Role of sulfated glycans in adherence of the microsporidian Encephalitozoon intestinalis to host cells in vitro

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.

New insights into Microsporidia polar tube function and invasion mechanism

Microsporidia comprise a large phylum of single-cell and obligate intracellular parasites that can infect a wide range of invertebrate and vertebrate hosts including humans. These fungal-related parasites are characterized by a highly reduced genome, a strong energy dependence on their host, but also by their unique invasion organelle known as the polar tube which is coiled within the resistant spore. Upon appropriate environmental stimulation, the long hollow polar tube (ranging from 50 to 500 μm in length) is extruded at ultra-fast speeds (300 μm/s) from the spore acting as a harpoon-like organelle to transport and deliver the infectious material or sporoplasm into the host cell. To date, seven polar tube proteins (PTPs) with distinct localizations along the extruded polar tube have been described. For example, the specific location of PTP4 and PTP7 at the tip of the polar tube supports their role in interacting with cellular receptor(s). This chapter provides a brief overview on the current understanding of polar tube structure and dynamics of extrusion, primarily through recent advancements in cryo-tomography and 3D reconstruction. It also explores the various mechanisms used for host cell invasion. Finally, recent studies on the structure and maturation of sporoplasm and its moving through the tube are discussed.

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.

Heat-killed Malassezia pachydermatis suspension modulates the activity of macrophages challenged with Encephalitozoon cuniculi

Phagocytic responses are critical for effective host defense against opportunistic fungal pathogens, such as Encephalitozoon cuniculi, an obligate intracellular fungus that causes emerging encephalitozoonosis in humans and other animals. Malassezia has immunomodulatory effects and can modulate the production of pro- and anti-inflammatory cytokines via keratinocytes and human monocytes. In this study, we evaluated the modulatory effects of heat-killed Malassezia pachydermatis suspension on macrophages challenged with Encephalitozoon cuniculi. Macrophages were treated with heat-killed M. pachydermatis suspension before being infected with spores of E. cuniculi. The cultures were stained with calcofluor, and the spores, internalized or not, were counted to determine their phagocytic capacity and index (PC and PI, respectively). Microbicidal and phagocytic activities were evaluated by transmission electron microscopy (TEM). The untreated macrophages had higher PC and PI and number of phagocytosed spores than treated macrophages. However, TEM revealed that treated macrophages had higher microbicidal activity because there were few spores in different degrees of degeneration and amorphous materials in the phagocytic vacuoles. Macrophages treated with heat-killed M. pachydermatis suspension had lower PC and PI and incipient presence of E. cuniculi in phagosomes. Treated macrophages had a mixed pattern of cytokine release with Th1, Th2, and Th17 profiles, with emphasis on interleukin (IL)-10, IL-4, IL-17, IL-6, and interferon (IFN)-γ secretion, and particularly high production of anti-inflammatory cytokines. Our results suggest that treatment with heat-killed M. pachydermatis suspension increases the release of cytokines and decreases the phagocytic activity of macrophages challenged with E. cuniculi.

Generation of Resistance to Nosema bombycis (Dissociodihaplophasida: Nosematidae) by Degrading NbSWP12 Using the Ubiquitin-Proteasome Pathway in Sf9-III Cells

Nosema bombycis Naegeli (Dissociodihaplophasida: Nosematidae), an obligate intracellular parasite of the silkworm Bombyx mori, causes a devastating disease called pébrine. Every year pébrine will cause huge losses to the sericulture industry worldwide. Until now, there are no effective methods to inhibit the N. bombycis infection in silkworms. In this study, we first applied both the novel protein degradation Trim-Away technology and NSlmb (F-box domain-containing in the N-terminal part of supernumerary limbs from Drosophila melanogaster) to lepidopteran Sf9-III cells to check for specific degradation of a target protein in combination with a single-chain Fv fragment (scFv). Our results showed that the Trim-Away and NSlmb systems are both amenable to Sf9-III cells. We then created transgenic cell lines that overexpressed the protein degradation system and N. bombycis chimeric scFv targeting spore wall protein NbSWP12 and evaluated the effects of the insect transgenic cell lines on the proliferation of N. bombycis. Both methods could be applied to cell lines and both Trim-Away and NSlmb ubiquitin degradation systems effectively inhibited the proliferation of N. bombycis. Further, either of these degradation systems could be applied to individual silkworms through a transgenic platform, which would yield individual silkworms with high resistance to N. bombycis, thus greatly speeding up the process of acquiring resistant strains.

MULTI-STATE OCCUPANCY MODEL ESTIMATES PROBABILITY OF DETECTION OF AN AQUATIC PARASITE USING ENVIRONMENTAL DNA: PSEUDOLOMA NEUROPHILIA IN ZEBRAFISH AQUARIA

Detecting the presence of important parasites within a host and its environment is critical to understanding the dynamics that influence a pathogen's ability to persist, while accurate detection is also essential for the implementation of effective control strategies. Pseudoloma neurophilia is the most common pathogen reported in zebrafish (Danio rerio) research facilities. The only assays currently available for P. neurophilia are through lethal sampling, often requiring euthanasia of the entire population for accurate estimates of prevalence in small populations. We present a non-lethal screening method to detect P. neurophilia in tank water based on the detection of environmental DNA (eDNA) from this microsporidium, using a previously developed qPCR assay that was adapted to the digital PCR (dPCR) platform to complement current surveillance protocols. Using the generated dPCR data, a multi-state occupancy model was also implemented to predict the probability of detecting the microsporidium in tank water under different flow regimes and pathogen prevalence. The occupancy model revealed that samples collected in static conditions were more informative than samples collected from flow-through conditions, with a probability of detection at 80% and 47%, respectively. There was also a positive correlation between the frequency of detection in water and prevalence in fish based on qPCR.

