Posterior Flagellum Research Articles

The Morphology, Ultrastructure and SSU rRNA Gene Sequence of a New Freshwater Flagellate, Neobodo borokensis n. sp. (Kinetoplastea, Excavata).

A small free-living freshwater bacteriotrophic flagellate Neobodo borokensis n. sp. was investigated by electron microscopy and analysis of its SSU ribosomal RNA gene. This protist has paraxonemal rods of typical bodonid structure in the flagella, mastigonemes on the proximal part of the posterior flagellum, two nearly parallel basal bodies, a compact kinetoplast, and discoid mitochondrial cristae. The flagellar pocket is supported by three microtubular roots (R1, R2 and R3) originating from the kinetosome. The cytopharynx is supported by the root R2, a microtubular prism, cytopharynx associated additional microtubules (CMT) and cytostome associated microtubules (FAS) bands. Symbiotic bacteria and small glycosomes were found in the cytoplasm. Cysts have not been found. The flagellate prefers freshwater habitats, but tolerates salinity up to 3-4‰. The overall morphological and ultrastructural features confirm that N. borokensis represents a new species of the genus Neobodo. Phylogenetic analysis of SSU rRNA genes is congruent with the ultrastructure and strongly supports the close relationship of N. borokensis to Neobodo saliens, N. designis, Actuariola, and a misidentified sequence of "Bodo curvifilus" within the class Kinetoplastea.

Ubiquitous distribution of helmchrome in phototactic swarmers of the stramenopiles.

Most swarmers (swimming cells) of the stramenopile group, ranging from unicellular protist to giant kelps (brown algae), have two heterogeneous flagella: a long anterior flagellum (AF) and a relatively shorter posterior flagellum (PF). These flagellated cells often exhibit phototaxis upon light stimulation, although the mechanism by which how the phototactic response is regulated remains largely unknown. A flavoprotein concentrating at the paraflagellar body (PFB) on the basal part of the PF, which can emit green autofluorescence under blue light irradiance, has been proposed as a possible blue light photoreceptor for brown algal phototaxis although the nature of the flavoprotein still remains elusive. Recently, we identified helmchrome as a PF-specific flavoprotein protein in a LC-MS/MS-based proteomics study of brown algal flagella (Fu et al. 2014). To verify the conservation of helmchrome, in the present study, the absence or presence and the localization of helmchrome in swarmers of various algal species were investigated. The results showed that helmchrome was only detected in phototactic swarmers but not the non-phototactic ones of the stramenopile group. Electron microscopy further revealed that the helmchrome detectable swarmers bear a conserved PFB-eyespot complex, which may serve as structural basis for light sensing. It is speculated that all three conserved properties: helmchrome, the PFB structure, and the eyespot apparatus, will be essential parts for phototaxis of stramenopile swarmers.

Microgrooves and fluid flows provide preferential passageways for sperm over pathogen Tritrichomonas foetus

Successful mammalian reproduction requires that sperm migrate through a long and convoluted female reproductive tract before reaching oocytes. For many years, fertility studies have focused on biochemical and physiological requirements of sperm. Here we show that the biophysical environment of the female reproductive tract critically guides sperm migration, while at the same time preventing the invasion of sexually transmitted pathogens. Using a microfluidic model, we demonstrate that a gentle fluid flow and microgrooves, typically found in the female reproductive tract, synergistically facilitate bull sperm migration toward the site of fertilization. In contrast, a flagellated sexually transmitted bovine pathogen, Tritrichomonas foetus, is swept downstream under the same conditions. We attribute the differential ability of sperm and T. foetus to swim against flow to the distinct motility types of sperm and T. foetus; specifically, sperm swim using a posterior flagellum and are near-surface swimmers, whereas T. foetus swims primarily via three anterior flagella and demonstrates much lower attraction to surfaces. This work highlights the importance of biophysical cues within the female reproductive tract in the reproductive process and provides insight into coevolution of males and females to promote fertilization while suppressing infection. Furthermore, the results provide previously unidentified directions for the development of in vitro fertilization devices and contraceptives.

