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PubMed2006

Involvement of Toll-like receptor 5 in the recognition of flagellated bacteria.

Toll-like receptors (TLRs) are key components of the immune system that detect microbial infection and trigger antimicrobial host defense responses. TLR5 is a sensor for monomeric flagellin, which is a component of bacterial flagella known to be a virulence factor. In this study we generated TLR5-deficient mice and investigated the role of TLR5 signaling in the detection of flagellin and antibacterial immune responses to Salmonella typhimurium and Pseudomonas aeruginosa. We found that TLR5 is essential for the recognition of bacterial flagellin both in vivo and ex vivo. TLR5 contribution to antibacterial host response to i.p. infection with S. typhimurium or intranasal administration of P. aeruginosa may be masked by TLR4 or other sensing mechanisms. By using radiation bone marrow chimera, we showed that upon i.p. injection of flagellin immune responses are mediated by lymphoid cells, whereas resident cells are required for the initiation of response upon intranasal flagellin administration. These results suggest that flagellin recognition in different organs is mediated by distinct TLR5-expressing cells and provide insights into the cooperation of the TLR5 and TLR4 signaling pathways used by the innate immune system in the recognition of bacterial pathogens.

Animals↗
PubMed1979

Adenine aminohydrolase: occurrence and possible significance in trypanosomid flagellates.

Adenine aminohydrolase (EC 3.5.4.2) from four species of Leishmania and from Crithidia fasciculata was examined for specific activities, affinity for substrate (adenine), and stability to heat. All were found to be strongly and non-competitively inhibited by both coformycin and deoxycoformycin, two tight-binding inhibitors of adenosine deaminase (adenosine aminohydrolase, EC 3.5.4.4). Deoxycoformycin is the more potent inhibitor of the two. Neither inhibitor was active against the purine phosphoribosyltransferases. When deoxycoformycin was added to the defined growth medium containing hypoxanthine as the purine source, the growth of C. fasciculata was unaffected, but when adenine was the purine source for the organism, severe inhibition resulted. This implies that hypoxanthine is the obligatory base for nucleotide synthesis and that the adenine phosphoribosyltransferase (AMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.7) is, in some manner,idenied access to exogenous substrate.

Adenosine Deaminase↗
PubMed2003

Mixotrophy of a photosynthetic flagellate viewed from an optimal foraging perspective.

Mixotrophy, a combination of phototrophic and phagotrophic nutrition, has been found in several classes of phytoplankton (Booras et al. 1988, Jones 2000) and appears to be a successful evolutionary strategy. Heterotrophic nutrition of phytoplankton has been suggested to be an important source of mineral nutrients (Nygaard and Tobiesen 1993). Potentially limiting mineral nutrients, particularly phosphorus (P), are often several orders of magnitude more concentrated in the biomass of food organisms of mixotrophs (e.g. in bacteria) than in the dissolved phase (Vadstein 2000). We used radioactive tracer experiments to show that the simultaneous uptake of P from dissolved inorganic and particular P sources by the marine phytoflagellate Chrysochromulina polylepis followed basic predictions of optimal foraging theory (Stephens and Krebs 1986). Chrysochromulina takes up its P rather unselectively from both bacterial P and dissolved P sources at low dissolved P concentrations, while it becomes more selective at higher dissolved inorganic P (DIP) concentrations. The onset of mixotrophic processes was dependent on DIP concentrations. These findings support the view of mixotrophy as a strategy of nutrient uptake in nutrient poor (oligotrophic) pelagic environments (Nygaard and Tobiesen 1993) and show that ideas of optimal foraging can be applied to unicellular organisms.

Animals↗
PubMed1967

Flagellar regeneration in protozoan flagellates.

