Microsporidia evolved from ancestral sexual fungi

Polyploidy is widespread in Microsporidia

Microsporidia are obligate intracellular eukaryotic parasites with an extremely broad host range. They have both economic and public health importance. Ploidy in microsporidia is variable, with a few species formally identified as diploid and one as polyploid. Given the increase in the number of studies sequencing microsporidian genomes, it is now possible to assess ploidy levels across all currently explored microsporidian diversity. We estimate ploidy for all microsporidian data sets available on the Sequence Read Archive using k-mer-based analyses, indicating that polyploidy is widespread in Microsporidia and that ploidy change is dynamic in the group. Using genome-wide heterozygosity estimates, we also show that polyploid microsporidian genomes are relatively homozygous, and we discuss the implications of these findings on the timing of polyploidization events and their origin.IMPORTANCEMicrosporidia are single-celled intracellular parasites, distantly related to fungi, that can infect a broad range of hosts, from humans all the way to protozoans. Exploiting the wealth of microsporidian genomic data available, we use k-mer-based analyses to assess ploidy status across the group. Understanding a genome's ploidy is crucial in order to assemble it effectively and may also be relevant for better understanding a parasite's behavior and life cycle. We show that tetraploidy is present in at least six species in Microsporidia and that these polyploidization events are likely to have occurred independently. We discuss why these findings may be paradoxical, given that Microsporidia, like other intracellular parasites, have extremely small, reduced genomes.

Aquaculture of Animal Species: Their Eukaryotic Parasites and the Control of Parasitic Infections

Parasites are very diverse and common in both natural populations and in stocks kept in aquacultural facilities. For most cultured species, there are important bacteria and viruses causing diseases, but eukaryotic parasites are also very important. We review the various combinations of aquacultured species and eukaryotic parasitic groups and discuss other problems associated with aquaculture such as eutrophication, zoonotic species, and invasive species, and we conclude that further development of aquaculture in a sustainable manner must include a holistic approach (One Health) where many factors (e.g., human health, food safety, animal health and welfare, environmental and biodiversity protection and marketability mechanisms, etc.) are considered.

3D reconstructions of parasite development and the intracellular niche of the microsporidian pathogen Encephalitozoon intestinalis

Microsporidia are an early-diverging group of fungal pathogens with a wide host range. Several microsporidian species cause opportunistic infections in humans that can be fatal. As obligate intracellular parasites with highly reduced genomes, microsporidia are dependent on host metabolites for successful replication and development. Our knowledge of microsporidian intracellular development remains rudimentary, and our understanding of the intracellular niche occupied by microsporidia has relied on 2D TEM images and light microscopy. Here, we use serial block-face scanning electron microscopy (SBF-SEM) to capture 3D snapshots of the human-infecting species, Encephalitozoon intestinalis, within host cells. We track E. intestinalis development through its life cycle, which allows us to propose a model for how its infection organelle, the polar tube, is assembled de novo in developing spores. 3D reconstructions of parasite-infected cells provide insights into the physical interactions between host cell organelles and parasitophorous vacuoles, which contain the developing parasites. The host cell mitochondrial network is substantially remodeled during E. intestinalis infection, leading to mitochondrial fragmentation. SBF-SEM analysis shows changes in mitochondrial morphology in infected cells, and live-cell imaging provides insights into mitochondrial dynamics during infection. Our data provide insights into parasite development, polar tube assembly, and microsporidia-induced host mitochondria remodeling.

Needles in fungal haystacks: Discovery of a putative a-factor pheromone and a unique mating strategy in the Leotiomycetes

The Leotiomycetes is a hugely diverse group of fungi, accommodating a wide variety of important plant and animal pathogens, ericoid mycorrhizal fungi, as well as producers of antibiotics. Despite their importance, the genetics of these fungi remain relatively understudied, particularly as they don't include model taxa. For example, sexual reproduction and the genetic mechanisms that underly this process are poorly understood in the Leotiomycetes. We exploited publicly available genomic and transcriptomic resources to identify genes of the mating-type locus and pheromone response pathway in an effort to characterize the mating strategies and behaviors of 124 Leotiomycete species. Our analyses identified a putative a-factor mating pheromone in these species. This significant finding represents the first identification of this gene in Pezizomycotina species outside of the Sordariomycetes. A unique mating strategy was also discovered in Lachnellula species that appear to have lost the need for the primary MAT1-1-1 protein. Ancestral state reconstruction enabled the identification of numerous transitions between homothallism and heterothallism in the Leotiomycetes and suggests a heterothallic ancestor for this group. This comprehensive catalog of mating-related genes from such a large group of fungi provides a rich resource from which in-depth, functional studies can be conducted in these economically and ecologically important species.

The microsporidian polar tube: origin, structure, composition, function, and application

Microsporidia are a class of obligate intracellular parasitic unicellular eukaryotes that infect a variety of hosts, even including humans. Although different species of microsporidia differ in host range and specificity, they all share a similar infection organelle, the polar tube, which is also defined as the polar filament in mature spores. In response to the appropriate environmental stimulation, the spore germinates with the polar filament everted, forming a hollow polar tube, and then the infectious cargo is transported into host cells via the polar tube. Hence, the polar tube plays a key role in microsporidian infection. Here, we review the origin, structure, composition, function, and application of the microsporidian polar tube, focusing on the origin of the polar filament, the structural differences between the polar filament and polar tube, and the characteristics of polar tube proteins. Comparing the three-dimensional structure of PTP6 homologous proteins provides new insight for the screening of additional novel polar tube proteins with low sequence similarity in microsporidia. In addition, the interaction of the polar tube with the spore wall and the host are summarized to better understand the infection mechanism of microsporidia. Due to the specificity of polar tube proteins, they are also used as the target in the diagnosis and prevention of microsporidiosis. With the present findings, we propose a future study on the polar tube of microsporidia.

