Nematode surface coats: Actively evading immunity

The Caenorhabditis elegans cuticle and precuticle: a model for studying dynamic apical extracellular matrices in vivo

Apical extracellular matrices (aECMs) coat the exposed surfaces of animal bodies to shape tissues, influence social interactions, and protect against pathogens and other environmental challenges. In the nematode Caenorhabditis elegans, collagenous cuticle and zona pellucida protein-rich precuticle aECMs alternately coat external epithelia across the molt cycle and play many important roles in the worm's development, behavior, and physiology. Both these types of aECMs contain many matrix proteins related to those in vertebrates, as well as some that are nematode-specific. Extensive differences observed among tissues and life stages demonstrate that aECMs are a major feature of epithelial cell identity. In addition to forming discrete layers, some cuticle components assemble into complex substructures such as ridges, furrows, and nanoscale pillars. The epidermis and cuticle are mechanically linked, allowing the epidermis to sense cuticle damage and induce protective innate immune and stress responses. The C. elegans model, with its optical transparency, facilitates the study of aECM cell biology and structure/function relationships and all the myriad ways by which aECM can influence an organism.

Strongyloides stercoralis infection in solid organ transplant recipients

PURPOSE OF REVIEW

Strongyloides stercoralis infection remains of concern due to its high associated morbidity among solid organ transplant recipients (SOTR) and the risk of donor-derived infection (DDI). We review key aspects of epidemiology to inform screening for and treatment of chronic infection among organ transplant candidates to reduce the risk of infectious complications in the posttransplant setting.

RECENT FINDINGS

In this work, we offer guidance regarding the optimal management of Strongyloides hyperinfection syndrome and disseminated infection and offer recommendations regarding posttreatment surveillance and the potential need for repeat treatment during subsequent periods of augmented immunosuppression. This review also provides updated recommendations for screening of deceased and living donors as recently proposed by the Organ Procurement and Transplantation Network's Ad Hoc Disease Transmission Advisory Committee.

SUMMARY

Risk reduction of Strongyloides infection in the SOTR population can be further enhanced by optimized treatment of infection, posttreatment surveillance during at-risk periods and recent proposed policy shifts to universal donor screening.

Introduction to Strongyloides stercoralis Anatomy

Strongyloides stercoralis, commonly known as the human threadworm, is a skin-penetrating gastrointestinal parasitic nematode that infects hundreds of millions of people worldwide. Like other Strongyloides species, S. stercoralis is capable of cycling through a single free-living generation. Although S. stercoralis and the free-living nematode Caenorhabditis elegans are evolutionarily distant, the free-living adults of S. stercoralis are similar enough in size and morphology to C. elegans adults that techniques for generating transgenics and knockouts in C. elegans have been successfully adapted for use in S. stercoralis. High-quality genomic and transcriptomic data are also available for S. stercoralis. Thus, one can use a burgeoning array of functional genomic tools in S. stercoralis to probe questions about parasitic nematode development, physiology, and behavior. Knowledge gained from S. stercoralis will inform studies of other parasitic nematodes such as hookworms that are not yet amenable to genetic manipulation. This review describes the basic anatomy of S. stercoralis.

Body stiffness is a mechanical property that facilitates contact-mediated mate recognition in Caenorhabditis elegans

Physical contact is prevalent in the animal kingdom to recognize suitable mates by decoding information about sex, species, and maturity. Although chemical cues for mate recognition have been extensively studied, the role of mechanical cues remains elusive. Here, we show that C. elegans males recognize conspecific and reproductive mates through short-range cues, and that the attractiveness of potential mates depends on the sex and developmental stages of the hypodermis. We find that a particular group of cuticular collagens is required for mate attractiveness. These collagens maintain body stiffness to sustain mate attractiveness but do not affect the surface properties that evoke the initial step of mate recognition, suggesting that males utilize multiple sensory mechanisms to recognize suitable mates. Manipulations of body stiffness via physical interventions, chemical treatments, and 3D-printed bionic worms indicate that body stiffness is a mechanical property for mate recognition and increases mating efficiency. Our study thus extends the repertoire of sensory cues of mate recognition in C. elegans and provides a paradigm to study the important roles of mechanosensory cues in social behaviors.

Ascaridia galli infection in chicken: Pathobiology and immunological orchestra

BACKGROUND

Ascaridia galli is the largest gut-dwelling helminth of chickens, which confers adverse effects on meat and egg production; thus, on the animal protein supply and the economy. Both adult and immature parasites affect gut health, but larval stages play a major role in pathology.

AIMS

Here, we present immunology and pathology of A. galli in chickens.

MATERIALS AND METHODS

Literatures were surveyed through online platforms such as PubMed, Google Scholar and Researchgate.

RESULTS

The larvae cause excessive mucus production, damage to the intestinal gland, hemorrhage, anemia, diarrhea, and malnutrition. The adult worms can cause death by intestinal obstruction and intussusception. Although both cellular and humoral immunity are involved in fighting against ascariasis, the role of naturally acquired immunity is poorly defined. In cellular immunity, Th-2 cytokines (IL-4, IL-5, IL-9, and IL-13), goblet cells (mucin), gut-associated lymphoid tissues, CD8α+ intraepithelial cells, TCRγδ + T cells, and TGF-β4 form a protective band. Type 2 immunity provides protection by forming a network of endogenous damage-associated molecular patterns, chitin, and parasitic antigens. Among antibodies, IgY is the most prominent in chickens and provides temporary humoral protection. During parasitic infection, infiltration of various immune cells is evident, especially in the intestinal epithelium, lamina propria, and crypts of the duodenum and jejunum. In chickens older than 12 weeks, gradual reduction of worm burden is more successful than the younger birds. Female chickens exert a short-lived but higher level of protection by passing IgY to chicks in the form of egg yolk antibodies. In laying conditions, immunity differs between breeds. This review provides an overview of the silent but inevitable pathological changes induced by A. galli and the interaction of host immunity with the parasite.

