prevalence of 18.39 %, 15.79 %, 13.56 % were recorded in Common garter snake, Pine snake, Hognose snake respectively. Eastern kingsnake has the lowest infection rate of 5.71 %. Genotype analysis identified 26 distinct genotypes: 8 known and 18 novel. Phylogenetic analysis revealed that 25 genotypes belonged to Group 1, which includes isolates from various animal hosts and humans. However, genotype GX29 was classified under Group 9. Our study indicates that pet snakes are one of the potential sources of transmission of zoonotic microsporidiosis in China.

A novel ATP-binding cassette protein (NoboABCG1.3) plays a role in the proliferation of Nosema bombycis

ATP-binding cassette (ABC) transporter proteins, one of the largest families of membrane transport proteins, participate in almost all biological processes and widely exist in living organisms. Microsporidia are intracellular parasites; they can reduce crop yields and pose a threat to human health. The ABC proteins are also present in microsporidia and play a critical role in their proliferation and energy transport. In this study, a novel ABC transporter protein of Nosema bombycis named NoboABCG1.3 was identified. The NoboABCG1.3 protein is comprised of 640 amino acids, which contain six transmembrane domains and one nucleotide-binding domain. After N. bombycis infection of cells or tissues, quantitative reverse transcription polymerase chain reaction analysis revealed a progressive elevation in the transcript levels of NoboABCG1.3. Downregulation of NoboABCG1.3 expression significantly inhibited N. bombycis proliferation. Subsequently, a transgenic cell line stably expressing an interfering fragment of NoboABCG1.3 was established, which exhibited extreme inhibition on the proliferation of N. bombycis. These findings indicate that NoboABCG1.3 plays a role in the proliferation of N. bombycis and holds promise as a target for developing N. bombycis-resistant silkworms.

Identification and distribution of some medico-veterinary important pathogens in muscid flies in two geographical regions of Türkiye

Some dipteran flies play an important role in the transmission of pathogens such as viruses, bacteria, fungi, protozoan and metazoan parasites in humans and other animals. Despite this importance, knowledge of the prevalence and molecular characteristics of some pathogens in flies is limited, and no data are available for Türkiye. In this study, we investigated the possible vector role of muscid fly species for the transmission of Enterocytozoon bieneusi Desportes (Chytridiopsida: Enterocytozoonidae), Encephalitozoon spp., Coxiella burnetii Derrick (Legionellales: Coxiellaceae) and Thelazia spp. using polymerase chain reaction (PCR) and sequence analysis. The flies were trapped in different animal-related places and surroundings from two different geographical regions of Türkiye including Central Anatolia and Middle Black Sea. According to the morphological keys, 850 (85%), 141 (14.1%) and 6 (0.6%) of the total of 1000 fly specimens identified as Musca domestica Linnaeus (Diptera: Muscidae), Stomoxys calcitrans Linnaeus (Diptera: Muscidae) and Musca autumnalis De Geer (Diptera: Muscidae), respectively. The other species including Haematobia irritans Linnaeus (Diptera: Muscidae), Muscina stabulans Fallén (Diptera: Muscidae) and Hydrotaea ignava Harris (Diptera: Muscidae) were each represented by a single specimen. Screening of the pathogens identified E. bieneusi only in M. domestica with a prevalence of 2.4%. Sequence analyses identified three known genotypes, Type IV, BEB6 and BEB8, and one novel genotype named AEUEb of E. bieneusi in M. domestica. Coxiella burnetii was detected in M. domestica and S. calcitrans with prevalences of 2.9% and 2.8%, respectively. The one specimen of H. ignava was also positive for C. burnetii. Encephalitozoon spp. and Thelazia spp. were not found in the examined specimens. Our results contribute to the current knowledge on the vector potential of muscid flies and their possible role in the transmission dynamics of certain pathogens, especially in regions where diseases are prevalent and affect public and animal health.

Bioinformatics analysis of the Microsporidia sp. MB genome: a malaria transmission-blocking symbiont of the Anopheles arabiensis mosquito

BACKGROUND

The use of microsporidia as a disease-transmission-blocking tool has garnered significant attention. Microsporidia sp. MB, known for its ability to block malaria development in mosquitoes, is an optimal candidate for supplementing malaria vector control methods. This symbiont, found in Anopheles mosquitoes, can be transmitted both vertically and horizontally with minimal effects on its mosquito host. Its genome, recently sequenced from An. arabiensis, comprises a compact 5.9 Mbp.

RESULTS

Here, we analyze the Microsporidia sp. MB genome, highlighting its major genomic features, gene content, and protein function. The genome contains 2247 genes, predominantly encoding enzymes. Unlike other members of the Enterocytozoonida group, Microsporidia sp. MB has retained most of the genes in the glycolytic pathway. Genes involved in RNA interference (RNAi) were also identified, suggesting a mechanism for host immune suppression. Importantly, meiosis-related genes (MRG) were detected, indicating potential for sexual reproduction in this organism. Comparative analyses revealed similarities with its closest relative, Vittaforma corneae, despite key differences in host interactions.

CONCLUSION

This study provides an in-depth analysis of the newly sequenced Microsporidia sp. MB genome, uncovering its unique adaptations for intracellular parasitism, including retention of essential metabolic pathways and RNAi machinery. The identification of MRGs suggests the possibility of sexual reproduction, offering insights into the symbiont's evolutionary strategies. Establishing a reference genome for Microsporidia sp. MB sets the foundation for future studies on its role in malaria transmission dynamics and host-parasite interactions.

Evaluation of in vivo pharmacokinetic study of the anti-cancer drug imatinib using silkworms as an animal model

Imatinib is an oral molecular targeted therapy that acts as a tyrosine kinase inhibitor. Silkworms present a promising experimental model for elucidating the pharmacokinetic and toxicity profiles of various compounds. This study aimed to establish an experimental paradigm for investigating the pharmacokinetics of imatinib in silkworms. A comparative analysis of imatinib pharmacokinetic parameters across silkworms, humans, mice, and rats revealed similarities in time to maximum concentration (Tmax) and apparent clearance values between silkworms and humans. However, differences in elimination half-life (t1/2) and apparent volume of distribution between silkworms and humans remained within 5- and 4-fold ranges, respectively. Importantly, mice demonstrated pharmacokinetic parameters closer to those of humans than rats during imatinib studies. Additionally, silkworms and mice exhibit similar Tmax and t1/2 values. This study highlights the potential of silkworms as valuable tools for investigating imatinib metabolism in pharmacokinetic studies. Furthermore, it underscores the applicability of silkworms in elucidating the pharmacokinetic parameters of various molecular-targeted drugs, thus facilitating advancements in drug development and evaluation.