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.

3D reconstructions of parasite development and the intracellular niche of the microsporidian pathogen E. intestinalis

Microsporidia are an early-diverging group of fungal pathogens that infect a wide range of hosts. Several microsporidian species infect humans, and infections can lead to fatal disease in immunocompromised individuals. As obligate intracellular parasites with highly reduced genomes, microsporidia are dependent on metabolites from their hosts for successful replication and development. Our knowledge of how microsporidian parasites develop inside the host remains rudimentary, and our understanding of the intracellular niche occupied by microsporidia has thus far relied largely on 2D TEM images and light microscopy. Here, we use serial block face scanning electron microscopy (SBF-SEM) to capture 3D snapshots of the human-infecting microsporidian, Encephalitozoon intestinalis , within host cells. We track the development of E. intestinalis through its life cycle, which allows us to propose a model for how its infection organelle, the polar tube, is assembled de novo in each developing spore. 3D reconstructions of parasite-infected cells provide insights into the physical interactions between host cell organelles and parasitophorous vacuoles, which contain the developing parasites. The host cell mitochondrial network is substantially remodeled during E. intestinalis infection, leading to mitochondrial fragmentation. SBF-SEM analysis shows changes in mitochondrial morphology in infected cells, and live-cell imaging provides insights into mitochondrial dynamics during infection. Together, our data provide insights into parasite development, polar tube assembly, and microsporidia-induced mitochondrial remodeling in the host cell.

Prevalence of Encephalitozoon cuniculi Infection in Guinea Pigs (Cavia porcellus) in Poland with Different Clinical Disorders-A Pilot Study

Encephalitozoonosis is a disease caused by E. cuniculi. It is diagnosed primarily in rabbits but is less frequently so in other animal species. E. cuniculi is classified among Microsporidia-fungi frequently found in the environment, that are resistant to numerous external factors. Apart from rabbits, rodents form the next group of animals most exposed to infection with these pathogens. The objective of the study was to analyze the prevalence of E. cuniculi infection in guinea pigs with different clinical disorders. The study included 67 animals with E. cuniculi infection confirmed via real-time PCR. The infected animals most frequently exhibited nervous and urinary system symptoms, as well as issues with vision organs, while several animals were also recorded as having problems with the respiratory system and thyroid gland dysfunction. The study shows that encephalitozoonosis constitutes a significant problem in rodents kept as domestic animals, which in turn may be a source of infection for humans.

Mycotic Diseases in Chelonians

Turtles and 'tortoises' populations are declining in number, the factors driving extinction risks being related to habitat loss and degradation, climate change, introduction of invasive plant and animal species, consumption by humans for food and medicinal use, and collection for international pet trade. Fungal infections represent one of the main threats for ecosystem health. The present narrative review deals with conventional and emerging mycoses of Chelonians. Although conventional mycoses in captive and pet reptiles would depend on poor husbandry, being the agents mostly opportunistic pathogens, some fungal species were reported to occur more frequently, such as the entomopathogen Purpureocillium lilacinum. Furthermore, emerging agents such as the Fusarium solani species complex have been recognized as a real threat for the surviving of some aquatic species, acting as primary pathogens. This complex has been recently included within pathogens in One Health issues. Emydomyces testavorans is recognized as an emerging threat, although, due its recent identification, information about its epidemiology is limited. Data about treatments and outcomes of mycoses in Chelonians are also referred.

Down-Regulation of Lipid Metabolism in the Hepatopancreas of Shrimp Litopenaeus vannamei upon Light and Heavy Infection of Enterocytozoon hepatopenaei: A Comparative Proteomic Study

Enterocytozoon hepatopenaei (EHP) is the pathogen of hepatopancreatic microsporidiosis (HPM) in shrimp. The diseased shrimp Litopenaeus vannamei exhibits a slow growth syndrome, which causes severe economic losses. Herein, 4D label-free quantitative proteomics was employed to analyze the hepatopancreas of L. vannamei with a light (EHPptp2 < 103 copies/50 ng hpDNA, L group) and heavy (EHPptp2 > 104 copies/50 ng hpDNA, H group) load of EHP to better understand the pathogenesis of HPM. Exactly 786 (L group) and 1056 (H group) differentially expressed proteins (DEPs) versus the EHP-free (C group) control were mainly clustered to lipid metabolism, amino acid metabolism, and energy production processing. Compared with the L group, the H group exhibited down-regulation significantly in lipid metabolism, especially in the elongation and degradation of fatty acid, biosynthesis of unsaturated fatty acid, metabolism of α-linolenic acid, sphingolipid, and glycerolipid, as well as juvenile hormone (JH) degradation. Expression pattern analysis showed that the degree of infection was positively correlated with metabolic change. About 479 EHP proteins were detected in infected shrimps, including 95 predicted transporters. These findings suggest that EHP infection induced the consumption of storage lipids and the entire down-regulation of lipid metabolism and the coupling energy production, in addition to the hormone metabolism disorder. These were ultimately responsible for the stunted growth.