The flagella of populations of three protozoan species (Ochromonas, Euglena, and Astasia) were amputated and allowed to regenerate. The kinetics of regeneration in all species were characterized by a lag phase during which there was no apparent flagellar elongation; this phase was followed by elongation at a rate which constantly decelerated as the original length was regained. Inhibition by cycloheximide applied at the time of flagellar amputation showed that flagellar regeneration was dependent upon de novo protein synthesis. This was supported by evidence showing that a greater amount of leucine was incorporated into the proteins of regenerating than nonregenerating flagella. The degree of inhibition of flagellar elongation observed with cycloheximide depended on how soon after flagellar amputation it was applied: when applied to cells immediately following amputation, elongation was almost completely inhibited, but its application at various times thereafter permitted considerable elongation to occur prior to complete inhibition of flagellar elongation. Hence, a sufficient number of precursors were synthesized and accumulated prior to addition of cycloheximide so that their assembly (elongation) could occur for a time under conditions in which protein synthesis had been inhibited. Evidence that the site of this assembly may be at the tip of the elongating flagellum was obtained from radioautographic studies in which the flagella of Ochromonas were permitted to regenerate part way in the absence of labeled leucine and to complete their regeneration in the presence of the isotope. Possible mechanisms which may be operating to control flagellar regeneration are discussed in light of these and other observations.

Amino Acids↗
PubMed1973

Biochemical cytology of trichomonad flagellates. I. Subcellular localization of hydrolases, dehydrogenases, and catalase in Tritrichomonas foetus.

To determine the localization of several enzymes in Tritrichomonas foetus, the axenic KV-1 strain was grown in Diamond's medium with bovine serum, homogenized in 0.25 M sucrose, and subjected to analytical differential and isopycnic centrifugation. The fractions were assayed for their enzymatic composition and examined electron microscopically. NADH and NADPH dehydrogenases, about 90% of the catalase, and two hydrolases, alpha-galactosidase and manganese-activated beta-galactosidase I are in the nonsedimentable part of the cytoplasm. alpha-Glycerophosphate and malate dehydrogenases are associated with a large particle, whose equilibrium density in sucrose gradients is 1.24. This particle corresponds to that population of the paracostal and paraxostylar granules which, having a uniform granular matrix surrounded by a single membrane, resemble microbodies from other organisms. The small sedimentable portion of catalase (about 10% of the total activity) is not associated with these granules and equilibrates at density 1.22. The nature of the subcellular entity carrying catalase could not be ascertained. Hydrolases with a pH optimum around 6-6.5 (protease, beta-N-acetylglucosaminidase, beta-N-acetylgalactosaminidase, and cation-independent beta-galactosidase II), as well as a large part of acid phosphatase, are associated with a population of large particles which equilibrate at densities from 1.15 to 1.20. The hydrolases in these granules lose their structure-bound latency easily after freezing and thawing. These particles correspond to another population of the paracostal and paraxostylar granules which have varied shape and inhomogeneous content with frequent myelin figures, indicating a digestive function. The rest of the phosphatase and most of the acid beta-glucuronidase activity are in a smaller granule fraction with an equilibrium density around 1.18. The latency of these enzymes is quite resistant to freezing and thawing. This particle population consists of smaller, very often flattened vesicles and granules, many of which are clearly fragments of the prominent Golgi apparatus of the cell.

Acid Phosphatase↗
PubMed1977

Chitinous fibrils in the lorica of the flagellate chrysophyte Poteriochromonas stipitata (syn. Ochromonas malhamensis).

Ordered microfibrils are formed on the membrane of the cytoplasmic tail of the alga Poteriochromonas after attachment to a substrate. The ultrastructure of native and extracted stalk fibrils was studied with electron microscope methods. In addition, the structural polysaccharide was characterized by hydrolyses, separation of the monomers by thin-layer chromatography, gas-liquid chromatography and amino acid analysis, and by X-ray diffraction. The alkali-resistant fibrils yielded mostly glucosamine upon extensive hydrolysis, and showed X-ray diffraction patterns similar to those of fugal chitin. It is concluded that the resistant core of the fibrils is chitinous.

Chitin↗
PubMed1956

The relationship between chlorophyll and the carotenoids in the algal flagellate, Euglena.

1. We have obtained an action spectrum for chlorophyll formation in Euglena gracilis. This action spectrum is similar to the absorption spectrum of protochlorophyll. However, efforts to isolate and identify this pigment have been unsuccessful. 2. Porphyrins have been extracted from both the normal and dark-adapted Euglena and a chlorophyll-free mutant. 3. The "action" spectra for chlorophyll and carotenoid synthesis have been found to almost coincide, indicating that the same porphyrin-like molecule may influence the synthesis of both pigments. 4. It is indicated that two porphyrin-like systems are in operation simultaneously, one concerned with carotenoid "removal" and another involved in carotenoid and chlorophyll synthesis.

