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At least 19 recordsLinked to original sources
PubMed2025

Anaerobic breviate protist survival in microcosms depends on microbiome metabolic function.

Anoxic and hypoxic environments serve as habitats for diverse microorganisms, including unicellular eukaryotes (protists) and prokaryotes. To thrive in low-oxygen environments, protists and prokaryotes often establish specialized metabolic cross-feeding associations, such as syntrophy, with other microorganisms. Previous studies show that the breviate protist Lenisia limosa engages in a mutualistic association with a denitrifying Arcobacter bacterium based on hydrogen exchange. Here, we investigate if the ability to form metabolic interactions is conserved in other breviates by studying five diverse breviate microcosms and their associated bacteria. We show that five laboratory microcosms of marine breviates live with multiple hydrogen-consuming prokaryotes that are predicted to have different preferences for terminal electron acceptors using genome-resolved metagenomics. Protist growth rates vary in response to electron acceptors depending on the make-up of the prokaryotic community. We find that the metabolic capabilities of the bacteria and not their taxonomic affiliations determine protist growth and survival and present new potential protist-interacting bacteria from the Arcobacteraceae, Desulfovibrionaceae, and Terasakiella lineages. This investigation uncovers potential nitrogen and sulfur cycling pathways within these bacterial populations, hinting at their roles in syntrophic interactions with the protists via hydrogen exchange.

Anaerobiosis↗
PubMed2025

Modes and mechanisms for the inheritance of mitochondria and plastids in pathogenic protists.

Pathogenic protists are responsible for many diseases that significantly impact human and animal health across the globe. Almost all protists possess mitochondria or mitochondrion-related organelles, and many contain plastids. These endosymbiotic organelles are crucial to survival and provide well-validated and widely utilised drug targets in parasitic protists such as Plasmodium and Toxoplasma. However, mutations within the organellar genomes of mitochondria and plastids can lead to drug resistance. Such mutations ultimately challenge our ability to control and eradicate the diseases caused by these pathogenic protists. Therefore, it is important to understand how organellar genomes, and the resistance mutations encoded within them, are inherited during protist sexual reproduction and how this may impact the spread of drug resistance and future therapeutic approaches to target these organelles. In this review, we detail what is known about mitochondrial and plastid inheritance during sexual reproduction across different pathogenic protists, often turning to their better studied, nonpathogenic relatives for insight.

Plastids↗
PubMed1992

Should there be a separate code of nomenclature for the protists?

The present Botanical and Zoological Codes of Nomenclature are often inadequate for resolution of all the peculiar problems caused by the very nature of the numerous and diverse groups of the so-called 'lower' eukaryotic organisms known as protists. Whether or not a separate code should therefore be created for these species--many but not all of which are unicellular in structure and microscopic in size--is complicated by several factors. The principal one is related to the wide dispersal of protists throughout many taxonomic classes and phyla/divisions; sometimes even multiple kingdoms are involved. If recognition of a single kingdom Protista is no longer tenable, then even the concept of one code per kingdom is not applicable. Other difficulties arise primarily from long-standing differences in major provisions of present Botanical and Zoological Codes. Numerous 'ambiregnal' forms exist, species currently under dual code jurisdiction. The matter of names for suprafamilial taxa of protists, irrespective of their ultimate kingdom assignment, poses another set of concerns not yet resolved. A plea is made to recognize the legitimacy of having distinct high-level ranks for protist species that seem to be widely separated phylogenetically from fellow protists or from other eukaryotic assemblages.

Animals↗
PubMed1978

Protist classification and the kingdoms of organisms.

Traditional classification imposed a division into plant-like and animal-like forms on the unicellular eukaryotes, or protists; in a current view the protists are a diverse assemblage of plant-, animal- and fungus-like groups. Classification of these into phyla is difficult because of their relatively simple structure and limited geological record, but study of ultrastructure and other characteristics is providing new insight on protist classification. Possible classifications are discussed, and a summary classification of the living world into kingdoms (Monera, Protista, Fungi, Animalia, Plantae) and phyla is suggested. This classification also suggests groupings of phyla into superphyla and form-superphyla, and a broadened kingdom Protista (including green algae, oomycotes and slime molds but excluding red and brown algae). The classification thus seeks to offer a compromise between the protist and protoctist kingdoms of Whittaker and Margulis and to combine a full listing of phyla with grouping of these for synoptic treatment.