Encephalitozoon spp. as a potential human pathogen

Encephalitzoon spp. are microsporidia, and intracellular opportunistic pathogens. The hosts of these pathogens include vertebrates, invertebrates, and certain protozoa. In people microsporidia may be opportunistic pathogens for immunocompromised patients (with AIDS or after organ transplantation). Infection with these microorganisms was also described in persons with diarrhea and corneal diseases.

The species causing rare infections in humans, Encephalitozooncuniculi, had previously been described from animal hosts. However, several new microsporidial species, including E. intestinalis and E. hellem, have been discovered in humans, raising the question of their natural origin. Vertebrate animals are now identified as hosts for all three microsporidial species infecting humans, implying a zoonotic nature of these microorganisms. Molecular studies have identified phenotypic and/or genetic variability within these species, indicating that they are not uniform, and have allowed the question of their zoonotic potential to be addressed. The focus of this review is to present the zoonotic potential of E. intestinalis, E. cuniculi, and E. hellem.

Recent Advances in the Biocontrol of Nosemosis in Honey Bees (Apis mellifera L.)

Nosemosis is a disease triggered by the single-celled spore-forming fungi Nosema apis and Nosema ceranae, which can cause extensive colony losses in honey bees (Apis mellifera L.). Fumagillin is an effective antibiotic treatment to control nosemosis, but due to its toxicity, it is currently banned in many countries. Accordingly, in the beekeeping sector, there is a strong demand for alternative ecological methods that can be used for the prevention and therapeutic control of nosemosis in honey bee colonies. Numerous studies have shown that plant extracts, RNA interference (RNAi) and beneficial microbes could provide viable non-antibiotic alternatives. In this article, recent scientific advances in the biocontrol of nosemosis are summarized.

Mechanics of Microsporidian Polar Tube Firing

As obligate intracellular parasites with reduced genomes, microsporidia must infect host cells in order to replicate and cause disease. They can initiate infection by utilizing a harpoon-like invasion organelle called the polar tube (PT). The PT is both visually and functionally a striking organelle and is a characteristic feature of the microsporidian phylum. Outside the host, microsporidia exist as transmissible, single-celled spores. Inside each spore, the PT is arranged as a tight coil. Upon germination, the PT undergoes a large conformational change into a long, linear tube and acts as a tunnel for the delivery of infectious cargo from the spore to a host cell. The firing process is extremely rapid, occurring on a millisecond timescale, and the emergent tube may be as long as 20 times the size of the spore body. In this chapter, we discuss what is known about the structure of the PT, the mechanics of the PT firing process, and how it enables movement of material from the spore body.

Successful use of albendazole and fenbendazole therapy in a cat with persistent diarrhea due <i>Enterocytozoon bieneusi</i>

Enterocytozoon bieneusi, also known as microsporidia, is an obligate, opportunistic, and neglected intracellular pathogen that causes diarrhea in humans. Although identified in the cat feces by epidemiological studies, no association with diarrhea has been demonstrated. We demonstrated a case of chronic enteritis by E. bieneusi in a 1-year-old male Maine Coon cat, neutered with diarrhea for nine months, by histopathological analysis of gastrointestinal biopsies and PCR of feces. The treatment with albendazole (10 days) followed by fenbendazole (5 days) proved to be effective and safe after diagnosis. This description highlights the need to investigate these pathogens in cases of diarrhea due to their importance in public health since they are zoonotic agents.

Microsporidial Stromal Keratitis: Epidemiological Features, Slit-Lamp Biomicroscopic Characteristics, and Therapy

PURPOSE

Microsporidial stromal keratitis is a rare form of infectious keratitis, with only 7 cases reported in the United States to date. This study was performed to evaluate risk factors, clinical features, and response to therapy.

METHODS

A retrospective review of the medical records of all patients diagnosed with microsporidial stromal keratitis seen in the practices of the authors between 1999 and 2020 was performed. Diagnosis was determined by cytology or histopathology in corneal specimens. Risk factors, presence or absence of distinctive clinical features, and response to medical and surgical therapies were recorded.

RESULTS

Nine patients-7M:2F, aged 7 to 99 years-with microsporidial stromal keratitis were identified. Exposures to recreational water and hymenopteran insect bites, both epidemiologically linked risk factors for systemic microsporidial infection, were identified in our patients. Presence of stromal edema with features of disciform keratitis and a distinctive granular keratitis were observed in 6 of 9 and 5 of 9 patients, respectively. Poor response to medical therapy was noted. Penetrating keratoplasty was effective in curing the infection. Final visual acuity was 20/40 or better in 6 of 9 patients.

CONCLUSIONS

In patients with slowly progressive keratitis, history of exposure to recreational water or hymenopteran insects should be sought. In patients with corneal edema consistent with disciform keratitis, with evolution to a granular keratitis, microsporidia should be considered in the differential diagnosis. In cases of established microsporidial stromal keratitis, penetrating keratoplasty should be considered if prompt response to medical therapy is not noted.

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.

