Optical function of the finite-thickness corrugated pellicle of euglenoids

We explore the electromagnetic response of the pellicle of selected species of euglenoids. These microorganisms are bounded by a typical surface pellicle formed by S-shaped overlapping bands that resemble a corrugated film. We investigate the role played by this structure in the protection of the cell against UV radiation. By considering the pellicle as a periodically corrugated film of finite thickness, we applied the C-method to compute the reflectance spectra. The far-field results revealed reflectance peaks with a Q-factor larger than 10³ in the UV region for all the illumination conditions investigated. The resonant behavior responsible for this enhancement has also been illustrated by near-field computations performed by a photonic simulation method. These results confirm that the corrugated pellicle of euglenoids shields the cell from harmful UV radiation and open up new possibilities for the design of highly UV-reflective surfaces.

Ultrastructural alterations in Phacus brachykentron (Euglenophyta) due to excess of organic matter in the culture medium

Morphological and ultrastructural changes induced by exposure to excess of organic matter were analyzed in Phacus brachykentron (Pochm.). The cells were isolated from sites in Matanza River, Buenos Aires, Argentina, which have a high degree of organic matter contamination coming from waste waters discharges of the meat industry. Master strains were cultured on soil water medium and a toxicity bioassay was performed. As a result of the enriched medium, several morphological and ultrastructural cellular alterations were observed by optical, scanning, and transmission electron microscopy. Among these, we can point out changes in cell dimensions, remarkable widening of some pellicle bands, increased number and volume of paramylon grains, displacement of the nucleus from the central to the lateral position, some chloroplasts with their thylakoids disordered, and cell lysis. The response to organic enrichment was very fast, i.e. during the 48h of the bioassay. Therefore, any significant increase of organic matter would rapidly affect wild euglenoids. Our results suggest that the alterations observed, such as the presence of large intracellular paramylon bodies or the deformation of euglenoid cells in natural samples, have the potential to be used as environmental bioindicators.

Reconciling the bizarre inheritance of microtubules in complex (euglenid) microeukaryotes

We introduce a hypothetical model that explains how surface microtubules in euglenids are generated, integrated and inherited with the flagellar apparatus from generation to generation. The Euglenida is a very diverse group of single-celled eukaryotes unified by a complex cell surface called the "pellicle", consisting of proteinaceous strips that run along the longitudinal axis of the cell and articulate with one another along their lateral margins. The strips are positioned beneath the plasma membrane and are reinforced with subtending microtubules. Euglenids reproduce asexually, and the two daughter cells inherit pellicle strips and associate microtubules from the parent cell in a semi-conservative pattern. In preparation for cell division, nascent pellicle strips develop from the anterior end of the cell and elongate toward the posterior end between two parent (mature) strips, so that the total number of pellicle strips and underlying microtubules is doubled in the predivisional cell. Each daughter cell inherits an alternating pattern of strips consisting of half of the nascent strips and half of the parent (mature) strips. This observation combined with the fact that the microtubules underlying the strips are linked to the flagellar apparatus created a cytoskeletal riddle: how do microtubules associated with an alternating pattern of nascent strips and mature strips maintain their physical relationship to the flagellar apparatus when the parent cell divides? The model of microtubular inheritance articulated here incorporates known patterns of cytoskeletal semi-conservatism and two new inferences: (1) a multigenerational "pellicle microtubule organizing center" (pMTOC) extends from the dorsal root of the flagellar apparatus, encircles the flagellar pocket, and underpins the microtubules of the pellicle; and (2) prior to cytokinesis, nascent pellicle microtubules fall within one of two "left/right" constellations that are linked to one of the two new dorsal basal bodies.