NHR-23 activity is necessary for C. elegans developmental progression and apical extracellular matrix structure and function

Nematode molting is a remarkable process where animals must repeatedly build a new apical extracellular matrix (aECM) beneath a previously built aECM that is subsequently shed. The nuclear hormone receptor NHR-23 (also known as NR1F1) is an important regulator of C. elegans molting. NHR-23 expression oscillates in the epidermal epithelium, and soma-specific NHR-23 depletion causes severe developmental delay and death. Tissue-specific RNAi suggests that nhr-23 acts primarily in seam and hypodermal cells. NHR-23 coordinates the expression of factors involved in molting, lipid transport/metabolism and remodeling of the aECM. NHR-23 depletion causes dampened expression of a nas-37 promoter reporter and a loss of reporter oscillation. The cuticle collagen ROL-6 and zona pellucida protein NOAH-1 display aberrant annular localization and severe disorganization over the seam cells after NHR-23 depletion, while the expression of the adult-specific cuticle collagen BLI-1 is diminished and frequently found in patches. Consistent with these localization defects, the cuticle barrier is severely compromised when NHR-23 is depleted. Together, this work provides insight into how NHR-23 acts in the seam and hypodermal cells to coordinate aECM regeneration during development.

A comparative 'omics' approach for prediction of candidate Strongyloides stercoralis diagnostic coproantigens

Human infection with the intestinal nematode Strongyloides stercoralis is persistent unless effectively treated, and potentially fatal in immunosuppressed individuals. Epidemiological data are lacking, partially due to inadequate diagnosis. A rapid antigen detection test is a priority for population surveillance, validating cure after treatment, and for screening prior to immunosuppression. We used a targeted analysis of open access 'omics' data sets and used online predictors to identify S. stercoralis proteins that are predicted to be present in infected stool, Strongyloides-specific, and antigenic. Transcriptomic data from gut and non-gut dwelling life cycle stages of S. stercoralis revealed 328 proteins that are differentially expressed. Strongyloides ratti proteomic data for excreted and secreted (E/S) proteins were matched to S. stercoralis, giving 1,057 orthologues. Five parasitism-associated protein families (SCP/TAPS, prolyl oligopeptidase, transthyretin-like, aspartic peptidase, acetylcholinesterase) were compared phylogenetically between S. stercoralis and outgroups, and proteins with least homology to the outgroups were selected. Proteins that overlapped between the transcriptomic and proteomic datasets were analysed by multiple sequence alignment, epitope prediction and 3D structure modelling to reveal S. stercoralis candidate peptide/protein coproantigens. We describe 22 candidates from seven genes, across all five protein families for further investigation as potential S. stercoralis diagnostic coproantigens, identified using open access data and freely-available protein analysis tools. This powerful approach can be applied to many parasitic infections with 'omic' data to accelerate development of specific diagnostic assays for laboratory or point-of-care field application.

The Coincidental Evolution of Virulence Partially Explains the Virulence in a Generalist Entomopathogenic

PURPOSE

The parasites' virulence is labile after jumping to a new host species, and it might derivate in gaining virulence against a new host as a side effect of living in a non-host environment (coincidental evolution of virulence hypothesis).

METHODS

To test this hypothesis, we monitored the experimental evolution of the Rhabditis regina nematode for over 290 generations (4 years) in three environments (strains): (1) the natural host, Phyllophaga polyphylla, (2) an alternate host, Tenebrio molitor, and (3) saprophytic medium (beef; the food that may provide evidence for the coincidental evolution of virulence). Each strain was exposed to P. polyphylla, T. molitor, or Galleria mellonella. We compared the host survival and immune response (proPO, PO, and lytic activity) of infected versus uninfected hosts.

RESULTS

The saprophytic nematodes gained virulence only against G. mellonella. However, the P. polyphylla strain was more effective in killing P. polyphylla than T. molitor, and the T. molitor strain was more effective against T. molitor than P. polyphylla. Additionally, one dauer larva was sufficient to kill the hosts. Finally, the immune response did not differ between the challenged and control groups.

CONCLUSION

The coincidental evolution of virulence partially explains our results, but they might also support the short-sighted hypothesis. Additionally, we found evidence for immunomodulation because nematodes passed unnoticed to the immune response. It is crucial to analyze the virulence of entomopathogens from the point of view of the evolution of virulence to be aware of potential scenarios that might limit biological control.

External and Internal Microbiomes of Antarctic Nematodes are Distinct, but More Similar to each other than the Surrounding Environment

Host-associated microbiomes have primarily been examined in the context of their internal microbial communities, but many animal species also contain microorganisms on external host surfaces that are important to host physiology. For nematodes, single strains of bacteria are known to adhere to the cuticle (e.g., Pasteuria penetrans), but the structure of a full external microbial community is uncertain. In prior research, we showed that internal gut microbiomes of nematodes (Plectus murrayi, Eudorylaimus antarcticus) and tardigrades from Antarctica's McMurdo Dry Valleys were distinct from the surrounding environment and primarily driven by host identity. Building on this work, we extracted an additional set of individuals containing intact external microbiomes and amplified them for 16S and 18S rRNA metabarcoding. Our results showed that external bacterial microbiomes were more diverse than internal microbiomes, but less diverse than the surrounding environment. Host-specific bacterial compositional patterns were observed, and external microbiomes were most similar to their respective internal microbiomes. However, external microbiomes were more influenced by the environment than the internal microbiomes were. Non-host eukaryotic communities were similar in diversity to internal eukaryotic communities, but exhibited more stochastic patterns of assembly compared to bacterial communities, suggesting the lack of a structured external eukaryotic microbiome. Altogether, we provide evidence that nematode and tardigrade cuticles are inhabited by robust bacterial communities that are substantially influenced by the host, albeit less so than internal microbiomes are.

Identification and characterization of epicuticular proteins of nematodes sharing motifs with cuticular proteins of arthropods