A global view on fungal infections in humans and animals: opportunistic infections and microsporidioses

After cardiovascular diseases, infectious diseases are the second most common cause of death worldwide. Although these infections are caused mainly by viruses or bacteria, a systematically growing prevalence of human and animal opportunistic fungal infections is noticeable worldwide. More attention is being paid to this problem, especially due to the growing frequency of recalcitrant and recurrent mycoses. The latter are classically divided into superficial, which are the most common type, subcutaneous, and systemic. This work discusses opportunistic fungal pathogens without proven horizontal transmission between different animal species including humans and microsporidia as spore-forming unicellular parasites related to fungi; however, with a yet undetermined taxonomic position. The review also mentions aetiological agents, risk factors, epidemiology, geographical distribution, and finally symptoms characteristic for individual disease entities. This paper provides insight into fungal infections from a global perspective and simultaneously draws attention to emerging pathogens, whose prevalence is continuously increasing. Finally, this work also takes into consideration the correct nomenclature of fungal disease entities and the importance of secondary metabolites in the pathogenesis of fungal infections.

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.

Microsporidial Keratitis Related to Water Exposure: A Case Series

The objective of this retrospective study was to present a series of cases involving the rare ocular disease of microsporidia keratitis treated at a private practice clinic and describe the details regarding specific water exposure, clinical course, voriconazole treatment, and increased prevalence of this infection in Augusta, Georgia, USA. Our analysis was based on the accumulated data from all patients (n=15) diagnosed with microsporidia keratitis at our private practice clinic; the clinical course of three cases is discussed in detail in this article. Specific environmental exposures were documented in 10 patients. All patients self-reported that they had no acquired immunodeficiency. In all cases, patients had complete resolution of active symptoms after receiving treatment with 1-2% topical voriconazole, with an approximate average primary treatment duration of 40.1 ± 17.1 days (median: 40 days, range: 14-70 days). None of the patients reported any clinically significant adverse effects from therapy.

There have been increasing reports about this emerging infectious pathogen, particularly in Asia. However, there is limited data in the literature on the etiology, pathogenesis, and treatment of microsporidia-caused ophthalmic diseases. In this case series, we highlight the strong correlation of our patients' condition with specific types of water exposure in the USA as well as the complete resolution of active disease in all our patients as a result of monotherapy with topical voriconazole.

Encephalitozoon intestinalis: A new target for auranofin in a mice model

Despite the fact that many approaches have been developed over years to find efficient and well-tolerated therapeutic regimens for microsporidiosis, the effectiveness of current drugs remains doubtful, and effective drugs against specific targets are still scarce. The present study is the first that was designed to evaluate the potency of auranofin, an anti-rheumatoid FDA approved drug, against intestinal Encephalitozoon intestinalis. Evaluation of the drug was achieved through counting of fecal and intestinal spores, studying the intestinal histopathological changes, measuring of intestinal hydrogen peroxide level, and post therapy follow-up of mice for 2 weeks for detection of relapse. Results showed that auranofin has promising anti-microsporidia potential. It showed a promising efficacy in mice experimentally infected with E. intestinalis. It has revealed an obvious reduction in fecal spore shedding and intestinal tissue spore load, amelioration of intestinal tissue pathological changes, and improvement of the local inflammatory infiltration without significant changes in hydrogen peroxide level. Interestingly, auranofin prevented the relapse of infection. Thus, considering the results of the present work, auranofin could be considered a therapeutic alternative for the gold standard drug 'albendazole' against the intestinal E. intestinalis infection especially in relapsing cases.

Identification of novel miRNAs from the microsporidian parasite Nosema ceranae

Previously, six miRNAs were identified from the microsporidian parasite Nosema ceranae. By taking advantage of the recently updated N. ceranae and honey bee genome assemblies, we re-analyzed the deep sequencing datasets. Three novel miRNAs were identified, which were further validated by plasmid cloning and sequencing. The miRNAs correlated with significantly higher number of genes from the parasite than the host. Our data suggest the parasitic miRNAs are involved in self-regulation during the proliferation.

Silver nanoparticles are effective in controlling microsporidia

Many approaches and technologies have been developed as treatments for microsporidian, infections but effective, broad-spectrum, and sustainable therapeutic approaches have not been found. Silver nanoparticles (AgNPs) have antimicrobial activity and are widely used against many different pathogens. AgNPs provide an opportunity to develop formulations that will control microsporidia. In this study, we synthesized AgNPs via a chemical reduction method and evaluated their formation, morphology, and stability using transmission electron microscopy (TEM) and ultraviolet spectroscopy analysis. We verified that AgNPs could disrupt the spore cell membrane and spore germination of microsporidia Nosema bombycis. This resulted in the release of microsporidia nucleic acids, proteins, and respiratory chain enzymes. The anti-microsporidia activity of AgNPs was studied by measuring the silkworm larvae survival rate and spore genome replication after microsporidia infection. AgNPs have anti-microsporidian activity and could be effective components of formulations for treating or preventing microsporidia infection.