Exopolysaccharides from Microalgae and Cyanobacteria: Diversity of Strains, Production Strategies, and Applications

Microalgae and cyanobacteria are photosynthetic organisms that can produce/accumulate biomolecules with industrial interest. Among these molecules, EPSs are macromolecular polysaccharidic compounds that present biological activities and physico-chemical properties, allowing to consider their valorization in diverse commercial markets, such as cosmetic, therapeutic, nutraceutic, or hydrocolloids areas. The number of microalgae and cyanobacteria strains described to produce such EPSs has increased in recent years as, among the 256 producing strains gathered in this review, 86 were published in the last 10 years (~33%). Moreover, with the rise of research on microalgae EPSs, a variety of monosaccharides compositions have been discovered, highlighting the versatility of these organisms. If some production strategies can be applied to increase EPS production yields, it appears that case by case studies are needed to promote EPS synthesis by a strain, as many responses exist. This paper proposes an up-to-date state of the art of the diversity of microalgae and cyanobacteria EPS-producing strains, associated to the variability of compositions. The strategies for the production and extraction of the polymers are also discussed. Finally, an overview of the biological activities and physico-chemical properties allow one to consider their use on several commercial markets.

Exploring the Diversity of Red Microalgae for Exopolysaccharide Production

Microalgae constitute a remarkable biological diversity but a limited number of them have been the object of study for their ability to produce exoplysaccharides (EPS). Among them, the red marine microalgae Porphyridium or Rhodella produce sulphated EPS, exhibiting some biological activities with potential interest in the pharmaceutical and cosmetic industries. EPS from Porphyridium and Rhodella being relatively similar in their composition, it has long been considered that all the red microalgae produced similar EPS and no attention was paid to other red microalgae. The objective of our work was then to explore the diversity of red microalgae for the production of EPS, focusing in this first step on the screening of the strains for their ability to produce EPS and preliminary structural characterization. The study was conducted with 11 microalgae strains belonging to the proteorhodophytina subphylum. All microalgae were able to produce EPS, released in the culture medium (strains belonging to Porphyridiophyceae and Rhodellophyceae classes) or remaining bound to the cells (strains from Stylonematophyceae class). The analysis of monosaccharides composition was found significantly different, with for instance high levels of glucuronic acids in the EPS from C. japonica and N. cyanea, but also strong differences in the sulphation degrees of polymers (between 1.2 and 28.7% eq. SO4).

Proteomic Analysis of Spore Surface Proteins and Characteristics of a Novel Spore Wall Protein and Biomarker, EhSWP3, from the Shrimp Microsporidium Enterocytozoon hepatopenaei (EHP)

Enterocytozoon hepatopenaei, a spore-forming and obligate intracellular microsporidium, mainly infects shrimp and results in growth retardation and body length variation, causing huge economic losses to the Asian shrimp aquaculture industry. However, the lack of a full understanding of the surface proteins of spores associated with host infection has hindered the development of technologies for the detection of EHP. In this study, the surface proteins of EHP spores were extracted using the improved SDS method, and 130 proteins were identified via LC-MS/MS analysis. Bioinformatic analysis revealed that these proteins were enriched in biological processes (67), cellular components (62), and molecular functions (71) based on GO terms. KEGG pathway analysis showed that 20 pathways, including the proteasome (eight proteins) and the fatty acid metabolism (15 proteins), were enriched. Among 15 high-abundance surface proteins (HASPs), EhSWP3 was identified as a novel spore wall protein (SWP), and was localized on the endospore of the EHP spores with an indirect immunofluorescence and immunoelectron microscopy assay. Polyclonal antibodies against EhSWP3 showed strong species specificity and high sensitivity to the hepatopancreas of EHP-infected shrimp. As a specific high-abundance protein, EhSWP3 is therefore a promising target for the development of immunoassay tools for EHP detection, and may play a crucial role in the invasion of EHP into the host.

An intestinally secreted host factor promotes microsporidia invasion of C. elegans

Microsporidia are ubiquitous obligate intracellular pathogens of animals. These parasites often infect hosts through an oral route, but little is known about the function of host intestinal proteins that facilitate microsporidia invasion. To identify such factors necessary for infection by Nematocida parisii, a natural microsporidian pathogen of Caenorhabditis elegans, we performed a forward genetic screen to identify mutant animals that have a Fitness Advantage with Nematocida (Fawn). We isolated four fawn mutants that are resistant to Nematocida infection and contain mutations in T14E8.4, which we renamed aaim-1 (Antibacterial and Aids invasion by Microsporidia). Expression of AAIM-1 in the intestine of aaim-1 animals restores N. parisii infectivity and this rescue of infectivity is dependent upon AAIM-1 secretion. N. parisii spores in aaim-1 animals are improperly oriented in the intestinal lumen, leading to reduced levels of parasite invasion. Conversely, aaim-1 mutants display both increased colonization and susceptibility to the bacterial pathogen Pseudomonas aeruginosa and overexpression ofaaim-1 reduces P. aeruginosa colonization. Competitive fitness assays show that aaim-1 mutants are favored in the presence of N. parisii but disadvantaged on P. aeruginosa compared to wild-type animals. Together, this work demonstrates how microsporidia exploits a secreted protein to promote host invasion. Our results also suggest evolutionary trade-offs may exist to optimizing host defense against multiple classes of pathogens.

The Function and Structure of the Microsporidia Polar Tube

Microsporidia are obligate intracellular pathogens that were initially identified about 160 years ago. Current phylogenetic analysis suggests that they are grouped with Cryptomycota as a basal branch or sister group to the fungi. Microsporidia are found worldwide and can infect a wide range of animals from invertebrates to vertebrates, including humans. They are responsible for a variety of diseases once thought to be restricted to immunocompromised patients but also occur in immunocompetent individuals. The small oval spore containing a coiled polar filament, which is part of the extrusion and invasion apparatus that transfers the infective sporoplasm to a new host, is a defining characteristic of all microsporidia. When the spore becomes activated, the polar filament uncoils and undergoes a rapid transition into a hollow tube that will transport the sporoplasm into a new cell. The polar tube has the ability to increase its diameter from approximately 100 nm to over 600 nm to accommodate the passage of an intact sporoplasm and penetrate the plasmalemma of the new host cell. During this process, various polar tube proteins appear to be involved in polar tube attachment to host cell and can interact with host proteins. These various interactions act to promote host cell infection.