Animals↗
PubMed1988

Molecular evolution of the 5'-terminal domain of large-subunit rRNA from lower eukaryotes. A broad phylogeny covering photosynthetic and non-photosynthetic protists.

This paper summarizes the present status of an analysis of protist phylogeny using rapid partial sequencing of 28S rRNA. Data from 12 protistan phyla are now available and have been used to construct a tentative dendrogram based on a distance matrix method. The tree is robust and has considerable internal consistency. The following salient points are observed: a number of flagellate groups (particularly Euglenozoa) emerge very early among eukaryotes, whereas ciliates and dinoflagellates emerge late, suggesting that some characteristics that had been considered as primitive may in fact be derived. Both chlorophytic and chromophytic photosynthetic protists emerge very late in the tree, close to the Metazoa-Metaphyta-Fungi radiation, suggesting relatively late occurrence of the photosynthetic symbiosis. Taxonomic and phylogenetic information is also obtained within a phylum where rRNA of enough species are sequenced. A deep trichotomy is thus observed within the ciliates. The data are discussed with respect to classical protist phylogenies.

Animals↗
PubMed1988

The secondary structure of large-subunit rRNA divergent domains, a marker for protist evolution.

The secondary structure of the large-subunit ribosomal RNA (24-26S rRNA) has been studied with emphasis on comparative analysis of the folding patterns of the divergent domains in the available protist sequences, that is Prorocentrum micans (dinoflagellate), Saccharomyces carlsbergensis (yeast), Tetrahymena thermophila (ciliate), Physarum polycephalum and Dictyostelium discoideum (slime moulds), Crithidia fasciculata and Giardia lamblia (parasitic flagellates). The folding for the D3, D7a and D10 divergent domains has been refined and a consensus model for the protist 24-26S rRNA structure is proposed. Two hundred seventy-seven nucleotide-long aligned sequences representing all or part of the D3, H32-33, D8, D9 and D10 divergent domains are used for the construction of unrooted phylogenetic trees either calculated from a nucleotide difference matrix, or determined with the PAUP programme based on the parsimony method. Both phylogenies suggest three major branchings, the first leading to the dinoflagellate (which branches off first), ciliate and yeast, the second to the slime moulds, and the last to the parasitic flagellates.

Animals↗
PubMed1992

Energy metabolism of ancestral eukaryotes: a hypothesis based on the biochemistry of amitochondriate parasitic protists.

Parasitic amitochondriate protists, representatives of early branches of eukaryote evolution, differ considerably in their central, energy metabolism from mitochondrion-bearing cells. These differences are: significant metabolic functions of inorganic pyrophosphate, major role of iron-sulfur proteins in key metabolic steps and in hydrogenosome-bearing organisms the disposal of electrons by H2 formation. Cytochrome-mediated electron transport and electron transport-linked phosphorylation are absent. All proteins which have been sequenced so far were found to be homologous to isofunctional proteins from other organisms. A few reactions, however, are catabolized by proteins which are not homologous to enzymes performing similar reactions in other eukaryotes. Two significantly different types of metabolism of amitochondriate protists can be distinguished: (a) without compartmentation and (b) with cytosol/hydrogenosome compartmentation. It is likely that these metabolic types have conserved certain traits present in ancestral eukaryotes before mitochondria became established.

Animals↗
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↗
PubMed1991

A molecular phylogeny of dinoflagellate protists (pyrrhophyta) inferred from the sequence of 24S rRNA divergent domains D1 and D8.

