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At least 181 records · Page 10Linked to original sources
PubMed1997

Centrin and the cytoskeleton of the protist Holomastigotoides.

The cytoskeleton of the parabasalid protozoan Holomastigotoides was investigated by epifluorescence, scanning confocal, and transmission electron microscopy using antibodies to centrin, tubulin, and MPM-2 epitopes. Previous microscopic analysis of Holomastigotoides spp. has shown that up to 10,000 flagella are arranged in 2-8 spiral bands encircling the cell. Spindle poles are associated with two flagellar bands. Sheets of cytoplasmic microtubules (MTs) called axostyles originate in the cell apex and extend to the cell base. Antibodies to centrin, a member of the EF-hand family of calcium-binding proteins, labeled a number of structures in Holomastigotoides, namely axostyles, the mitotic spindle, and portions of flagellar bands. The identity of these structures was confirmed by transmission electron microscopy and by immunofluorescence microscopy using antibodies to tubulin and MPM-2 epitopes. Antibodies to tubulin labeled MTs in basal bodies, flagella, axostyles, and the mitotic spindle. MPM-2 antibodies labeled spindle poles and short segments of flagellar bands to which the spindle poles are attached. Centrin is known to show calcium-sensitive contractile behavior. The pattern of flagellar band staining by antibodies to centrin was affected by [Ca2+]. In detergent-extracted cell fragments, the centrin staining pattern could be changed by changing [Ca2+]. This Ca2+ effect was modulated by a monoclonal antibody to centrin (20H5), indicating that centrin plays a role in altering flagellar band structure. These results show that centrin is located in key positions for maintaining cell polarity and directing cell movement through interactions with other cytoskeletal elements. Calcium may regulate the morphology of centrin-containing structures.

Animals↗
PubMed2001

Changes in the Epilimnetic Bacterial Community Composition, Production, and Protist-Induced Mortality along the Longitudinal Axis of a Highly Eutrophic Reservoir.

We studied changes in the epilimnetic bacterial community composition (BCC), bacterial biomass and production, and protistan succession and bacterivory along the longitudinal axis of the canyon-shaped, highly eutrophic Sau Reservoir (NE Spain) during two sampling campaigns, in April and July 1997. Longitudinal changes in BCC from the river inflow to the dam area of the reservoir were detected by using oligonucleotide probes targeted to the kingdom Bacteria, to the alpha, beta, and gamma subclasses (ALFA, BETA, and GAMA) of the class Proteobacteria, and to the Cytophaga/Flavobacterium (CF) cluster. In general, the inflow of the organically loaded Ter river, with highly abundant allochthonous bacterial populations, induced a clearly distinguishable longitudinal succession of the structure of the microbial food web. The most dynamic changes in microbial parameters occurred at the plunge point, the mixing area of river water and the reservoir epilimnion. Changes within members of BETA and CF were the most important in determining changes in BCC, bacterial abundance and biomass. Much less relevant changes occurred within the less abundant ALFA and GAMA bacteria. From the plunge point downstream, we described a significant shift in BCC in the form of decreased proportions of BETA and CF. This shift spatially coincided with the highest values of heterotrophic nanoflagellate bacterivory (roughly doubled the bacterial production). CF numerically dominated throughout the reservoir without any marked longitudinal changes in their mean cell volume. In contrast, very large cells affiliated to BETA clearly dominated in the allochthonous bacterial biomass brought by the river. BETA showed a marked downstream trend of decreasing mean cell volume. We conclude that the observed BCC shift and the longitudinal shift in food web structure (bacteria-heterotrophic nanoflagellates-ciliates) resulted from highly complex interactions brought about by several major factors: varying hydrology, the high localized allochthonous input of organic matter brought by the river, downstream changing substrate availability, and selective protistan bacterivory.

Journal Article↗
PubMed2005

The ecology of testate amoebae (Protists) in sphagnum in North-western Poland in relation to peatland ecology.

