Aralia Leon Coria

Myxozoans are a monophyletic taxon of approximately 2,400 described species of parasites from the phylum Cnidaria. The recent focus on their negative impacts on fisheries, on their evolution from free-living ancestors, and on their emergence into new fish host populations has stressed the critical need for genomic resources for this parasitic group. Here, we describe the genome assembly and annotation of Myxobolus rasmusseni, an emerging parasite of fathead minnows in Alberta, Canada. The assembly is 174.6 Mb in size, 68% of which is made up of repetitive elements, making it one of the most repetitive animal genomes sequenced to date. Through comparisons to other myxozoans, we show that widespread gene loss, a known phenomenon of this group of parasites, is consistent with closely related species. Additionally, we assembled the M. rasmusseni mitochondrial genome which is nearly twice the size of the typical animal mitochondrial genome yet contains only five of the canonical mitochondrial protein-coding genes and open reading frames not found in other myxozoans. These results add to our understanding of the gene- and genome-level diversity observed in myxozoans.

Co-infections are a common reality but understanding how the immune system responds in this context is complex and can be unpredictable. Heligmosomoides bakeri (parasitic roundworm, previously Heligmosomoides polygyrus) and Toxoplasma gondii (protozoan parasite) are well studied organisms that stimulate a characteristic Th2 and Th1 response, respectively. Several studies have demonstrated reduced inflammatory cytokine responses in animals co-infected with such organisms. However, while general cytokine signatures have been examined, the impact of the different cytokine producing lymphocytes on parasite control/clearance is not fully understood. We investigated five different lymphocyte populations (NK, NKT, γδ T, CD4⁺ T and CD8⁺ T cells), five organs (small intestine, Peyer’s patches, mesenteric lymph nodes, spleen and liver), and 4 cytokines (IFN©, IL-4, IL-10 and IL-13) at two different time points (days 5 and 10 post T. gondii infection). We found that co-infected animals had significantly higher mortality than either single infection. This was accompanied by transient and local changes in parasite loads and cytokine profiles. Despite the early changes in lymphocyte and cytokine profiles, severe intestinal pathology in co-infected mice likely contributed to early mortality due to significant damage by both parasites in the small intestine. Our work demonstrates the importance of taking a broad view during infection research, studying multiple cell types, organs/tissues and time points to link and/or uncouple immunological from pathological findings. Our results provide insights into how co-infection with parasites stimulating different arms of the immune system can lead to drastic changes in infection dynamics.

Background The Myxozoa is a group of at least 2,400 endoparasites within the phylum Cnidaria. All myxozoans have greatly reduced in size and morphology compared to free-living members of the phylum. They are best known for causing disease in economically important fish across the world; for example, Myxobolus cerebralis causes whirling disease, which can kill 90% of infected juvenile salmonid fish. In 2017, a new myxozoan species was identified in Alberta. Myxobolus rasmusseni n. sp. causes distinct lesions in fathead minnows, which are ultimately fatal. Here, we sequenced, assembled and analyzed the genome of M. rasmusseni to understand how the parasite interacts with its fish host and identify potential strategies to counter this emerging threat. Results At 185 Mb, the M. rasmusseni genome is the largest myxozoan genome sequenced so far. This large genome size is, in part, due to the high repetitive content; 68% of the genome was interspersed repeats, with the MULE-MuDR transposon covering 18% of the M. rasmusseni genome. Similar to myxozoan genomes, the M. rasmusseni genome has lost many genes well conserved in other eukaryotes. However, we also identified multiple expansions in gene families—serine proteases, hexokinases, and FLYWCH-domain containing proteins—which suggests their functional importance in the parasite. The mitochondrial genome of M. rasmusseni encodes only five of the thirteen protein-coding genes typically found in animals. We found that the mitochondrial gene atp6 was transferred to the nucleus and acquired a mitochondria-targeting signal in M. rasmusseni. Conclusions Our study provides valuable insights into myxozoan biology and identify promising avenues for future research. We also propose that M. rasmusseni is promising myxozoan model to explore host-parasite interactions in these parasites.