Trachelomonas (Euglenophyta) from a eutrophic reservoir in Central Mexico

This study provides valuable information on the ultrastructure and environmental conditions of the Trachelomonas Ehr. (Euglenophyceae) genus in the Guadalupe Dam, a eutrophic reservoir located in the suburbs of Mexico City, which receives a considerable volume of wastewaters. Specimens were collected at surface level between November 2005 and May 2006. Using LM and SEM twelve taxa from phytoplankton were identified of which, 9 are new records for Mexico. The reservoir is warm monomictic, with basic pH values (7.4-10.1), a high concentration of chlorophyll a(18-101 microg l(-1), a permanent anoxic bottom, specific conductivity (K25) of 205 to 290 microS cm(-1), N-NO3, 0.19-1.2 mg l(-1) and P-PO4 0.22-1.6 mg l(-1). Water temperature was 15.6-23.0 degrees C. Most of the Trachelomonas species were found during the dry season, when concentrations of organic matter, nitrogen and phosphorus as well as the temperature were the highest. Higher species richness was also associated with the warmer months. This research contributes to increase our knowledge on Trachelomonas in Mexico and constitutes the first detailed description of lorica ultrastructure of 12 taxa that grow in a body of water with high concentration of nutrients and a moderate amount of mineral contents.

Description of Rhynchopus euleeides n. sp. (Diplonemea), a free-living marine euglenozoan

We describe Rhynchopus euleeides n. sp., using light and electron microscopy. This free-living flagellate, which was isolated earlier from a marine habitat, can be grown axenically in a rich medium based on modified seawater. In the trophic stage, cells are predominantly elliptical and laterally flattened, but frequently change their shape (metaboly). Gliding is the predominant manner of locomotion. The two flagella, which are typically concealed in their pocket, are short stubs of unequal length, have conventional axonemes, but apparently lack a paraxonemal rod. Swarmer cells, which form only occasionally, are smaller in size and carry two conspicuous flagella of more than 2 times the body length. Cells are decorated with a prominent apical papillum. Both the flagellar pocket and the adjacent feeding apparatus seem to merge together into a single sub-apical opening. The mitochondrion, which is most likely single, is located peripherally. It is reticulated in shape and contains only a few lamellar cristae. Mitochondrial DNA is abundant and evenly distributed throughout the organelle. Morphological synapomorphies confirm the affiliation of the species with the genus Rhynchopus (Diplonemea, Euglenozoa). We discuss the characters that distinguish Rhynchopus from Diplonema corroborating the validity of the two genera.

Unusual Mitochondrial Genome Structures throughout the Euglenozoa

Mitochondrial DNA of Kinetoplastea is composed of different chromosomes, the maxicircle (bearing 'regular' genes) and numerous minicircles (specifying guide RNAs involved in RNA editing). In trypanosomes [Kinetoplastea], DNA circles are compacted into a single dense body, the kinetoplast. This report addresses the question whether multi-chromosome mitochondrial genomes and compacted chromosome organization are restricted to Kinetoplastea or rather occur throughout Euglenozoa, i.e., Kinetoplastea, Euglenida and Diplonemea. To this end, we investigated the diplonemid Rhynchopus euleeides and the euglenids Petalomonas cantuscygni, Peranema trichophorum and Entosiphon sulcatum, using light and electron microscopy and molecular techniques. Our findings together with previously published data show that multi-chromosome mitochondrial genomes prevail across Euglenozoa, while kinetoplast-like mtDNA packaging is confined to trypanosomes.

Dinoflagellate, Euglenid, or Cercomonad? The ultrastructure and molecular phylogenetic position of Protaspis grandis n. sp

Protaspis is an enigmatic genus of marine phagotrophic biflagellates that have been tentatively classified with several different groups of eukaryotes, including dinoflagellates, euglenids, and cercomonads. This uncertainty led us to investigate the phylogenetic position of Protaspis grandis n. sp. with ultrastructural and small subunit (SSU) rDNA sequence data. Our results demonstrated that the cells were dorsoventrally flattened, shaped like elongated ovals with parallel lateral sides, 32.5-55.0 mum long and 20.0-35.0 mum wide. Moreover, two heterodynamic flagella emerged through funnels that were positioned subapically, each within a depression and separated by a distinctive protrusion. A complex multilayered wall surrounded the cell. Like dinoflagellates and euglenids, the nucleus contained permanently condensed chromosomes and a large nucleolus throughout the cell cycle. Pseudopodia containing numerous mitochondria with tubular cristae emerged from a ventral furrow through a longitudinal slit that was positioned posterior to the protrusion and flagellar apparatus. Batteries of extrusomes were present within the cytoplasm and had ejection sites through pores in the cell wall. The SSU rDNA phylogeny demonstrated a very close relationship between the benthic P. grandis n. sp. and the planktonic Cryothecomonas longipes. These ultrastructural and molecular phylogenetic data for Protaspis indicated that the current taxonomy of Protaspis and Crythecomonas is in need of re-evaluation. The composition and identity of Protaspis is reviewed and suggestions for future taxonomic changes are presented. Problems within the genus Cryothecomonas are highlighted as well, and the missing data needed to resolve ambiguities between the two genera are clarified.