Variation in the saccharide lectin binding pattern from different isolates of Tritrichomonas foetus

Tritrichomonas foetus (T. foetus) is the causal agent of bovine tritrichomonosis (BT), a venereal disease that causes significant economic losses in the bovine livestock industry. The structural organization of T. foetus presents a cell membrane, an undulating membrane which extends along the parasite, three anterior flagella and a recurrent posterior flagellum. The interaction between the superficial glycoconjugates of the parasite and the host cell is one of the most relevant pathogenic mechanisms. In the present study, we analyzed the saccharide pattern through lectincytochemistry of the cell membrane, undulating membrane, cytoplasm and flagella of 28 isolates of T. foetus. Lectins that labeled most of the isolates were WGA, Con-A, RCA-I, LCA, GS-II and PHA-E showing the presence of D-mannose, D-glucose, N-acetylglucosamine and sialic acid. On the other hand, no labeling was observed in any of the structures with VVA, STA, LEA, Jacalin, GS-I, SJA, PHA-L, DSA, and weak labeling was observed with DBA, PNA, SBA and UEA I, showing therefore a low expression of N-acetylgalactosamine, L-fucose and galactose. In addition, GS II labeled in a granular pattern when lectincytochemistry was positive, whereas LCA strongly labeled the membranes and weakly the cytoplasms. The labeling variations observed among the isolates analyzed in the present work, could be related to differences in the pathogenic behavior of the isolates.

Structure of the flagellar apparatus of the bacterivorous flagellate Histiona aroides Pascher, 1943 (Jakobida, Excavata)

The structure of the flagellar apparatus of excavate flagellate Histiona aroides has been studied. Two naked flagella emerge from the bottom of ventral groove. The proximal part of the kinetosome has an osmiophilic cone. The posterior short flagellum bears a wide fold, which directs to the cell and contains striated material. The wide dorsal microtubular band starts close by the kinetosome of the anterior flagellum, the left and right bands of the band are divided in turn into two bands, and a single microtubule begins nearby the kinetosome of the posterior flagellum. Amorphous and striated fibrils accompany these bands. The left external band and a multilayer structure (band C) penetrate into the epipodium. The microtubular bands reinforce the bottom of the ventral groove and the external margin of the velum. In addition, the vesicular nucleus, extrusomes, contractile vacuole, and mitochondria with tubular cristae are visible on the cell sections. The similarity of H. aroides with representatives of the Jakobida family and other Excavata is discussed.

Proteomics Analysis of Heterogeneous Flagella in Brown Algae (Stramenopiles)

Flagella are conserved organelles among eukaryotes and they are composed of many proteins, which are necessary for flagellar assembly, maintenance and function. Stramenopiles, which include brown algae, diatoms and oomycetes, possess two laterally inserted flagella. The anterior flagellum (AF) extends forward and bears tripartite mastigonemes, whilst the smooth posterior flagellum (PF) often has a paraflagellar body structure. These heterogeneous flagella have served as crucial structures in algal studies especially from a viewpoint of phylogeny. However, the protein compositions of the flagella are still largely unknown. Here we report a LC-MS/MS based proteomics analysis of brown algal flagella. In total, 495 flagellar proteins were identified. Functional annotation of the proteome data revealed that brown algal flagellar proteins were associated with cell motility, signal transduction and various metabolic activities. We separately isolated AF and PF and analyzed their protein compositions. This analysis led to the identification of several AF- and PF-specific proteins. Among the PF-specific proteins, we found a candidate novel blue light receptor protein involved in phototaxis, and named it HELMCHROME because of the steering function of PF. Immunological analysis revealed that this protein was localized along the whole length of the PF and concentrated in the paraflagellar body.

