36 research outputs found
Evidence from the resurrected family Polyrhabdinidae Kamm, 1922 (Apicomplexa: Gregarinomorpha) supports the epimerite, an attachment organelle, as a major eugregarine innovation
No full textBackgroundGregarines are a major group of apicomplexan parasites of invertebrates. The gregarine classification is largely incomplete because it relies primarily on light microscopy, while electron microscopy and molecular data in the group are fragmentary and often do not overlap. A key characteristic in gregarine taxonomy is the structure and function of their attachment organelles (AOs). AOs have been commonly classified as “mucrons” or “epimerites” based on their association with other cellular traits such as septation. An alternative proposal focused on the AOs structure, functional role, and developmental fate has recently restricted the terms “mucron” to archigregarines and “epimerite” to eugregarines.MethodsLight microscopy and scanning and transmission electron microscopy, molecular phylogenetic analyses of ribosomal RNA genes.ResultsWe obtained the first data on fine morphology of aseptate eugregarines Polyrhabdina pygospionis and Polyrhabdina cf. spionis, the type species. We demonstrate that their AOs differ from the mucron in archigregarines and represent an epimerite structurally resembling that in other eugregarines examined using electron microscopy. We then used the concatenated ribosomal operon DNA sequences (SSU, 5.8S, and LSU rDNA) of P. pygospionis to explore the phylogeny of eugregarines with a resolution superior to SSU rDNA alone. The obtained phylogenies show that the Polyrhabdina clade represents an independent, deep-branching family in the Ancoroidea clade within eugregarines. Combined, these results lend strong support to the hypothesis that the epimerite is a synapomorphic innovation of eugregarines. Based on these findings, we resurrect the family Polyrhabdinidae Kamm, 1922 and erect and diagnose the family Trollidiidae fam. n. within the superfamily Ancoroidea Simdyanov et al., 2017. Additionally, we re-describe the characteristics of P. pygospionis, emend the diagnoses of the genus Polyrhabdina, the family Polyrhabdinidae, and the superfamily Ancoroidea
Apicomplexan-like parasites are polyphyletic and widely but selectively dependent on cryptic plastid organelles
No full textThe phylum Apicomplexa comprises human pathogens such as Plasmodium but is also an under-explored hotspot of evolutionary diversity central to understanding the origins of parasitism and non-photosynthetic plastids. We generated single-cell transcriptomes for all major apicomplexan groups lacking large-scale sequence data. Phylogenetic analysis reveals that apicomplexan-like parasites are polyphyletic and their similar morphologies emerged convergently at least three times. Gregarines and eugregarines are monophyletic, against most expectations, and rhytidocystids and Eleutheroschizon are sister lineages to medically important taxa. Although previously unrecognized, plastids in deep-branching apicomplexans are common, and they contain some of the most divergent and AT-rich genomes ever found. In eugregarines, however, plastids are either abnormally reduced or absent, thus increasing known plastid losses in eukaryotes from two to four. Environmental sequences of ten novel plastid lineages and structural innovations in plastid proteins confirm that plastids in apicomplexans and their relatives are widespread and share a common, photosynthetic origin
Polyphyletic origin, intracellular invasion, and meiotic genes in the putatively asexual agamococcidians (Apicomplexa incertae sedis)
No full textAbstract Agamococcidians are enigmatic and poorly studied parasites of marine invertebrates with unexplored diversity and unclear relationships to other sporozoans such as the human pathogens Plasmodium and Toxoplasma . It is believed that agamococcidians are not capable of sexual reproduction, which is essential for life cycle completion in all well studied parasitic apicomplexans. Here, we describe three new species of agamococcidians belonging to the genus Rhytidocystis . We examined their cell morphology and ultrastructure, resolved their phylogenetic position by using near-complete rRNA operon sequences, and searched for genes associated with meiosis and oocyst wall formation in two rhytidocystid transcriptomes. Phylogenetic analyses consistently recovered rhytidocystids as basal coccidiomorphs and away from the corallicolids, demonstrating that the order Agamococcidiorida Levine, 1979 is polyphyletic. Light and transmission electron microscopy revealed that the development of rhytidocystids begins inside the gut epithelial cells, a characteristic which links them specifically with other coccidiomorphs to the exclusion of gregarines and suggests that intracellular invasion evolved early in the coccidiomorphs. We propose a new superorder Eococcidia for early coccidiomorphs. Transcriptomic analysis demonstrated that both the meiotic machinery and oocyst wall proteins are preserved in rhytidocystids. The conservation of meiotic genes and ultrastructural similarity of rhytidocystid trophozoites to macrogamonts of true coccidians point to an undescribed, cryptic sexual process in the group
Description of Colponema vietnamica sp.n. and Acavomonas peruviana n. gen. n. sp., two new alveolate phyla (Colponemidia nom. nov. and Acavomonidia nom. nov.) and their contributions to reconstructing the ancestral state of alveolates and eukaryotes.