Food vacuole contents in the ciliate, Balantidium jocularum (Balantididae), a symbiont in the intestine of the surgeonfish, Naso tonganus (Acanthuridae)

During the past 16 years, the ciliate Balantidium jocularum has been collected from the intestines of many specimens of its fish host, Naso tonganus, all collected from the Great Barrier Reef near Lizard Island, Australia. Ciliates for this study of food consumption were isolated in 1988, 1989, 2003, and 2005. Nineteen specimens of B. jocularum were examined in the transmission electron microscope to determine the contents of both food vacuoles and a putative discharging cytoproct vacuole. Food vacuoles contained rod-shaped bacteria, tightly coiled spirilliform bacteria, and one or more euglenid flagellates. In several balantidia of somewhat different form than the type species of B. jocularum, the large bacterium, Epulopiscium fishelsoni, was observed in light microscope protargol preparations. Some putative phagolysosomes retained spirilliform bacteria that were apparently intact, and others contained partially digested flagellates. Food in a single discharging cytoproct vacuole consisted of normal appearing spirilliform bacteria, some other bacteria, and no flagellates. The results argue for non-selective ingestion of food and selective digestion; hence, somewhat inefficient food processing.

Unique mitochondrial genome structure in diplonemids, the sister group of kinetoplastids

Kinetoplastid flagellates are characterized by uniquely massed mitochondrial DNAs (mtDNAs), the kinetoplasts. Kinetoplastids of the trypanosomatid group possess two types of mtDNA molecules: maxicircles bearing protein and mitoribosomal genes and minicircles specifying guide RNAs, which mediate uridine insertion/deletion RNA editing. These circles are interlocked with one another to form dense networks. Whether these peculiar mtDNA features are restricted to kinetoplastids or prevail throughout Euglenozoa (euglenids, diplonemids, and kinetoplastids) is unknown. Here, we describe the mitochondrial genome and the mitochondrial ultrastructure of Diplonema papillatum, a member of the diplonemid flagellates, the sister group of kinetoplastids. Fluorescence and electron microscopy show a single mitochondrion per cell with an ultrastructure atypical for Euglenozoa. In addition, DNA is evenly distributed throughout the organelle rather than compacted. Molecular and electron microscopy studies distinguish numerous 6- and 7-kbp-sized mitochondrial chromosomes of monomeric circular topology and relaxed conformation in vivo. Remarkably, the cox1 gene (and probably other mitochondrial genes) is fragmented, with separate gene pieces encoded on different chromosomes. Generation of the contiguous cox1 mRNA requires trans-splicing, the precise mechanism of which remains to be determined. Taken together, the mitochondrial gene/genome structure of Diplonema is not only different from that of kinetoplastids but unique among eukaryotes as a whole.

[Potentially toxic and harmful phytoflagellates from the Mexican Pacific coasts]

The phytoflagellates are a heterogeneous group of autotrophic, heterotrophic and mixothrophic flagellates of trophic importance in several ecosystems. As in the rest of Latin America, the phytoflagellates that occur in the Mexican Pacific coasts are virtually unknown except for a few records. Their study require complicated collection and analysis methods, a probable cause for the scarce knowledge of this group in tropical and subtropical areas. Material recently collected from various localities along the Mexican Pacific coasts was used to study phytoflagellates, including toxic and potentially toxic species. Plankton samples were treated by gravity and pump filtration, using different methods for fixation and analysis. The phyla Euglenophyta, Heterokontophyta and Haptophyta were found. They occur as plankton in oceanic and shallow coastal waters.

Did trypanosomatid parasites have photosynthetic ancestors?