Nosema bombycis: A remarkable unicellular parasite infecting insects

Microsporidia are opportunistic fungal-like pathogens that cause microsporidiosis, which results in significant economic losses and threatens public health. Infection of domesticated silkworms by the microsporidium Nosema bombycis causes pébrine disease, for which this species of microsporidia has received much attention. Research has been conducted extensively on this microsporidium over the past few decades to better understand its infection, transmission, host-parasite interaction, and detection. Several tools exist to study this species including the complete genome sequence of N. bombycis. In addition to the understanding of N. bombycis being important for the silkworm industry, this species has become a model organism for studying microsporidia. Research on biology of N. bombycis will contribute to the development of knowledge regarding microsporidia and potential antimicrosporidia drugs. Furthermore, this will provide insight into the molecular evolution and functioning of other fungal pathogens.

Establishment of a Secretory Protein-Inducible CRISPR/Cas9 System for Nosema bombycis in Insect Cells

Gene editing techniques are widely and effectively used for the control of pathogens, but it is difficult to directly edit the genes of Microsporidia due to its unique spore wall structure. Innovative technologies and methods are urgently needed to break through this limitation of microsporidia therapies. Here, we establish a microsporidia-inducible gene editing system through core components of microsporidia secreted proteins, which could edit target genes after infection with microsporidia. We identified that Nosema bombycis NB29 is a secretory protein and found to interact with itself. The NB29-N3, which lacked the nuclear localization signal, was localized in the cytoplasm, and could be tracked into the nucleus after interacting with NB29-B. Furthermore, the gene editing system was constructed with the Cas9 protein expressed in fusion with the NB29-N3. The system could edit the exogenous gene EGFP and the endogenous gene BmRpn3 after overexpression of NB29 or infection with N. bombycis.

Dual oxidase 2 (duox 2) participates in the intestinal antibacterial innate immune responses of Procambarus clarkii by regulating ROS levels

Dual oxidase (Duox) a member of the nicotinamide adenine dinucleotide phosphate oxidase (NOX) family can induce the production of reactive oxygen species (ROS). In vertebrates, the duox gene was indicated to be associated with the mucosal immunity. The roles of the duox gene in invertebrates were mainly studied in insects for the function of maintaining intestinal flora balance. In recent years, some studies have reported that Duox is involved in regulating the production of ROS and plays an important role in defending against the intestinal pathogen infection. However, the molecular mechanism has not been fully illuminated. In this study, a duox 2 involved in the production of H2O2 was identified for the first time in P. clarkii. Mature Pc-Duox 2 is a 7-transmembrane protein molecule that includes PHD, FAD, and NAD domains. Pc-duox 2 was mainly expressed in hemocytes and intestinal tissue. Its expression levels were obviously upregulated after intramuscular or oral infection with V. harveyi. In the RNAi assay, the upregulated trends of H2O2 and total ROS levels in crayfish intestine were significantly suppressed when Pc-duox 2 was knocked down. Compared with the slightly affected SOD activity, the upregulated CAT activity was suppressed more obviously in the crayfish intestine. Furthermore, Pc-duox 2 had an important effect on the maintenance of the structural stability of crayfish the intestine. Further research revealed that the knockdown of Pc-duox 2 could cause an obvious suppression in the upregulated levels of Toll signalling pathway-related genes, including Pc-toll 1, Pc-toll 3, Pc-dorsal, Pc-ALF 5, Pc-crustin 1, and Pc-lysozyme. Ultimately, these changes triggered the accelerated death of crayfish. Overall, we speculated that Pc-duox 2 played an important role in antibacterial innate immunity in the crayfish intestine by regulating the total ROS level.

Transcriptomic changes in the microsporidia proliferation and host responses in congenitally infected embryos and larvae

Congenital infection caused by vertical transmission of microsporidia N. bombycis can result in severe economic losses in the silkworm-rearing industry. Whole-transcriptome analyses have revealed non-coding RNAs and their regulatory networks in N. bombycis infected embryos and larvae. However, transcriptomic changes in the microsporidia proliferation and host responses in congenitally infected embryos and larvae remains unclear. Here, we simultaneously compared the transcriptomes of N. bombycis and its host B. mori embryos of 5-day and larvae of 1-, 5- and 10-day during congenital infection. For the transcriptome of N. bombycis, a comparison of parasite expression patterns between congenital-infected embryos and larva showed most genes related to parasite central carbon metabolism were down-regulated in larvae during infection, whereas the majority of genes involved in parasite proliferation and growth were up-regulated. Interestingly, a large number of distinct or shared differentially expressed genes (DEGs) were revealed by the Venn diagram and heat map, many of them were connected to infection related factors such as Ricin B lectin, spore wall protein, polar tube protein, and polysaccharide deacetylase. For the transcriptome of B. mori infected with N. bombycis, beyond numerous DEGs related to DNA replication and repair, mRNA surveillance pathway, RNA transport, protein biosynthesis, and proteolysis, with the progression of infection, a large number of DEGs related to immune and infection pathways, including phagocytosis, apoptosis, TNF, Toll-like receptor, NF-kappa B, Fc epsilon RI, and some diseases, were successively identified. In contrast, most genes associated with the insulin signaling pathway, 2-oxacarboxylic acid metabolism, amino acid biosynthesis, and lipid metabolisms were up-regulated in larvae compared to those in embryos. Furthermore, dozens of distinct and three shared DEGs that were involved in the epigenetic regulations, such as polycomb, histone-lysine-specific demethylases, and histone-lysine-N-methyltransferases, were identified via the Venn diagram and heat maps. Notably, many DEGs of host and parasite associated with lipid-related metabolisms were verified by RT-qPCR. Taken together, simultaneous transcriptomic analyses of both host and parasite genes lead to a better understanding of changes in the microsporidia proliferation and host responses in embryos and larvae in N. bombycis congenital infection.

A monoclonal antibody targeting spore wall protein 1 inhibits the proliferation of Nosema bombycis in Bombyx mori

IMPORTANCE

There are a few reports on the resistance of microsporidia, including Nosema bombycis. Here, the alkali-soluble germination proteins of N. bombycis were used as immunogens to prepare a monoclonal antibody, and its single-chain variable fragments effectively blocked microsporidia infection. Our study has provided novel strategies for microsporidiosis control and demonstrated a useful method for the potential treatment of other microsporidia diseases.