No full textThe evolutionary and ecological importance of predatory flagellates are too often overlooked. This is not only a gap in our understanding of microbial diversity, but also impacts how we interpret their better-studied relatives. A prime example of these problems is found in the alveolates. All well-studied species belong to three large clades (apicomplexans, dinoflagellates, and ciliates), but the predatory colponemid flagellates are also alveolates that are rare in nature and seldom cultured, but potentially important to our understanding of alveolate evolution. Recently we reported the first cultivation and molecular analysis of several colponemid-like organisms representing two novel clades in molecular trees. Here we provide ultrastructural analysis and formal species descriptions for both new species, Colponema vietnamica n. sp. and Acavomonas peruviana n. gen. n. sp. Morphological and feeding characteristics concur with molecular data that both species are distinct members of alveolates, with Acavomonas lacking the longitudinal phagocytotic groove, a defining feature of Colponema. Based on ultrastructure and molecular phylogenies, which both provide concrete rationale for a taxonomic reclassification of Alveolata, we establish the new phyla Colponemidia nom. nov. for the genus Colponema and its close relatives, and Acavomonidia nom. nov. for the genus Acavomonas and its close relatives. The morphological data presented here suggests that colponemids are central to our understanding of early alveolate evolution, and suggest they also retain features of the common ancestor of all eukaryotes
Colponemids Represent Multiple Ancient Alveolate Lineages
No full textSummaryThe alveolates comprise three well-studied protist lineages of significant environmental, medical, and economical importance: apicomplexans (e.g., Plasmodium), dinoflagellates (e.g., Symbiodinium), and ciliates (e.g., Tetrahymena). These major lineages have evolved distinct and unusual characteristics, the origins of which have proved to be difficult evolutionary puzzles. Mitochondrial genomes are a prime example: all three groups depart from canonical form and content, but in different ways. Reconstructing such ancient transitions is difficult without deep-branching lineages that retain ancestral characteristics. Here we describe two such lineages and how they illuminate the ancestral state of alveolate mitochondrial genomes. We established five clonal cultures of colponemids, predatory alveolates without cultured representatives and molecular data. Colponemids represent at least two independent lineages at the phylum level in multilocus phylogenetic analysis; one sister to apicomplexans and dinoflagellates, and the other at a deeper position. A genome survey from one strain showed that ancestral state of the mitochondrial genomes in the three major alveolate lineages consisted of an unusual linear chromosome with telomeres and a substantially larger gene set than known alveolates. Colponemid sequences also identified several environmental lineages as colponemids, altogether suggesting an untapped potential for understanding the origin and evolution of apicomplexans, dinoflagellates, and ciliates
Motility in blastogregarines (Apicomplexa): Native and drug-induced organisation of Siedleckia nematoides cytoskeletal elements.
No full textRecent studies on motility of Apicomplexa concur with the so-called glideosome concept applied for apicomplexan zoites, describing a unique mechanism of substrate-dependent gliding motility facilitated by a conserved form of actomyosin motor and subpellicular microtubules. In contrast, the gregarines and blastogregarines exhibit different modes and mechanisms of motility, correlating with diverse modifications of their cortex. This study focuses on the motility and cytoskeleton of the blastogregarine Siedleckia nematoides Caullery et Mesnil, 1898 parasitising the polychaete Scoloplos cf. armiger (Müller, 1776). The blastogregarine moves independently on a solid substrate without any signs of gliding motility; the motility in a liquid environment (in both the attached and detached forms) rather resembles a sequence of pendular, twisting, undulation, and sometimes spasmodic movements. Despite the presence of key glideosome components such as pellicle consisting of the plasma membrane and the inner membrane complex, actin, myosin, subpellicular microtubules, micronemes and glycocalyx layer, the motility mechanism of S. nematoides differs from the glideosome machinery. Nevertheless, experimental assays using cytoskeletal probes proved that the polymerised forms of actin and tubulin play an essential role in the S. nematoides movement. Similar to Selenidium archigregarines, the subpellicular microtubules organised in several layers seem to be the leading motor structures in blastogregarine motility. The majority of the detected actin was stabilised in a polymerised form and appeared to be located beneath the inner membrane complex. The experimental data suggest the subpellicular microtubules to be associated with filamentous structures (= cross-linking protein complexes), presumably of actin nature
