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PubMed2000

The chimeric eukaryote: origin of the nucleus from the karyomastigont in amitochondriate protists.

We present a testable model for the origin of the nucleus, the membrane-bounded organelle that defines eukaryotes. A chimeric cell evolved via symbiogenesis by syntrophic merger between an archaebacterium and a eubacterium. The archaebacterium, a thermoacidophil resembling extant Thermoplasma, generated hydrogen sulfide to protect the eubacterium, a heterotrophic swimmer comparable to Spirochaeta or Hollandina that oxidized sulfide to sulfur. Selection pressure for speed swimming and oxygen avoidance led to an ancient analogue of the extant cosmopolitan bacterial consortium "Thiodendron latens." By eubacterial-archaebacterial genetic integration, the chimera, an amitochondriate heterotroph, evolved. This "earliest branching protist" that formed by permanent DNA recombination generated the nucleus as a component of the karyomastigont, an intracellular complex that assured genetic continuity of the former symbionts. The karyomastigont organellar system, common in extant amitochondriate protists as well as in presumed mitochondriate ancestors, minimally consists of a single nucleus, a single kinetosome and their protein connector. As predecessor of standard mitosis, the karyomastigont preceded free (unattached) nuclei. The nucleus evolved in karyomastigont ancestors by detachment at least five times (archamoebae, calonymphids, chlorophyte green algae, ciliates, foraminifera). This specific model of syntrophic chimeric fusion can be proved by sequence comparison of functional domains of motility proteins isolated from candidate taxa.

Animals↗
PubMed2003

Plant functional group diversity promotes soil protist diversity.

We tested whether effects of plant diversity can propagate through food webs, down to heterotrophic protists not linked directly to plants. To this end we synthesised grassland ecosystems with varying numbers of plant functional groups (FGN) and assessed corresponding changes in testate amoebae communities. The number of plant species was kept constant. When FGN was increased from 1 to 3, species number and total community density of live testate amoebae were enhanced according to a linear and a saturating function, respectively. From FGN 1 to 2, the appearance of new testate amoebae species did not affect the presence of the resident species, whereas, from FGN 2 to 3 about one quarter of the resident testate amoebae species was replaced, without altering the total species number. Overall, density by species increased, while evenness of the testate amoebae community was not affected by FGN; although Trinema lineare, one of the most common species, became more abundant. The observed relationship between plant functional group diversity and testate amoebae diversity could shed new light on the biogeographical distribution patterns of protists.

Amoeba↗
PubMed2005

Comprehensive multigene phylogenies of excavate protists reveal the evolutionary positions of "primitive" eukaryotes.

Many of the protists thought to represent the deepest branches on the eukaryotic tree are assigned to a loose assemblage called the "excavates." This includes the mitochondrion-lacking diplomonads and parabasalids (e.g., Giardia and Trichomonas) and the jakobids (e.g., Reclinomonas). We report the first multigene phylogenetic analyses to include a comprehensive sampling of excavate groups (six nuclear-encoded protein-coding genes, nine of the 10 recognized excavate groups). Excavates coalesce into three clades with relatively strong maximum likelihood bootstrap support. Only the phylogenetic position of Malawimonas is uncertain. Diplomonads, parabasalids, and the free-living amitochondriate protist Carpediemonas are closely related to each other. Two other amitochondriate excavates, oxymonads and Trimastix, form the second monophyletic group. The third group is comprised of Euglenozoa (e.g., trypanosomes), Heterolobosea, and jakobids. Unexpectedly, jakobids appear to be specifically related to Heterolobosea. This tree topology calls into question the concept of Discicristata as a supergroup of eukaryotes united by discoidal mitochondrial cristae and makes it implausible that jakobids represent an independent early-diverging eukaryotic lineage. The close jakobids-Heterolobosea-Euglenozoa connection demands complex evolutionary scenarios to explain the transition between the presumed ancestral bacterial-type mitochondrial RNA polymerase found in jakobids and the phage-type protein in other eukaryotic lineages, including Euglenozoa and Heterolobosea.

Animals↗
PubMed2001

Pyruvate : NADP+ oxidoreductase from the mitochondrion of Euglena gracilis and from the apicomplexan Cryptosporidium parvum: a biochemical relic linking pyruvate metabolism in mitochondriate and amitochondriate protists.