Tetra disseminated microsporidiosis: a novel disease in ornamental fish caused by Fusasporis stethaprioni n. gen. n. sp

A novel microsporidial disease was documented in two ornamental fish species, black tetra Gymnocorymbus ternetzi Boulenger 1895 and cardinal tetra Paracheirodon axelrodi Schultz 1956. The non-xenoma-forming microsporidium occurred diffusely in most internal organs and the gill, thus referring to the condition as tetra disseminated microsporidiosis (TDM). The occurrence of TDM in black tetra was associated with chronic mortality in a domestic farmed population, while the case in cardinal tetra occurred in moribund fish while in quarantine at a public aquarium. Histology showed that coelomic visceral organs were frequently necrotic and severely disrupted by extensive infiltrates of macrophages. Infected macrophages were presumed responsible for the dissemination of spores throughout the body. Ultrastructural characteristics of the parasite developmental cycle included uninucleate meronts directly in the host cell cytoplasm. Sporonts were bi-nucleated as a result of karyokinesis and a parasite-produced sporophorous vesicle (SPV) became apparent at this stage. Cytokinesis resulted in two spores forming within each SPV. Spores were uniform in size, measuring about 3.9 ± 0.33 long by 2.0 ± 0.2 μm wide. Ultrastructure demonstrated two spore types, one with 9-12 polar filament coils and a double-layered exospore and a second type with 4-7 polar filament coils and a homogenously electron-dense exospore, with differences perhaps related to parasite transmission mechanisms. The 16S rDNA sequences showed closest identity to the genus Glugea (≈ 92%), though the developmental cycle, specifically being a non-xenoma-forming species and having two spores forming within a SPV, did not fit within the genus. Based on combined phylogenetic and ultrastructural characteristics, a new genus (Fusasporis) is proposed, with F. stethaprioni n. gen. n. sp. as the type species.

Coexistence of genetically different Rhizophagus irregularis isolates induces genes involved in a putative fungal mating response

Arbuscular mycorrhizal fungi (AMF) are of great ecological importance because of their effects on plant growth. Closely related genotypes of the same AMF species coexist in plant roots. However, almost nothing is known about the molecular interactions occurring during such coexistence. We compared in planta AMF gene transcription in single and coinoculation treatments with two genetically different isolates of Rhizophagus irregularis in symbiosis independently on three genetically different cassava genotypes. Remarkably few genes were specifically upregulated when the two fungi coexisted. Strikingly, almost all of the genes with an identifiable putative function were known to be involved in mating in other fungal species. Several genes were consistent across host plant genotypes but more upregulated genes involved in putative mating were observed in host genotype (COL2215) compared with the two other host genotypes. The AMF genes that we observed to be specifically upregulated during coexistence were either involved in the mating pheromone response, in meiosis, sexual sporulation or were homologs of MAT-locus genes known in other fungal species. We did not observe the upregulation of the expected homeodomain genes contained in a putative AMF MAT-locus, but observed upregulation of HMG-box genes similar to those known to be involved in mating in Mucoromycotina species. Finally, we demonstrated that coexistence between the two fungal genotypes in the coinoculation treatments explained the number of putative mating response genes activated in the different plant host genotypes. This study demonstrates experimentally the activation of genes involved in a putative mating response and represents an important step towards the understanding of coexistence and sexual reproduction in these important plant symbionts.

3-Dimensional organization and dynamics of the microsporidian polar tube invasion machinery

Microsporidia, a divergent group of single-celled eukaryotic parasites, harness a specialized harpoon-like invasion apparatus called the polar tube (PT) to gain entry into host cells. The PT is tightly coiled within the transmissible extracellular spore, and is about 20 times the length of the spore. Once triggered, the PT is rapidly ejected and is thought to penetrate the host cell, acting as a conduit for the transfer of infectious cargo into the host. The organization of this specialized infection apparatus in the spore, how it is deployed, and how the nucleus and other large cargo are transported through the narrow PT are not well understood. Here we use serial block-face scanning electron microscopy to reveal the 3-dimensional architecture of the PT and its relative spatial orientation to other organelles within the spore. Using high-speed optical microscopy, we also capture and quantify the entire PT germination process of three human-infecting microsporidian species in vitro: Anncaliia algerae, Encephalitozoon hellem and E. intestinalis. Our results show that the emerging PT experiences very high accelerating forces to reach velocities exceeding 300 μm⋅s-1, and that firing kinetics differ markedly between species. Live-cell imaging reveals that the nucleus, which is at least 7 times larger than the diameter of the PT, undergoes extreme deformation to fit through the narrow tube, and moves at speeds comparable to PT extension. Our study sheds new light on the 3-dimensional organization, dynamics, and mechanism of PT extrusion, and shows how infectious cargo moves through the tube to initiate infection.

Impact of Protoporphyrin Lysine Derivatives on the Ability of Nosema ceranae Spores to Infect Honeybees

Simple Summary

Honeybees, which are important for the development and maintenance of natural ecosystems, are infected by microsporidia, Nosema apis and N. ceranae. These parasites induce a disease named nosemosis contributing to the impairment of digestion and nutrient absorption, ultimately leading to total colony collapse. The need for research into the control of N. ceranae has become increasingly important. Promising compounds for the treatment of nosemosis are porphyrins. In the present study, we examined the effects of three different porphyrins on the infectivity of N. ceranae microsporidia. A significantly lower level of infection was observed in the bees infected with the porphyrin-treated spores than in the control bees (infected with untreated spores). We showed that protoporphyrin lysine derivatives in particular prevented the development of Nosema spores and simultaneously extended bee life spans (up to 50%). The results also indicate that these porphyrins may contribute to the reduction in digestive nutrient absorption disorders in bees. The present findings can be used to develop a new class of drugs for combating nosemosis. These compounds may serve as preventive or disinfection agents through direct inactivation of Nosema both in the midgut and outside the host body, i.e., in the hive.