Carotenoids↗
PubMed2003

Structure of the bc1 complex from Seculamonas ecuadoriensis, a jakobid flagellate with an ancestral mitochondrial genome.

In eubacteria, the respiratory bc(1) complex (complex III) consists of three or four different subunits, whereas that of mitochondria, which have descended from an alpha-proteobacterial endosymbiont, contains about seven additional subunits. To understand better how mitochondrial protein complexes evolved from their simpler bacterial predecessors, we purified complex III of Seculamonas ecuadoriensis, a member of the jakobid protists, which possess the most bacteria-like mitochondrial genomes known. The S. ecuadoriensis complex III has an apparent molecular mass of 460 kDa and exhibits antimycin-sensitive quinol:cytochrome c oxidoreductase activity. It is composed of at least eight subunits between 6 and 46 kDa in size, including two large "core" subunits and the three "respiratory" subunits. The molecular mass of the S. ecuadoriensis bc(1) complex is slightly lower than that reported for other eukaryotes, but about 2x as large as complex III in bacteria. This indicates that the departure from the small bacteria-like complex III took place at an early stage in mitochondrial evolution, prior to the divergence of jakobids. We posit that the recruitment of additional subunits in mitochondrial respiratory complexes is a consequence of the migration of originally alpha-proteobacterial genes to the nucleus.

Amino Acid Sequence↗
PubMed2002

The chaperonin genes of jakobid and jakobid-like flagellates: implications for eukaryotic evolution.

The jakobids are free-living mitochondriate protists that share ultrastructural features with certain amitochondriate groups and possess the most bacterial-like mitochondrial genomes described thus far. Jakobids belong to a diverse group of mitochondriate and amitochondriate eukaryotes, the excavate taxa. The relationships among the various excavate taxa and their relationships to other putative deep-branching protist groups are largely unknown. With the hope of clarifying these issues, we have isolated the cytosolic chaperonin CCTalpha gene from the jakobid Reclinomonas americana (strains 50394 and 50283), the jakobid-like malawimonad Malawimonas jakobiformis, two heteroloboseans (Acrasis rosea and Naegleria gruberi), a euglenozoan (Trypanosoma brucei), and a parabasalid (Monocercomonas sp.). We also amplified the CCTdelta gene from M. jakobiformis. The Reclinomonas and Malawimonas sequences presented here are among the first nuclear protein-coding genes to be described from these organisms. Unlike other putative early diverging protist lineages, a high density of spliceosomal introns was found in the jakobid and malawimonad CCTs-similar to that observed in vertebrate protein-coding genes. An analysis of intron positions in CCT genes from protists, plants, animals, and fungi suggests that many of the intron-sparse or intron-lacking protist lineages may not be primitively so but have lost spliceosomal introns during their evolutionary history. In phylogenetic trees constructed from CCTalpha protein sequences, R. americana (but not M. jakobiformis) shows a weak but consistent affinity for the Heterolobosea and Euglenozoa.

Animals↗
PubMed1999

Graviresponses of certain ciliates and flagellates.

Protozoa are eukaryotic cells and represent suitable model systems to study the mechanisms of gravity perception and signal transduction due to their clear gravity-induced responses (gravitaxis and gravikinesis). Among protists, parallel evolution for graviperception mechanisms have been identified: either sensing by distinct stato-organelles (e.g., the Müller vesicles of the ciliate Loxodes) or by sensing the density difference between the whole cytoplasm and the extracellular medium (as proposed for Paramecium and Euglena). These two models are supported by experiments in density-adjusted media, as the gravitaxis of Loxodes was not affected, whereas the orientation of Paramecium and Euglena was completely disturbed. Both models include the involvement of ion channels in the cell membrane. Diverse experiments gave new information on the mechanism of graviperception in unicellular systems, such as threshold values in the range of 10% of gravity, relaxation of the responses after removal of the stimulus, and no visible adaptation phenomena during exposure to hypergravity or microgravity conditions for up to 12 days.

Animals↗