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At least 127 records · Page 7Linked to original sources
PubMed2005

Eccrinales (Trichomycetes) are not fungi, but a clade of protists at the early divergence of animals and fungi.

The morphologically diverse orders Eccrinales and Amoebidiales have been considered members of the fungal class Trichomycetes (Zygomycota) for the last 50 years. These organisms either inhabit the gut or are ectocommensals on the exoskeleton of a wide range of arthropods--Crustacea, Insecta, and Diplopoda--in varied habitats. The taxonomy of both orders is based on a few micromorphological characters. One species, Amoebidium parasiticum, has been axenically cultured and this has permitted several biochemical and phylogenetic analyses. As a consequence, the order Amoebidiales has been removed from the Trichomycetes and placed in the class Mesomycetozoea. An affinity between Eccrinales and Amoebidiales was first suggested when the class Trichomycetes was erected by Duboscq et al. [Arch. Zool. Exp. Gen. 86 (1948) 29]. Subsequently, molecular markers have been developed to study the relationship of these orders to other groups. Ribosomal gene (18S and 28S) sequence analyses generated by this study do not support a close association of these orders to the Trichomycetes or to other fungi. Rather, Eccrinales share a common ancestry with the Amoebidiales and belong to the protist class Mesomycetozoea, placed at the animal-fungi boundary.

Base Sequence↗
PubMed2000

Peptide deformylase of eukaryotic protists: a target for new antiparasitic agents?

Peptide deformylase is found only in Eubacteria, making it a logical target for discovering new antibacterial agents. Although this protein is absent from animal or fungal cells, evidence supports its existence in eukaryotic protists, including the causative agents of malaria, sleeping sickness, Chagas disease and leishmaniosis. Here, Thierry Meinnel discusses the idea that deformylase inhibitors could be used as very broad-spectrum antibiotics against bacterial infections, as well as parasitic diseases.

Amidohydrolases↗
PubMed2003

A Narf-like gene from Cryptosporidium parvum resembles homologues observed in aerobic protists and higher eukaryotes.

Here we report a Narf-like gene from the apicomplexan Cryptosporidium parvum (CpNARF). CpNARF is an intronless, single-copy gene of 1680 bp which encodes a putative protein of 560 amino acids with a calculated molecular mass of 63.1 kDa. This gene contains a single highly conserved N-terminal iron-sulfur cluster ([4Fe-4S]) binding site, as well as most of the H-cluster conserved residues. Reverse transcription polymerase chain reaction analysis indicates that CpNARF is expressed by the intracellular stages of C. parvum. Although the function of this gene is as yet unknown, phylogenetic analyses suggest that CpNARF belongs to the group of NARF-like proteins from aerobic protists and higher eukaryotes, which are thought to have had an ancestor in common with [Fe]-hydrogenases.

Aerobiosis↗
PubMed2001

Overlapping genes in parasitic protist Giardia lamblia.

The parasitic protist Giardia lamblia lacks mitochondria and peroxisomes, as well as many typical membrane-bound organella characteristics of higher eukaryotic cells, together with extremely economized usage of DNA sequence, as demonstrated by the lack of introns. We describe here the presence of overlapping genes in G. lamblia, in which a part of the protein coding sequence of one mRNA exists in a region corresponding to the 3'-noncoding region of another mRNA transcribed from a gene on the opposite strand. Recently we isolated 13 kinesin-related cDNAs from G. lamblia. Nine of these cDNAs contain long 3'-noncoding sequences in which long open reading frames (ORFs) exist (in the remaining four cDNAs, the lengths of the 3'-noncoding sequences are very short). The predicted amino acid sequences of these ORFs were subjected to a search for homologies with sequences in databases. The amino acid sequences of the six ORFs exhibited significant sequence similarities with known sequences. These lines of evidence suggest the frequent occurrence of gene overlap in Giardial genome.

Animals↗
PubMed2002

LINEs and SINE-like elements of the protist Entamoeba histolytica.

A survey of whole genome shotgun sequences of the protozoan parasite Entamoeba histolytica revealed three families of non-long terminal repeat (LTR) retrotransposons or long interspersed elements (LINEs) (called EhLINEs in this report). The 4.8 kb EhLINEs each had a single open reading frame with a putative nucleic acid binding motif (CCHC) and restriction enzyme-like endonuclease domain located downstream of the reverse transcriptase (RT) domain. Phylogenetic analysis of the RT domain placed the EhLINEs in the R4 clade of non-LTR elements, a mixed clade of non-LTR elements that includes members from nematodes, insects, and vertebrates. EhLINE1 (which was previously identified as HMc and EhRLE) shared a common 3' end with a highly transcribed 0.55 kb short interspersed element (SINE)-like element previously identified as IE or ehapt2 and called EhLSINE1 in this report. Similarly, EhLINE2 shared a common 3' end with a highly transcribed 0.65 kb SINE-like element called EhLSINE2 in this report. The shared 3' end sequences of the EhLINEs and EhLSINEs suggested that EhLINEs are involved in the retrotransposition of the EhLSINEs. EhLSINEs were flanked by target site duplications and contained conserved 5' sequences, which likely regulate their transcription. The EhLSINEs are the first protist SINE-like elements identified that share a common 3' sequence with LINEs, and the first SINE-like elements that have been associated with the R4 clade of non-LTR elements.