Increased susceptibility to encephalitozoonosis associated with mixed Th1/Th2 profile and M1/M2 profile in mice immunosuppressed with cyclophosphamide

Encephalitozoon cuniculi is a unicellular, spore-forming, obligate intracellular eukaryote belonging to the phylum Microsporidia. It is known to infect mainly immunocompromised and immunocompetent mammals, including humans. The parasite-host relationship has been evaluated using both in vitro cell culturing and animal models. For example, Balb/c and C57BL/6 mouse strains have been used interchangeably, although the latter has been considered more susceptible due to the higher fungal load observed after infection. In the present study, we identified the characteristics of the immune response of C57BL/6 mice treated or not with the immunosuppressant cyclophosphamide (Cy) and challenged with E. cuniculi by intraperitoneal route. After 14 days of infection, serum was collected to analyze Th1, Th2, and Th17 cytokine levels. In addition, peritoneal washes were performed, and the spleen sample was collected for immune cell phenotyping, whereas liver, spleen, kidney, lung, intestine, and central nervous system (CNS) samples were collected for histopathological analysis. Although infected mice displayed a reduced absolute number of macrophages, they showed an M1 profile, an elevated number of CD4+T, CD8+T, B-1, and B-2 lymphocytes, with a predominance of Th1 inflammatory cytokines (interferon [IFN]-γ, tumor necrosis factor [TNF]-α, and interleukin [IL]-2) and Th17. Furthermore, Cy-Infected mice showed a reduced absolute number of macrophages with an M1 profile but a reduced number of CD4+T, CD8+T, B-1, and B-2 lymphocytes, with a predominance of Th1 inflammatory cytokines (IFN-γ, TNF-α, and IL-2) and Th2 (IL-4). This group displayed a higher fungal burden as well and developed more severe encephalitozoonosis, which was associated with a reduced number of T and B lymphocytes and a mixed profile of Th1 and Th2 cytokines.

Metabolomic analysis of lipid changes in Bombyx mori infected with Nosema bombycis

The silkworm (Bombyx mori) is a model species of lepidopteran insect. Microsporidium spp. are obligate intracellular eukaryotic parasites. Infection by the microsporidian Nosema bombycis (Nb) results in an outbreak of Pébrine disease in silkworms and causes substantial losses to the sericulture industry. It has been suggested that Nb depends on nutrients from host cells for spore growth. However, little is known about changes in lipid levels after Nb infection. In this study, ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was performed to analyze the effect of Nb infection on lipid metabolism in the midgut of silkworms. A total of 1601 individual lipid molecules were detected in the midgut of silkworms, of which 15 were significantly decreased after Nb challenge. Classification, chain length, and chain saturation analysis revealed that these 15 differential lipids can be classified into different lipid subclasses, of which 13 belong to glycerol phospholipid lipids and two belong to glyceride esters. The results indicated that Nb uses the host lipids to complete its own replication, and the acquisition of host lipid subclasses is selective; not all lipid subclasses are required for microsporidium growth or proliferation. Based on lipid metabolism data, phosphatidylcholine (PC) was found to be an important nutrient for Nb replication. Diet supplementation with lecithin substantially promoted the replication of Nb. Knockdown and overexpression of the key enzyme phosphatidate phosphatase (PAP) and phosphatidylcholine (Bbc) for PC synthesis also confirmed that PC is necessary for Nb replication. Our results showed that most lipids in the host midgut decreased when silkworms were infected with Nb. Reduction of or supplementation with PC may be a strategy to suppress or promote microsporidial replication.

Non-coding RNAs identification and regulatory networks in pathogen-host interaction in the microsporidia congenital infection

BACKGROUND

The interaction networks between coding and non-coding RNAs (ncRNAs) including long non-coding RNA (lncRNA), covalently closed circular RNA (circRNA) and miRNA are significant to elucidate molecular processes of biological activities and interactions between host and pathogen. Congenital infection caused by vertical transmission of microsporidia N. bombycis can result in severe economic losses in the silkworm-feeding industry. However, little is known about ncRNAs that take place in the microsporidia congenital infection. Here we conducted whole-transcriptome RNA-Seq analyses to identify ncRNAs and regulatory networks for both N. bombycis and host including silkworm embryos and larvae during the microsporidia congenital infection.

RESULTS

A total of 4,171 mRNAs, 403 lncRNA, 62 circRNAs, and 284 miRNAs encoded by N. bombycis were identified, among which some differentially expressed genes formed cross-talk and are involved in N. bombycis proliferation and infection. For instance, a lncRNA/circRNA competing endogenous RNA (ceRNA) network including 18 lncRNAs, one circRNA, and 20 miRNAs was constructed to describe 14 key parasites genes regulation, such as polar tube protein 3 (PTP3), ricin-B-lectin, spore wall protein 4 (SWP4), and heat shock protein 90 (HSP90). Regarding host silkworm upon N. bombycis congenital infection, a total of 14,889 mRNAs, 3,038 lncRNAs, 19,039 circRNAs, and 3,413 miRNAs were predicted based on silkworm genome with many differentially expressed coding and non-coding genes during distinct developmental stages. Different species of RNAs form interacting network to modulate silkworm biological processes, such as growth, metamorphosis and immune responses. Furthermore, a lncRNA/circRNA ceRNA network consisting of 140 lncRNAs, five circRNA, and seven miRNAs are constructed hypothetically to describe eight key host genes regulation, such as Toll-6, Serpin-6, inducible nitric oxide synthase (iNOS) and Caspase-8. Notably, cross-species analyses indicate that parasite and host miRNAs play a vital role in pathogen-host interaction in the microsporidia congenital infection.

CONCLUSION

This is the first comprehensive pan-transcriptome study inclusive of both N. bombycis and its host silkworm with a specific focus on the microsporidia congenital infection, and show that ncRNA-mediated regulation plays a vital role in the microsporidia congenital infection, which provides a new insight into understanding the basic biology of microsporidia and pathogen-host interaction.

Germination of Microsporidian Spores: The Known and Unknown

Microsporidia are a large group of mysterious obligate intracellular eukaryotic parasites. The microsporidian spore can survive in the absence of nutrients for years under harsh conditions and germinate within seconds under the stimulation of environmental changes like pH and ions. During germination, microsporidia experience an increase in intrasporal osmotic pressure, which leads to an influx of water into the spore, followed by swelling of the polaroplasts and posterior vacuole, which eventually fires the polar filament (PF). Infectious sporoplasm was transported through the extruded polar tube (PT) and delivered into the host cell. Despite much that has been learned about the germination of microsporidia, there are still several major questions that remain unanswered, including: (i) There is still a lack of knowledge about the signaling pathways involved in spore germination. (ii) The germination of spores is not well understood in terms of its specific energetics. (iii) Limited understanding of how spores germinate and how the nucleus and membranes are rearranged during germination. (iv) Only a few proteins in the invasion organelles have been identified; many more are likely undiscovered. This review summarizes the major resolved and unresolved issues concerning the process of microsporidian spore germination.