Specific collagens and insoluble proteins called cuticlins are major constituents of the nematode cuticles. The epicuticle, which forms the outermost electron-dense layer of the cuticle, is composed of another category of insoluble proteins called epicuticlins. It is distinct from the insoluble cuticlins localized in the cortical layer and the fibrous ribbon underneath lateral alae. Our objective was to identify and characterize genes and their encoded proteins forming the epicuticle. The combination between previously obtained laboratory results and recently made available data through the whole-genome shotgun contigs (WGS) and the transcriptome Shotgun Assembly (TSA) sequencing projects of Ascaris suum allowed us to identify the first epicuticlin gene, Asu-epic-1, on the chromosome VI. This gene is formed of exon1 (55 bp) and exon2 (1067 bp), separated by an intron of 1593 bp. Exon 2 is formed of tandem repeats (TR) whose number varies in different cDNA and genomic clones of Asu-epic-1. These variations could be due to slippage of the polymerases during DNA replication and RNA transcription leading to insertions and deletions (Indels). The deduced protein, Asu-EPIC-1, consists of a signal peptide of 20 amino acids followed by 353 amino acids composed of seven TR of 49 or 51 amino acids each. Three highly conserved tyrosine motifs characterize each repeat. The GYR motif is the Pfam motif PF02756 present in several cuticular proteins of arthropods. Asu-EPIC-1 is an intrinsically disordered protein (IDP) containing seven predicted molecular recognition features (MoRFs). This type of protein undergoes a disorder-to-order transition upon binding protein partners. Three epicuticular sequences have been identified in A. suum, Ascaris lumbricoides, and Toxocara canis. Homologous epicuticular proteins were identified in over 50 other nematode species. The potential of this new category of proteins in forming the nematode cuticle through covalent interactions with other cuticular components, particularly with collagens, is discussed. Their localization in the outermost layer of the nematode body and their unique structure render them crucial candidates for biochemical and molecular interaction studies and targets for new biotechnological and biomedical applications.

Aphelenchoides besseyi Ab-FAR-1 Interacts with Arabidopsis thaliana AtADF3 to Interfere with Actin Cytoskeleton, and Promotes Nematode Parasitism and Pathogenicity

Fatty acid and retinol binding proteins (FAR) are unique proteins found in nematodes and are considered potential targets for controlling these parasites. However, their functions in nematode parasitism and pathogenicity and interaction with hosts are still unclear. In this study, we investigated the specific roles of rice white tip nematodes (RWTNs), Aphelenchoides besseyi, and a protein, Ab-FAR-1, to elucidate the parasitic and pathogenic processes of nematodes. The results showed that the expression level of Ab-far-1 was significantly up-regulated after A. besseyi infection of the plant. The immunofluorescence and subcellular localisation showed that Ab-FAR-1 was secreted into plant tissues mainly through the body wall of nematodes and might act in the nucleus and cytoplasm of plant cells. The pathogenicity of RWTNs was enhanced in Arabidopsis thaliana overexpressing Ab-FAR-1 and inhibited in Ab-far-1 RNAi A. thaliana. Yeast two-hybrid, Co-IP, BiFC, and nematode inoculation experiments showed that Ab-FAR-1 could interact with the A. thaliana actin-depolymerizing factor protein AtADF3, and the A. thaliana adf3 mutant was more susceptible to nematodes. An in vitro actin filament depolymerisation assay demonstrated that Ab-FAR-1 could inhibit AtADF3-mediated depolymerisation of actin filaments, and the turnover process of cellular actin filaments was also affected in A. thaliana overexpressing Ab-FAR-1. In addition, flg22-mediated host defence responses were suppressed in A. thaliana overexpressing Ab-FAR-1 and adf3 mutants. Therefore, this study confirmed that RWTNs can affect the turnover of actin filament remodelling mediated by AtADF3 through Ab-FAR-1 secretion and thus inhibit plant PAMP-triggered immunity (PTI), promoting the parasitism and pathogenicity of nematodes.

The Angiostrongylus vasorum Excretory/Secretory and Surface Proteome Contains Putative Modulators of the Host Coagulation

Angiostrongylus vasorum is a cardiopulmonary nematode of canids and is, among others, associated with bleeding disorders in dogs. The pathogenesis of such coagulopathies remains unclear. A deep proteomic characterization of sex specific A. vasorum excretory/secretory proteins (ESP) and of cuticular surface proteins was performed, and the effect of ESP on host coagulation and fibrinolysis was evaluated in vitro. Proteins were quantified by liquid chromatography coupled to mass spectrometry and functionally characterized through gene ontology and pathway enrichment analysis. In total, 1069 ESP (944 from female and 959 from male specimens) and 1195 surface proteins (705 and 1135, respectively) were identified. Among these were putative modulators of host coagulation, e.g., von Willebrand factor type D domain protein orthologues as well as several proteases, including serine type proteases, protease inhibitors and proteasome subunits. The effect of ESP on dog coagulation and fibrinolysis was evaluated on canine endothelial cells and by rotational thromboelastometry (ROTEM). After stimulation with ESP, tissue factor and serpin E1 transcript expression increased. ROTEM revealed minimal interaction of ESP with dog blood and ESP did not influence the onset of fibrinolysis, leading to the conclusion that Angiostrongylus vasorum ESP and surface proteins are not solely responsible for bleeding in dogs and that the interaction with the host's vascular hemostasis is limited. It is likely that coagulopathies in A. vasorum infected dogs are the result of a multifactorial response of the host to this parasitic infection.

When Appearance Misleads: The Role of the Entomopathogen Surface in the Relationship with Its Host

Currently, potentially harmful insects are controlled mainly by chemical synthetic insecticides, but environmental emergencies strongly require less invasive control techniques. The use of biological insecticides in the form of entomopathogenic organisms is undoubtedly a fundamental resource for the biological control of insect pests in the future. These infectious agents and endogenous parasites generally act by profoundly altering the host's physiology to death, but their success is closely related to the neutralization of the target insect's immune response. In general, entomopathogen parasites, entomopathogenic bacteria, and fungi can counteract immune processes through the effects of secretion/excretion products that interfere with and damage the cells and molecules typical of innate immunity. However, these effects are observed in the later stages of infection, whereas the risk of being recognized and neutralized occurs very early after penetration and involves the pathogen surface components and molecular architecture; therefore, their role becomes crucial, particularly in the earliest pathogenesis. In this review, we analyze the evasion/interference strategies that entomopathogens such as the bacterium Bacillus thuringiensis, fungi, nematocomplexes, and wasps implement in the initial stages of infection, i.e., the phases during which body or cell surfaces play a key role in the interaction with the host receptors responsible for the immunological discrimination between self and non-self. In this regard, these organisms demonstrate evasive abilities ascribed to their body surface and cell wall; it appears that the key process of these mechanisms is the capability to modify the surface, converting it into an immunocompatible structure, or interaction that is more or less specific to host factors.