Ricin B lectin-like proteins of the microsporidian Encephalitozoon cuniculi and Anncaliia algerae are involved in host-cell invasion

Microsporidia are obligate intracellular pathogens capable of infecting a wide variety of hosts ranging from invertebrates to vertebrates. The infection process requires a step of prior adherence of Microsporidia to the surface of host cells. A few studies demonstrated the involvement of proteins containing a ricin-B lectin (RBL) domain in parasite infection. In this study Anncalia algerae and Encephalitozoon cuniculi genomes were screened by bioinformatic analysis to identify proteins with an extracellular prediction and possessing RBL-type carbohydrate-binding domains, being both potentially relevant factors contributing to host cell adherence. Three proteins named AaRBLL-1 and AaRBLL-2 from A. algerae and EcRBLL-1 from E. cuniculi, were selected and comparative analysis of sequences suggested their belonging to a multigenic family, with a conserved structural RBL domain despite a significant amino acid sequence divergence. The production of recombinant proteins and antibodies against the three proteins allowed their subcellular localization on the spore wall and/or the polar tube. Adherence inhibition assays based on pre-treatments with recombinant proteins or antibodies highlighted the significant decrease of the proliferation of both E. cuniculi and A. algerae, strongly suggesting that these proteins are involved in the infection process.

Natural extracts as potential control agents for Nosema ceranae infection in honeybees, Apis mellifera

Nosema disease is one factor that can cause colony decline in honeybees (Apis mellifera L.) worldwide. Nosema ceranae has outcompeted Nosema apis in the Western honeybee (A. mellifera) which is its original host. Fumagilin is an effective antibiotic treatment to control Nosema infection but currently it is forbidden in many countries. In this study, 12 plant extracts were evaluated for their toxicity to adult bees and antimicrosporidian activity under laboratory and field conditions. N. ceranae-infected adult bees were fed ad libitum with 50% sucrose solution containing 1% and 5% (w/v) of each plant extract. Bee mortality in N. ceranae-infected groups fed with plant extracts was higher than that in the control group treated with fumagilin. The results demonstrated that 9 of 12 extracts had high antimicrosporidian activity against N. ceranae and their efficacies were comparable to fumagilin. Spore reduction in infected bees was 4-6 fold less after extract treatment. Following laboratory screening, Annona squamosa, Ocimum basilicum, Psidium guajava and Syzygium jambos were tested in honeybee colonies. Plant extracts of 2% concentration (w/v) inhibited the development of Nosema spores after 30 days of treatment. At the end of experiment (90 days), spores in the plant extract treated groups were lower than in group treated with fumagilin but there was no significant difference. Although, extracts tested in this study showed high toxicity to bee in laboratory cages, they did not show negative affects on bees under whole colony conditions. Therefore, the effectiveness of plant extracts tested in this study was notable and warrants further study as potential Nosema control agents in honey bees. Plant extracts would offer a non-antibiotic alternative for Nosema control and help reduce the overuse of antibiotics in livestock.

Effects of Agaricus bisporus Mushroom Extract on Honey Bees Infected with Nosema ceranae

Simple Summary

Nosema ceranae affects honey bee (Apis mellifera L.) causing nosemosis disease that often induces serious problems in apiculture. Antibiotic fumagillin is the only licenced treatment against nosemosis, but its effectiveness is questioned and its usage associated with risk of bee mortality and appearance of residues in bee products. In search for alternative treatment for the control of nosemosis, water crude extract of Agaricus bisporus was tested on bees in laboratory (cage) experiments. Bee survival and food consumption were monitored together with Nosema infection level and expression of five genes (abaecin, hymenoptaecin, defensin, apidaecin, and vitellogenin) were evaluated in bees sampled on days 7 and 15. Apart from the gene for defensin, the expression of all tested genes was up-regulated in bees supplemented with A. bisporus extract. Both anti-Nosema and immune protective effects of A. bisporus extract were observed when supplementation started at the moment of N. ceranae infection or preventively (before or simultaneously with the Nosema infection).

Abstract

Agaricus bisporus water crude extract was tested on honey bees for the first time. The first part of the cage experiment was set for selecting one concentration of the A. bisporus extract. Concentration of 200 µg/g was further tested in the second part of the experiment where bee survival and food consumption were monitored together with Nosema infection level and expression of five genes (abaecin, hymenoptaecin, defensin, apidaecin, and vitellogenin) that were evaluated in bees sampled on days 7 and 15. Survival rate of Nosema-infected bees was significantly greater in groups fed with A. bisporus-enriched syrup compared to those fed with a pure sucrose syrup. Besides, the anti-Nosema effect of A. bisporus extract was greatest when applied from the third day which coincides with the time of infection with N. ceranae. Daily food consumption did not differ between the groups indicating good acceptability and palatability of the extract. A. bisporus extract showed a stimulative effect on four out of five monitored genes. Both anti-Nosema and nutrigenomic effects of A. bisporus extract were observed when supplementation started at the moment of N. ceranae infection or preventively (before or simultaneously with the infection).

Microsporidiosis in Humans

Microsporidia are obligate intracellular pathogens identified ∼150 years ago as the cause of pébrine, an economically important infection in silkworms. There are about 220 genera and 1,700 species of microsporidia, which are classified based on their ultrastructural features, developmental cycle, host-parasite relationship, and molecular analysis. Phylogenetic analysis suggests that microsporidia are related to the fungi, being grouped with the Cryptomycota as a basal branch or sister group to the fungi. Microsporidia can be transmitted by food and water and are likely zoonotic, as they parasitize a wide range of invertebrate and vertebrate hosts. Infection in humans occurs in both immunocompetent and immunodeficient hosts, e.g., in patients with organ transplantation, patients with advanced human immunodeficiency virus (HIV) infection, and patients receiving immune modulatory therapy such as anti-tumor necrosis factor alpha antibody. Clusters of infections due to latent infection in transplanted organs have also been demonstrated. Gastrointestinal infection is the most common manifestation; however, microsporidia can infect virtually any organ system, and infection has resulted in keratitis, myositis, cholecystitis, sinusitis, and encephalitis. Both albendazole and fumagillin have efficacy for the treatment of various species of microsporidia; however, albendazole has limited efficacy for the treatment of Enterocytozoon bieneusi. In addition, immune restoration can lead to resolution of infection. While the prevalence rate of microsporidiosis in patients with AIDS has fallen in the United States, due to the widespread use of combination antiretroviral therapy (cART), infection continues to occur throughout the world and is still seen in the United States in the setting of cART if a low CD4 count persists.