Structure of the flagellar apparatus in the bacteriotrophic flagellate Parabodo nitrophilus Skuja, 1948 (Kinetoplastea Excavata)

The structure of the flagellar apparatus in the excavate flagellate Parabodo nitrophilus Skuja has been studied. Two smooth heterodynamic flagella emerge from the bottom of the flagellar apparatus. The kinetosomes connected by their proximal ends lie under an acute angle to each other and bear against the plate on the anteior wall of kinetoplast. The dorsal and ventral rootlets emerge from the kinetosomes and are transformed into dorsal and ventral bands. The latter accompanies the posterior flagellum. The MTR band begins inside the wall of the flagellar pocket. The upper part of the cytopharynx is armored by MTR and FAS bands, cross-banded fibril and structure, and additional microtubules. The MTR band and three additional microtubules surround the bottom part of cytopharynx. The mitochondrium contains compact kinetoplast and discoid cristae. The resemblance of Parabodo nitrophilus with other free-living kinetoplastids is discussed.

Ultrastructure and Molecular Phylogenetic Position of Neometanema parovale sp. nov. (Neometanema gen. nov.), a Marine Phagotrophic Euglenid with Skidding Motility

Heteronema is a commonly encountered genus of phagotrophic euglenids that contains very different morphotypes, including elongate gliding species and ovoid skidding forms. We report the first ultrastructural and sequence data from a culture of an ovoid skidding heteronemid, KM051. Cells were 8-23.5 μm long with 22 pellicular strips and a fibrous extracellular layer. The tubular extrusomes had dense centre sections. The feeding apparatus was barely visible by light microscopy, but included two microtubule-supported rods. The flagella had hollow, inflated transition zones, heteromorphic paraxonemal rods, and sheaths of flagellar hairs. The posterior flagellum bore a knob that, unusually, sat >2 μm distal to the flagellar base. No ultrastructural features were uniquely shared by KM051 and the elongate, gliding species Heteronema scaphurum. Conversely, the pellicular microtubule array resembles that in deep-branching primary osmotrophs (Aphagea). 18S ribosomal DNA (18S rDNA) phylogenies showed that KM051 is related to a recently obtained Heteronema c.f. exaratum sequence. These skidding heteronemids are not closely related to H. scaphurum, and instead are closely related to Dinema, Anisonema and specifically, Aphagea. The skidding species in Heteronema are transferred to Neometanema gen. nov. (along with most species of Metanema Klebs, 1893), with KM051 described as Neometanema parovale sp. nov.

Culture of the cladoceran Moina macrocopa: Mortality associated with flagellate infection

Cladocerans are important food animals in aquaculture, key grazers in freshwater ecosystems, and model animals for ecotoxicological investigations. Their epibiont community, extensively studied in Daphnia, includes filamentous bacteria, fungi, algae, peritrich ciliates, and rotifers; although epibionts are usually benign, heavy infections can be detrimental. During our laboratory culture of female Moina macrocopa Straus, we observed a novel flagellate infection associated with mortality. At day 10, all M. macrocopa were alive in uninfected cultures, whereas in untreated infected cultures, the survival was significantly lower: only 26% of cladocerans were alive. In infected cultures treated with humic substances (as 25mgL−1 dissolved organic carbon), mortalities were comparable to those in the untreated infected cultures; in contrast, in the infected cultures treated with 4gL−1 sea salt, mortalities were arrested, and 76% of the M. macrocopa were alive at day 10. Moribund cladocerans were transparent, had empty digestive tracts, and greatly reduced motor activity. Free-swimming flagellates moved forward with a wobbling motion, rotating around their long axis; they also attached to cladoceran tissue, the Petri dish, and the glass slide, by the tip of their posterior flagellum. Flagellates preserved for scanning electron microscopy were 6.9±0.7μm long and 2.1±0.3μm wide, with a short anterior flagellum (6.8±1.1μm) and long posterior flagellum (14.1±1.5μm). Multi-functionality of a flagellum, for locomotion and adhesion, is relatively rare, and previously reported from genera within the Kinetoplastea, suggesting that the flagellate on M. macrocopa may belong to this group. To combat flagellate mass occurrence in Moina cultures, we recommend a treatment with 4gL−1 sea salt.