High Prevalence of Microsporidia in the North African Hedgehog (Atelerix algirus) in the Canary Islands, Spain

Microsporidia are unicellular eukaryotic obligate intracellular parasites with a wide range of hosts reported worldwide; however, little is known about the epidemiological data on microsporidia infection in animals from the Canary Islands. Since data on microsporidia infection in hedgehog species are scarce, the aim of this study was to analyze the presence and identity of microsporidia in a group of North African hedgehogs (Atelerix algirus) using microscopic and molecular methods. From December 2020 to September 2021, a total of 36 fecal samples were collected from naturally deceased hedgehogs from Tenerife and Gran Canaria. All samples showed spore-compatible structures (100%; 36/36) under microscopic analysis, of which 61.1% (22/36) were amplified via the nested-polymerase chain reaction (PCR) targeting the partial sequence of the 16S rRNA gene, the internal transcribed spacer (ITS) region, and the partial sequence of the 5.8S rRNA gene. After Sanger sequencing and ITS analysis, Enterocytozoon bieneusi was detected in 47.2% (17/36) of the samples, identifying two novel genotypes (AAE1 and AAE2), followed by the detection of an undetermined species in 8.3% (3/36) and Encephalitozoon cuniculi genotype I in 5.6% (2/36) of the samples. This study constitutes the first report of microsporidia species in Atelerix algirus worldwide, highlighting the high prevalence of zoonotic species.

pathology, epidemiology, and phylogenyof mussel egg disease due to the microsporidianSteinhausia mytilovum(Field, 1924)in the Mediterranean mussel (Mytilus galloprovincialis)

Microsporidia are well known fungal pathogens of aquatic animals. However, the taxonomy of microsporidia is generally poorly resolved, which has consequently constrained our understanding of their pathology and epidemiology in marine animals. To date, microsporidia have been reported in both bivalves and gastropods, and microsporidia from mollusks have been classified in different genera. Despite ongoing work to better describe these genera, including detailed microscopic and ultrastructural images, so far we lack information on microsporidian phylogeny and pathogenicity of species within these genera. Here we investigate the microsporidian parasite Steinhausia mytilovum associated with the mussel, Mytilus galloprovincialis, in natural beds and farms along coast of southern Italy. A survey of M. galloprovincialis was conducted in 13 mussel farms and one natural bed between 2009 and 2020. We found the presence of S. mytilovum in 10 of the investigated farms, with a prevalence ranging between 14-100% of female mussels, depending on the population and season in which they were sampled. The parasite developed in the oocytes within a sporophorous vesicle (SV) where it produced 1-3 spores per cell, both in the cytoplasm and in the nucleus. Stenhausia mytilovum elicited an infiltrative (24.8%) or a strong capsular inflammatory response (43.4%) at gonadal follicles and surrounding vesicular connective tissue, in some cases accompanied by gonadal atresia (24.8%), leading to loss of gonadal architecture. In 7% of cases no reaction was observed. Ultrastructural observations revealed a mitochondrial re-organization to interact with all the phases of parasite development; the mitochondria were arranged outside the parasitophorous vesicle (PV) or directly interacting with the spore inside vesicle. There are five taxonomic clades of microsporidians as identified by SSU ribosomal gene sequence data. Maximum likelihood analysis assigned S. mytilovum within the Clade IV, defined as the Class Terresporidia, with closest genetic relationship (83.6% identity) to an undetermined invertebrate ovarian microsporidian. The constant presence, prevalence, and severity of S. mytilovum in coastline populations of M. galloprovincialis populations in southern Italy may indirectly reflect immunocompetence at both individual and population levels.

A mouse ear skin model to study the dynamics of innate immune responses against the microsporidian Encephalitozoon cuniculi

Microsporidia are obligate intracellular parasites related to fungi that cause severe infections in immunocompromised individuals. Encephalitozoon cuniculi is a microsporidian species capable of infecting mammals, including human and rodents. In response to microsporidian infection, innate immune system serves as the first line of defense and allows a partial clearance of the parasite via the innate immune cells, namely macrophages, neutrophils, dendritic cells, and Natural Killer cells. According to the literature, microsporidia bypass this response in vitro by modulating the response of macrophages. In order to study host-parasites interactions in vivo, we developed a model using the mouse ear pinna in combination with an intravital imaging approach. Fluorescent E. cuniculi spores were inoculated into the skin tissue to follow for the first time in real time in an in vivo model the recruitment dynamics of EGFP + phagocytic cells in response to the parasite. The results show that parasites induce an important inflammatory recruitment of phagocytes, with alterations of their motility properties (speed, displacement length, straightness). This cellular response persists in the injection zone, with spores detected inside the phagocytes up to 72 h post-infection. Immunostainings performed on ear tissue cryosections evoke the presence of developing infectious foci from 5 days post-infection, in favor of parasite proliferation in this tissue. Overall, the newly set up mice ear pinna model will increase our understanding of the immunobiology of microsporidia and in particular, to know how they can bypass and hijack the host immune system of an immunocompetent or immunosuppressed host.

Microsporidian Infection in Mosquitoes (Culicidae) Is Associated with Gut Microbiome Composition and Predicted Gut Microbiome Functional Content

The animal gut microbiota consist of many different microorganisms, mainly bacteria, but archaea, fungi, protozoans, and viruses may also be present. This complex and dynamic community of microorganisms may change during parasitic infection. In the present study, we investigated the effect of the presence of microsporidians on the composition of the mosquito gut microbiota and linked some microbiome taxa and functionalities to infections caused by these parasites. We characterised bacterial communities of 188 mosquito females, of which 108 were positive for microsporidian DNA. To assess how bacterial communities change during microsporidian infection, microbiome structures were identified using 16S rRNA microbial profiling. In total, we identified 46 families and four higher taxa, of which Comamonadaceae, Enterobacteriaceae, Flavobacteriaceae and Pseudomonadaceae were the most abundant mosquito-associated bacterial families. Our data suggest that the mosquito gut microbial composition varies among host species. In addition, we found a correlation between the microbiome composition and the presence of microsporidians. The prediction of metagenome functional content from the 16S rRNA gene sequencing suggests that microsporidian infection is characterised by some bacterial species capable of specific metabolic functions, especially the biosynthesis of ansamycins and vancomycin antibiotics and the pentose phosphate pathway. Moreover, we detected a positive correlation between the presence of microsporidian DNA and bacteria belonging to Spiroplasmataceae and Leuconostocaceae, each represented by a single species, Spiroplasma sp. PL03 and Weissella cf. viridescens, respectively. Additionally, W. cf. viridescens was observed only in microsporidian-infected mosquitoes. More extensive research, including intensive and varied host sampling, as well as determination of metabolic activities based on quantitative methods, should be carried out to confirm our results.