The sequence of two divergent domains (D1 and D8) from dinoflagellate 24S large subunit rRNA was determined by primer extension using total RNA as template. Nucleotide sequence alignments over 401 bases have been analyzed in order to investigate phylogenetic relationships within this highly divergent and taxonomically controversial group of protists of the division Pyrrhophyta. Data are provided confirming that dinoflagellates represent a monophyletic group. For 11 out of the 13 investigated laboratory grown species, an additional domain (D2) could not be completely sequenced by reverse transcription because of a hidden break located near its 3'-terminus. Two sets of sequence alignments were used to infer dinoflagellate phylogeny. The first [199 nucleotides (nt)] included conservative sequences flanking the D1 and D8 divergent domains. It was used to reconstruct a broad evolutionary tree for the dinoflagellates, which was rooted using Tetrahymena thermophila as the outgroup. To confirm the tree topology, and mainly the branchings leading to closely related species, a second alignment (401 nt) was considered, which included the D1 and D8 variable sequences in addition to the more conserved flanking regions. Species that showed sequence similarities with other species lower than 60% on average (Knuc values higher than 0.550) were removed from this analysis. A coherent and convincing evolutionary pattern was obtained for the dinoflagellates, also confirmed by the position of the hidden break within the D2 domain, which appears to be group specific. The reconstructed phylogeny indicates that the early emergence of Oxyrrhis marina preceded that of most Peridiniales, a large order of thecate species, whereas the unarmored Gymnodiniales appeared more recently, along with members of the Prorocentrales characterized by two thecal plates. In addition, the emergence of heterotrophic species preceded that of photosynthetic species. These results provide new perspectives on proposed evolutionary trees for the dinoflagellates based on morphology, biology, and fossil records.

Animals↗
PubMed1985

5 S and 5.8 S ribosomal RNA sequences and protist phylogenetics.

More than 100 5 S 5.8 S rRNA sequences from protists, including fungi, are known. Through a combination of quantitative treeing and special consideration of "signature' nucleotide combinations, the most significant phylogenetic implications of these data are emphasized. Also, limitations of the data for phylogenetic inferences are discussed and other significant data are brought to bear on the inferences obtained. 5 S sequences from red algae are seen as the most isolated among eukaryotics. A 5 S sequence lineage consisting of oomycetes, euglenoids, most protozoa, most slime molds and perhaps dinoflagellates and mesozoa is defined. Such a lineage is not evident from 5.8 S rRNA or cytochrome c sequence data. 5 S sequences from Ascomycota and Basidiomycota are consistent with the proposal that each is derived from a mycelial form with a haploid yeast phase and simple septal pores, probably most resembling present Taphrinales. 5 S sequences from Chytridiomycota and Zygomycota are not clearly distinct from each other and suggest that a major lineage radiation occurred in the early history of each. Qualitative biochemical data clearly supports a dichotomy between an Ascomycota-Basidiomycota lineage and a Zygomycota-Chytridiomycota lineage.

Animals↗
PubMed1988

The thraustochytrids: a protist group with mixed affinities.

The thraustochytrids, a group of marine, monocentric protists are reconsidered phylogenetically drawing upon ultrastructural and biochemical characters. They appear to have affiliations with both heterokont groups and other phyla of marine organisms, but still remain an essentially independent entity.

Animals↗
PubMed1990

Molecular analysis of the hydrogenosomal ferredoxin of the anaerobic protist Trichomonas vaginalis.

We have determined the primary structure of the [2Fe-2S]ferredoxin of the anaerobic protist Trichomonas vaginalis. This protein, situated in the hydrogenosome, is composed of 93 amino acids. A comparison of T. vaginalis ferredoxin with greater than 80 other ferredoxins shows the closest similarity to [2Fe-2S]putidaredoxin of the aerobic bacterium Pseudomonas putida and a lesser one to mitochondrial [2Fe-2S]ferredoxins of vertebrates. This similarity is reflected in the overall primary structure and in the spacing of cysteine residues coordinating the iron-sulfur center. The primary structure, but not the environment of the iron-sulfur center, also shows similarity with [2Fe-2S]ferredoxins of photosynthetic organisms and halobacteria. We have cloned and analyzed the T. vaginalis ferredoxin gene. The gene is present in a single copy and devoid of introns. It gives rise to a transcript with unusually short 5' and 3' untranslated regions of 16 and 18 nucleotides, respectively. DNA sequence analysis of the gene predicts an additional 8 amino acids at the amino terminus which are absent from the purified protein. This amino-terminal region of the protein is characterized by properties typical of mitochondrial presequences.

Amino Acid Sequence↗
PubMed1969

Chromosome number of a small protist: accurate determination.

Electron micrographs of serial sections through a meiotic prophase nucleus of the mycetozoan Labyrinthula sp. show that there are nine separate and distinct synaptinemal complexes. Since each complex represents a set of paired homologous chromosomes, it follows that the haploid chromosome number of this protist is nine.