Cthulhu Macrofasciculumque n. g., n. sp. and Cthylla Microfasciculumque n. g., n. sp., a Newly Identified Lineage of Parabasalian Termite Symbionts

The parabasalian symbionts of lower termite hindgut communities are well-known for their large size and structural complexity. The most complex forms evolved multiple times independently from smaller and simpler flagellates, but we know little of the diversity of these small flagellates or their phylogenetic relationships to more complex lineages. To understand the true diversity of Parabasalia and how their unique cellular complexity arose, more data from smaller and simpler flagellates are needed. Here, we describe two new genera of small-to-intermediate size and complexity, represented by the type species Cthulhu macrofasciculumque and Cthylla microfasciculumque from Prorhinotermes simplex and Reticulitermes virginicus, respectively (both hosts confirmed by DNA barcoding). Both genera have a single anterior nucleus embeded in a robust protruding axostyle, and an anterior bundle flagella (and likely a single posterior flagellum) that emerge slightly subanteriorly and have a distinctive beat pattern. Cthulhu is relatively large and has a distinctive bundle of over 20 flagella whereas Cthylla is smaller, has only 5 anterior flagella and closely resembles several other parababsalian genera. Molecular phylogenies based on small subunit ribosomal RNA (SSU rRNA) show both genera are related to previously unidentified environmental sequences from other termites (possibly from members of the Tricercomitidae), which all branch as sisters to the Hexamastigitae. Altogether, Cthulhu likely represents another independent origin of relatively high cellular complexity within parabasalia, and points to the need for molecular characterization of other key taxa, such as Tricercomitus.

Esquamula lacrimiformis n. g., n. sp., a New Member of Thaumatomonads that Lacks Siliceous Scales

We report a new naked cercozoan flagellate, Esquamula lacrimiformis n. g., n. sp., collected from a sandy beach in Japan. Its cells were 4.5-11.3μm in length and 3.9-8.8μm in width and possess two unequal flagella. Cells move in a smooth gliding motion and have a trailing long posterior flagellum. Phylogenetic analyses with small and large subunit ribosomal RNA genes revealed that E. lacrimiformis forms a novel lineage within the Thaumatomonadida, the members of which are flagellates with siliceous scales. However, our light and electron microscopic observations indicated that E. lacrimiformis cells do not possess any siliceous structures. Furthermore, other morphological characteristics, such as the shape of the extrusomes and the structural arrangement of the microbody, were clearly different from those of previously described thaumatomonads. On the basis of a combination of these morphological observations and our phylogenetic analyses, we conclude that E. lacrimiformis should be treated as a new species of a new genus and placed into a new family, Esquamulidae n. fam., under Thaumatomonadida.

Ultrastructural analysis of flagellar development in plurilocular sporangia of Ectocarpus siliculosus (Phaeophyceae).

Flagellar development in the plurilocular zoidangia of sporophytes of the brown alga Ectocarpus siliculosus was analyzed in detail using transmission electron microscopy and electron tomography. A series of cell divisions in the plurilocular zoidangia produced the spore-mother cells. In these cells, the centrioles differentiated into flagellar basal bodies with basal plates at their distal ends and attached to the plasma membrane. The plasma membrane formed a depression (flagellar pocket) into where the flagella elongated and in which variously sized vesicles and cytoplasmic fragments accumulated. The anterior and posterior flagella started elongating simultaneously, and the vesicles and cytoplasmic fragments in the flagellar pocket fused to the flagellar membranes. The two flagella (anterior and posterior) could be clearly distinguished from each other at the initial stage of their development by differences in length, diameter and the appendage flagellar rootlets. Flagella continued to elongate in the flagellar pocket and maintained their mutually parallel arrangement as the flagellar pocket gradually changed position. In mature zoids, the basal part of the posterior flagellum (paraflagellar body) characteristically became swollen and faced the eyespot region. Electron dense materials accumulated between the axoneme and the flagellar membrane, and crystallized materials could also be observed in the swollen region. Before liberation of the zoospores from the plurilocular zoidangia, mastigoneme attachment was restricted to the distal region of the anterior flagellum. Structures just below the flagellar membrane that connected to the mastigonemes were clearly visible by electron tomography.