Amino Acid Sequence↗
PubMed2003

Gene organization and homology modeling of two iron superoxide dismutases of the early branching protist Perkinsus marinus.

The facultative intracellular oyster parasite, Perkinsus marinus, taxonomically related to both dinoflagellates and apicomplexans, possesses at least two distinct genes (PmSOD1 and PmSOD2) predicted to encode iron-containing superoxide dismutases (FeSOD). DNA blots and sequence analysis suggest that both PmSOD1 and PmSOD2 are single copy and are unlinked. PmSOD1 and PmSOD2 are composed of five and six exons, respectively. All introns are delimited by canonical GT/AG boundaries, and have some features more similar to apicomplexan than dinoflagellate introns. Interestingly, exon 1 of PmSOD2 encodes putative transmembrane and spacer domains with no homology to FeSODs, while exon 2 begins with a methionine codon and is homologous to the N-terminus of FeSODs. The position of introns is not highly conserved between PmSOD1 and PmSOD2, although one intron is in a similar location. Comparison of the intron positions of PmSOD1 and PmSOD2 to those of available apicomplexan FeSODs shows that the intron position shared by PmSOD1 and PmSOD2 is also observed in the FeSOD of Toxoplasma gondii. Comparison of the untranscribed regions 5' and 3' of the coding regions for PmSOD1 and PmSOD2 reveals few motifs in common. Instead, each gene possesses a distinct set of putative upstream transcription factor binding sites. Although the proteins encoded by PmSOD1 and PmSOD2 are only 38% identical to each other, homology modeling indicates that they have nearly identical active site structures. The divergent genomic organizations of two FeSOD genes in the same organism illustrates the complexity of the antioxidant system of even simple, early-branching protists such as P. marinus.

Amino Acid Sequence↗
PubMed1998

Phylogenetic position of symbiotic protist Dinenympha [correction of Dinemympha] exilis in the hindgut of the termite Reticulitermes speratus inferred from the protein phylogeny of elongation factor 1 alpha.

The phylogenetic position of the symbiotic oxymonad Dinenympha exilis, found in the hindgut of the lower termite Reticulitermes speratus, was determined by analysis of translation elongation factor 1 alpha (EF-1 alpha). cDNA corresponding to a major part of the amino acid coding region of EF-1 alpha mRNA was amplified by the reverse transcription polymerase chain reaction (RT-PCR) method from total mRNA of termite hindgut microorganisms without cultivation. The product was cloned into a plasmid vector, pGEM-T, and the clones were isolated and sequenced. One of the EF-1 alpha clones isolated was assigned to the protist D. exilis by whole-cell in-situ hybridization using a specific oligonucleotide probe with enzymatic signal amplification. The deduced amino acid sequence was aligned with those of other eukaryotic and archaeabacterial EF-1 alpha s, and the phylogenetic relationships among early branching eukaryotes were inferred by using the distance matrix method and the maximum parsimony method. The phylogenetic analysis indicated that the D. exilis offshoot occurred before mitochondria-containing organisms and D. exilis branched out after the diplomonads clade. These results indicate that the oxymonad D. exilis is one of the early branching organisms and suggest that the oxymonads form a lineage independent of other early branching organisms.

Amino Acid Sequence↗
PubMed2003

A thraustochytrid protist isolated from Mercenaria mercenaria: molecular characterization and host defense responses.

A previously undescribed thraustochytrid protist, designated C9G, was isolated from the gills of a clam, Mercenaria mercenaria, collected from the Bay of Fundy, Canada. Sequence data analysis showed C9G to be related to the clam pathogen QPX, quahog parasite unknown; however, it is not enveloped by secreted mucoid material as is the case for QPX. Clam hemocytes recognized and phagocytized C9G in vitro in the absence of plasma recognition factors. Hemocytes were also capable of killing ingested C9G, as shown by the use of a tetrazolium reduction viability assay. The mechanisms underlying intracellular antimicrobial activity are not yet established, but no detectable cytotoxic reactive oxygen species were generated during phagocytosis of C9G. Clam plasma proteins were shown to inhibit C9G growth at concentrations similar to those in unfractionated hemolymph.