Chromosomes↗
PubMed1969

Direct measurement of acetylesterase in living protist cells.

The fluorogenic acetylesterase (acetic ester hydrolase EC 3.1.1.6.) substrate, fluorescein diacetate, was used to measure enzyme activity in living protist cells. The visual enzyme assay was done by monitoring fluorochromasia by fluorescent microscopy. Quantitative fluorogenic assays were done by measuring the evolved fluorescein in a fluorometer. Of 59 strains of bacteria, 35 were fluorochromatically positive. Eight of the fluorochromatically negative strains were fluorogenically positive. Of 22 strains of slime molds and fungi, all were fluorochromatically positive. Three out of 12 different algae were fluorochromatically positive. Several unidentified protozoa were also fluorochromatically positive. Four out of six protozoa were fluorochromatically positive. Structures of special interest showing acetylesterase activity were: the growing hyphal tips of fungi, the vacuolated areas of yeast and protozoa, newly formed bacterial spores or immature fungal spores, "mesosome-like" bodies in Bacillus megaterium, and the cell membrane and nuclear region of green algae. Yeast protoplasts and bacterial protoplasts and spheroplasts were fluorochromatically positive when derived from positive cells and negative when derived from negative cells. There was no correlation between the possession of a capsule and acetylesterase activity. There was no effect on the viability of bacterial cells incubated in the presence of fluorescein diacetate. Paraoxon inhibited bacterial and yeast enzyme at 10(-5)m. Eserine (10(-5)m) and Paraoxon (10(-7)m) inhibited B. megaterium enzyme. Sodium acetate at 10(-2)m did not inhibit bacterial enzyme. The implications of these findings on the location and expression of esterase activity in living cells are discussed.

Acetates↗
PubMed2025

Subcellular proteomics of the protist Paradiplonema papillatum reveals the digestive capacity of the cell membrane and the plasticity of peroxisomes across euglenozoans.

Diplonemids are among the most diverse and abundant protists in the deep ocean, have extremely complex and ancient cellular systems, and exhibit unique metabolic capacities. Despite this, we know very little about this major group of eukaryotes. To establish a model organism for comprehensive investigation, we performed subcellular proteomics on Paradiplonema papillatum and localized 4,870 proteins to 22 cellular compartments. We additionally confirmed the predicted location of several proteins by epitope tagging and fluorescence microscopy. To probe the metabolic capacities of P. papillatum, we explored the proteins predicted to the cell membrane compartment in our subcellular proteomics dataset. Our data revealed an accumulation of many carbohydrate-degrading enzymes (CDZymes). Our predictions suggest that these CDZymes are exposed to the extracellular space, supporting proposals that diplonemids may specialize in breaking down carbohydrates in plant and algal cell walls. Further exploration of carbohydrate metabolism revealed an evolutionary divergence in the function of glycosomes (modified peroxisomes) in diplonemids versus kinetoplastids. Our subcellular proteome provides a resource for future investigations into the unique cell biology of diplonemids.

Peroxisomes↗
PubMed1989

Effect of gossypol on the morphology, motility and metabolism of a flagellated protist, Dunaliella bioculata.

Gossypol, a natural polyphenolic compound extracted from cotton seed, is known for its contraceptive properties on human beings and several other mammals. Gossypol induces disorders of spermatogenesis and inhibition of spermatozoal motility. To determine the molecular mechanism inhibiting the motility of cells, a flagellar protist (Dunaliella bioculata) has been chosen as a cellular model because of the heterogeneity of spermatozoa populations. Inhibition of cell motility by gossypol, measured by Laser Doppler Velocimetry, was observed with these cells at the same doses as for spermatozoa (30-50 mumoles/l). Mitochondria were found to be swollen in gossypol-treated algae and, in parallel, respiratory exchanges were decreased and photosynthesis was inhibited, although the chloroplast did not seem to be morphologically altered. A diminution of the essential ATP production was also found at the same doses. Therefore, the inhibition of flagellar motility could be explained by such a decrease. The rapid and parallel inhibition of respiration and photosynthesis at non-lethal concentrations leads us to the hypothesis of a common target involving both ubiquinone and plastoquinone, although this remains to be proved.

Adenosine Triphosphate↗