퍼킨서스편모충(Perkinsus olseni) 유주자 (Zoospore) 의 미세구조 관찰

Protozoan parasites belonging to the genus Perkinsus elicit severe inflammatory responses and are associated with mass mortality of commercially important marine shellfish worldwide. In the present study, we examined the external features of P. olseni zoospores in detail using light and scanning electron microscopy. Our study showed that the zoospores have an oval body with a long anterior flagellum and a short posterior flagellum. The anterior flagellum has a unilateral array of mastigonemes. Mean body dimensions were 3.37 ± 0.33 μm × 1.72 ± 0.22 μm. The average length of the anterior and posterior flagella was 16.34 ± 1.52 μm and 8.25 ± 1.39 μm, respectively. Zoospores of P. olseni found in Korean waters have shorter and narrower bodies, longer anterior flagella, and shorter posterior flagella than zoospores of Perkinsus spp. found in the mollusks of North America and Europe.

Phytoplankton Chytridiomycosis: Fungal Parasites of Phytoplankton and Their Imprints on the Food Web Dynamics

Parasitism is one of the earlier and common ecological interactions in the nature, occurring in almost all environments. Microbial parasites typically are characterized by their small size, short generation time, and high rates of reproduction, with simple life cycle occurring generally within a single host. They are diverse and ubiquitous in aquatic ecosystems, comprising viruses, prokaryotes, and eukaryotes. Recently, environmental 18S rDNA surveys of microbial eukaryotes have unveiled major infecting agents in pelagic systems, consisting primarily of the fungal order of Chytridiales (chytrids). Chytrids are considered the earlier branch of the Eumycetes and produce motile, flagellated zoospores, characterized by a small size (2–6 μm), and a single, posterior flagellum. The existence of these dispersal propagules includes chytrids within the so-called group of zoosporic fungi, which are particularly adapted to the plankton lifestyle where they infect a wide variety of hosts, including fishes, eggs, zooplankton, algae, and other aquatic fungi but primarily freshwater phytoplankton. Related ecological implications are huge because chytrids can killed their hosts, release substrates for microbial processes, and provide nutrient-rich particles as zoospores and short fragments of filamentous inedible hosts for the grazer food chain. Furthermore, based on the observation that phytoplankton chytridiomycosis preferentially impacts the larger size species, blooms of such species (e.g., filamentous cyanobacteria) may not totally represent trophic bottlenecks. Besides, chytrid epidemics represent an important driving factor in phytoplankton seasonal successions. In this review, I summarize the knowledge on the diversity, community structure, quantitative importance, and functional roles of fungal chytrids, primarily those who are parasites of phytoplankton, and infer the ecological implications and potentials for the food web dynamics and properties. I reach the conclusion that phytoplankton chytridiomycosis represents an important but as yet overlooked ecological driving force in aquatic food web dynamics and network organization.

TAXONOMY AND PHYLOGENY OF NEPHROSELMIS CLAVISTELLA SP. NOV. (NEPHROSELMIDOPHYCEAE, CHLOROPHYTA)(1).

Nephroselmis clavistella D. G. Faria et S. Suda sp. nov. is collected from coastal sand samples from the eastern and western coasts of Okinawa-jima Island, Japan. The description of the cultured strains is based on light and electron microscopic observations. The cultured strains are phylogenetically analyzed based on 18S rDNA sequences. The cells are remarkably right-left flattened and appear round or ellipse when viewed from their right or left side, and are ∼5.0 μm in diameter. The posterior flagellum curved around the cell body at rest. A single, parietal, crescent chloroplast is yellowish green and contains one conspicuous eyespot in its anterior-ventral edge near the short flagellum base. A pyrenoid with one starch sheath is located dorsal of the chloroplast. The cells are divided by transverse binary cell division, as is common in other species of this genus. The cell body is covered with five types of scales, and among them four scale types are similar to Nephroselmis rotunda. The fifth scale type is a distinctive spiny and club-shaped stellate scale with 10 spines, four of the 10 spines extended ∼150 nm and each are slightly curved with a hook at the end, whereas six spines are club-shaped blunt ended. This scale morphology, an important taxonomic characteristic, has never been described before for the genus Nephroselmis. The cell's morphology is distinctive from previously described Nephroselmis species, and its unique scale characteristics led us to name this newly proposed species "clavistella," meaning club star.