Infection by the castrating parasitic nematode Sphaerularia bombi changes gene expression in Bombus terrestris bumblebee queens

Parasitism can result in dramatic changes in host phenotype, which are themselves underpinned by genes and their expression. Understanding how hosts respond at the molecular level to parasites can therefore reveal the molecular architecture of an altered host phenotype. The entomoparasitic nematode Sphaerularia bombi is a parasite of bumblebee (Bombus) hosts where it induces complex behavioural changes and host castration. To examine this interaction at the molecular level, we performed genome-wide transcriptional profiling using RNA-Sequencing (RNA-Seq) of S. bombi-infected Bombus terrestris queens at two critical time-points: during and just after overwintering diapause. We found that infection by S. bombi affects the transcription of genes underlying host biological processes associated with energy usage, translation, and circadian rhythm. We also found that the parasite affects the expression of immune genes, including members of the Toll signalling pathway providing evidence for a novel interaction between the parasite and the host immune response. Taken together, our results identify host biological processes and genes affected by an entomoparasitic nematode providing the first steps towards a molecular understanding of this ecologically important host-parasite interaction.

Plants and Associated Soil Microbiota Cooperatively Suppress Plant-Parasitic Nematodes

Disease suppressive soils with specific suppression of soil-borne pathogens and parasites have been long studied and are most often of microbiological origin. As for the plant-parasitic nematodes (PPN), which represent a huge threat to agricultural crops and which successfully defy many conventional control methods, soil progression from conducive to suppressive state is accompanied by the enrichment of specific antagonistic microbial consortia. However, a few microbial groups have come to the fore in diminishing PPN in disease suppressive soils using culture-dependent methods. Studies with cultured strains resulted in understanding the mechanisms by which nematodes are antagonized by microorganisms. Recent culture-independent studies on the microbiome associated with soil, plant roots, and PPN contributed to a better understanding of the functional potential of disease suppressive microbial cohort. Plant root exudation is an important pathway determining host-microbe communication and plays a key role in selection and enrichment of a specific set of microbial antagonists in the rhizosphere as first line of defense against crop pathogens or parasites. Root exudates comprising primary metabolites such as amino acids, sugars, organic acids, and secondary metabolites can also cause modifications in the nematode surface and subsequently affect microbial attachment. A positive interaction between hosts and their beneficial root microbiota is correlated with a low nematode performance on the host. In this review, we first summarized the historical records of nematode-suppressive soils and then focused on more recent studies in this aspect, emphasizing the advances in studying nematode-microbe interactions over time. We highlighted nematode biocontrol mechanisms, especially parasitism, induced systemic resistance, and volatile organic compounds using microbial consortia, or bacterial strains of the genera Pasteuria, Bacillus, Pseudomonas, Rhizobium, Streptomyces, Arthrobacter, and Variovorax, or fungal isolates of Pochonia, Dactylella, Nematophthora, Purpureocillium, Trichoderma, Hirsutella, Arthrobotrys, and Mortierella. We discussed the importance of root exudates in plant communication with PPN and soil microorganisms, emphasizing their role in microbial attachment to the nematode surface and subsequent events of nematode parasitism. Comprehensive understanding of the plant-beneficial microbial consortia and the mechanisms underlying disease suppression may help to develop synthetic microbial communities for biocontrol of PPN, thereby reducing nematicides and fertilizers inputs.

Bacteria isolated from the cuticle of plant-parasitic nematodes attached to and antagonized the root-knot nematode Meloidogyne hapla

Plant-parasitic nematodes are associated with specifically attached soil bacteria. To investigate these bacteria, we employed culture-dependent methods to isolate a representative set of strains from the cuticle of the infective stage (J2) of the root-knot nematode Meloidogyne hapla in different soils. The bacteria with the highest affinity to attach to J2 belonged to the genera Microbacterium, Sphingopyxis, Brevundimonas, Acinetobacter, and Micrococcus as revealed by 16S rRNA gene sequencing. Dynamics of the attachment of two strains showed fast adhesion in less than two hours, and interspecific competition for attachment sites. Isolates from the cuticle of M. hapla J2 attached to the lesion nematode Pratylenchus penetrans, and vice versa, suggesting similar attachment sites on both species. Removal of the surface coat by treatment of J2 with the cationic detergent CTAB reduced bacterial attachment, but did not prevent it. Some of the best attaching bacteria impaired M. hapla performance in vitro by significantly affecting J2 mortality, J2 motility and egg hatch. Most of the tested bacterial attachers significantly reduced the invasion of J2 into tomato roots, suggesting their beneficial role in soil suppressiveness against M. hapla.

Fatty acid and retinol-binding protein: A novel antigen for immunodiagnosis of human strongyloidiasis

The tenacious human parasitic helminth Strongyloides stercoralis is a significant health problem worldwide. The current lack of a definitive diagnostic laboratory test to rule out this infection necessitates designing more specific diagnostic methods. Fatty acid and retinol-binding protein (FAR) plays a crucial role in the development and reproduction of nematodes. We generated a recombinant form of this protein and determined its applicability for immunodiagnosis of S. stercoralis. The L3 form of S. stercoralis was harvested and used for RNA extraction and cDNA synthesis. The coding sequence of S. stercoralis FAR (SsFAR) was cloned into pET28a(+) vector, expressed in E. coli BL21 and purified. ELISA and immunoblotting were employed to determine the specificity and sensitivity of rSsFAR using a set of defined sera. In addition, we analyzed the phylogenetic relationship of SsFAR with different FAR sequences from other nematodes. The cloned SsFAR had an open reading frame of 447 bp encoding 147 amino acids, with a deduced molecular mass of 19 kD. The SsFAR amino acid sequence was 93% identical to FAR of S. ratti. For differential immunodiagnosis of strongyloidiasis, rSsFAR exhibited 100% sensitivity and 97% specificity. However, cross-reactivity with FAR proteins of other parasites, namely Toxocara canis and Echinococcus granulosus, was noted. Our results provide a novel approach for immunodiagnosis of S. stercoralis infections using rSsFAR with reliable sensitivity and specificity.