Abstract

The effect of two protoporphyrin IX derivatives conjugated with single (PP[Lys(TFA)-OH)]₂) or double (PP[Lys(TFA)-Lys(TFA)-OH]₂) lysine moieties on the infectious capacity of Nosema ceranae spores was examined, and their efficacies were compared with those of a cationic porphyrin (H₂TTMePP). Honeybees were inoculated with spores preincubated with porphyrins or with untreated spores (control). A significantly lower level of infection was observed in the bees infected with the porphyrin-treated spores than in the infected control. Porphyrins 1 and 2 reduced the infectious capability of microsporidia more efficiently than porphyrin 3, with bee mortality declining to almost 50%. Confocal analysis of the midguts of infected bees revealed distinct differences in the number of spores between the control group and the group infected with PP[Lys(TFA)-Lys(TFA)-OH]₂-treated spores. Notably, bees with a reduced level of infection consumed less sucrose syrup than the control bees, indicating a reduction in digestive disorders and an improvement in food absorption.

The genomic survey of Tc1-like elements in the silkworm microsporidia Nosema bombycis

BACKGROUND

Microsporidia Nosema bombycis is the destructive pathogen in the production of sericulture. The Tc1/mariner elements belong to important component of DNA transposon.

METHODS

The genomic data of N. bombycis and related Nosema species were screened to identify the Tc1-like elements and analyzed the phylogenetic relationship, based on bioinformational analysis. High-throughput data of transcriptomes and small RNAs were used to evaluate the expressed level and potential rasiRNAs for the Tc1-like elements of N. bombycis.

RESULTS

Twelve complete Tc1-like elements belonging to DD34,E clade is confirmed in the whole genome of N. bombycis, and divided into two branches. Six of them are sole in N. bombycis and thereby would be the molecular marker to differentiate this species from others Nosema spp. Most of the elements have the transcriptional active and are the source of sRNAs.

CONCLUSION

Abundant Tc1-like elements in N. bombycis reflect the expansion of transposons for this genomic characters, comparing with others Nosema spp. The finding of distribution, phylogeny and potential functional activity for Tc1Nbs in N. bombycis will help understanding the role of the DNA transposon in genomic evolution of microsporidia.

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.

E Pluribus Unum: The Fungal Kingdom as a Rosetta Stone for Biology and Medicine

THE Genetics Society of America's (GSA's) Edward Novitski Prize recognizes a single experimental accomplishment or a body of work in which an exceptional level of creativity, and intellectual ingenuity, has been used to design and execute scientific experiments to solve a difficult problem in genetics. The 2019 recipient is Joseph Heitman, who is recognized for his work on fungal pathogens of humans and for ingenious experiments using yeast to identify the molecular targets of widely used immunosuppressive drugs. The latter work, part of Heitman's postdoctoral research, proved to be a seminal contribution to the discovery of the conserved Target of Rapamycin (TOR) pathway. In his own research group, a recurring theme has been the linking of fundamental insights in fungal biology to medically important problems. His studies have included defining fungal mating-type loci, including their evolution and links to virulence, and illustrating convergent transitions from outcrossing to inbreeding in fungal pathogens of plants and animals. He has led efforts to establish new genetic and genomic methods for studying pathogenesis in Cryptococcus species. Heitman's group also discovered unisexual reproduction, a novel mode of fungal reproduction with implications for pathogen evolution and the origins of sexual reproduction.

Prevalence and Population Genetics Analysis of Enterocytozoon bieneusi in Dairy Cattle in China

Enterocytozoon bieneusi, an obligate intracellular pathogen, can infect various hosts. In this study, 3527 dairy cattle fecal specimens were collected from different geographic locations in China (including 673 from Shandong province, 1,440 from Guangdong province and 1,414 from Gansu province) and examined for the presence of E. bieneusi using polymerase chain reactions targeting the ribosomal internal transcribed spacer (ITS). The dominant genotypes identified were further subtyped by multilocus sequence typing. The overall prevalence of E. bieneusi was 14.2% (501/3527), with a significant difference in prevalence among the different geographical locations (P < 0.001). Our logistic regression analysis showed that all four variables (farming model, location, age, and clinical manifestations) had strong effects on the risk of contracting E. bieneusi. Sequence analysis revealed 11 genotypes: eight known genotypes (J, I, BEB4, BEB10, D, EbpC, CM19, and CM21) and three novel genotypes (named here as CGC1, CGC2, and CGC3). Genotypes J and I, the commonest, were found on all farms across the three provinces. Our linkage disequilibrium analysis showed a clonal population structure in the E. bieneusi dairy cattle population but the ITS genotypes had different population structures. Phylogenetic and haplotype network analysis showed the absence of geographical segregation in the E. bieneusi dairy cattle populations. Instead, they revealed the presence of host adaptation to the E. bieneusi populations in various animals. Our findings augment the current understanding of E. bieneusi transmission dynamics.

Whole-Genome Sequence Data Uncover Widespread Heterothallism in the Largest Group of Lichen-Forming Fungi

Fungal reproduction is regulated by the mating-type (MAT1) locus, which typically comprises two idiomorphic genes. The presence of one or both allelic variants at the locus determines the reproductive strategy in fungi—homothallism versus heterothallism. It has been hypothesized that self-fertility via homothallism is widespread in lichen-forming fungi. To test this hypothesis, we characterized the MAT1 locus of 41 genomes of lichen-forming fungi representing a wide range of growth forms and reproductive strategies in the class Lecanoromycetes, the largest group of lichen-forming fungi. Our results show the complete lack of genetic homothallism suggesting that lichens evolved from a heterothallic ancestor. We argue that this may be related to the symbiotic lifestyle of these fungi, and may be a key innovation that has contributed to the accelerated diversification rates in this fungal group.