PvML1 suppresses bacterial infection by recognizing LPS and regulating AMP expression in shrimp

Toll and Toll-like receptors (TLRs) play essential roles in the innate immunity of Drosophila and mammals. Recent studies have revealed the presence of Toll-mediated immune signaling pathways in shrimp. However, the recognition and activation mechanism of Toll signaling pathways in crustaceans remain poorly understood due to the absence of key recognition molecules, such as peptidoglycan recognition proteins. Here, a novel MD2-related lipid-recognition (ML) member named PvML1 was characterized in Penaeus vannamei. We found that PvML1 shared a similar 3D structure with human MD2 that could specifically recognize lipopolysaccharides (LPS) participating in LPS-mediated TLR4 signaling. PvML1 was highly expressed in hemocytes and remarkably upregulated after Vibrio parahemolyticus challenge. Furthermore, the binding and agglutinating assays showed that PvML1 possessed strong binding activities to LPS and its key portion lipid A as well as Vibrio cells, and the binding of PvML1 with bacterial cells led to the agglutination of bacteria, suggesting PvML1 may act as a potential pathogen recognition protein upon interaction with LPS. Besides, coating V. parahemolyticus with recombinant PvML1 promoted bacterial clearance in vivo and increased the survival rate of bacterium-challenged shrimp. This result was further confirmed by RNAi experiments. The knockdown of PvML1 remarkably suppressed the clearance of bacteria in hemolymph and decreased the survival rate of infected shrimp. Meanwhile, the silencing of PvML1 severely impaired the expression of a few antimicrobial peptides (AMPs). These results demonstrated the significant correlation of bacterial clearance mediated by PvML1 with the AMP expression. Interestingly, we found that PvML1 interacted with the extracellular region of PvToll2, which had been previously shown to participate in bacterial clearance by regulating AMP expression. Taken together, the proposed antibacterial model mediated by PvML1 might be described as follows. PvML1 acted as a potential recognition receptor for Gram-negative bacteria by binding to LPS, and then it activated PvToll2-mediated signaling pathway by interacting with PvToll2 to eliminate invading bacteria through producing specific AMPs. This study provided new insights into the recognition and activation mechanism of Toll signaling pathways of invertebrates and the defense functions of ML members.

Effect of amide protoporphyrin derivatives on immune response in Apis mellifera

The intracellular microsporidian parasite Nosema ceranae is known to compromise bee health by induction of energetic stress and downregulation of the immune system. Porphyrins are candidate therapeutic agents for controlling Nosema infection without adverse effects on honeybees. In the present work, the impact of two protoporphyrin IX derivatives, i.e. PP[Asp]2 and PP[Lys]2, on Apis mellifera humoral immune response has been investigated in laboratory conditions in non-infected and N. ceranae-infected honeybees. Fluorescence spectroscopy analysis of hemolymph showed for the first time that porphyrin molecules penetrate into the hemocoel of honeybees. Phenoloxidase (PO) activity and the expression of genes encoding antimicrobial peptides (AMPs: abaecin, defensin, and hymenoptaecin) were assessed. Porphyrins significantly increased the phenoloxidase activity in healthy honeybees but did not increase the expression of AMP genes. Compared with the control bees, the hemolymph of non-infected bees treated with porphyrins had an 11.3- and 6.1-fold higher level of PO activity after the 24- and 48-h porphyrin administration, respectively. Notably, there was a significant inverse correlation between the PO activity and the AMP gene expression level (r =  - 0.61696, p = 0.0143). The PO activity profile in the infected bees was completely opposite to that in the healthy bees (r =  - 0.5118, p = 0.000), which was related to the changing load of N. ceranae spores in the porphyrin treated-bees. On day 12 post-infection, the spore loads in the infected porphyrin-fed individuals significantly decreased by 74%, compared with the control bees. Our findings show involvement of the honeybee immune system in the porphyrin-based control of Nosema infection. This allows the infected bees to improve their lifespan considerably by choosing an optimal PO activity/AMP expression variant to cope with the varying level of N. ceranae infection.

Expression of anti-NbHK single-chain antibody in fusion with NSlmb enhances the resistance to Nosema bombycis in Sf9-III cells

Nosema bombycis is a destructive and specific intracellular parasite of silkworm, which is extremely harmful to the silkworm industry. N. bombycis is considered as a quarantine pathogen of sericulture because of its long incubation period and horizontal and vertical transmission. Herein, two single-chain antibodies targeting N. bombycis hexokinase (NbHK) were cloned and expressed in fusion with the N-terminal of Slmb (a Drosophila melanogaster FBP), which contains the F-box domain. Western blotting demonstrated that Sf9-III cells expressed NSlmb-scFv-7A and NSlmb-scFv-6H, which recognized native NbHK. Subsequently, the NbHK was degraded by host ubiquitination system. When challenged with N. bombycis, the transfected Sf9-III cells exhibited better resistance relative to the controls, demonstrating that NbHK is a prospective target for parasite controls and this approach represents a potential solution for constructing N. bombycis-resistant Bombyx mori.

A Novel Ig Domain-Containing C-Type Lectin Triggers the Intestine-Hemocyte Axis to Regulate Antibacterial Immunity in Crab

The C-type lectin family with the signature C-type lectin-like domain promotes antibacterial host defense within the animal kingdom. We examined the role of Chinese mitten crab, Eriocheir sinensis (H. Milne-Edwards) (Decapoda: Grapsidae) Ig domain-containing C-type lectin (EsIgLectin), a novel and poorly understood member of the C-type lectin family. EsIgLectin was expressed primarily by both hemocytes (E sinensis) and intestines, with significantly induced mRNA expression on intestinal or hemolymph bacterial infections. As a soluble protein, both its C-type lectin-like domain and the Ig domain were required for bacterial binding, bacterial agglutination, bacterial growth inhibition, and in vivo bacterial clearance. Polymeric EsIgLectin could be constructed via the disulfide bond in the Ig domain, significantly enhancing EsIgLectin antibacterial activity. EsIgLectin promoted bacterial phagocytosis in an Ig domain-dependent manner in hemocytes, while it controlled microbial homeostasis and protected against bacteria-induced inflammation in the intestine. Protein interaction studies revealed that the EsIgLectin Ig domain bound to the first Ig domain of the polymeric Ig receptor, which was essential for EsIgLectin-induced bacterial phagocytosis. The temporal sequence of cell interactions during intestinal inflammation is only beginning to be understood. In this article, we show that hemocyte-derived EsIgLectin entered the intestinal wall at the later phase of intestinal inflammation. Moreover, EsIgLectin protected the host against intestinal and hemolymph infections in a polymeric Ig receptor-dependent manner. Therefore, the EsIgLectin promoted bacterial clearance and protected against inflammatory disease through an independent or synergistic effect of hemocytes and intestines in invertebrates.