Potential of Fumagillin and Agaricus blazei Mushroom Extract to Reduce Nosema ceranae in Honey Bees

Depending on the infection level and colony strength, Nosema ceranae, a microsporidian endoparasite of the honey bee may have significant consequences on the health, reproduction and productivity of bee colonies. Despite exerting some side effects, fumagillin is most often used for Nosema control. In this study, in a cage experiment, N. ceranae infected bees were treated with fumagillin or the extract of Agaricus blazei mushroom, a possible alternative for Nosema control. Bee survival, Nosema spore loads, the expression levels of immune-related genes and parameters of oxidative stress were observed. Fumagillin treatment showed a negative effect on monitored parameters when applied preventively to non-infected bees, while a noticeable anti-Nosema effect and protection from Nosema-induced immunosuppression and oxidative stress were proven in Nosema-infected bees. However, a protective effect of the natural A. blazei extract was detected, without any side effects but with immunostimulatory activity in the preventive application. The results of this research suggest the potential of A. blazei extract for Nosema control, which needs to be further investigated.

Advancement in our understanding of immune response against Encephalitozoon infection

Microsporidia are a group of obligate, intracellular, spore-forming eukaryotic pathogens, which predominantly infects immunocompromised individuals worldwide. Encephalitozoon spp. is one of the most prevalent microsporidia known to infect humans. Host immune system plays a major role in combating pathogens including Encephalitozoon spp. infecting humans. Both innate and adaptive arms of host immune system work together in combating Encephalitozoon infection. Researchers are conducting studies to elucidate the role of both arms of immune system against Encephalitozoon infection. In addition to cell-mediated adaptive immunity, role of innate immunity is also being highlighted in clearance of Encephalitozoon spp. from host body. Therefore, the current review will give a clear and consolidated update on the role of innate as well as adaptive immunity in protection against Encephalitozoon spp.

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.

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.

An Ultrastructural Study of the Extruded Polar Tube of Anncaliia algerae (Microsporidia)

All microsporidia share a unique, extracellular spore stage, containing the infective sporoplasm and the apparatus for initiating infection. The polar filament/polar tube when exiting the spore transports the sporoplasm through it into a host cell. While universal, these structures and processes have been enigmatic. This study utilized several types of microscopy, describing and extending our understanding of these structures and their functions. Cryogenically preserved polar tubes vary in diameter from 155 to over 200 nm, noticeably larger than fixed-sectioned or negatively stained samples. The polar tube surface is pleated and covered with fine fibrillar material that projects from the surface and is organized in clusters or tufts. These fibrils may be the sites of glycoproteins providing protection and aiding infectivity. The polar tube surface is ridged with 5-6 nm spacing between ridges, enabling the polar tube to rapidly increase its diameter to facilitate the passage of the various cargo including cylinders, sacs or vesicles filled with particulate material and the intact sporoplasm containing a diplokaryon. The lumen of the tube is lined with a membrane that facilitates this passage. Careful examination of the terminus of the tube indicates that it has a closed tip where the membranes for the terminal sac are located.

Natural variation in the roles of C. elegans autophagy components during microsporidia infection

Natural genetic variation can determine the outcome of an infection, and often reflects the co-evolutionary battle between hosts and pathogens. We previously found that a natural variant of the nematode Caenorhabditis elegans from Hawaii (HW) has increased resistance against natural microsporidian pathogens in the Nematocida genus, when compared to the standard laboratory strain of N2. In particular, HW animals can clear infection, while N2 animals cannot. In addition, HW animals have lower levels of initial colonization of Nematocida inside intestinal cells, compared to N2. Here we investigate how this natural variation in resistance relates to autophagy. We found that there is much better targeting of autophagy-related machinery to parasites under conditions where they are cleared. In particular, ubiquitin targeting to Nematocida cells correlates very well with their subsequent clearance in terms of timing, host strain and age, as well as species of Nematocida. Furthermore, clearance correlates with targeting of the LGG-2/LC3 autophagy protein to parasite cells, with HW animals having much more efficient targeting of LGG-2 to parasite cells than N2 animals. Surprisingly, however, we found that LGG-2 is not required to clear infection. Instead, we found that LGG-2/LC3 regulates Nematocida colonization inside intestinal cells. Interestingly, LGG-2/LC3 regulates intracellular colonization only in the HW strain, and not in N2. Altogether these results demonstrate that there is natural genetic variation in an LGG-2-dependent process that regulates microsporidia colonization inside intestinal cells, although not microsporidia clearance.

Microsporidia: Obligate Intracellular Pathogens Within the Fungal Kingdom

Microsporidia are obligate intracellular pathogens related to Fungi. These organisms have a unique invasion organelle, the polar tube, which upon appropriate environmental stimulation rapidly discharges out of the spore, pierces a host cell's membrane, and serves as a conduit for sporoplasm passage into the host cell. Phylogenetic analysis suggests that microsporidia are related to the Fungi, being either a basal branch or sister group. Despite the description of microsporidia over 150 years ago, we still lack an understanding of the mechanism of invasion, including the role of various polar tube proteins, spore wall proteins, and host cell proteins in the formation and function of the invasion synapse. Recent advances in ultrastructural techniques are helping to better define the formation and functioning of the invasion synapse. Over the past 2 decades, proteomic approaches have helped define polar tube proteins and spore wall proteins as well as the importance of posttranslational modifications such as glycosylation in the functioning of these proteins, but the absence of genetic techniques for the manipulation of microsporidia has hampered research on the function of these various proteins. The study of the mechanism of invasion should provide fundamental insights into the biology of these ubiquitous intracellular pathogens that can be integrated into studies aimed at treating or controlling microsporidiosis.

Identification, characterization and heparin binding capacity of a spore-wall, virulence protein from the shrimp microsporidian, Enterocytozoon hepatopenaei (EHP)

Background

The microsporidian Enterocytozoon hepatopenaei (EHP) is a spore-forming, intracellular parasite that causes an economically debilitating disease (hepatopancreatic microsporidiosis or HPM) in cultured shrimp. HPM is characterized by growth retardation and wide size variation that can result in economic loss for shrimp farmers. Currently, the infection mechanism of EHP in shrimp is poorly understood, especially at the level of host-parasite interaction. In other microsporidia, spore wall proteins have been reported to be involved in host cell recognition. For the host, heparin, a glycosaminoglycan (GAG) molecule found on cell surfaces, has been shown to be recognized by many parasites such as Plasmodium spp. and Leishmania spp.