Entamoeba histolytica (Eh) is a protozoan parasite of humans that colonizes the outer colonic mucus layer. Under conditions not fully understood, Eh breaches innate host defenses and invades the intestinal mucosa-causing amebic colitis and liver abscess. In asymptomatic infection, Eh interacts with and feeds on resident microbiota that forms biofilms on the outer colonic mucus layer. Despite the close association between Eh and commensal microbiota, we still lack basic knowledge on whether microbiota and/or their metabolites influence Eh virulence traits critical in disease pathogenesis. In the pathogenesis of intestinal amebiasis, Eh overcomes the protective mucus layer using a combination of mucinase/glycosidase and potent mucus secretagogue activity. In this addendum, we discuss the interconnected role of a healthy mucus barrier and the role commensal microbiota play in shaping innate host defense against Eh-induced pro-inflammatory and secretory responses critical in disease pathogenesis.

Amebiasis is caused by the protozoan parasite Entamoeba histolytica (Eh), a potentially fatal disease occurring mainly in developing countries. How Eh interacts with innate host factors in the gut is poorly understood. Eh resides and feed in/on the outer colonic mucus layer and thus share an ecological niche with indigenous microbiota. As gut microbiota regulates innate immune responses, in this study we characterized the cooperative roles that microbiota and the mucus layer play in Eh-induced pro-inflammatory responses in the colon. To study this, we used antibiotics treated and non-treated specific pathogen free Muc2^-/- and Muc2^+/+ littermates and germ-free mice inoculated with Eh in colonic loops as a short infection model. In antibiotic treated Muc2^-/- and Muc2^+/+ littermates, Eh elicited robust mucus and water secretions, enhanced pro-inflammatory cytokines and chemokine expression with elevated MPO activity and higher pathology scores as compared to the modest response observed in non-antibiotic treated littermates. Host responses were microbiota specific as mucus secretion and pro-inflammatory responses were attenuated following homologous fecal microbial transplants in antibiotic-treated Muc2^+/+ quantified by secretion of ³H-glucosamine newly synthesized mucin, Muc2 mucin immunostaining and immunohistochemistry. Eh-elicited pro-inflammatory responses and suppressed goblet cell transcription factor Math1 as revealed by in vivo imaging of Eh-colonic loops in Math1^GFP mice, and in vitro using Eh-stimulated LS174T human colonic goblet cells. Eh in colonic loops increased bacterial translocation of bioluminescent E. coli and indigenous bacteria quantified by FISH and quantitative PCR. In germ-free animals, Eh-induced mucus/water secretory responses, but acute pro-inflammatory responses and MPO activity were severely impaired, allowing the parasite to bind to and disrupt mucosal epithelial cells. These findings have identified key roles for intestinal microbiota and mucus in regulating innate host defenses against Eh, and implicate dysbiosis as a risk factor for amebiasis that leads to exacerbated immune responses to cause life-threatening disease. Entamoeba histolytica (Eh) is a human protozoan parasite and the causative agent of amebiasis. Amebic colitis causes cellular destruction of the colonic mucosal layers allowing parasites to disseminate to the liver through blood causing amoebic liver abscess, or to other soft organs like the brain and lungs. Eh in the colon shares an environment with resident intestinal microbiota that lives, feeds and multiplies on the mucus layer. Both microbiota and mucus play critical protective roles in innate host defense however, to date, little is known about the interactions between ameba-microbiota and the mucus layers. Here we show that microbial dysbiosis worsen the outcome of Eh infection, favoring bacterial translocation, increasing pro-inflammatory responses independently of the mucus layer, as well as regulating mucus release from goblet cells. The absence of microbiota in germ-free mice altered the host from mounting a proper innate immune response towards Eh allowing parasites to bind to and disrupt mucosal epithelial cells. These data highlight critical roles for indigenous microbiota in imprinting and educating mucosal innate host defenses critical for host defense against E. histolytica invasion.