Some molecular phylogenies of plastid-like genes suggest that chloroplasts (the structures responsible for photosynthesis in plants and algae) might have been secondarily lost in trypanosomatid parasites. Chloroplasts are present in some euglenids, which are closely related to trypanosomatids, and it has been argued that chloroplasts arose early in the diversification of the lineage Euglenozoa, to which trypanosomatids and euglenids belong (plastids-early hypothesis). This article reviews how euglenid ultrastructural systems are functionally integrated and phylogenetically correlated. I argue that chloroplast acquisition profoundly altered the structure of certain euglenids, and that the complete absence of these modifications in other euglenozoans is most consistent with their never having had a chloroplast. Ultrastructural evidence suggests that chloroplasts arose relatively recently within a specific subgroup of euglenids and that trypanosomatids are not secondarily non-photosynthetic (plastids-recent hypothesis).

Comparative morphology of the euglenid pellicle. II. Diversity of strip substructure

The morphological diversity associated with the strip substructure of the euglenid pellicle was examined, and after identifying characters and states, we outlined hypotheses about their evolution. We have attempted to standardize terms necessary for analytical comparisons of strips by providing a glossary and comparing published synonyms. Most of the substructural diversity found in euglenids is demonstrated with 13 representative taxa. Strips are generally composed of two subcomponents: frames and projections. Frames support the basic shape of strips and many can be described as either S-shaped, plateau-shaped, M-shaped, or A-shaped. Projections branch laterally from the frames, are usually periodic, and can be described as thread-like structures, an indented plate, tooth-like structures, and plate-like structures. The ancestral state included strips that were few in number, flat, and fused. The strips became S-shaped and disjoined in the lineage leading to most euglenid taxa. These strips became secondarily flattened and fused in one lineage. In some lineages of phototrophs, the strips became increasingly robust. Two strips of different morphology formed the repeating pellicular unit or doublet in four taxa. These doublets evolved convergently at least three times and may provide insights into developmental patterns of the cytoskeleton.

Comparative morphology of the euglenid pellicle. I. Patterns of strips and pores

In anticipation that improved knowledge of euglenid morphology will provide robust apomorphy-based definitions for clades, transmission and scanning electron microscopy were used to reveal novel morphological patterns associated with the euglenid pellicle. In some taxa, the number of pellicle strips around the cell periphery reduces as discrete whorls at the anterior and posterior ends of the cell. The number of whorls at either end varies between selected euglenid taxa but is invariant within a taxon. The pattern of strip reduction associated with these whorls is shown to have at least three evolutionarily linked states: exponential, pseudoexponential, and linear. Two general equations describe these states near the posterior end of euglenid cells. Exponential patterns of strip reduction near the anterior end are described by a third equation. In addition, several euglenid taxa were found to possess conspicuous pellicle pores. These pores are arranged in discrete rows that follow the articulation zones between adjacent strips. The number of strips between rows of pores varies between taxa and displays a series of consecutive character states that differ by a power of two. The patterns of pores may not only have phylogenetical and taxonomical value but may provide morphological markers for following strip maturation during cytoskeletal reproduction.

The Glu-modification of alpha-tubulin in the feeding apparatus of the primitive flagellate Entosiphon sulcatum is only apparent after detergent treatment

Using specific monoclonal antibodies, we investigated the distribution of post-translational modified Tyr- and Glu-tubulins during interphase of the primitive flagellate Entosiphon sulcatum. Immunofluorescence studies of simultaneously permeabilized and fixed cells revealed that microtubular structures comprising Ca(2+)-labile subpellicular and flagellar MTs and Ca(2+)-stable MTs in the siphon complex (feeding organelle) reacted surprisingly unorthodox with antibodies against Tyr- and Glu-tubulin: Unexpectedly, the siphon complex consisting of Ca(2+)-stable MTs appeared exclusively Tyr-positive, whereas the Ca(2+)-labile subpellicular and flagellar MTs reacted with the Glu- as well as with the Tyr-antibody. That the siphon MTs were indeed Ca(2+)-stable and all other MTs had become solubilized, was verified by EM-observation. This surprising result contrasting considerably with the permanent nature of the siphon complex, was reconsidered after preceding lysis and extraction procedures. Depending on the type of detergent used and on extraction times applied, the MTs of the siphon complex now always showed also Glu-positivity, indicating the presence of detyrosinated alpha-tubulin as a biochemical marker of stabilized MTs. Since saponin, irrespective of subsequent extraction times, always produced a Glu-positive reaction and ultrastructural analysis never gave compelling evidence for a drastic MAP-removal, we conclude that the Glu-epitope became freely accessible due to conformational changes in the tubulin polymeres.