Comparative ultrastructure of cells and cuticle in the anterior chamber and papillate region of Porcellioscaber (Crustacea, Isopoda) hindgut

Isopod hindgut consists of two anatomical and functional parts, the anterior chamber, and the papillate region. This study provides a detailed ultrastructural comparison of epithelial cells in the anterior chamber and the papillate region with focus on cuticle ultrastructure, apical and basal plasma membrane labyrinths, and cell junctions. Na⁺/K⁺-ATPase activity in the hindgut epithelial cells was demonstrated by cytochemical localisation. The main difference in cuticle ultrastructure is in the thickness of epicuticle which is almost as thick as the procuticle in the papillate region and only about one sixth of the thickness of procuticle in the anterior chamber. The apical plasma membrane in both hindgut regions forms an apical plasma membrane labyrinth of cytoplasmic strands and extracellular spaces. In the papillate region the membranous infoldings are deeper and the extracellular spaces are wider. The basal plasma membrane is extensively infolded and associated with numerous mitochondria in the papillate region, while it forms relatively scarce basal infoldings in the anterior chamber. The junctional complex in both hindgut regions consists of adherens and septate junctions. Septate junctions are more extensive in the papillate region. Na⁺/K⁺-ATPase was located mostly in the apical plasma membranes in both hindgut regions. The ultrastructural features of hindgut cuticle are discussed in comparison to exoskeletal cuticle and to cuticles of other arthropod transporting epithelia from the perspective of their mechanical properties and permeability. The morphology of apical and basal plasma membranes and localisation of Na⁺/K⁺-ATPase are compared with other arthropod-transporting epithelia according to different functions of the anterior chamber and the papillate region.

Knockdown of a mucin-like gene in Meloidogyne incognita (Nematoda) decreases attachment of endospores of Pasteuria penetrans to the infective juveniles and reduces nematode fecundity

Mucins are highly glycosylated polypeptides involved in many host-parasite interactions, but their function in plant-parasitic nematodes is still unknown. In this study, a mucin-like gene was cloned from Meloidogyne incognita (Mi-muc-1, 1125 bp) and characterized. The protein was found to be rich in serine and threonine with numerous O-glycosylation sites in the sequence. Quantitative real-time polymerase chain reaction (qRT-PCR) showed the highest expression in the adult female and in situ hybridization revealed the localization of Mi-muc-1 mRNA expression in the tail area in the region of the phasmid. Knockdown of Mi-muc-1 revealed a dual role: (1) immunologically, there was a significant decrease in attachment of Pasteuria penetrans endospores and a reduction in binding assays with human red blood cells (RBCs), suggesting that Mi-MUC-1 is a glycoprotein present on the surface coat of infective second-stage juveniles (J2s) and is involved in cellular adhesion to the cuticle of infective J2s; pretreatment of J2s with different carbohydrates indicated that the RBCs bind to J2 cuticle receptors different from those involved in the interaction of Pasteuria endospores with Mi-MUC-1; (2) the long-term effect of RNA interference (RNAi)-mediated knockdown of Mi-muc-1 led to a significant reduction in nematode fecundity, suggesting a possible function for this mucin as a mediator in the interaction between the nematode and the host plant.

Nematobacterial Complexes and Insect Hosts: Different Weapons for the Same War

Entomopathogenic nematodes (EPNs) are widely used as biological control agents against insect pests, the efficacy of these organisms strongly depends on the balance between the parasitic strategies and the immune response of the host. This review summarizes roles and relationships between insect hosts and two well-known EPN species, Steinernema feltiae and Steinernema carpocapsae and outlines the main mechanisms of immune recognition and defense of insects. Analyzing information and findings about these EPNs, it is clear that these two species use shared immunosuppression strategies, mainly mediated by their symbiotic bacteria, but there are differences in both the mechanism of evasion and interference of the two nematodes with the insect host immune pathways. Based on published data, S. feltiae takes advantage of the cross reaction between its body surface and some host functional proteins, to inhibit defensive processes; otherwise, secretion/excretion products from S. carpocapsae seem to be the main nematode components responsible for the host immunosuppression.

Predator-prey interactions of nematode-trapping fungi and nematodes: both sides of the coin

Nematode-trapping fungi develop complex trapping devices to capture and consume nematodes. The dynamics of these organisms is especially important given the pathogenicity of nematodes and, consequently, the potential application of nematode-trapping fungi as biocontrol agents. Furthermore, both the nematodes and nematode-trapping fungi can be easily grown in laboratories, making them a unique manipulatable predator-prey system to study their coevolution. Several different aspects of these fungi have been studied, such as their genetics and the different factors triggering trap formation. In this review, we use the nematode-trapping fungus Arthrobotrys oligospora (which forms adhesive nets) as a model to describe the trapping process. We divide this process into several stages; namely attraction, recognition, trap formation, adhesion, penetration, and digestion. We summarize the latest findings in the field and current knowledge on the interactions between nematodes and nematode-trapping fungi, representing both sides of the predator-prey interaction.

Surface protein components from entomopathogenic nematodes and their symbiotic bacteria: effects on immune responses of the greater wax moth, Galleria mellonella (Lepidoptera: Pyralidae)

BACKGROUND

Steinernema carpocapsae is a nematocomplex widely used as an alternative to chemicals for the biological control of insect pests; this nematode is symbiotically associated with the bacterium Xenorhabdus nematophila and both contribute to host death. The architecture and functions of structures and molecular components of the surface of nematodes and their symbiont bacteria are integral to early interactions with their hosts; thus, we assessed the role of protein pools isolated from the surface of S. carpocapsae and from phase I X. nematophila against Galleria mellonella.

RESULTS

Using high-salt treatments, we isolated the surface proteins and assayed them on G. mellonella haemocytes; haemocyte viability and phagocytic activity were investigated in the presence of surface proteins from nematodes or bacteria. Proteins from live S. carpocapsae possessed mild cytotoxicity on the haemocytes, whereas those from live X. nematophila markedly affected the host cells' viability. Bacterial proteins inhibited phagocytic activity, although they strongly triggered the host proPO (prophenoloxidase-phenoloxidase) system.

CONCLUSION

Nematocomplex surface compounds play a key role in immunoevasion/depression of insect hosts, causing a severe physiological disorder. Natural compounds newly identified as active against pests could improve the pest management of species potentially harmful to plants in urban green spaces and agriculture. © 2018 Society of Chemical Industry.

