Host-Protozoan Interactions Protect from Mucosal Infections through Activation of the Inflammasome.

While conventional pathogenic protists have been extensively studied, there is an underappreciated constitutive protist microbiota that is an integral part of the vertebrate microbiome. The impact of these species on the host and their potential contributions to mucosal immune homeostasis remain poorly studied. Here, we show that the protozoan Tritrichomonas musculis activates the host epithelial inflammasome to induce IL-18 release. Epithelial-derived IL-18 promotes dendritic cell-driven Th1 and Th17 immunity and confers dramatic protection from mucosal bacterial infections. Along with its role as a "protistic" antibiotic, colonization with T. musculis exacerbates the development of T-cell-driven colitis and sporadic colorectal tumors. Our findings demonstrate a novel mutualistic host-protozoan interaction that increases mucosal host defenses at the cost of an increased risk of inflammatory disease.

Fine structure and molecular characterization of two new parabasalid species that naturally colonize laboratory mice, Tritrichomonas musculus and Tritrichomonas casperi.

Tritrichomonas muris is a common flagellated protist isolated from the cecum of wild rodents. This commensal protist has been shown previously to alter immune phenotypes in laboratory mice. Other trichomonads, referred to as Tritrichomonas musculis and Tritrichomonas rainier, also naturally colonize laboratory mice and cause immune alterations. This report formally describes two new trichomonads, Tritrichomonas musculus n. sp., and Tritrichomonas casperi n. sp., at the ultrastructural and molecular level. These two protists were isolated from laboratory mice and were differentiated by their size and the structure of their undulating membrane and posterior flagellum. Analysis at the 18S rRNA and trans-ITS genetic loci supported their designation as distinct species, related to T. muris. To assess the true extent of parabasalid diversity infecting laboratory mice, 135 mice bred at the National Institutes of Health (NIH) were screened using pan-parabasalid primers that amplify the trans-ITS region. Forty-four percent of mice were positive for parabasalids, encompassing a total of eight distinct sequence types. Tritrichomonas casperi and Trichomitus-like protists were dominant. T. musculus and T. rainier were also detected, but T. muris was not. Our work establishes a previously underappreciated diversity of commensal trichomonad flagellates that naturally colonize the enteric cavity of laboratory mice.

PopNet: A Markov Clustering Approach to Study Population Genetic Structure.

With the advent of low cost, high-throughput genome sequencing technology, population genomic data sets are being generated for hundreds of species of pathogenic, industrial, and agricultural importance. The challenge is how best to analyze and visually display these complex data sets to yield intuitive representations capable of capturing complex evolutionary relationships. Here we present PopNet, a novel computational method that identifies regions of shared ancestry in the chromosomes of related strains through clustering patterns of genetic variation. These relationships are subsequently visualized within a network by a novel implementation of chromosome painting. We apply PopNet to three diverse populations that feature differential rates of recombination and demonstrate its ability to capture evolutionary relationships as well as associate traits to specific loci. Compared with existing tools, PopNet provides substantial advances by both removing the need to predefine a single reference genome that can bias interpretation of population structure, as well as its ability to visualize multiple evolutionary relationships, such as recombination events and shared ancestry, across hundreds of strains.

A Lipolytic Lecithin:Cholesterol Acyltransferase Secreted by Toxoplasma Facilitates Parasite Replication and Egress.

The protozoan parasite Toxoplasma gondii develops within a parasitophorous vacuole (PV) in mammalian cells, where it scavenges cholesterol. When cholesterol is present in excess in its environment, the parasite expulses this lipid into the PV or esterifies it for storage in lipid bodies. Here, we characterized a unique T. gondii homologue of mammalian lecithin:cholesterol acyltransferase (LCAT), a key enzyme that produces cholesteryl esters via transfer of acyl groups from phospholipids to the 3-OH of free cholesterol, leading to the removal of excess cholesterol from tissues. TgLCAT contains a motif characteristic of serine lipases "AHSLG" and the catalytic triad consisting of serine, aspartate, and histidine (SDH) from LCAT enzymes. TgLCAT is secreted by the parasite, but unlike other LCAT enzymes it is cleaved into two proteolytic fragments that share the residues of the catalytic triad and need to be reassembled to reconstitute enzymatic activity. TgLCAT uses phosphatidylcholine as substrate to form lysophosphatidylcholine that has the potential to disrupt membranes. The released fatty acid is transferred to cholesterol, but with a lower transesterification activity than mammalian LCAT. TgLCAT is stored in a subpopulation of dense granule secretory organelles, and following secretion, it localizes to the PV and parasite plasma membrane. LCAT-null parasites have impaired growth in vitro, reduced virulence in animals, and exhibit delays in egress from host cells. Parasites overexpressing LCAT show increased virulence and faster egress. These observations demonstrate that TgLCAT influences the outcome of an infection, presumably by facilitating replication and egress depending on the developmental stage of the parasite.