Multilocus Sequence Typing and Population Genetic Analysis of Enterocytozoon bieneusi: Host Specificity and Its Impacts on Public Health

Microsporidia comprise a large class of unicellular eukaryotic pathogens that are medically and agriculturally important, but poorly understood. There have been nearly 1,500 microsporidian species described thus far, which are variable in biology, genetics, genomics, and host specificity. Among those, Enterocytozoon bieneusi is the well-known species responsible for the most recorded cases of human microsporidian affections. The pathogen can colonize a broad range of mammals and birds and most of the animals surveyed share some genotypes with humans, posing a threat to public health. Based on DNA sequence analysis of the ribosomal internal transcribed spacer (ITS) and phylogenetic analysis, several hundreds of E. bieneusi genotypes have been defined and clustered into different genetic groups with varied levels of host specificity. However, single locus-based typing using ITS might have insufficient resolution to discriminate among E. bieneusi isolates with complex genetic or hereditary characteristics and to assess the elusive reproduction or transmission modes of the organism, highlighting the need for exploration and application of multilocus sequence typing (MLST) and population genetic tools. The present review begins with a primer on microsporidia and major microsporidian species, briefly introduces the recent advances on E. bieneusi ITS genotyping and phylogeny, summarizes recent MLST and population genetic data, analyzes the inter- and intragroup host specificity at the MLST level, and interprets the public health implications of host specificity in zoonotic or cross-species transmission of this ubiquitous fungus.

Dicer regulates Nosema ceranae proliferation in honeybees

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

Importance of clinical signs leading to the diagnosis in a case of microbiological smear negative ocular microsporidiosis

A 28-year-old patient presented to us with multifocal coarse raised epithelial lesions in the left eye associated with pain watering redness and blurred vision with a visual acuity of 20/40 in the left eye. The patient had been managed elsewhere with a course of topical moxifloxacin eye-drops four times a day and topical steroids (prednisolone acetate) 1% three times a day for 2 weeks without any resolution, which was stopped 2 days ago prior to presentation at our centre. Gram stain was negative for bacteria as well as microsporidial spores. 10% KOH was negative for fungal hyphae. Based on strong clinical signs of corneal microsporidiosis, in spite of the negative microbiology smear, the patient was started on voriconazole eye-drops five times a day. The lesions started resolving in 5 days and completely healed after 17 days of therapy. No relevant history pertaining to exposure of contaminated water, swimming or history of trauma could be elicited.

The invasive cell coat at the microsporidian Trachipleistophora hominis-host cell interface contains secreted hexokinases

Microsporidia are obligate intracellular parasites causing significant disease in humans and economically important animals. In parallel to their extreme genetic reduction, Microsporidia have evolved novel mechanisms for exploiting host metabolism. A number of microsporidians confer secretion of otherwise cytosolic proteins by coding for signal peptides that direct entry into the endoplasmic reticulum. The human pathogen Trachipleistophora hominis encodes for four hexokinases, three of which have signal peptides at the N‐terminus. Here, we localized hexokinase 2 and hexokinase 3 through developmental stages of T. hominis using light and electron microscopy. Both proteins were concentrated in an extracellular coat previously termed the plaque matrix (PQM). The PQM (containing hexokinases) was morphologically dynamic, infiltrating the host cytoplasm predominantly during replicative stages. Throughout development the PQM interacted closely with endoplasmic reticulum that was demonstrated to be active in membrane protein biosynthesis and export. The impact of hexokinase on the host metabolism was probed using the fluorescent analog of glucose, 2‐NBDG, which displayed spatially restricted increases in signal intensity at the parasite/vacuole surface, coincident with hexokinase/PQM distribution. Gross metabolic aberrations, measured using metabolic profiling with the Seahorse XF Analyzer, were not detectable in mixed stage cocultures. Overall, these results highlight a role for the extended cell coat of T. hominis in host–parasite interactions, within which secreted hexokinases may work as part of a metabolic machine to increase glycolytic capacity or ATP generation close to the parasite surface.

Confirmed microsporidial graft infection in a HIV-negative renal transplant recipient: A case report and review of the literature

Microsporidia are intracellular organisms most commonly known to cause opportunistic infection in patients with human immunodeficiency virus (HIV). There have been several case reports of infection in solid organ and bone marrow transplant recipients. Here, we report a case of a non-HIV-infected renal transplant patient with microsporidiosis of the renal tract associated with acute graft dysfunction. We also review the literature of 12 previously reported cases of microsporidiosis in patients with renal transplants who had described graft involvement. We review the pattern of illness as well as the common renal biopsy features when microsporidial infection is associated with renal graft infection.

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.

Molecular Tools for Carotenogenesis Analysis in the Mucoral Mucor circinelloides

The carotene producer Mucor circinelloides is the fungus within the Mucoromycota phylum with the widest repertoire of molecular tools to manipulate its genome. The initial development of an effective procedure for genetic transformation and later improvements have resulted in an expansion of available tools, which include gene replacement, inactivation of gene expression by RNA silencing, gene overexpression, and functional genomics. Moreover, sequencing of its genome has given a definitive boost to these techniques making attainable the study of genes involved in many physiological or developmental processes, including carotenoid biosynthesis. Here, we describe in detail the latest molecular techniques currently used in M. circinelloides that have made it a valuable model for studying gene function within its phylum.