Most eukaryotes perform the oxidative decarboxylation of pyruvate in mitochondria using pyruvate dehydrogenase (PDH). Eukaryotes that lack mitochondria also lack PDH, using instead the O(2)-sensitive enzyme pyruvate : ferredoxin oxidoreductase (PFO), which is localized either in the cytosol or in hydrogenosomes. The facultatively anaerobic mitochondria of the photosynthetic protist Euglena gracilis constitute a hitherto unique exception in that these mitochondria oxidize pyruvate with the O(2)-sensitive enzyme pyruvate : NADP oxidoreductase (PNO). Cloning and analysis of Euglena PNO revealed that the cDNA encodes a mitochondrial transit peptide followed by an N-terminal PFO domain that is fused to a C-terminal NADPH-cytochrome P450 reductase (CPR) domain. Two independent 5.8-kb full-size cDNAs for Euglena mitochondrial PNO were isolated; the gene was expressed in cultures supplied with 2% CO(2) in air and with 2% CO(2) in N(2). The apicomplexan Cryptosporidium parvum was also shown to encode and express the same PFO-CPR fusion, except that, unlike E. gracilis, no mitochondrial transit peptide for C. parvum PNO was found. Recombination-derived remnants of PNO are conserved in the genomes of Saccharomyces cerevisiae and Schizosaccharomyces pombe as proteins involved in sulfite reduction. Notably, Trypanosoma brucei was found to encode homologs of both PFO and all four PDH subunits. Gene organization and phylogeny revealed that eukaryotic nuclear genes for mitochondrial, hydrogenosomal, and cytosolic PFO trace to a single eubacterial acquisition. These findings suggest a common ancestry of PFO in amitochondriate protists with Euglena mitochondrial PNO and Cryptosporidium PNO. They are also consistent with the view that eukaryotic PFO domains are biochemical relics inherited from a facultatively anaerobic, eubacterial ancestor of mitochondria and hydrogenosomes.

Amino Acid Sequence↗
PubMed2003

Protists decrease in size linearly with temperature: ca. 2.5% degrees C(-1).

An inverse relationship between organism size and rearing temperature is widely observed in ectotherms ('the temperature-size rule', TSR). This has rarely been quantified for related taxa, and its applicability to protists also required testing. Here, we quantify the relationship between temperature and mean cell volume within the protists by a meta-analysis of published data covering marine, brackish water and freshwater autotrophs and heterotrophs. In each of 44 datasets, a linear relationship between temperature and size could not be rejected, and a negative trend was found in 32 cases (20 gave significant negative regressions, p < 0.05). By combining 65 datasets, we revealed, for each 1 degrees C increase, a cell-size reduction of 2.5% (95% CI of 1.7-3.3%) of the volume observed at 15 degrees C. The value did not differ across taxa (amoebae, ciliates, diatoms, dinoflagellates, flagellates), habitats, modes of nutrition or combinations of these. The data are consistent with two hypotheses that are capable of explaining the TSR in ectotherms generally: (i) resource, especially respiratory gas, limitation; and (ii) fitness gains from dividing earlier as population growth increases. Using the above relationship we show how changes in cell numbers with temperature can be estimated from changes in biomass and vice versa; ignoring this relationship would produce a systematic error.

Animals↗
PubMed2004

The plasma membrane of microaerophilic protists: oxidative and nitrosative stress.

The trans-plasma-membrane electrochemical potential of microaerophilic protists was monitored by the use of voltage-sensitive charged lipophilic fluorophores; of the many available probes, the anionic oxonol dye bis(1,3-dibarbituric acid)-trimethine oxonol [DiBAC(4)(3)] is an example of one which has been successfully employed using fluorescence microscopy, confocal laser-scanning microscopy and flow cytometry. Several microaerophilic protists have been investigated with this dye; these were Giardia intestinalis, Trichomonas vaginalis, Tritrichomonas foetus, Hexamita inflata and Mastigamoeba punctachora. Under conditions where they exhibit normal vitality, these organisms exclude DiBAC(4)(3) by virtue of their maintenance of a plasma-membrane potential (negative inside). Uptake of the fluorophore is indicative of disturbance to this membrane (i.e. by inhibition of pump/leak balance, blockage of channels or generation of ionic leaks), and is indicative of metabolic perturbation or environmental stress. Here, it is shown that oxidative or nitrosative stress depolarizes the plasma membranes of the aforementioned O(2)-sensitive organisms and allows DiBAC(4)(3) influx. Oxonol uptake thereby provides a sensitive and early indication of plasma-membrane perturbation by agents that may lead to cytotoxicity and eventually to cell death by necrotic or apoptotic pathways.

Animals↗
PubMedDate not supplied

Protists as opportunistic pathogens: public health impact in the 1990s and beyond.