The physicochemical fingerprint of Necator americanus

Necator americanus, a haematophagous hookworm parasite, infects ~10% of the world's population and is considered to be a significant public health risk. Its lifecycle has distinct stages, permitting its successful transit from the skin via the lungs (L3) to the intestinal tract (L4 maturing to adult). It has been hypothesised that the L3 larval sheath, which is shed during percutaneous infection (exsheathment), diverts the immune system to allow successful infection and reinfection in endemic areas. However, the physicochemical properties of the L3 larval cuticle and sheath, which are in direct contact with the skin and its immune defences, are unknown. In the present study, we controlled exsheathment, to characterise the sheath and underlying cuticle surfaces in situ, using atomic force microscopy (AFM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). AFM revealed previously unseen surface area enhancing nano-annuli exclusive to the sheath surface and confirmed greater adhesion forces exist between cationic surfaces and the sheath, when compared to the emergent L3 cuticle. Furthermore, ToF-SIMS elucidated different chemistries between the surfaces of the cuticle and sheath which could be of biological significance. For example, the phosphatidylglycerol rich cuticle surface may support the onward migration of a lubricated infective stage, while the anionic and potentially immunologically active heparan sulphate rich deposited sheath could result in the diversion of immune defences to an inanimate antigenic nidus. We propose that our initial studies into the surface analysis of this hookworm provides a timely insight into the physicochemical properties of a globally important human pathogen at its infective stage and anticipate that the development and application of this analytical methodology will support translation of these findings into a biological context.

The gastropod shell has been co-opted to kill parasitic nematodes

Exoskeletons have evolved 18 times independently over 550 MYA and are essential for the success of the Gastropoda. The gastropod shell shows a vast array of different sizes, shapes and structures, and is made of conchiolin and calcium carbonate, which provides protection from predators and extreme environmental conditions. Here, I report that the gastropod shell has another function and has been co-opted as a defense system to encase and kill parasitic nematodes. Upon infection, cells on the inner layer of the shell adhere to the nematode cuticle, swarm over its body and fuse it to the inside of the shell. Shells of wild Cepaea nemoralis, C. hortensis and Cornu aspersum from around the U.K. are heavily infected with several nematode species including Caenorhabditis elegans. By examining conchology collections I show that nematodes are permanently fixed in shells for hundreds of years and that nematode encapsulation is a pleisomorphic trait, prevalent in both the achatinoid and non-achatinoid clades of the Stylommatophora (and slugs and shelled slugs), which diverged 90–130 MYA. Taken together, these results show that the shell also evolved to kill parasitic nematodes and this is the only example of an exoskeleton that has been co-opted as an immune system.

The Caenorhabditis elegans Excretory System: A Model for Tubulogenesis, Cell Fate Specification, and Plasticity

The excretory system of the nematode Caenorhabditis elegans is a superb model of tubular organogenesis involving a minimum of cells. The system consists of just three unicellular tubes (canal, duct, and pore), a secretory gland, and two associated neurons. Just as in more complex organs, cells of the excretory system must first adopt specific identities and then coordinate diverse processes to form tubes of appropriate topology, shape, connectivity, and physiological function. The unicellular topology of excretory tubes, their varied and sometimes complex shapes, and the dynamic reprogramming of cell identity and remodeling of tube connectivity that occur during larval development are particularly fascinating features of this organ. The physiological roles of the excretory system in osmoregulation and other aspects of the animal's life cycle are only beginning to be explored. The cellular mechanisms and molecular pathways used to build and shape excretory tubes appear similar to those used in both unicellular and multicellular tubes in more complex organs, such as the vertebrate vascular system and kidney, making this simple organ system a useful model for understanding disease processes.

A Phosphorylcholine-Containing Glycolipid-like Antigen Present on the Surface of Infective Stage Larvae of Ascaris spp. Is a Major Antibody Target in Infected Pigs and Humans

BACKGROUND

The pig parasite Ascaris suum plays and important role in veterinary medicine and represents a suitable model for A. lumbricoides, which infects over 800 million people. In pigs, continued exposure to Ascaris induces immunity at the level of the gut, protecting the host against migrating larvae. The objective of this study was to identify and characterize parasite antigens targeted by this local immune response that may be crucial for parasite invasion and establishment and to evaluate their protective and diagnostic potential.

METHODOLOGY/PRINCIPAL FINDINGS

Pigs were immunized by trickle infection for 30 weeks, challenged with 2,000 eggs at week 32 and euthanized two weeks after challenge. At necropsy, there was a 100% reduction in worms recovered from the intestine and a 97.2% reduction in liver white spots in comparison with challenged non-immune control animals. Antibodies purified from the intestinal mucus or from the supernatant of cultured antibody secreting cells from mesenteric lymph nodes of immune pigs were used to probe L3 extracts to identify antibody targets. This resulted in the recognition of a 12kDa antigen (As12) that is actively shed from infective Ascaris L3. As12 was characterized as a phosphorylcholine-containing glycolipid-like antigen that is highly resistant to different enzymatic and chemical treatments. Vaccinating pigs with an As12 fraction did not induce protective immunity to challenge infection. However, serological analysis using sera or plasma from experimentally infected pigs or naturally infected humans demonstrated that the As12 ELISA was able to detect long-term exposure to Ascaris with a high diagnostic sensitivity (98.4% and 92%, respectively) and specificity (95.5% and 90.0%) in pigs and humans, respectively.

CONCLUSIONS/SIGNIFICANCE

These findings show the presence of a highly stage specific, glycolipid-like component (As12) that is actively secreted by infectious Ascaris larvae and which acts as a major antibody target in infected humans and pigs.

The genome, transcriptome, and proteome of the nematode Steinernema carpocapsae: evolutionary signatures of a pathogenic lifestyle

The entomopathogenic nematode Steinernema carpocapsae has been widely used for the biological control of insect pests. It shares a symbiotic relationship with the bacterium Xenorhabdus nematophila, and is emerging as a genetic model to study symbiosis and pathogenesis. We obtained a high-quality draft of the nematode’s genome comprising 84,613,633 bp in 347 scaffolds, with an N50 of 1.24 Mb. To improve annotation, we sequenced both short and long RNA and conducted shotgun proteomic analyses. S. carpocapsae shares orthologous genes with other parasitic nematodes that are absent in the free-living nematode C. elegans, it has ncRNA families that are enriched in parasites, and expresses proteins putatively associated with parasitism and pathogenesis, suggesting an active role for the nematode during the pathogenic process. Host and parasites might engage in a co-evolutionary arms-race dynamic with genes participating in their interaction showing signatures of positive selection. Our analyses indicate that the consequence of this arms race is better characterized by positive selection altering specific functions instead of just increasing the number of positively selected genes, adding a new perspective to these co-evolutionary theories. We identified a protein, ATAD-3, that suggests a relevant role for mitochondrial function in the evolution and mechanisms of nematode parasitism.