The influence of the mating type on virulence of Mucor irregularis

Mucor irregularis is an emerging fungal pathogen that cause cutaneous infection and could cause death. However, little is known about its mechanism of pathogenesis. There is evidence suggesting virulence vary with mating types in fungi, including the Mucorales. Here, we characterized the mating type locus of M. irregularis and the mating type ratio of 17 clinical isolates in China. Genomic data indicated M. irregularis is heterothallic having two mating types – bearing either SexP or SexM allele. Also, we employed a mice model to study the inflammation and pathological effects of different mating types. The comparison of the inflammatory response, cytokine profiles and Th-1, Th-2 and Th-17 cells numbers in each mating type treated mice showed that the severity and disease progress were enhanced in (+) mating type treated mice. One (+/0) mutant strain, with multiple mutations at the mating locus, had defects in sexual mating ability but appeared to be more virulent than the (−) mating type. Although (+) mating type appeared to be more virulent, most of our clinical isolates presented belonged to (−) mating type. Our findings support the involvement of MAT genes in sexual fertility, and the influence of mating type on the severity of cutaneous infection.

Fungal Sex: The Ascomycota

This article provides an overview of sexual reproduction in the ascomycetes, a phylum of fungi that is named after the specialized sacs or "asci" that hold the sexual spores. They have therefore also been referred to as the Sac Fungi due to these characteristic structures that typically contain four to eight ascospores. Ascomycetes are morphologically diverse and include single-celled yeasts, filamentous fungi, and more complex cup fungi. The sexual cycles of many species, including those of the model yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe and the filamentous saprobes Neurospora crassa, Aspergillus nidulans, and Podospora anserina, have been examined in depth. In addition, sexual or parasexual cycles have been uncovered in important human pathogens such as Candida albicans and Aspergillus fumigatus, as well as in plant pathogens such as Fusarium graminearum and Cochliobolus heterostrophus. We summarize what is known about sexual fecundity in ascomycetes, examine how structural changes at the mating-type locus dictate sexual behavior, and discuss recent studies that reveal that pheromone signaling pathways can be repurposed to serve cellular roles unrelated to sex.

Dynamics of parasitophorous vacuoles formed by the microsporidian pathogen Encephalitozoon cuniculi

It has been a long-standing debate if sexual development occurs in the microsporidian lineages. Previous studies, including morphological observations, ploidy analysis, and the presence of a sex-related locus, provided evidence of possible extant of sexual development. This study presents another line of evidence by monitoring the parasitophorous vacuoles (PVs) formed by Encephalitozoon cuniculi. Time lapse observations of infection cycles of E. cuniculi revealed that multiple PVs can be formed in a single host cell and the PVs in the single cell can merge (fusion) or split (fission). The dynamics of PVs may provide a route for interactions between genetically distinct microsporidian isolates during host infections.

Fungal Sex: The Mucoromycota

Although at the level of resolution of genes and molecules most information about mating in fungi is from a single lineage, the Dikarya, many fundamental discoveries about mating in fungi have been made in the earlier branches of the fungi. These are nonmonophyletic groups that were once classified into the chytrids and zygomycetes. Few species in these lineages offer the potential of genetic tractability, thereby hampering the ability to identify the genes that underlie those fundamental insights. Research performed during the past decade has now established the genes required for mating type determination and pheromone synthesis in some species in the phylum Mucoromycota, especially in the order Mucorales. These findings provide striking parallels with the evolution of mating systems in the Dikarya fungi. Other discoveries in the Mucorales provide the first examples of sex-cell type identity being driven directly by a gene that confers mating type, a trait considered more of relevance to animal sex determination but difficult to investigate in animals. Despite these discoveries, there remains much to be gleaned about mating systems from these fungi.

Intestinal microsporidiosis in Iran: infection in immune-compromised and immunocompetent patients

Background and Purpose:

Gastroenteritis and the clinical profile caused by Microsporidia, an opportunistic pathogen, may be severe in immunocompromised individuals, especially in AIDS patients. Conventionally, it is necessary to detect the small infective spores in stained smears. However, due to the limitations of the microscopy-based methods, several DNA-based methods such as polymerase chain reaction (PCR) have recently been developed to enhance diagnosis sensitivity. Therefore, we sought to evaluate the rate of infection in immunocompromised patients as compared with immunocompetent patients in Kerman, Iran.

Materials and Methods:

We collected stool samples of 199 human subjects (116 males and 83 females), aged 1 to 69 years old. They were divided into immunocompromised (i.e., AIDS [n=72] and cancer-positive patients [n=59]) and immunocompetent (n=68) groups. We comparatively examined the fecal materials using the microscopy and PCR methods.

Results:

The overall prevalence rate of Microsporidia infection was 10.05% (20/199). Entrocytozoon bieneusi was the only species within the Microsporidia genus that was identified in 14.5% (19/131) of the immunocompromised patients and 1.47% (1/68) of the immunocompetent individuals.

Conclusion:

Considering the higher prevalence rate of microsporidiosis in patients with immunodeficiency (10.03%), we suggest performing sensitive and specific techniques such as PCR for the detection of these parasites in immunocompromised patients.