The Ultrastructure of Ancyromonas; a Eukaryote without Supergroup Affinities

The small heterotrophic flagellate Ancyromonas (=Planomonas) lacks close relatives in most molecular phylogenies, and it is suspected that it does not belong to any of the recognized eukaryote 'supergroups', making it an organism of great evolutionary interest. Proposed relatives include apusomonads and excavates, but limited understanding of the ancyromonad cytoskeleton has precluded identification of candidate structural homologies. We present a detailed analysis of the ultrastructure of Ancyromonas through computer-based reconstruction of serial sections. We confirm or extend previous observations of its major organelles (mitochondria, Golgi body, extrusomes, etc.) and pellicle, and distinguish a system of stacked endomembranes that may be developmentally connected to the glycocalyx. Ancyromonas has two basal bodies, each with its own flagellar pocket. The anterior basal body associates with two microtubular elements: a doublet root that runs from between the basal bodies to support the cell's rostrum, and a short singlet root. The posterior basal body is associated with two multi-microtubular structures and a singlet root. One multi-microtubular structure, L1, is a conventional microtubular root. The other structure appears as a curved ribbon of ∼8 microtubules near the basal body, but then flares out into two multi-microtubular elements, L2 and L3, plus two single microtubules. The posterior singlet root originates independently near this second complex. L1, the singlet, L2, and L3 all support the posterior flagellar pocket and channel. We also identified several groups of peripheral microtubules. Possible homologies with the flagellar apparatus of both apusomonads and excavates include a splitting root on the right side of the posterior basal body and a singlet root, both supporting a longitudinal channel or groove associated with the posterior flagellum. The anterior flagellar apparatus in each includes a root supporting structures to the left of the anterior flagellum. Given the probable deep divergences of Ancyromonas, apusomonads and excavates within eukaryotes, it is possible that the eukaryotic cenancestor also possessed these features.

Sequencing the fungal tree of life

Sequencing the Fungal Tree of Life F. Martin 1 , D. Cullen 2 , D. Hibbett 3 , A. Pisabarro 4 , J. W. Spatafora 5 , S. E. Baker 6,7, I. V. Grigoriev 7 UMR INRA/UHP 1136, Interactions Arbres/Micro-Organismes, INRA-Nancy, 54280 Champenoux, France University of Wisconsin-Madison, Madison, WI, USA Clark University, Worcester, MA, USA Department of Agrarian Production, Public University of Navarre, 31006 Pamplona, Spain Dept. Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331 Chemical and Biological Process Development Group, Pacific Northwest National Laboratory, Richland, Washington, USA, 99352 US DOE Joint Genome Institute, Walnut Creek, California, USA March 2011 The work conducted by the U.S. Department of Energy Joint Genome Institute is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02- 05CH11231 DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor The Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or The Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or The Regents of the University of California.

Cell Morphology and Formal Description of Ergobibamus cyprinoides n. g., n. sp., Another Carpediemonas‐Like Relative of Diplomonads