Protist organisms (protozoa and fungi) have become increasingly prominent as opportunistic pathogens among persons infected with human immunodeficiency virus (HIV) and among organ transplant recipients--two immunocompromised populations that have increased dramatically in the past two decades. Pneumocystis carinii pneumonia continues to be the most common serious opportunistic infection (OI) among HIV-infected persons in the United States, occurring frequently among persons not previously receiving medical care. Toxoplasmosis, cryptococcosis, cryptosporidiosis, and isosporiasis occur frequently in HIV-infected persons in the developing world. Candidiasis and aspergillosis are common OIs in organ transplant recipients. As these populations of immunosuppressed patients continue to expand worldwide new OIs caused by protist pathogens are likely to emerge.

AIDS-Related Opportunistic Infections↗
PubMedDate not supplied

A model of biocomplexity and its application to the analysis of some terrestrial and marsh eukaryotic microbial communities with an emphasis on amoeboid protists.

Biocomplexity theory has become increasingly important in understanding ecosystem dynamics as we realize that the interactions among subunits in a multi-component system often produce elaborate states that are not easily explained in terms of the individual parts of the system. A Euclidean geometric model of biocomplexity is presented and illustrated using protistan communities. The model is based on three quantitative biotic dimensions (indices) for small subsamples (0.01 g) taken from each sample core of substratum: (1) richness of morphospecies expressed as mean count per 0.01 g, (2) spatial diversity of protists expressed as then umber of unique morphospecies (i.e. those occurring in only one of the 0.01-g subsamples and not in any of the other subsamples), and (3) patchiness (non-uniform aggregation) of the distribution of protists across the 0.01-g subsamples. These three indices are mapped into a three-dimensional Euclidean space model, and the position of each point and its geometric distance from the origin are used as a general index of biocomplexity. The usefulness of the model is illustrated by applying it to a range of terrestrial and marsh communities. Within the set of 15 samples examined in this study, the marsh rhizosphere samples are among the most complex.

Amoeba↗
PubMedDate not supplied

The new higher level classification of eukaryotes with emphasis on the taxonomy of protists.

This revision of the classification of unicellular eukaryotes updates that of Levine et al. (1980) for the protozoa and expands it to include other protists. Whereas the previous revision was primarily to incorporate the results of ultrastructural studies, this revision incorporates results from both ultrastructural research since 1980 and molecular phylogenetic studies. We propose a scheme that is based on nameless ranked systematics. The vocabulary of the taxonomy is updated, particularly to clarify the naming of groups that have been repositioned. We recognize six clusters of eukaryotes that may represent the basic groupings similar to traditional "kingdoms." The multicellular lineages emerged from within monophyletic protist lineages: animals and fungi from Opisthokonta, plants from Archaeplastida, and brown algae from Stramenopiles.

Animal Population Groups↗
PubMedDate not supplied

Protist genetic diversity in the acidic hydrothermal environments of Lassen Volcanic National Park, USA.

We examined eukaryote genetic diversity in the hydrothermal environments of Lassen Volcanic National Park (LVNP), Northern California. We sampled hydrothermal areas of the Bumpass Hell, Sulfur Works, Devil's Kitchen, and Boiling Springs Lake sites, all of which included diverse acidic pools, mud pots, and streams with visible algal mats and biofilms. Temperatures varied from 15 to 85 degrees C and pH from 1.7 to 5.8. DNA extraction methods compared by denaturing gradient gel electrophoresis fingerprinting exhibited similar patterns, and showed limited diversity of eukaryotic small subunit (SSU) rRNA genes compared with prokaryotes. We successfully amplified eukaryotic SSU rRNA genes from most environments up to 68 degrees C. Cloned rDNA sequences reveal acidophilic protists dominate eukaryotes in LVNP hydrothermal environments. Most sites showed phototrophic assemblages dominated by chlorophytes and stramenopiles (diatoms and chrysophytes). Heterotrophic taxa, though less abundant, included diverse alveolates (ciliates), amoebae, and flagellates. Fungi were also found at most sites, and metazoans (hexapods, nematodes, platyhelminths) were sometimes detected in less acidic environments, especially in algal mats. While many cloned rDNA sequences showed 95%-99% identity to known acidophilic isolates or environmental clones from other acidic sites (Rio Tinto), sequence diversity generally declined both with decreasing pH and increasing temperature, and both were controlling physical variables on the abundance and distribution of organisms at our sites. However, a pool at 68 degrees C with pH 1.7 yielded the greatest number of distinct sequences. While some were likely contaminants from nearby cooler sites, we suggest that Lassen's acidic hydrothermal features may harbor novel protists.

Acids↗
PubMed1998

Cloning and expression of an iron-containing superoxide dismutase in the parasitic protist, Trichomonas vaginalis.