Animals↗
PubMed2001

Protist tubulins: new arrivals, evolutionary relationships and insights to cytoskeletal function.

The protists exhibit probably the most extravagant expression of microtubule-containing structures found in any organism. These structures--flagella, cilia, axostyles, spindles and a veritable constellation of microtubule bundles and cortical arrays--provide shape, form, motility, anchorage and apparatuses for feeding. The cytoskeletal structures have a precise order (i.e. size, position and number) that must be replicated and segregated with fidelity at each division, some components being inherited conservatively and others semi-conservatively. Intriguingly, it is now apparent that much of the high-order organisation, which was recognised and described by light and electron microscopy during the last century, is a reflection of molecular polarities set by assembly of constituent proteins. Tubulins and microtubules lie at the heart of this morphogenetic pattern.

Animals↗
PubMed1999

Sequence analysis of genes encoding ribosomal proteins of amitochondriate protists: L1 of Trichomonas vaginalis and L29 of Giardia lamblia.

Two genes encoding the ribosomal proteins were cloned and sequenced from amitochondriate protists, L1 (L10a in mammalian nomenclature) from Trichomonas vaginalis and L29 (L35 in mammalian nomenclature) from Giardia lamblia. The deduced amino acid sequences were analyzed by sequence alignments and phylogenetic reconstructions. Both the T. vaginalis L1 and the G. lamblia L29 displayed eukaryotic sequence features, when compared with all the homologs from the three primary kingdoms.

Amino Acid Sequence↗
PubMed1999

Motile chemosensory behaviour of phagotrophic protists: mechanisms for and efficiency in congregating at food patches.

Phagotrophic protists are capable of congregating at point sources of food within a few minutes, from distances of up to several cm in the case of ciliates, or several mm in the case of microflagellates. This is exemplified by four ciliate species and a heterotrophic flagellate. Congregation is accomplished by the combined effect of more than one type of chemosensory motile behaviour including "kinetic responses", "temporal-gradient sensing", and "helical klinotaxis". The results are discussed in terms of microscale patchiness in nature.

Animals↗
PubMed2002

The significance of inter- and intraspecific variation in bacterivorous and herbivorous protists.

This paper reviews the emerging evidence on the significance of inter- and intraspecific variation in the feeding behaviour of aquatic protists. Small heterotrophic nanoflagellates (HNF) have been identified as the primary bacterial consumers in most aquatic environments. Recent research using novel techniques such as flow cytometry and high resolution video microscopy revealed that their feeding strategies and grazing rates are diverse. There is an important conceptual difference between uptake rates measured in short-term (min to h) experiments and grazing rates averaged over a longer-term (d). This is because the latter are strongly affected by digestion rates which are species-specific, i.e. the same bacterial prey may be digested differently by various grazers, and the same predator may selectively digest variable prey. Planktonic ciliates are the most important algal consumers in many lakes and marine systems. Large species-specific differences in their feeding behaviour and growth rates have been documented for closely related species. Intraspecific variation, which is, most likely, caused by varying clonal composition may be as important as interspecific variation. Finally, there is some evidence that the individual variability within a given population is generally large, both among bacterivorous HNF and among herbivorous ciliates. The consequences of this diversity becoming apparent at the levels of the species, population, clone and individual need to be considered by aquatic ecologists in their conceptual models.

Animals↗
PubMed2005

The genome of the protist parasite Entamoeba histolytica.

Entamoeba histolytica is an intestinal parasite and the causative agent of amoebiasis, which is a significant source of morbidity and mortality in developing countries. Here we present the genome of E. histolytica, which reveals a variety of metabolic adaptations shared with two other amitochondrial protist pathogens: Giardia lamblia and Trichomonas vaginalis. These adaptations include reduction or elimination of most mitochondrial metabolic pathways and the use of oxidative stress enzymes generally associated with anaerobic prokaryotes. Phylogenomic analysis identifies evidence for lateral gene transfer of bacterial genes into the E. histolytica genome, the effects of which centre on expanding aspects of E. histolytica's metabolic repertoire. The presence of these genes and the potential for novel metabolic pathways in E. histolytica may allow for the development of new chemotherapeutic agents. The genome encodes a large number of novel receptor kinases and contains expansions of a variety of gene families, including those associated with virulence. Additional genome features include an abundance of tandemly repeated transfer-RNA-containing arrays, which may have a structural function in the genome. Analysis of the genome provides new insights into the workings and genome evolution of a major human pathogen.

Animals↗
PubMed2003

Molecular and structural characterization of NADPH-dependent d-glycerate dehydrogenase from the enteric parasitic protist Entamoeba histolytica.