About 20 new isolates of Carpediemonas-like organisms (CLOs) have been reported since 2006. Small subunit rRNA gene phylogenies divide CLOs into six major clades: four contain described exemplars (i.e. Carpediemonas, Dysnectes, Hicanonectes, and Kipferlia), but two include only undescribed organisms. Here we describe a representative of one of these latter clades as Ergobibamus cyprinoides n. g., n. sp., and catalogue its ultrastructure. Ergobibamus cyprinoides is a bean-shaped biflagellated cell, 7-11.5 μm long, with a conspicuous groove. Instead of classical mitochondria there are cristae-lacking rounded organelles 300-400 nm in diameter. The posterior flagellum has a broad ventral vane and small dorsal vane. There are normally four basal bodies, two non-flagellated. There is one anterior root (AR), containing six microtubules. The posterior flagellar apparatus follows the "typical excavate" pattern of a splitting right root supported by fibres "I,""B," and "A," a "composite" fibre, a singlet root, and a left root (LR) with a "C" fibre. The B fibre originates against the LR--a synapomorphy of the taxon Fornicata--supporting the assignation of Ergobibamus to Fornicata, along with diplomonads, retortamonads, and other CLOs. Distinctive features of E. cyprinoides include the complexity of the AR, which is intermediate between Hicanonectes, and Carpediemonas and Dysnectes, and a dorsal extension of the C fibre.

Surface and Flagella Morphology of the Motile Form of Chromera velia Revealed by Field-Emission Scanning Electron Microscopy

Chromera velia(Chromerida; Alveolata) is an autotrophic protist isolated from stony corals.Ch. veliapossesses a chloroplast thought to be most closely related to the apicoplasts of non-photosynthetic apicomplexa. Phylogenetic analyses placeCh. veliaas a close relative of parasitic apicomplexa and predatory colpodellids. We have used field-emission scanning electron microscopy of cells sputter-coated with gold or chromium and non-coated cells to characterise the surface ultrastructure of the motile form ofCh. velia. In overall morphology the biflagellatedCh. veliacells resemble the colpodellidColpodella edax, but with some notable differences. The ventral side of the flagellatedCh. veliacell has two grooves extending from the anterior flagella insertion point with a ridge rising towards the anterior apex of the cell. The anterior flagellum is shorter than the posterior flagellum and possesses a distinct, small curved appendage. The insertion point of the anterior flagellum is partly enclosed by a flap extending from the cell. The posterior flagellum is approximately four times the length of the cell and possesses mastigonemes. The combination of coating techniques proved superior to the commonly used gold coating to determine fine surface ultrastructure. This new ultrastructural information forCh. veliaallowed us to emend its diagnosis.

Ultrastructure of the intracellular parasite Parvilucifera sinerae (Alveolata, Myzozoa) infecting the marine toxic planktonic dinoflagellate Alexandrium minutum (Dinophyceae)

This ultrastructural study follows the infection by a parasite, Parvilucifera sinerae, of the marine toxic dinoflagellate Alexandrium minutum. In clonal cultures, infective zoospores, which are the infectious stage, entered host cells where they developed into sporangia. Mature, dark-colored sporangia were released from the dead dinoflagellate cells by the break-up of the host theca. The sporangial cytoplasm ultimately differentiated into many minute zoospores that escaped one host cell and subsequently infected healthy cells. The zoospores are 1.2–1.8 μm in diameter and possess an anterior (transverse) and shorter posterior flagellum in addition to alveoli, a refractile body, a mitochondrion with tubular cristae, micronemes, rhoptries, and a pseudoconoid. As in the other Parvilucifera species, the zoospore has a heteromorphic pair of central microtubules in the anterior axoneme and a reduced pseudoconoid. The micronemes have bulbous posterior ends and, as in other known species of the genus, there are (pseudo)conoid-associated micronemes. A comparison of these ultrastructural data with those available from the other two Parvilucifera species showed that, as in Parvilucifera infectans, the periphery of the nucleus is filled with thin fibers, in contrast to the syndinean-like nucleus of Parvilucifera prorocentri. Also, as in P. infectans, the transition region of the flagellar axoneme contains a dense structure, and the basal body a black globule; however, both structures are absent in P. prorocentri. There are no morphological differences of the zoospores from P. sinerae and P. infectans. The main difference between P. infectans and P. sinerae relay on the sporangium wall and ornamentation. The sporangium wall in P. sinerae consisted of three layers instead of two described layers in P. infectans. Therefore, morphologically, P. sinerae shows greater similarity to P. infectans than to P. prorocentri.