A superoxide dismutase (SOD) gene of the parasitic protist Trichomonas vaginalis was cloned, sequenced, expressed in Escherichia coli, and its gene product characterized. It is an iron-containing dimeric protein with a monomeric mass of 22,067 Da. Southern blots analyses suggested the presence of seven iron-containing (FeSOD) gene copies. Hydrophobic cluster analysis revealed some peculiarities in the 2D structure of the FeSOD from T. vaginalis and a strong structural conservation between prokaryotic and eukaryotic FeSODs. Phylogenetic reconstruction of the SOD sequences confirmed the dichotomy between FeSODs and manganese-containing SODs. FeSODs of protists appeared to group together with homologous proteobacterial enzymes suggesting a possible origin of eukaryotic FeSODs through an endosymbiotic event.

Amino Acid Sequence↗
PubMed2006

Cell surface lectin-binding glycoconjugates on marine planktonic protists.

Carbohydrate-protein interactions appear to play an important role in the phagocytosis of microbial prey by free-living protozoa. The present study utilizes FITC-labelled plant lectins to investigate the presence and localization of cell surface glycoconjugates on live and fixed planktonic protists (Dunaliella primolecta, Oxyrrhis marina, Goniomonas amphinema, Paraphysomonas vestita and Euplotes vannus). With live flagellate preparations, lectins primarily bound to external cell surfaces, with minimal internal staining observed. In contrast, cell fixation permeabilized cell membranes, allowing lectins to bind to internal structures, such as nuclear membranes and food vacuoles, interfering with the characterization of cell surface glycoconjugates. The method developed to label cell surface sugar moieties of live planktonic protists successfully overcomes the problems associated with fixation, and thus provides a useful protocol for future studies on protistan cell surface carbohydrate characterization.

Animals↗
PubMed2005

Catalyzed reported deposition-fluorescence in situ hybridization protocol to evaluate phagotrophy in mixotrophic protists.

We describe a catalyzed reported deposition-fluorescence in situ hybridization (CARD-FISH) protocol particularly suited to assess the phagotrophy of mixotrophic protists on prokaryotes, since it maintains cell and plastid integrity, avoids cell loss and egestion of prey, and allows visualization of labeled prey against plastid autofluorescence. This protocol, which includes steps such as Lugol's-formaldehyde-thiosulfate fixation, agarose cell attachment, cell wall permeabilization with lysozyme plus achromopeptidase, and signal amplification with Alexa-Fluor 488, allowed us to detect almost 100% of planktonic prokaryotes (Bacteria and Archaea) and, for the first time, to show archaeal cells ingested by mixotrophic protists.

Archaea↗
PubMed1996

The secretory pathway of protists: spatial and functional organization and evolution.

All cells secrete a diversity of macromolecules to modify their environment or to protect themselves. Eukaryotic cells have evolved a complex secretory pathway consisting of several membrane-bound compartments which contain specific sets of proteins. Experimental work on the secretory pathway has focused mainly on mammalian cell lines or on yeasts. Now, some general principles of the secretory pathway have become clear, and most components of the secretory pathway are conserved between yeast cells and mammalian cells. However, the structure and function of the secretory system in protists have been less extensively studied. In this review, we summarize the current knowledge about the secretory pathway of five different groups of protists: Giardia lamblia, one of the earliest lines of eukaryotic evolution, kinetoplastids, the slime mold Dictyostelium discoideum, and two lineages within the "crown" of eukaryotic cell evolution, the alveolates (ciliates and Plasmodium species) and the green algae. Comparison of these systems with the mammalian and yeast system shows that most elements of the secretory pathway were presumably present in the earliest eukaryotic organisms. However, one element of the secretory pathway shows considerable variation: the presence of a Golgi stack and the number of cisternae within a stack. We suggest that the functional separation of the plasma membrane from the nucleus-endoplasmic reticulum system during evolution required a sorting compartment, which became the Golgi apparatus. Once a Golgi apparatus was established, it was adapted to the various needs of the different organisms.

Animals↗
PubMed2004

Mitochondria of protists.

Over the past several decades, our knowledge of the origin and evolution of mitochondria has been greatly advanced by determination of complete mitochondrial genome sequences. Among the most informative mitochondrial genomes have been those of protists (primarily unicellular eukaryotes), some of which harbor the most gene-rich and most eubacteria-like mitochondrial DNAs (mtDNAs) known. Comparison of mtDNA sequence data has provided insights into the radically diverse trends in mitochondrial genome evolution exhibited by different phylogenetically coherent groupings of eukaryotes, and has allowed us to pinpoint specific protist relatives of the multicellular eukaryotic lineages (animals, plants, and fungi). This comparative genomics approach has also revealed unique and fascinating aspects of mitochondrial gene expression, highlighting the mitochondrion as an evolutionary playground par excellence.