We studied the relationship between testate amoebae (Protozoa) communities and the depth to the water table (DWT), pH, conductivity, and microhabitat type in Sphagnum dominated peatlands of north-western Poland and built predictive (transfer function) models for inferring DWT and pH based on the testate amoebae community structure. Such models can be used for peatland monitoring and paleoecology. A total of 52 testate amoebae taxa were recorded. In a redundancy analysis, DWT and pH explained 20.1% of the variation in the species data and allowed us to identify three groups of taxa: species that are associated with (1) high DWT and low pH, (2) low DWT and low pH, and (3) high pH and mid-range DWT. Our transfer function models allow DWT and pH to be estimated with mean errors of 9.89 cm and 0.71 pH units. The prediction error of the DWT model and the tolerance of the species both increase with increasing dryness. This pattern mirrors the ecology of Sphagnum mosses: Species growing in wet habitats are more sensitive to change in water table depth than the species growing in drier microhabitats. Our results are consistent with studies of testate amoeba ecology in other regions, and they provide additional support for the use of these organisms in paleoecological and biomonitoring contexts.

Adaptation, Physiological↗
PubMed2006

Relationship between testate amoeba (protist) communities and atmospheric heavy metals accumulated in Barbula indica (bryophyta) in Vietnam.

We studied the relationships between testate amoeba communities and heavy metal (Pb, Cd, Zn, Ni, Cu, Mn, and Fe) concentrations in the moss Barbula indica sampled at 29 sites in and around the city of Hanoi (Vietnam). Our first approach was to compare the heavy metal concentrations and testate amoeba variables between the city (zone 1) and the surrounding (zone 2). Mean moss concentrations of Pb, Cd, Zn, Ni, and Cu were significantly higher and testate amoeba species richness and abundance were significantly lower in zone 1 and the abundance of eight taxa differed significantly between the two zones. We then studied the correlation between heavy metals and testate amoebae. Species richness and abundance were correlated negatively to Pb concentration. Shannon H' was negatively correlated to both Pb and Cd. The abundance of several species was negatively correlated with Pb, Cd, Zn, and Ni; however, at the community level, Pb emerged as the only significant variable in a redundancy analysis. Our results suggest that testate amoebae are sensitive to and may be good bioindicators for heavy metal pollution, especially lead. Further research is needed to understand the causal relationships underlying the observed patterns.

Air Pollutants↗
PubMed2005

Differential gene expression during stationary phase between amicronucleates and micronucleates of the ciliated protist, Pseudourostyla cristata.

Ciliates are unicellular eukaryotic organisms with two types of nuclei, the 'germline' micronucleus (MIC) and the 'somatic' macronucleus (MAC). We previously reported that when the MIC of Pseudourostyla cristata was eliminated by amputation, the resultant amicronucleate organisms exhibited a lower viability and abnormal oral structures. To gain insight into the genetic reorganization involved in or induced by removal of the MIC and the mechanism by which nuclear dimorphism was established, we investigated gene expression differences between amicronucleates and micronucleates, using suppression subtractive hybridization (SSH) techniques. Approximately 250 clones from each library were screened by cDNA array dot blotting. Altogether, 22 unique genes from the forward-subtractive library (micronucleates as tester, amicronucleates as driver) and 23 unique genes from the reverse-subtractive library (micronucleates as driver and amicronucleates as tester) were shown to be differentially expressed. These 45 differentially expressed genes were found to be homologs of genes involved in various cellular processes including signal transduction, transcription, cell cycle accomplishment and general metabolism, cell structure, and stress response. We highlighted 14 genes, 7 that were unique from both the forward-subtractive and the reverse-subtractive libraries, using real time semi-quantitative RT-PCR. The characterization of these cDNAs represents a starting point in understanding the molecular mechanisms of amicronucleates disruption.

Animals↗
PubMed2006

On the origin and functions of RNA-mediated silencing: from protists to man.

Double-stranded RNA has been shown to induce gene silencing in diverse eukaryotes and by a variety of pathways. We have examined the taxonomic distribution and the phylogenetic relationship of key components of the RNA interference (RNAi) machinery in members of five eukaryotic supergroups. On the basis of the parsimony principle, our analyses suggest that a relatively complex RNAi machinery was already present in the last common ancestor of eukaryotes and consisted, at a minimum, of one Argonaute-like polypeptide, one Piwi-like protein, one Dicer, and one RNA-dependent RNA polymerase. As proposed before, the ancestral (but non-essential) role of these components may have been in defense responses against genomic parasites such as transposable elements and viruses. From a mechanistic perspective, the RNAi machinery in the eukaryotic ancestor may have been capable of both small-RNA-guided transcript degradation as well as transcriptional repression, most likely through histone modifications. Both roles appear to be widespread among living eukaryotes and this diversification of function could account for the evolutionary conservation of duplicated Argonaute-Piwi proteins. In contrast, additional RNAi-mediated pathways such as RNA-directed DNA methylation, programmed genome rearrangements, meiotic silencing by unpaired DNA, and miRNA-mediated gene regulation may have evolved independently in specific lineages.