Modulation of immune responses of Rhynchophorus ferrugineus (Insecta: Coleoptera) induced by the entomopathogenic nematode Steinernema carpocapsae (Nematoda: Rhabditida)

Aim of this study was to investigate relationships between the red palm weevil (RPW) Rhynchophorus ferrugineus (Olivier) and the entomopathogenic nematode Steinernema carpocapsae (EPN); particularly, the work was focused on the immune response of the insect host in naive larvae and after infection with the EPN. Two main immunological processes have been addressed: the activity and modulation of host prophenoloxidase-phenoloxidase (proPO) system, involved in melanization of not-self and hemocytes recognition processes responsible for not-self encapsulation. Moreover, immune depressive and immune evasive strategies of the parasite have been investigated. Our results suggest that RPW possess an efficient immune system, however in the early phase of infection, S. carpocapsae induces a strong inhibition of the host proPO system. In addition, host cell-mediated mechanisms of encapsulation, are completely avoided by the parasite, the elusive strategies of S. carpocapsae seem to be related to the structure of its body-surface, since induced alterations of the parasite cuticle resulted in the loss of its mimetic properties. S. carpocapsae before the release of its symbiotic bacteria, depress and elude RPW immune defenses, with the aim to arrange a favorable environment for its bacteria responsible of the septicemic death of the insect target.

Whole-animal mounts of Caenorhabditis elegans for 3D imaging using atomic force microscopy

The 3D surface of Caenorhabditis elegans was imaged at nanometer resolution using atomic force microscopy (AFM). Oscillation of a medium stiffness silicon AFM cantilever at the upper second amplitude peak, typically 6 times above the fundamental frequency, vastly improved image quality on the moist, sticky, and soft worms. Whole-animal mounts of normal and double-headed mutants of the nematode worm were prepared and scanned. Well-preserved anatomical features including annuli, furrows, alae, and rows of never before seen nanometer-sized pores dotting the molted worm's outermost surface coat were resolved. Well-preserved anatomical features including annuli, furrows, alae, and rows of nanometer-sized pores or struts dotting the molted worm's outermost surface were resolved. This AFM method represents a simple and rapid new approach for nanometer-resolved 3D imaging and analysis of whole-animal specimens of C. elegans.

FROM THE CLINICAL EDITOR

In this interesting article the authors describe a new AFM sampling method to allow better images on whole-animal mounts such as C. elegans. This method would generate more information and in the future may be useful for differentiating even individual animals with different genetic backgrounds.

Caenorhabditis evolution in the wild

Recent research has filled many gaps about Caenorhabditis natural history, simultaneously exposing how much remains to be discovered. This awareness now provides means of connecting ecological and evolutionary theory with diverse biological patterns within and among species in terms of adaptation, sexual selection, breeding systems, speciation, and other phenomena. Moreover, the heralded laboratory tractability of C. elegans, and Caenorhabditis species generally, provides a powerful case study for experimental hypothesis testing about evolutionary and ecological processes to levels of detail unparalleled by most study systems. Here, I synthesize pertinent theory with what we know and suspect about Caenorhabditis natural history for salient features of biodiversity, phenotypes, population dynamics, and interactions within and between species. I identify topics of pressing concern to advance Caenorhabditis biology and to study general evolutionary processes, including the key opportunities to tackle problems in dispersal dynamics, competition, and the dimensionality of niche space.

Adaptive amino acid composition in collagens of parasitic nematodes

Amino acid composition was analyzed in the glycine-rich repeat region of 306 collagens belonging to three major families of collagens from both parasitic and free-living nematodes. The collagens of parasitic species showed a tendency toward decreased usage of the hydrophilic residues A, D, and Q and increased usage of the hydrophobic resides I, L, and M; and this trend was seen in parasitic species of both the order Rhabdita and the order Spirurida. The amino acid composition of collagens of parasitic Rhabdita thus tended to resemble those of Spirurida more than that of free-living Rhabdita, suggesting an association between amino acid composition and a parasitic lifestyle. Computer predictions suggested that the more hydrophobic amino acid composition was associated with a reduction of the propensity towards B-cell epitope formation, suggesting that evasion of host immune responses may be a major selective factor responsible for the parasite-specific trend in collagen amino acid composition.

Caenorhabditis elegans bacterial pathogen resistant bus-4 mutants produce altered mucins

Caenorabditis elegans bus-4 glycosyltransferase mutants are resistant to infection by Microbacterium nematophilum, Yersinia pestis and Yersinia pseudotuberculosis and have altered susceptibility to two Leucobacter species Verde1 and Verde2. Our objective in this study was to define the glycosylation changes leading to this phenotype to better understand how these changes lead to pathogen resistance. We performed MALDI-TOF MS, tandem MS and GC/MS experiments to reveal fine structural detail for the bus-4 N- and O-glycan pools. We observed dramatic changes in O-glycans and moderate ones in N-glycan pools compared to the parent strain. Ce core-I glycans, the nematode's mucin glycan equivalent, were doubled in abundance, halved in charge and bore shifts in terminal substitutions. The fucosyl O-glycans, Ce core-II and neutral fucosyl forms, were also increased in abundance as were fucosyl N-glycans. Quantitative expression analysis revealed that two mucins, let-653 and osm-8, were upregulated nearly 40 fold and also revealed was a dramatic increase in GDP-Man 4,6 dehydratease expression. We performed detailed lectin binding studies that showed changes in glycoconjugates in the surface coat, cuticle surface and intestine. The combined changes in cell surface glycoconjugate distribution, increased abundance and altered properties of mucin provide an environment where likely the above pathogens are not exposed to normal glycoconjugate dependent cues leading to barriers to these bacterial infections.

Defects in the C. elegans acyl-CoA synthase, acs-3, and nuclear hormone receptor, nhr-25, cause sensitivity to distinct, but overlapping stresses

Metazoan transcription factors control distinct networks of genes in specific tissues, yet understanding how these networks are integrated into physiology, development, and homeostasis remains challenging. Inactivation of the nuclear hormone receptor nhr-25 ameliorates developmental and metabolic phenotypes associated with loss of function of an acyl-CoA synthetase gene, acs-3. ACS-3 activity prevents aberrantly high NHR-25 activity. Here, we investigated this relationship further by examining gene expression patterns following acs-3 and nhr-25 inactivation. Unexpectedly, we found that the acs-3 mutation or nhr-25 RNAi resulted in similar transcriptomes with enrichment in innate immunity and stress response gene expression. Mutants of either gene exhibited distinct sensitivities to pathogens and environmental stresses. Only nhr-25 was required for wild-type levels of resistance to the bacterial pathogen P. aeruginosa and only acs-3 was required for wild-type levels of resistance to osmotic stress and the oxidative stress generator, juglone. Inactivation of either acs-3 or nhr-25 compromised lifespan and resistance to the fungal pathogen D. coniospora. Double mutants exhibited more severe defects in the lifespan and P. aeruginosa assays, but were similar to the single mutants in other assays. Finally, acs-3 mutants displayed defects in their epidermal surface barrier, potentially accounting for the observed sensitivities. Together, these data indicate that inactivation of either acs-3 or nhr-25 causes stress sensitivity and increased expression of innate immunity/stress genes, most likely by different mechanisms. Elevated expression of these immune/stress genes appears to abrogate the transcriptional signatures relevant to metabolism and development.