Putative NADPH-dependent GDH (L-glycerate dehydrogenase) of the protozoan parasite Entamoeba histolytica (EhGDH) has been characterized. The EhGDH gene encodes a protein of 318 amino acids with a calculated isoelectric point of 6.29 and a molecular mass of 35.8 kDa. EhGDH showed highest identities with GDH from epsilon-proteobacteria. This close kinship was also supported by phylogenetic analyses, suggesting possible lateral transfer of the gene from epsilon-proteobacteria to E. histolytica. In contrast with the implications from protein alignment and phylogenetic analysis, kinetic studies revealed that the amoebic GDH showed biochemical properties similar to those of mammalian GDH, i.e. a preference for NADPH as cofactor and higher affinities towards NADPH and beta-hydroxypyruvate than towards NADP+ and L-glycerate. Whereas the amino acids involved in nucleotide binding and catalysis are totally conserved in EhGDH, substitution of a negatively charged amino acid with a non-charged hydroxy-group-containing amino acid is probably responsible for the observed high affinity of EhGDH for NADP+/NADPH. In addition, the amoebic GDH, dissimilar to the bacterial and mammalian GDHs, lacks glyoxylate reductase activity. Native and recombinant EhGDH showed comparable subunit structure, kinetic parameters and elution profiles on anion-exchange chromatography. We propose that the GDH enzyme is likely to be involved in regulation of the intracellular concentration of serine, and, thus, also in controlling cysteine biosynthesis located downstream of serine metabolic pathways in this protist.

Amino Acid Sequence↗
PubMed2004

Molecular evidence links cryptic diversification in polar planktonic protists to Quaternary climate dynamics.

It is unknown how pelagic marine protists undergo diversification and speciation. Superficially, the open ocean appears homogeneous, with few clear barriers to gene flow, allowing extensive, even global, dispersal. Yet, despite the apparent lack of opportunity for genetic isolation, diversity is prevalent within marine taxa. A lack of candidate isolating mechanisms would seem to favor sympatric over allopatric speciation models to explain the diversity and biogeographic patterns observed in the oceans today. However, the ocean is a dynamic system, and both current and past circulation patterns must be considered in concert to gain a true perspective of gene flow through time. We have derived a comprehensive picture of the mechanisms potentially at play in the high latitudes by combining molecular, biogeographic, fossil, and paleoceanographic data to reconstruct the evolutionary history of the polar planktonic foraminifer Neogloboquadrina pachyderma sinistral. We have discovered extensive genetic diversity within this morphospecies and that its current "extreme" polar affinity did not appear until late in its evolutionary history. The molecular data demonstrate a stepwise progression of diversification starting with the allopatric isolation of Atlantic Arctic and Antarctic populations after the onset of the Northern Hemisphere glaciation. Further diversification occurred only in the Southern Hemisphere and seems to have been linked to glacial-interglacial climate dynamics. Our findings demonstrate the role of Quaternary climate instability in shaping the modern high-latitude plankton. The divergent evolutionary history of N. pachyderma sinistral genotypes implies that paleoceanographic proxies based on this taxon should be calibrated independently.

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↗
PubMed1997

Transient and selectable transformation of the parasitic protist Trichomonas vaginalis.

We have developed methods to transiently and selectably transform the human-infective protist Trichomonas vaginalis. This parasite, a common cause of vaginitis worldwide, is one of the earlier branching eukaryotes studied to date. We have introduced three heterologous genes into T. vaginalis by electroporation and have used the 5' and 3' untranslated regions of the endogenous gene alpha-succinyl CoA synthetase B (alpha-SCSB) to drive transcription of these genes. Transient expression of two reporter proteins, chloramphenicol acetyltransferase (CAT) or luciferase, was detected when electroporating in the presence of 50 microg closed-circular construct. Optimal levels of expression were observed using approximately 2.5 x 10(8) T. vaginalis cells and 350 volts, 960 microFd for electroporation; however, other conditions also led to significant reporter gene expression. A time course following the expression of CAT in T. vaginalis transient transformants revealed the highest level of expression 8-21 hr postelectroporation and showed that CAT activity is undetectable using TLC by 99 hr postelectroporation. The system we established to obtain selectable transformants uses the neomycin phosphotransferase (neo) gene as the selectable marker. Cells electroporated with 20 microg of the NEO construct were plated in the presence of 50 microg/ml paromomycin and incubated in an anaerobic chamber. The paromomycin-resistant colonies that formed within 3-5 days were cultivated in the presence of drug and DNA was isolated for analyses. The NEO construct was shown to be maintained episomally, as a closed-circle, at between 10-30 copies per cell. The ability to transiently and selectably transform T. vaginalis should greatly enhance research on this important human parasite.

Animals↗