Animals↗
PubMed2003

Morphogenesis during division and griseofulvin-induced changes of the microtubular cytoskeleton in the parasitic protist, Trichomonas vaginalis.

The behavior of microtubular structures during division was followed by immunofluorescence in Trichomonas vaginalis using an anti-alpha-tubulin monoclonal antibody together with nuclear staining by DAPI, allowing us to describe successive mitotic stages. In contrast to recent reports, we showed that: (1) the microtubular axostyle-pelta complex depolymerized during division, (2) the flagella were assembled during mitosis, and (3) the flagellar number was restored in each daughter kinetid before cytokinesis. Observation of griseofulvin-treated T. vaginalis cells revealed that the elongation of the mitotic spindle or paradesmosis was not the main motile force separating the daughter kinetids to opposite poles during division, suggesting the existence of other mechanisms and/or molecules involved in this morphogenetic event. Examination of treated cells re-incubated in fresh medium showed the nucleation of microtubules radiating from the perinuclear area, the origin of which is discussed. Finally, we confirm the effectiveness of griseofulvin against T. vaginalis and propose that this antifungal drug could be a promising antitrichomonal agent.

Animals↗
PubMed2001

The promise of a protist: the Dictyostelium genome project.

The genome of Dictyostelium discoideum is being sequenced by an international consortium and is scheduled for completion in the next few years. The sequence will accelerate research into a number of phenomena carried out by these versatile soil amoebae, providing insight into analogous processes that operate in a wide range of eukaryotes. These include the dynamic regulation of the cytoskeleton during chemotaxis, intercellular communication during multicellular development and the intracellular growth of bacterial pathogens. The current state of the genome project is summarized and the challenges of sequencing a genome with unusually low guanine and cytosine content and with a bimodal base composition distribution are discussed. The prospects for functional analyses at the genomic scale are also considered.

Animals↗
PubMed1984

Fructose 2,6-bisphosphate, a potent regulator of carbohydrate metabolism, inhibits trehalose phosphorylase from protist Euglena gracilis.

Partially purified trehalose phosphorylase (EC 2.4.1.64) from Euglena gracilis SM-ZK was inhibited by fructose 2,6-bisphosphate in both synthetic and degradative directions. Ki value for trehalose phosphorolysis was 1.2 microM and that for trehalose synthesis was 0.5 microM. Functions of fructose 2,6-bisphosphate in Euglena, particularly in the regulative mechanism of the two reserve carbohydrates, paramylon and trehalose, are discussed.

Adenine Nucleotides↗
PubMed1991

Subcellular distribution of enzymes involved in the biosynthesis of cyanelle murein in the protist Cyanophora paradoxa.

Cyanelle containing organisms, notably Cyanophora paradoxa, the best studied among them, are unique with respect to the occurrence of peptidoglycan (murein) within an eukaryotic cell. Enzyme activities involved in the biosynthesis of UDP-N-acetyl-muramylpentapeptide could be localized within the cyanelle compartment. Some of the enzymes performing later steps of murein biosynthesis were detected in the postcyanelle supernatant rather than in the cyanelle lysate. This is taken to reflect a 'periplasmic' location of these enzymes that are partially liberated upon rupture of the cyanelle outer membrane.

Carboxypeptidases↗
PubMed1992

Novel ion channels in the protists, Mougeotia and Saprolegnia, using sub-gigaseals.

Protoplasts of the filamentous alga, Mougeotia, and the filamentous fungal oomycete, Saprolegnia ferax, exhibit two K+ ion channels (2-6 pA) using the patch-clamp technique when the seals are less than 1 G omega (about 100 M omega). The membrane potential of the protoplasts was near 0 mV as measured intracellularly with double-barreled micropipettes; thus, inward K+ flux is due solely to concentration differences. Although conductances are in the range expected for K+ channels, the activity at 0 mV is not seen in other organisms under gigaseal conditions. This paper draws attention to the usefulness of this subsidiary patch-clamp technique and the novel characteristics of ion channels in Mougeotia and Saprolegnia.