Characterization of Sf9 cell clones with differential susceptibilities to Sf-rhabdovirus X+3.7 and Sf-rhabdovirus X- replication.

Our laboratory previously discovered a novel rhabdovirus in the Spodoptera frugiperda Sf9 insect cell line that was designated as Sf-rhabdovirus. Using limiting dilution, this cell line was found to be a mixed population of cells infected by Sf-rhabdovirus variants containing either the full length X accessory gene with a 3.7 kb internal duplication (designated as Sf-rhabdovirus X+3.7) or lacking the duplication and part of the X gene (designated as Sf-rhabdovirus X-), and cells that were negative for Sf-rhabdovirus. In this paper, we found that the Sf-rhabdovirus negative cell clones had sub-populations with different susceptibilities to the replication of Sf-rhabdovirus X+3.7 and X- variants: cell clone Sf9-13F12 was more sensitive to replication by both virus variants compared to Sf9-3003; moreover, Sf9-3003 showed more resistance to X+3.7 replication than to X- replication. RNA-Seq analysis indicated significant differentially expressed genes in the Sf9-13F12 and Sf9-3003 cell clones further supporting that distinct sub-populations of virus-negative cells co-exist in the parent Sf9 cell line.

Commensal protist Tritrichomonas musculus exhibits a dynamic life cycle that induces extensive remodeling of the gut microbiota.

Commensal protists and gut bacterial communities exhibit complex relationships, mediated at least in part through host immunity. To improve our understanding of this tripartite interplay, we investigated community and functional dynamics between the murine protist Tritrichomonas musculus and intestinal bacteria in healthy and B-cell-deficient mice. We identified dramatic, protist-driven remodeling of resident microbiome growth and activities, in parallel with Tritrichomonas musculus functional changes, which were accelerated in the absence of B cells. Metatranscriptomic data revealed nutrient-based competition between bacteria and the protist. Single-cell transcriptomics identified distinct Tritrichomonas musculus life stages, providing new evidence for trichomonad sexual replication and the formation of pseudocysts. Unique cell states were validated in situ through microscopy and flow cytometry. Our results reveal complex microbial dynamics during the establishment of a commensal protist in the gut, and provide valuable data sets to drive future mechanistic studies.

Ultrastructural identification and molecular characterization of two new parabasalid species that naturally colonize laboratory mice, Tritrichomonas musculus and Tritrichomonas casperi.

Tritrichomonas muris is a flagellated protist isolated from the cecum of wild mice in the Czech Republic. This commensal protist has been shown previously to alter immune phenotypes in laboratory mice. Other trichomonads, previously referred to as Tritrichomonas musculis and Tritrichomonas rainier , also naturally colonize laboratory mice and cause immune alterations. This report formally describes two new trichomonads, Tritrichomonas musculus n. sp., and Tritrichomonas casperi n. sp., at the ultrastructural and molecular level. These two protists were isolated from laboratory mice, and were differentiated by their size and the structure of their undulating membrane and posterior flagellum. Analysis at the 18S rRNA and trans- ITS genetic loci supported their designation as distinct species, related to T. muris . To further assess the true extent of parabasalid diversity infecting laboratory mice, 135 mice were screened at the NIH using pan-parabasalid primers that amplify the trans- ITS region. Forty-four percent of mice were positive for parabasalids, encompassing a total of 8 distinct sequence types. Tritrichomonas casperi and Trichomitus- like protists were dominant. T. musculus and T. rainier were also detected, but T. muris was not. Our work establishes a previously underappreciated diversity of commensal trichomonad protists that naturally colonize the enteric cavity of laboratory mice.

The commensal protist Tritrichomonas musculus exhibits a dynamic life cycle that induces extensive remodeling of the gut microbiota.

Commensal protists and gut bacterial communities exhibit complex relationships, mediated at least in part through host immunity. To improve our understanding of this tripartite interplay, we investigated community and functional dynamics between the murine protist Tritrichomonas musculus ( T. mu ) and intestinal bacteria in healthy and B cell-deficient mice. We identified dramatic, protist-driven remodeling of resident microbiome growth and activities, in parallel with T. mu functional changes, accelerated in the absence of B cells. Metatranscriptomic data revealed nutrient-based competition between bacteria and the protist. Single cell transcriptomics identified distinct T. mu life stages, providing new evidence for trichomonad sexual replication and the formation of pseudocysts. Unique cell states were validated in situ through microscopy and flow cytometry. Our results reveal complex microbial dynamics during the establishment of a commensal protist in the gut, and provide valuable datasets to drive future mechanistic studies.