Results

We identified and characterized the first spore wall protein of EHP (EhSWP1). EhSWP1 contains three heparin binding motifs (HBMs) at its N-terminus and a Bin-amphiphysin-Rvs-2 (BAR2) domain at its C-terminus. A phylogenetic analysis revealed that EhSWP1 is similar to an uncharacterized spore wall protein from Enterospora canceri. In a cohabitation bioassay using EHP-infected shrimp with naïve shrimp, the expression of EhSWP1 was detected by RT-PCR in the naïve test shrimp at 20 days after the start of cohabitation. Immunofluorescence analysis confirmed that EhSWP1 was localized in the walls of purified, mature spores. Subcellular localization by an immunoelectron assay revealed that EhSWP1 was distributed in both the endospore and exospore layers. An in vitro binding assay, a competition assay and mutagenesis studies revealed that EhSWP1 is a bona fide heparin binding protein.

Conclusions

Based on our results, we hypothesize that EhSWP1 is an important host-parasite interaction protein involved in tethering spores to host-cell-surface heparin during the process of infection.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2758-z) contains supplementary material, which is available to authorized users.

The roles of microsporidia spore wall proteins in the spore wall formation and polar tube anchorage to spore wall during development and infection processes

Microsporidia are highly specialized obligate intracellular, spore forming divergent fungi with a wide variety host range that includes most vertebrates and invertebrates. The resistant spores are surrounded by a rigid cell wall which consists of three layers: the electron-lucent chitin and protein inner endospore, the outer-electron-dense and mainly proteinaceous exospore and plasma membrane. Interestingly, microsporidia owns a special invasion organelle, called polar tube, coiled within the interior of the spore wall and attached to anchoring disk at the anterior end of spore. Spore wall and polar tube are the major apparatuses for mature spores adhering and infecting to the host cells. In this review, we summarize the research advances in spore wall proteins (SWPs) related to spore adherence and infection, and SWPs and deproteinated chitin spore coats (DCSCs) interaction associated with SWPs deposit processes and spore wall assembly. Furthermore, we highlight the SWPs-polar tube proteins (PTPs) interaction correlated to polar tube orderly orientation, arrangement and anchorage to anchoring disk. Based on results obtained, it is helpful to improve understanding of the spore wall assembly and polar tube orderly arrangement mechanisms and molecular pathogenesis of microsporidia infection. Also, such information will provide a basis for developing effective control strategies against microporidia.

A Novel Spore Wall Protein from Antonospora locustae (Microsporidia: Nosematidae) Contributes to Sporulation

Microsporidia are obligate intracellular parasites, existing in a wide variety of animal hosts. Here, we reported AlocSWP2, a novel protein identified from the spore wall of Antonospora locustae (formerly, Nosema locustae, and synonym, Paranosema locustae), containing four cysteines that are conserved among the homologues of several Microspodian pathogens in insects and mammals. AlocSWP2 was detected in the wall of mature spores via indirect immunofluorescence assay. In addition, immunocytochemistry localization experiments showed that the protein was observed in the wall of sporoblasts, sporonts, and meronts during sporulation within the host body, also in the wall of mature spores. AlocSWP2 was not detected in the fat body of infected locust until the 9th day after inoculating spores via RT‐PCR experiments. Furthermore, the survival percentage of infected locusts injected with dsRNA of AlocSWP2 on the 15th, 16th, and 17th days after inoculation with microsporidian were significantly higher than those of infected locusts without dsRNA treatment. Conversely, the amount of spores in locusts infected with A. locustae after treated with RNAi AlocSWP2 was significantly lower than those of infected locusts without RNAi of this gene. This novel spore wall protein from A. locustae may be involved in sporulation, thus contributing to host mortality.

A Nested PCR Assay to Avoid False Positive Detection of the Microsporidian Enterocytozoon hepatopenaei (EHP) in Environmental Samples in Shrimp Farms

Hepatopancreatic microsporidiosis (HPM) caused by Enterocytozoon hepatopenaei (EHP) is an important disease of cultivated shrimp. Heavy infections may lead to retarded growth and unprofitable harvests. Existing PCR detection methods target the EHP small subunit ribosomal RNA (SSU rRNA) gene (SSU-PCR). However, we discovered that they can give false positive test results due to cross reactivity of the SSU-PCR primers with DNA from closely related microsporidia that infect other aquatic organisms. This is problematic for investigating and monitoring EHP infection pathways. To overcome this problem, a sensitive and specific nested PCR method was developed for detection of the spore wall protein (SWP) gene of EHP (SWP-PCR). The new SWP-PCR method did not produce false positive results from closely related microsporidia. The first PCR step of the SWP-PCR method was 100 times (104 plasmid copies per reaction vial) more sensitive than that of the existing SSU-PCR method (106 copies) but sensitivity was equal for both in the nested step (10 copies). Since the hepatopancreas of cultivated shrimp is not currently known to be infected with microsporidia other than EHP, the SSU-PCR methods are still valid for analyzing hepatopancreatic samples despite the lower sensitivity than the SWP-PCR method. However, due to its greater specificity and sensitivity, we recommend that the SWP-PCR method be used to screen for EHP in feces, feed and environmental samples for potential EHP carriers.

Ricin-B-lectin enhances microsporidia Nosema bombycis infection in BmN cells from silkworm Bombyx mori

Nosema bombycis is an obligate intracellular parasitic fungus that utilizes a distinctive mechanism to infect Bombyx mori Spore germination can be used for host cell invasion; however, the detailed mechanism remains to be elucidated. The ricin-B-lectin (RBL) gene is significantly differentially regulated after N. bombycis spore germination, and NbRBL might play roles in spore germination and infection. In this study, the biological function of NbRBL was examined. Protein sequence analysis showed that NbRBL is a secreted protein that attaches to carbohydrates. The relative expression level of the NbRBL gene was low during the first 30 h post-infection (hpi) in BmN cells, and high expression was detected from 42 hpi. Gene cloning, prokaryotic expression, and antibody preparation for NbRBL were performed. NbRBL was detected in total and secreted proteins using western blot analysis. Subcellular localization analysis showed that NbRBL is an intracellular protein. Spore adherence and infection assays showed that NbRBL could enhance spore adhesion to BmN cells; the proliferative activities of BmN cells incubated with anti-NbRBL were higher than those in negative control groups after N. bombycis infection; and the treatment groups showed less damage from spore invasion. We therefore, propose that NbRBL is released during spore germination, enhances spore adhesion to BmN cells, and contributes to spore invasion.