Proteomic analysis of the excretory-secretory products from larval stages of Ascaris suum reveals high abundance of glycosyl hydrolases

BACKGROUND

Ascaris lumbricoides and Ascaris suum are socioeconomically important and widespread parasites of humans and pigs, respectively. The excretory-secretory (ES) molecules produced and presented at the parasite-host interface during the different phases of tissue invasion and migration are likely to play critical roles in the induction and development of protective immune and other host responses.

METHODOLOGY/PRINCIPAL FINDINGS

The aim of this study was to identify the ES proteins of the different larval stages (L3-egg, L3-lung and L4) by LC-MS/MS. In total, 106 different proteins were identified, 20 in L3-egg, 45 in L3-lung stage and 58 in L4. Although most of the proteins identified were stage-specific, 15 were identified in the ES products of at least two stages. Two proteins, i.e. a 14-3-3-like protein and a serpin-like protein, were present in the ES products from the three different larval stages investigated. Interestingly, a comparison of ES products from L4 with those of L3-egg and L3-lung showed an abundance of metabolic enzymes, particularly glycosyl hydrolases. Further study indicated that most of these glycolytic enzymes were transcriptionally upregulated from L4 onwards, with a peak in the adult stage, particularly in intestinal tissue. This was also confirmed by enzymatic assays, showing the highest glycosidase activity in protein extracts from adult worms gut.

CONCLUSIONS/SIGNIFICANCE

The present proteomic analysis provides important information on the host-parasite interaction and the biology of the migratory stages of A. suum. In particular, the high transcriptional upregulation of glycosyl hydrolases from the L4 stage onwards reveals that the degradation of complex carbohydrates forms an essential part of the energy metabolism of this parasite once it establishes in the small intestine.

Phage-display library biopanning as a novel approach to identifying nematode vaccine antigens

Infections with parasitic nematodes are of significant welfare and economic importance worldwide, and because of the emergence of anthelmintic resistance, this has lead to alternative methods of parasite control being required. Vaccination offers a feasible alternative control, and the majority of research has focused on the production of recombinant versions of native antigens previously identified as protective in vaccinated animals. Attempts at the production of protective recombinant subunit vaccines have been hindered, however, as these antigens have invariably failed to replicate the same level of protective immune response as seen with the native versions. It has been proposed that these failures are owing to the fact that the recombinant proteins do not contain the appropriate post-translational modifications to retain the protective capacity of the native molecules. In this review, we discuss a novel approach to vaccine antigen identification through the application of random peptide phage-display libraries and their use to identify peptide sequences that potentially mimic the structure(s) of antigenic epitopes. This area of research is still relatively novel with respect to parasites, and the current state of the art will be discussed here.

Steinernema glaseri surface enolase: molecular cloning, biological characterization, and role in host immune suppression

Entomopathogenic nematodes are widely used as biological control agents that can suppress or evade the host immune defense upon entry into insects. The surface coat of Steinernema glaseri has been shown to play important roles in defeating the host immune system. In this work, a protein fraction with antiphagocytic activity was separated by electro-elution and further analyzed by two-dimensional electrophoresis (2-DE). LC-MS/MS analysis of one protein spot from a 2-DE gel gave five peptides that were highly similar to enolases of many organisms. A 1311 bp cDNA was cloned that encodes a 47 kDa protein with high sequence identity to enolases from different species of nematodes. The deduced protein, Sg-ENOL, was expressed in Escherichia coli, and its glycolytic activity was demonstrated by the conversion of 2-phospho-d-glycerate to phosphoenolpyruvate. Recombinant Sg-ENOL significantly reduced the LT(50)s of Xenorhabdus poinarii and Metarhizium anisopliae when co-injected into Galleria mellonella and Locusta migratoria manilensis Meyen, respectively. Using immuno-gold transmission electron microscopy, native Sg-ENOL was confirmed to be localized to both the nematode cuticle and the surface coat. In vitro, secretion of Sg-ENOL was inducible rather than constitutive. In vivo, Sg-ENOL was detected in the host hemolymph after infection of G. mellonella with S. glaseri, indicating that Sg-ENOL was secreted into the insect hemocoel and was involved in infection. This is the first report of the cloning and characterization of a surface coat protein in an entomopathogenic nematode. Our findings provide clear evidence for an important role for a cell surface enolase in S. glaseri infection and host immune suppression.

Silencing of essential genes by RNA interference in Haemonchus contortus

In this study we assessed three technologies for silencing gene expression by RNA interference (RNAi) in the sheep parasitic nematode Haemonchus contortus. We chose as targets five genes that are essential in Caenorhabditis elegans (mitr-1, pat-12, vha-19, glf-1 and noah-1), orthologues of which are present and expressed in H. contortus, plus four genes previously tested by RNAi in H. contortus (ubiquitin, tubulin, paramyosin, tropomyosin). To introduce double-stranded RNA (dsRNA) into the nematodes we tested (1) feeding free-living stages of H. contortus with Escherichia coli that express dsRNA targetting the test genes; (2) electroporation of dsRNA into H. contortus eggs or larvae; and (3) soaking adult H. contortus in dsRNA. For each gene tested we observed reduced levels of mRNA in the treated nematodes, except for some electroporation conditions. We did not observe any phenotypic changes in the worms in the electroporation or dsRNA soaking experiments. The feeding method, however, elicited observable changes in the development and viability of larvae for five of the eight genes tested, including the ‘essential’ genes, Hc-pat-12, Hc-vha-19 and Hc-glf-1. We recommend the E. coli feeding method for RNAi in H. contortus and provide recommendations for future research directions for RNAi in this species.