Ultrastructure and 28S rDNA Phylogeny of Two Gregarines: Cephaloidophora cf. communis and Heliospora cf. longissima with Remarks on Gregarine Morphology and Phylogenetic Analysis
No full text18S rRNA gene sequences (SSU rDNA) in gregarines are problematic for phylogenetic analysis, mainly due to artifacts related to long branch attraction (LBA). In this study, we sequenced 18S rRNA (SSU rRNA), 5.8S rRNA, and 28S rRNA (LSU rRNA) genes of two gregarine species from crustacean hosts (gregarine superfamily Cephaloidophoroidea): Cephaloidophora cf. communis from a marine cirripedian Balanus balanus (White Sea), and Heliospora cf. longissima from the freshwater amphipods, Eulimnogammarus verrucosus and E. vittatus (Lake Baikal). Phylogenetic analyses of SSU rDNA sequences failed to produce a robust tree topology, for a limited taxon sample (31 operational taxonomic units (OTU), based on 1,604 sites), while LSU (2,869 sites), and concatenated dataset based on SSU, 5.8S, and LSU (4,627 sites) produced more consistent tree topologies for the same taxon sample. Analyses testing for LBA-influence were negative, therefore we suggested that the main reason of the failed topologies in SSU rDNA analyses is insufficient data (insufficient taxon sampling and limited molecular data), rather than LBA. Possible advantages of Bayesian analyses, compared to Maximum Likelihood, and usage of LSU rDNA within the context of apicomplexan phylogenetics were discussed. One of the advantages of LSU is likely its lower rate of evolution in long-branching apicomplexans (e.g., gregarines), relative to other (non-long-branching) apicomplexans, compared to SSU rDNA. Ultrastructure of the epicytic folds was studied. There are 3 to 5 apical arcs (also known as rippled dense structures) and 2 to 5 apical filaments in the tops of the folds. This small number of the apical structures fits into morphological diversity of the epicyte in other Cephaloidophoroidea, but this is not a synapomorphy of the group because this was also detected in several unrelated gregarines. C. cf. communis was found to contain a septum between the epimerite and the protomerite, which has not been reported in other gregarines. More exact terminology, which takes into account number of body sections and septa, is proposed for morphological descriptions of trophozoites and free mature gamonts of gregarines. In accordance with this, C. cf. communis gamonts are tricystid and biseptate, whereas H. cf. longissima gamonts are tricystid and uniseptate, similar to other eugregarines
Structures related to attachment and motility in the marine eugregarine Cephaloidophora cf. communis (Apicomplexa)
No full textUltrastructural features of <i>Eleutheroschizon duboscqi</i> early development.
No full text<p><b>A.</b> Early trophozoite in the process of transformation from an attached zoite, already enveloped by a host-derived PS. TEM. <b>B.</b> Early trophozoite. Note the numerous vesicles in the space between parasite and PS, especially in caudal region. TEM. <b>C-E.</b> Young trophozoite. D shows the space between the parasite caudal region and PS; E shows the host parasite interface at the attachment site. TEM. <b>F-H.</b> Maturing trophozoite. G shows an annular joint point of two host membranes; H focuses on the parasite caudal region and PS. TEM. <b>I.</b> Early trophozoite. SEM. <b>J.</b> Young trophozoite. SEM. <b>K.</b> Mature trophozoite. TEM. <b>L.</b> Detailed view of the attachment site of the trophozoite shown in K, focusing on the developing fascicles of filaments and the annular joint point. TEM. <i>a—</i>parasite amylopectin, <i>asterisk</i>—space between the parasite and PS, <i>black arrow</i>—PS, <i>black arrowhead—</i>parasite plasma membrane, <i>black double/paired arrowheads</i>—parasite cytomembranes, <i>c</i>—parasite cytoplasm, <i>cr</i>—crystalloid body, <i>er</i>—parasite endoplasmic reticulum, <i>fa</i>—attachment fascicles, <i>fi—</i>short attachment filaments, <i>g</i>—glycocalyx, <i>h—</i>host cell, <i>mc</i>—host microcilia, <i>mt</i>—parasite subpellicular microtubules, <i>mv</i>—host microvilli, <i>n</i>—parasite nucleus, <i>r</i>—parasite posterior ring, <i>sf—</i>parasite subpellicular filaments, <i>t</i>—tail of the PS, <i>v</i>—vesicles, <i>white arrow</i>—host cell plasma membrane, <i>white arrowhead</i>—dense band, <i>white double arrowhead</i>—base of the PS (membrane of host cell origin), <i>x</i>—forming attachment fascicles.</p