Interaction and assembly of two novel proteins in the spore wall of the microsporidian species Nosema bombycis and their roles in adherence to and infection of host cells

Microsporidia are obligate intracellular parasites with rigid spore walls that protect against various environmental pressures. Despite an extensive description of the spore wall, little is known regarding the mechanism by which it is deposited or the role it plays in cell adhesion and infection. In this study, we report the identification and characterization of two novel spore wall proteins, SWP7 and SWP9, in the microsporidian species Nosema bombycis. SWP7 and SWP9 are mainly localized to the exospore and endospore of mature spores and the cytoplasm of sporonts, respectively. In addition, a portion of SWP9 is targeted to the spore wall of sporoblasts earlier than SWP7 is. Both SWP7 and SWP9 are specifically colocalized to the spore wall in mature spores. Furthermore, immunoprecipitation, far-Western blotting, unreduced SDS-PAGE, and yeast two-hybrid data demonstrated that SWP7 interacted with SWP9. The chitin binding assay showed that, within the total spore protein, SWP9 and SWP7 can bind to the deproteinated chitin spore coats (DCSCs) of N. bombycis. However, binding of the recombinant protein rSWP7-His to the DCSCs is dependent on the combination of rSWP9-glutathione S-transferase (GST) with the DCSCs. Finally, rSWP9-GST, anti-SWP9, and anti-SWP7 antibodies decreased spore adhesion and infection of the host cell. In conclusion, SWP7 and SWP9 may have important structural capacities and play significant roles in modulating host cell adherence and infection in vitro. A possible major function of SWP9 is as a scaffolding protein that supports other proteins (such as SWP7) that form the integrated spore wall of N. bombycis.

NbHSWP11, a microsporidia Nosema bombycis protein, localizing in the spore wall and membranes, reduces spore adherence to host cell BME

Microsporidia are obligate intracellular parasites, and a derivative of fungi, which harbor a rigid spore wall to resist adverse environmental pressures. The spore wall protein, which is thought to be the first and direct protein interacting with the host cell, may play a key role in the process of microsporidia infection. In this study, we report a protein, NbHSWP11, with a dnaJ domain. The protein also has 6 heparin-binding motifs which are known to interact with extracellular glycosaminoglycans. Syntenic analysis indicated that gene loci of Nbhswp11 are conserved and syntenic between Nosema bombycis and Nosema ceranae. Phylogenetic tree analysis showed that Nbhswp11 clusters with fungal dnaJ proteins and has 98% identity with an N. bombycis dnaJ protein. Nbhswp11 was transcribed throughout the entire life stages, and gradually increased during 1-7 days, in a silkworm that was infected by N. bombycis, as determined by reverse-transcription PCR (RT-PCR). The recombinant protein NbHSWP11 (rSWP11-HIS) was obtained and purified using gene cloning and prokaryotic expression. Western blotting analysis displayed NbHSWP11 expressed in the total mature spore proteins and spore coat proteins. Indirect immunofluorescence assay revealed NbHSWP11 located at the spore wall of mature spores and the spore coats. Furthermore, immune electron microscopy showed that NbHSWP11 localized in the cytoplasm of the sporont. Within the developmental process of N. bombycis, a portion of NbHSWP11 is targeted to the spore wall of sporoblasts and mature spores. However, most of NbHSWP11 distributes on the membraneous structures of the sporoblast and mature spore. In addition, using a host cell binding assay, native protein NbHSWP11 in the supernatant of total soluble mature spore proteins is shown to bind to the host cell BmE surface. Finally, an antibody blocking assay showed that purified rabbit antibody of NbHSWP11 inhibits spore adherence and decreases the adherence rate of spores by 20% compared to untreated spores. Collectively, the present results suggest that NbHSWP11 is involved in host cell adherence in vitro. Therefore NbHSWP11, which has a dnaJ domain, may modulate protein assembly, disassembly, and translocation in N. bombycis.

Early development and tissue distribution of Pseudoloma neurophilia in the zebrafish, Danio rerio

The early proliferative stages of the microsporidian parasite, Pseudoloma neurophilia were visualized in larval zebrafish, Danio rerio, using histological sections with a combination of an in situ hybridization probe specific to the P. neurophilia small-subunit ribosomal RNA gene, standard hematoxylin-eosin stain, and the Luna stain to visualize spores. Beginning at 5 d post fertilization, fish were exposed to P. neurophilia and examined at 12, 24, 36, 48, 72, 96, and 120 h post exposure (hpe). At 12 hpe, intact spores in the intestinal lumen and proliferative stages developing in the epithelial cells of the anterior intestine and the pharynx and within hepatocytes were observed. Proliferative stages were visualized in the pancreas and kidney at 36-48 hpe and in the spinal cord, eye, and skeletal muscle beginning at 72 hpe. The first spore stages of P. neurophilia were observed at 96 hpe in the pharyngeal epithelium, liver, spinal cord, and skeletal muscle. The parasite was only observed in the brain of larval fish at 120 hpe. The distribution of the early stages of P. neurophilia and the lack of mature spores until 96 hpe indicates that the parasite gains access to organs distant from the initial site of entry, likely by penetrating the intestinal wall with the polar tube.

Encephalitozoon intestinalis infection increases host cell mutation frequency

Background

Microsporidia are obligate intracellular opportunistic fungi that cause significant pathology in immunocompromised hosts. However, 11 percent of immunocompetent individuals in the general population are microsporidia-seropositive, indicating that severe immune suppression may not be a prerequisite for infection. Encephalitozoon intestinalis is transmitted in contaminated water and initially infects gastro-intestinal enterocytes, leading to diarrheal disease. This organism can also disseminate to many other organs. A recent report suggests that microsporidia can establish persistent infections, which anti-fungal treatment does not eradicate. Like other intracellular pathogens, microsporidia infection stresses the host cell and infected individuals have elevated hydrogen peroxide and free radical levels.

Findings

As oxidative stress can lead to DNA damage, we hypothesized that E. intestinalis-infection would increase host cell nuclear mutation rate. Embryo fibroblasts from Big Blue^TM transgenic mice were E. intestinalis-infected and host nuclear mutation frequency was determined by selection of temperature-sensitive c-II gene mutant λ phage. The host mutation frequency in E. intestinalis-infected cultures was 2.5-fold higher than that observed in either mock-infected cells or cells infected with UV-inactivated E. intestinalis spores.