Early responses in Penaeus vannamei during experimental infection with Enterocytozoon hepatopenaei (EHP) spores by injection and oral routes

Hepatopancreatic microsporidiosis caused by Enterocytozoon hepatopenaei (EHP) is associated with severe production losses in Penaeus vannamei farming. Early responses in P. vannamei experimentally infected with EHP was assessed in this study by feeding infected hepatopancreatic tissue and by injecting purified EHP spores (∼1 × 10⁵ Spores/shrimp). Immune responses to EHP infection were assessed in the haemolymph by analysing the total haemocyte count (THC), superoxide dismutase (SOD) activity, prophenoloxidase activity (proPO), respiratory burst activity (RBA), catalase activity (CAT), lysozyme activity (LYS) and Toll gene expression in hepatopancreas at 0, 6, 12, 24, 36, 48, 60 and 72 h post-infection (hpi). Experimental infection with EHP resulted in a significant (p < 0.05) reduction in the immune parameters such THC, CAT and LYS at 6, 24 and 24 hpi respectively while there was a significant increase (p < 0.05) in the levels of SOD, proPO and RBA at 6 hpi. The expression of the Toll gene was significantly upregulated (p < 0.05) after experimental infection with EHP from 6 hpi. These findings on immune responses in P. vannamei during EHP infection will assist in the development of suitable management measures to reduce the negative impacts of EHP in P. vannamei farming. This is the first report on early responses in P. vannamei during EHP infection.

Phagocytosis Is the Sole Arm of Drosophila melanogaster Known Host Defenses That Provides Some Protection Against Microsporidia Infection

Microsporidia are obligate intracellular parasites able to infest specifically a large range of species, including insects. The knowledge about the biology of microsporidial infections remains confined to mostly descriptive studies, including molecular approaches such as transcriptomics or proteomics. Thus, functional data to understand insect host defenses are currently lacking. Here, we have undertaken a genetic analysis of known host defenses of the Drosophila melanogaster using an infection model whereby Tubulinosema ratisbonensis spores are directly injected in this insect. We find that phagocytosis does confer some protection in this infection model. In contrast, the systemic immune response, extracellular reactive oxygen species, thioester proteins, xenophagy, and intracellular antiviral response pathways do not appear to be involved in the resistance against this parasite. Unexpectedly, several genes such as PGRP-LE seem to promote this infection. The prophenol oxidases that mediate melanization have different functions; PPO1 presents a phenotype similar to that of PGRP-LE whereas that of PPO2 suggests a function in the resilience to infection. Similarly, eiger and Unpaired3, which encode two cytokines secreted by hemocytes display a resilience phenotype with a strong susceptibility to T. ratisbonensis.

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.

Fungi of entomopathogenic potential in Chytridiomycota and Blastocladiomycota, and in fungal allies of the Oomycota and Microsporidia

The relationship between entomopathogenic fungi and their insect hosts is a classic example of the co-evolutionary arms race between pathogen and target host. The present review describes the entomopathogenic potential of Chytridiomycota and Blastocladiomycota fungi, and two groups of fungal allies: Oomycota and Microsporidia. The Oomycota (water moulds) are considered as a model biological control agent of mosquito larvae. Due to their shared ecological and morphological similarities, they had long been considered a part of the fungal kingdom; however, phylogenetic studies have since placed this group within the Straminipila. The Microsporidia are parasites of economically-important insects, including grasshoppers, lady beetles, bumblebees, colorado potato beetles and honeybees. They have been found to display some fungal characteristics, and phylogenetic studies suggest that they are related to fungi, either as a basal branch or sister group. The Blastocladiomycota and Chytridiomycota, named the lower fungi, historically were described together; however, molecular phylogenetic and ultrastructural research has classified them in their own phylum. They are considered parasites of ants, and of the larval stages of black flies, mosquitoes and scale insects.

Transcriptome analysis of pacific white shrimp (Penaeus vannamei) intestines and hepatopancreas in response to Enterocytozoon hepatopenaei (EHP) infection

Penaeus vannamei is the most economically important species of shrimp cultured worldwide. Enterocytozoon hepatopenaei (EHP) is an emerging pathogen that severely affects the growth and development of shrimps. In this study, the transcriptome differences between EHP-infected and uninfected shrimp were investigated through next-generation sequencing. The unigenes were assembled with the reads from all the four libraries. The differentially expressed genes (DEGs) of intestines and hepatopancreas were analyzed. There were 2,884 DEGs in the intestines and 2,096 DEGs in the hepatopancreas. The GO and KEGG enrichment analysis indicated that DEGs were significantly enriched in signaling pathways associated with nutritional energy metabolism and mobilizing autoimmunity. Moreover, the results suggested the downregulation of key genes in energy synthesis pathways contributed greatly to shrimp growth retardation; the upregulation of immune-related genes enhanced the resistance of shrimp against EHP infection. This study provided identified genes and pathways associated with EHP infection revealing the molecular mechanisms of growth retardation.

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.

Pharmacokinetics of voriconazole and its alteration by Candida albicans infection in silkworms

Voriconazole (VRCZ) is a triazole antifungal agent used for the treatment and prophylaxis of invasive fungal infections. Therapeutic drug monitoring of VRCZ is widely applied clinically because of the large inter-individual variability that is generally observed in VRCZ exposure. The blood levels of VRCZ are increased during an underlying inflammatory reaction, which is associated with infections. Silkworms are useful experimental animals for evaluating the pharmacokinetics and toxicity of compounds. In this study, we investigated the pharmacokinetic parameters, such as elimination half-life, clearance, and distribution volume of VRCZ using silkworms. The pharmacokinetic parameters of VRCZ were determined based on the concentrations in silkworm hemolymph after injection of VRCZ. The elimination half-life of VRCZ in silkworms was found to be similar to that observed in humans. In addition, we assessed the impact of Candida albicans infection on VRCZ concentrations in a silkworm infection model. The VRCZ concentration at 12 h after injection in the Candida albicans-infected group was significantly higher than that in the non-infected group. In the silkworm infection model, we were able to reproduce the relationship between inflammation and VRCZ blood concentrations, as observed in humans. We demonstrate that silkworms can be an effective alternative model animal for studying the pharmacokinetics of VRCZ. We also show that silkworms can be used to indicate essential infection and inflammation-based pharmacokinetic variations in VRCZ, which is usually observed in the clinic.