Chlorophyta↗
PubMed1996

Purification and characterization of the acetate forming enzyme, acetyl-CoA synthetase (ADP-forming) from the amitochondriate protist, Giardia lamblia.

Giardia lamblia, an amitochondriate eukaryote, contains acetyl-CoA synthetase (ADP-forming), an enzyme known only from one other eukaryote (Entamoeba histolytica) and a few anaerobic prokaryotes. The enzyme has been purified about 350-fold. The activity in the direction of acetate formation was dependent on ADP and inorganic phosphate. The reverse reaction could not be detected. Succinyl-CoA, propionyl-CoA and dADP were utilized with lower efficiency. The enzyme did not utilize AMP plus PPi thus differs from the broadly distributed acetyl-CoA synthetase (AMP-forming). The enzyme is responsible for acetate production accompanied by ATP generation, thus plays an important role in G. lamblia metabolism.

Acetate-CoA Ligase↗
PubMed1990

A discrete, stochastic model for microbial filter feeding: a model for feeding of ciliated protists on spatially uniform, nondepletable suspensions.

Suspension-feeding ciliates, either bacteriovorous or planktonic, are adapted to feed on particulate food matter of size much smaller than their own size. These microorganisms collect their prey by generating water currents that draw prey toward their capture surfaces. Under such conditions food particles are treated in bulk, and captures of individual food particles from a suspension by individual single-celled organisms are discrete events that occur at random intervals of time. Each such event is followed by a sequence of additional events that also occur at random intervals of time. This sequence culminates in the incorporation of the digestible portion of the food particle into the cell's cytoplasm and the expulsion of the indigestible portion from the cell. In theory, the rate of the overall ingestion-digestion process can be limited by the passage of particles through any stage of this sequence of events. In this paper, we assume that only the initial events in the sequence, those that occur in the oral region of the cell, limit the rate of the ingestion-digestion process, and we develop a discrete, stochastic model of filter feeding based on that assumption. We use the model to show how advanced instrumentation, such as flow cytometry, can be used to measure parameters of the model and also to answer a number of important questions about the mechanism of filter feeding. We show also how the model can be applied to nonhomogeneous cell populations for which parameters of the model are distributed.

Animals↗
PubMed1994

Analysis of a single-domain P-glycoprotein-like gene in the early-diverging protist Trichomonas vaginalis.

We have characterized a gene encoding an Adenosine triphosphate (ATP) Binding Cassette (ABC) transmembrane protein from Trichomonas vaginalis, an early-diverging protozoan parasite. This gene, Tvpgp1, encodes a 589-amino acid protein with an amino-terminal hydrophobic region, 6 potential membrane-spanning segments and a carboxy-terminal ATP binding site. Tvpgp1 is most similar in sequence to mammalian P-glycoproteins, 170 kDa transport proteins which are frequently overexpressed in multiple drug-resistant (Mdr) tumor cell lines. However, Tvpgp1 is half the size of typical P-glycoproteins which are tandem duplications. These data suggest that the duplication/fusion events which gave rise to the bipartite structure comprised of 2 similar halves which characterize eukaryotic P-glycoproteins may have occurred after the divergence of trichomonads (Parabasalia) from the main line of eukaryotic evolutionary descent. We have examined 7 metronidazole resistant strains of T. vaginalis to determine whether the Tvpgp1 gene is overexpressed or amplified. 2 drug resistant strains show a 2-3-fold overexpression and one shows a 20-fold overexpression of Tvpgp mRNA. The gene is not amplified in any of the drug resistant strains. On the contrary, 4 of the 7 resistant strains lack one of 2 Tvpgp genes found in drug-sensitive strains.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1989

Rapid ribosomal RNA sequencing and the phylogenetic analysis of protists.

A newly described technique for rapidly obtaining the partial nucleotide sequence of ribosomal RNA is being applied to investigate phylogenetic relationships among living organisms. Alan Johnson and Peter Boverstock describe the importance of this method to parasitology in providing new information on the phylogenetic relationships of parasitic organisms previously placed in groups of convenience. The phylum Apicomplexo in particular, has been the object of much study using this technique, but the technology is likely to extend soon to the restructuring of the phylogenetic trees of many groups of parasites.

Journal Article↗