Conclusions

These data provide the first evidence that microsporidia infection can directly increase host cellular mutation frequency. Additionally, some event in the microsporidia developmental cycle between host cell attachment and parasitophorous vacuole formation is required for the observed effect. As there is considerable evidence linking infection with other intracellular pathogens and cancer, future studies to dissect the mechanism by which E. intestinalis infection increases host mutation frequency are warranted.

Effect of intravenous or oral sodium chlorate administration on the fecal shedding of Escherichia coli in sheep

The effect of gavage or intravenous (i.v.) administration of sodium chlorate salts on the fecal shedding of generic Escherichia coli in wether lambs was studied. To this end, 9 lambs (27 ± 2.5 kg) were administered 150 mg NaClO3/kg BW by gavage or i.v. infusion in a crossover design with saline-dosed controls. The crossover design allowed each animal to receive each treatment during 1 of 3 trial periods, resulting in 9 observations for each treatment. Immediately before and subsequent to dosing, jugular blood and rectal fecal samples were collected at 4, 8, 16, 24, and 36 h. Endpoints measured were fecal generic E. coli concentrations, blood packed cell volume (PCV), blood methemoglobin concentration, and serum and fecal sodium chlorate concentrations. Sodium chlorate had no effects (P > 0.05) on blood PVC or methemoglobin. Fecal generic E. coli concentrations were decreased (P < 0.05) approximately 2 log units (99%) relative to controls 16 and 24 h after sodium chlorate infusion and 24 h after sodium chlorate gavage. Within and across time and treatment, fecal chlorate concentrations were highly variable for both gavage and i.v. lambs. Average fecal sodium chlorate concentrations never exceeded 100 µg/g and were typically less than 60 µg/g from 4 to 24 h after dosing. Times of maximal average fecal sodium chlorate concentration did not correspond with times of lowered average generic E. coli concentrations. Within route of administration, serum sodium chlorate concentrations were greatest (P < 0.01) 4 h after dosing; at the same time point, serum chlorate was greater (P< 0.01) in i.v.-dosed lambs than gavaged lambs but not at 16 or 24 h (P > 0.05). At 8 h, serum chlorate concentrations of gavaged lambs were greater (P < 0.05) than in i.v.-dosed lambs. Serum chlorate data are consistent with earlier studies indicating very rapid transfer of orally dosed chlorate to systemic circulation, and fecal chlorate data are consistent with earlier data showing the excretion of low to marginal concentrations of sodium chlorate in orally dosed animals. Efficacy of sodium chlorate at reducing fecal E. coli concentrations after i.v. infusion suggests that low concentrations of chlorate in gastrointestinal contents, delivered by biliary excretion, intestinal cell sloughing, or simple diffusion, are effective at reducing fecal E. coli levels. Alternatively, chlorate could be eliciting systemic effects that influence fecal E. coli populations.

Identification of a protein interacting with the spore wall protein SWP26 of Nosema bombycis in a cultured BmN cell line of silkworm

Nosema bombycis is a silkworm parasite that causes severe economic damage to sericulture worldwide. It is the first microsporidia to be described in the literature, and to date, very little molecular information is available regarding microsporidian physiology and their relationships with their hosts. Therefore, the interaction between the microsporidia N. bombycis and its host silkworm, Bombyx mori, was analyzed in this study. The microsporidian spore wall proteins (SWPs) play a specific role in spore adherence to host cells and recognition by the host during invasion. In this study, SWP26 fused with enhanced green fluorescence protein (EGFP) was expressed in BmN cells by using a Bac-to-Bac expression system. Subsequently, the turtle-like protein of B. mori (BmTLP) was determined to interact with SWP26 via the use of anti-EGFP microbeads. This interaction was then confirmed by yeast two-hybrid analysis. The BmTLP cDNA encodes a polypeptide of 447 amino acids that includes a putative signal peptide of 27 amino acid residues. In addition, the BmTLP protein contains 2 immunoglobulin (IG) domains and 2 IGc2-type domains, which is the typical domain structure of IG proteins. The results of this study indicated that SWP26 interacts with the IG-like protein BmTLP, which contributes to the infectivity of N. bombycis to its host silkworm.

Microsporidia and 'the art of living together'

Parasitism, aptly defined as one of the 'living-together' strategies (Trager, 1986), presents a dynamic system in which the parasite and its host are under evolutionary pressure to evolve new and specific adaptations, thus enabling the coexistence of the two closely interacting partners. Microsporidia are very frequently encountered obligatory intracellular protistan parasites that can infect both animals and some protists and are a consummate example of various aspects of the 'living-together' strategy. Microsporidia, relatives of fungi in the superkingdom Opisthokonta, belong to the relatively small group of parasites for which the host cell cytoplasm is the site of both reproduction and maturation. The structural and physiological reduction of their vegetative stage, together with the manipulation of host cell physiology, enables microsporidia to live in the cytosolic environment for most of their life cycle in a way resembling endocytobionts. The ability to form structurally complex spores and the invention and assembly of a unique injection mechanism enable microsporidia to disperse within host tissues and between host organisms, resulting in long-lasting infections. Microsporidia have adapted their genomes to the intracellular way of life, evolved strategies how to obtain nutrients directly from the host and how to manipulate not only the infected cells, but also the hosts themselves. The enormous variability of host organisms and their tissues provide microsporidian parasites a virtually limitless terrain for diversification and ecological expansion. This review attempts to present a general overview of microsporidia, emphasising some less known and/or more recently discovered facets of their biology.

SWP5, a spore wall protein, interacts with polar tube proteins in the parasitic microsporidian Nosema bombycis

Microsporidia are a group of eukaryotic intracellular parasites that infect almost all vertebrates and invertebrates. The microsporidian invasion process involves the extrusion of a unique polar tube into host cells. Both the spore wall and the polar tube play an important role in microsporidian pathogenesis. So far, five spore wall proteins (SWP1, SWP2, Enp1, Enp2, and EcCDA) from Encephalitozoon intestinalis and Encephalitozoon cuniculi and five spore wall proteins (SWP32, SWP30, SWP26, SWP25, and NbSWP5) from the silkworm pathogen Nosema bombycis have been identified. Here we report the identification and characterization of a spore wall protein (SWP5) with a molecular mass of 20.3 kDa in N. bombycis. This protein has low sequence similarity to other eukaryotic proteins. Immunolocalization analysis showed SWP5 localized to the exospore and the region of the polar tube in mature spores. Immunoprecipitation, mass spectrometry, and immunofluorescence analyses revealed that SWP5 interacts with the polar tube proteins PTP2 and PTP3. Anti-SWP5 serum pretreatment of mature spores significantly decreased their polar tube extrusion rate. Taken together, our results show that SWP5 is a spore wall protein localized to the spore wall and that it interacts with the polar tube, may play an important role in supporting the structural integrity of the spore wall, and potentially modulates the course of infection of N. bombycis.