Infection effects of the new microsporidian species Tubulinosema suzukii on its host Drosophila suzukii

Microsporidian infections of insects are important natural constraints of population growth, often reducing lifespan, fecundity and fertility of the infected host. The recently discovered Tubulinosema suzukii infects Drosophila suzukii (spotted wing drosophila, SWD), an invasive pest of many fruit crops in North America and Europe. In laboratory tests, fitness effects on larval and adult stages were explored. High level infection after larval treatment caused up to 70% pupal mortality, a decreased lifespan and a 70% reduced oviposition of emerging adults in biparental infection clusters. A shift to higher proportion of female offspring compared to controls suggested a potential parthenogenetic effect after microsporidian infection. A clear sex-linkage of effects was noted; females were specifically impaired, as concluded from fecundity tests with only infected female parents. Additive effects were noted when both parental sexes were infected, whereas least effects were found with only infected male parents, though survival of males was most negatively affected if they were fed with T. suzukii spores in the adult stage. Although most negative effects on fitness parameters were revealed after larval treatment, infection of offspring was never higher than 4%, suggesting limited vertical transmission. For that reason, a self-reliant spread in natural SWD populations would probably only occur by spore release from cadavers or frass.

Characterization of a Murine Model for Encephalitozoon hellem Infection after Dexamethasone Immunosuppression

BACKGROUND

Encephalitozoon hellem (E. hellem) belongs to a group of opportunistic pathogens called microsporidia. Microsporidia infection symptoms vary and include diarrhea, ocular disorders and systemic inflammations. Traditionally, immunodeficient animals were used to study microsporidia infection. To overcome the difficulties in maintenance and operation using immunodeficient mice, and to better mimic natural occurring microsporidia infection, this study aims to develop a pharmacologically immunosuppressed murine model of E. hellem infection.

METHODS

Wild-type C57BL/6 mice were immunosuppressed with dexamethasone (Dex) and then E. hellem spores were inoculated into the mice intraperitoneally. Control groups were the Dex-immunosuppressed but noninoculated mice, and the Dex-immunosuppressed then lipopolysaccharide (LPS)-treated mice. Mice body weights were monitored and all animals were sacrificed at the 15th day after inoculation. Tissue fragments and immune cells were collected and processed.

RESULTS

Histopathological analysis demonstrated that E. hellem inoculation resulted in a disseminated nonlethal infection. Interestingly, E. hellem infection desensitized the innate immunity of the host, as shown by cytokine expressions and dendritic cell maturation. We also found that E. hellem infection greatly altered the composition of host gut microbiota. (4) Conclusions: Dex-immunosuppressed mice provide a useful tool for study microsporidiosis and the interactions between microsporidia and host immunity.

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.

Enterospora nucleophila (Microsporidia) in Gilthead Sea Bream (Sparus aurata): Pathological Effects and Cellular Immune Response in Natural Infections

Enterospora nucleophila is a microsporidian responsible for an emaciative disease in gilthead sea bream (Sparus aurata). Its intranuclear development and the lack of in vitro and in vivo models hinder its research. This study investigated the associated lesions, its detection by quantitative polymerase chain reaction, and the cellular immune response of naturally infected fish. The intensity of infection in the intestine was correlated with stunted growth and reduced body condition. At the beginning of the outbreaks, infection prevalence was highest in intestine and stomach, and in subsequent months, the prevalence decreased in the intestine and increased in hematopoietic organs and stomach. In heavy infections, the intestine had histologic lesions of enterocyte hypercellularity and proliferation of rodlet cells. Infected enterocytes had E. nucleophila spores in the cytoplasm, and a pyknotic nucleus, karyorhexis or karyolysis. Lymphocytes were present at the base of the mucosa, and eosinophilic granule cells were located between the enterocytes. In intestinal submucosa, macrophage aggregates containing spores were surrounded by lymphocytes and granulocytes, with submucosal infiltration of granulocytes. Macrophage aggregates appeared to develop into granulomata with necrotic areas containing parasite remnants. Immunohistochemistry revealed mast cells as the main type of granulocyte involved. Abundant IgM⁺ and IgT⁺ cells were identified by in situ hybridization in the submucosa when intracytoplasmic stages were present. This study describes the lesions of E. nucleophila in gilthead sea bream, an important aquaculture species.

A novel WSSV responsive plasma protein from Litopenaeus vannamei contributes to hemocytes anti-apoptosis

Litopenaeus vannamei, as an important marine aquaculture species, has attracted more and more attentions in past several years. More recently people got its genome fine mapping, which unveiled a gene treasure. In this study, we have identified a novel trypsin-like protein which came from previous WSSV-infected shrimp plasma iTRAQ data. This protein is a 39 kDa protein with 363 amino acids. It contains a conserved trypsin-domain and could be strongly induced with WSSV infection. Interestingly, knockdown of this protein made shrimps vulnerable to WSSV infection. Further exploration unveiled that this fragility was probably due to the fact that knockdown of this protein could cause shrimp hemocytes apoptosis, which indicated that this protein played key roles in preventing shrimp hemocytes from apoptosis. To further explore how LvTLAP protected shrimp hemocytes from apoptosis, GST pull down assay was applied to screen LvTLAP interacting protein in shrimp plasma. L. vannamei growth and transformation-dependent-like protein (LvGTD-like protein) was identified as a LvTLAP interacting protein, which played proapoptotic roles in cells. Thus, a possible explanation for LvTLAP anti-apoptosis activity was that this protein could block LvGTD-like protein proapoptotic activity to protect shrimp hemocytes from death. In general, our study has uncovered a novel WSSV responsive shrimp plasma protein, which played key roles in shrimp hemocytes anti-apoptosis and shrimp against WSSV infection.