Animals↗
PubMed2000

DNA fluorescent stain accumulates in the Golgi but not in the kinetosomes of amitochondriate protists.

Hindgut symbiotic trichomonads (uninucleate Caduceia versatilis, and multinucleate Stephanonympha sp. and Snyderella tabogae) from the dry-wood-eating termite Cryptotermes cavifrons (Kalotermitidae) accumulate DAPI (4,6diamidino-2-phenylindole) in the membranous sacs of the Golgi complex. This form of Golgi complex, typical of protists in the class Parabasalia, is called a parabasal body. Trichomonads contain organellar systems, mastigonts, that consist of four undulipodia (e.g. eukaryotic flagella and cilia), axostylar microtubules, a parabasal body and other structures. These cells bear from one (in the case of Caduceia) to hundreds (in the case of Snyderella) of mastigonts. These features are characteristic of their protist class (Parabasalia). The nuclei of all three species stained with DNA-specific stains: DAPI, SYTOX, acridine orange, propidium iodide, ethidium bromide and Feulgen, at optimal concentrations, but kinetosomes failed to stain at all. The nuclei, parabasal bodies and symbiotic bacteria (but no microtubular structures) fluoresced in glutaraldehyde-fixed cells stained with 1.45 microM DAPI. Parabasal bodies of Snyderella and Caduceia treated to remove lipids with Triton X-100, or treated with 5% trichloroacetic acid, lacked DAPI-fluorescence. I conclude that DNA, present as expected in nuclei and bacterial symbionts, is absent from and not associated with calonymphid kinetosomes. The reason for DNA-RNA stain accumulation in the Golgi cistemae is not clear.

Acridine Orange↗
PubMed1996

Tubulin post-translational modifications in the primitive protist Trichomonas vaginalis.

Using several specific monoclonal antibodies, we investigated the occurrence and distribution of different post-translationally modified tubulin during interphase and division of the primitive flagellated protist Trichomonas vaginalis. Immunoblotting and immunofluorescence experiments revealed that interphasic microtubular structures of T. vaginalis contained acetylated and glutamylated but non-tyrosinated and non-glycylated [Brugerolle and Adoutte, 1988: Bio Systems 21: 255-268] tubulin. Immunofluorescence studies performed on dividing cells showed that the extranuclear mitotic spindle (or paradesmosis) was acetylated and glutamylated, which contrast with the ephemeral nature of this structure. Newly formed short axostyles also contained acetylated and glutamylated tubulin suggesting that both post-translational modifications might take place very early after assembly of microtubular structures. Our results indicate that acetylation and glutamylation of tubulin appeared early in the history of eukaryotes and could reflect the occurrence of post-translational modifications of tubulin in the primitive eukaryotic cells. These cells probably had a highly ordered cross-linked microtubular cytoskeleton in which microtubules showed a low level of subunit exchange dynamics.

Acetylation↗
PubMed1992

Cortical ultrastructure and chemoreception in ciliated protists (Ciliophora).

The ciliated protists (ciliates) offer a unique opportunity to explore the relationship between chemoreception and cell structure. Ciliates resemble chemosensory neurons in their responses to stimuli and presence of cilia. Ciliates have highly patterned surfaces that should permit precise localization of chemoreceptors in relation to effector organelles. Furthermore, ciliates are easy to grow and to manipulate genetically; they can also be readily studied biochemically and by electrophysiological techniques. This review contains a comparative description of the ultrastructural features of the ciliate cell surface relevant to chemoreception, examines the structural features of putative chemoreceptive cilia, and provides a summary of the electron microscopic information available so far bearing on chemoreceptive aspects of swimming, feeding, excretion, endocytosis, and sexual responses of ciliates. The electron microscopic identification and localization of specific chemoreceptive macromolecules and organelles at the molecular level have not yet been achieved in ciliates. These await the development of specific probes for chemoreceptor and transduction macromolecules. Nevertheless, the electron microscope has provided a wealth of information about the surface features of ciliates where chemoreception is believed to take place. Such morphological information will prove essential to a complete understanding of reception and transduction at the molecular level. In the ciliates, major questions to be answered relate to the apportionment of chemoreceptive functions between the cilia and cell soma, the global distribution of receptors in relation to the anterior-posterior, dorsal-ventral, and left-right axes of the cell, and the relationship of receptors to ultrastructural components of the cell coat, cell membrane, and cytoskeleton.

Animals↗