Invasion and intracellular survival by protozoan parasites

Intracellular parasitism has arisen only a few times during the long ancestry of protozoan parasites including in diverse groups such as microsporidians, kinetoplastids, and apicomplexans. Strategies used to gain entry differ widely from injection (e.g. microsporidians), active penetration of the host cell (e.g. Toxoplasma), recruitment of lysosomes to a plasma membrane wound (e.g. Trypanosoma cruzi), to host cell-mediated phagocytosis (e.g. Leishmania). The resulting range of intracellular niches is equally diverse ranging from cytosolic (e.g. T. cruzi) to residing within a non-fusigenic vacuole (e.g. Toxoplasma, Encephalitozoon) or a modified phagolysosome (e.g. Leishmania). These lifestyle choices influence access to nutrients, interaction with host cell signaling pathways, and detection by pathogen recognition systems. As such, intracellular life requires a repertoire of adaptations to assure entry-exit from the cell, as well as to thwart innate immune mechanisms and prevent clearance. Elucidating these pathways at the cellular and molecular level may identify key steps that can be targeted to reduce parasite survival or augment immunologic responses and thereby prevent disease.

SWP25, a novel protein associated with the Nosema bombycis endospore

Microsporidia are eukaryotic, obligate intracellular, spore-forming parasites. The resistant spores, which harbor a rigid cell wall, are critical for their host-to-host transmission and persistence in the environment. The spore wall comprises two major layers: the exospore and the endospore. In Nosema bombycis, two spore wall proteins have been characterized--an endosporal protein, SWP30, and an exosporal protein, SWP32. Here, we report the identification of the third spore wall protein of N. bombycis, SWP25, the gene of which has no known homologue. SWP25 is predicted to posses a signal peptide and a heparin-binding motif. Immunoelectron microscopy analysis showed that this protein is localized to the endospore. This characterization of a new spore wall protein of N. bombycis may facilitate our investigation of the relationship between N. bombycis and its host, Bombyx mori.

Extreme reduction and compaction of microsporidian genomes

Microsporidia are fungi-related obligate intracellular parasites with a highly reduced and compact genome, as for Encephalitozoon species which harbor a genome smaller than 3 Mbp. Genome compaction is reflected by high gene density and, for larger microsporidian genomes, size variation is due to repeat elements that do not drastically affect gene density. Furthermore, these pathogens present strong host dependency illustrated by extensive gene loss. Such adaptations associated with genome compaction induced gene size reduction but also simplification of cellular processes such as transcription. Thus, microsporidia are excellent models for eukaryotic genome evolution and gene expression in the context of host-pathogen relationships.

A cell culture model for Nosema ceranae and Nosema apis allows new insights into the life cycle of these important honey bee-pathogenic microsporidia

The population of managed honey bees has been dramatically declining in the recent past in many regions of the world. Consensus now seems to be that pathogens and parasites (e.g. the ectoparasitic mite Varroa destructor, the microsporidium Nosema ceranae and viruses) play a major role in this demise. However, little is known about host-pathogen interactions for bee pathogens and attempts to develop novel strategies to combat bee diseases have been hampered by this gap in our knowledge. One reason for this dire situation is the complete lack of cell cultures for the propagation and study of bee pathogens. Here we present a cell culture model for two honey bee-pathogenic microsporidian species, Nosema apis and N. ceranae. Our cell culture system is based on a lepidopteran cell line, which proved to be susceptible to infection by both N. ceranae and N. apis and enabled us to illustrate the entire life cycle of these microsporidia. We observed hitherto undescribed spindle-shaped meronts and confirmed our findings in infected bees. Our cell culture model provides a previously unavailable means to explore the nature of interactions between the honey bee and its pathogen complex at a mechanistic level and will allow the development of novel treatment strategies.

Expression and Localization of an Hsp70 Protein in the Microsporidian Encephalitozoon cuniculi

Microsporidia spore surface proteins are an important, under investigated aspect of spore/host cell attachment and infection. For comparison analysis of surface proteins, we required an antibody control specific for an intracellular protein. An endoplasmic reticulum-associated heat shock protein 70 family member (Hsp70; ECU02_0100; "C1") was chosen for further analysis. DNA encoding the C1 hsp70 was amplified, cloned and used to heterologously express the C1 Hsp70 protein, and specific antiserum was generated. Two-dimensional Western blotting analysis showed that the purified antibodies were monospecific. Immunoelectron microscopy of developing and mature E. cuniculi spores revealed that the protein localized to internal structures and not to the spore surface. In spore adherence inhibition assays, the anti-C1 antibodies did not inhibit spore adherence to host cell surfaces, whereas antibodies to a known surface adhesin (EnP1) did so. In future studies, the antibodies to the 'C1' Hsp70 will be used to delineate spore surface protein expression.

Glycosylation of the major polar tube protein of Encephalitozoon cuniculi

To infect their host cells the Microsporidia use a unique invasion organelle, the polar tube complex. During infection, the organism is injected into the host cell through the hollow polar tube formed during spore germination. Currently, three proteins, PTP1, PTP2, and PTP3 have been identified by immunological and molecular techniques as being components of this structure. Genomic data suggests that Microsporidia are capable of O-linked, but not N-linked glycosylation as a post-translational protein modification. Cells were infected with Encephalitozoon cunicuili, labeled with radioactive mannose or glucosamine, and the polar tube proteins were examined for glycosylation. PTP1 was clearly demonstrated to be mannosylated consistent with 0-glycosylation. In addition, it was evident that several other proteins were mannosylated, but no labeling was seen with glucosamine. The observed post-translational mannosylation of PTP1 may be involved in the functional properties of the polar tube, including its adherence to host cells during penetration.