Invasion of Host Cells by Microsporidia

Microsporidia are found worldwide and both vertebrates and invertebrates can serve as hosts for these organisms. While microsporidiosis in humans can occur in both immune competent and immune compromised hosts, it has most often been seen in the immune suppressed population, e.g., patients with advanced HIV infection, patients who have had organ transplantation, those undergoing chemotherapy, or patients using other immune suppressive agents. Infection can be associated with either focal infection in a specific organ (e.g., keratoconjunctivitis, cerebritis, or hepatitis) or with disseminated disease. The most common presentation of microsporidiosis being gastrointestinal infection with chronic diarrhea and wasting syndrome. In the setting of advanced HIV infection or other cases of profound immune deficiency microsporidiosis can be extremely debilitating and carries a significant mortality risk. Microsporidia are transmitted as spores which invade host cells by a specialized invasion apparatus the polar tube (PT). This review summarizes recent studies that have provided information on the composition of the spore wall and PT, as well as insights into the mechanism of invasion and interaction of the PT and spore wall with host cells during infection.

Laser Tweezers Raman Spectroscopy (LTRS) to Detect Effects of Chlorine Dioxide on Individual Nosema bombycis Spores

The microsporidium Nosema bombycis (Nb) causes pebrine, a fatal disease in sericulture. Nb is effectively killed by chlorine dioxide (ClO₂); however, the precise killing mechanism remains unclear. We used laser tweezers Raman spectroscopy (LTRS) to monitor the action of ClO₂ on individual Nb spores in real time. Raman peaks of ClO₂ appeared in Nb spores, corresponding to decreased peaks of trehalose that gradually disappeared. A peak (1658 cm^-1) corresponding to the protein α-helix significantly weakened while that (1668 cm^-1) corresponding to irregular protein structures was enhanced; their intensities were negatively correlated in a certain time range and dependent on ClO₂ concentration. The intensities of peaks at 782 cm^-1 (nucleic acids) and 1004 cm^-1 (phenylalanine of protein) did not change evidently even under extremely high ClO₂ concentrations. Thus, ClO₂ rapidly permeates the Nb spore wall, changing the protein secondary structure to lose biological function and destroy permeability, causing trehalose to leak out. These effects are ClO₂ concentration-dependent, but no other obvious changes to biomacromolecules were detected. Single-cell analysis using LTRS is an effective method to monitor the action of chemical sporicides on microbes in real time, providing insight into the heterogeneity of cell stress resistance.

20-Hydroxyecdysone regulates the transcription of the lysozyme via Broad-Complex Z2 gene in silkworm, Bombyx mori

Broad-Complex Z2 (Br-C Z2) is an ecdysone inducible transcription factor that regulates physiological, innate immune and developmental events in insects. Here, we identified an orthologue of Br-C Z2 from silkworm, Bombyx mori (BmBr-C Z2) to study its involvement in immune responses. The quantitative real-time PCR analysis revealed that BmBr-C Z2 was expressed ubiquitously in all tested tissues under normal physiological conditions. Further, developmental profile displayed that BmBr-C Z2 expression was detectable in different developmental stages, however the gene's expression was highest in the molting and pre-pupal stages. Administration of 20-hydroxyecdysone (20E) enhanced the expression levels of BmBr-C Z2 in hemocytes. The challenge with pathogens and pathogen associated molecular patterns (PAMPs) also upregulated the mRNA levels of BmBr-C Z2 in hemocytes when compared with the control. By contrast, the ectopic expression of BmBr-C Z2 remarkably increased the production of antimicrobial peptides, while the knock-down of this gene by double stranded RNA decreased their production. Dual-luciferase assay exhibited that BmBr-C Z2 induced the expression of lysozyme by directly binding to its promoter region. The treatment of Escherichia coli following the knock-down of BmBr-C Z2 strongly reduced the survival rate of silkworm larvae. These results suggest that BmBr-C Z2 plays an important biological role in the innate immune responses of silkworm by regulating immune-related genes.

Host Age Effects in Invertebrates: Epidemiological, Ecological, and Evolutionary Implications

In most species, variation in age among individuals is the strongest and most visible form of phenotypic variation. Individual-level age effects on disease traits, caused by differences in the age at exposure of the host or its parents, have been widely documented in invertebrates. They can influence diverse traits, such as host susceptibility, virulence, parasite reproduction and further transmission, and may cascade to the population level, influencing disease prevalence and within-host competition. Here, I summarize what is known about the relationship between individual-level age/stage effects and infectious disease in invertebrates. I also attempt to link age effects to the theory of aging (senescence), and highlight the importance of population age structure to disease epidemiology and evolution. I conclude by identifying gaps in our understanding of individual- and population-level age effects in invertebrates. As the age structure of populations varies across space and time, age effects have strong epidemiological, ecological, and evolutionary implications for explaining variation in infectious diseases of invertebrates.

Rapid detection of Bombyx mori bidensovirus by loop-mediated isothermal amplification based lateral flow dipstick assay for field applications

Bombyx mori bidensovirus (BmBDV), is the only bipartite single-stranded DNA (ssDNA) insect virus reported to date. BmBDV causes fatal flacherie disease in silkworm, resulting in large economic losses to sericulture. We developed a loop-mediated isothermal amplification with lateral flow dipstick (LAMP-LFD) method that can successfully and rapidly detect BmBDV DNA with a low limit of detection (5 fg, 400 copies of the BmBDV genome). The method was evaluated and improved for direct field diagnosis using silkworm faeces. In the field, the actual limit of detection was ∼50 fg (4000 copies of the BmBDV genome). The results demonstrated that, compared with traditional methods for BmBDV detection, our new LAMP-LFD method was much more rapid, sensitive and cost-effective, with less dependence on equipment, making it easier to use. The method has potential to be translated into a new diagnostic product for field applications in the sericulture industry.

Two novel serine proteases from Scylla paramamosain involved in the synthesis of anti-lipopolysaccharide factors and activation of prophenoloxidase system

Serine proteases (SPs) are important in various immune responses, including prophenoloxidase (proPO) activation, antimicrobial peptides (AMPs) synthesis, and hemolymph coagulation in invertebrates. In this study, SP3 and SP5 of mud crab (Scylla paramamosain) were studied. SP3 and SP5 were expressed in all examined tissues (mainly in hemocytes), and are associated with the immune responses of mud crab to Vibrio parahemolyticus and Staphylococcus aureus, as well as interacted with TRAF6, and are involved in the activation of anti-lipopolysaccharide factors (ALFs) probably through the TLR/NF-κB pathway. Depletion of SP3 inhibited the expression of ALF1, ALF2, ALF3, and ALF6, while knockdown of SP5 significantly decreased ALF5, and ALF6. Furthermore, both SP5 and TRAF6 regulated the PO activity in the hemolymph of mud crab. Overexpression assay showed that both SP3 and SP5 could enhance the promoter activities of ALFs in mud crab. Taken together, the results of this study indicate that SP3 and SP5 might play important roles in the immune system of mud crab against pathogen invasion.