Showing papers on "Flagellate published in 1994"

The stramenopiles from a molecular perspective 16S-like rRNA sequences from Labyrinthuloides minuta and Cafeteria roenbergensis

Abstract: Comparisons of 16S-like ribosomal RNA sequences from the heterotrophic marine flagellate Cafeteria roenbergensis Fenchel et Patterson, the slime net Labyrinthuloides minuta Watson et Raper and other eukaryotes provide insights into the early branching patterns for protists with tripartite flagellar hairs, the heterokont stramenopiles. Within this monophyletic assemblage, heterotrophic bicosoecids and labyrinthulids diverge before the separation of oomycetes and autotrophic stramenopiles. We infer that stramenopiles evolved from a colourless flagellate. Other taxa with chloroplasts containing chlorophyll a + c (dinoflagellates, cryptomonads and haptophytes) represent independent evolutionary lineages that acquired their chloroplasts separately from the endosymbiotic event leading to the autotrophic stramenopiles.

A comparison of the growth kinetics of six marine heterotrophic nanoflagellates fed with one bacterial species.

Abstract: The growth kinetics of 6 species of marine heterotrophic nanoflagellates (5 to 13 mum) were compared. The maximum specific growth rates (mu(max)) of the flagellates ranged from 0.035 to 0.21 h-1 and the half-saturation constants (K(s)) ranged from 1.1 to 45 x 10(6) bacterial cells ml-1. Theoretical threshold concentrations were calculated for each flagellate and the values of these generally ranged from 2 to 10 x 10(4) bacterial cells ml-1. The flagellate yield values (Y), maximum uptake rates (U(max)) and maximum clearance rates (F(max)) for each flagellate species ranged from 0.3 to 13.2 x 10(-3) cells bacterium-1, 5 to 259 bacteria cell-1 h-1 and 1 to 58 nl cell-1 h-1 respectively while volume-specific clearance values ranged from 1.4 x 10(4) to 8.7 x 10(5) body volumes h-1.

Cell biology of phototaxis in flagellate algae

Abstract: Publisher Summary This chapter describes the structural aspects of different photoreceptive organelles including their interaction with cytoskeletal elements. It also examines the mechanisms used for signal generation and modulation, the photoreceptors used and the involved photoelectrical responses, and the currently known elements of the signal transduction or processing chains toward the flagellum. The photoreceptive apparatuses of flagellate algae exhibit an enormous structural variation and result from numerous parallel evolutionary processes. The phototactic systems of flagellate algae, including the sensory transduction chain, are optimized to detect a temporal pattern of light rather than the steady-state light intensity. Proper positioning of the functional eyespot apparatus during cell division is important for signal perception or generation in algal phototaxis and for correct coupling of the photoreceptive apparatus to the signaling effector, the flagellum. Different criteria can be applied for grouping the photoreceptive organelles of flagellate algae, such as ultrastructural characteristics, the used photoreceptor pigment, the mechanisms involved in primary signal amplification, and extension to low light intensities.

Goniomonas : rRNA sequences indicate that this phagotrophic flagellate is a close relative of the host component of cryptomonads

Abstract: The nucleotide sequence of the polymerase chain reaction (PCR)-amplified small subunit ribosomal RNA gene of Goniomonas truncata was determined Addition of the Goniomonas sequence to the eukaryotic phylogenetic tree revealed this heterotrophic flagellate to be the sister taxon of photosynthetic cryptomonads The molecular phylogeny supports morphological data suggesting that Goniomonas diverted from the cryptomonad lineage prior to their acquisition of a plastid through endosymbiosis of a eukaryote Goniomonas, which is phagotrophic, may thus represent an extant relative of the host component of cryptomonad algae

Temporal and spatial variations in heterotrophic nanoflagellate abundance in North Sea sediments

Abstract: Summer-winter variations in marine nanoflagellate densities at 3 depths in North Sea sediment~ (0-3, 30-33 and 60-63 mm) were studied using epifluorescence microscopy. Benthic flagellate densities in summer ranged from 7 to 859 X lo3 and in winter from 9 to l100 X 103 cells ~ m ~ . T h e effect of season on flagellate densities was different among stations. At 10 out of 15 stations summer values were significantly higher than winter values. The effect of season on flagellate densities was the same at all 3 depths. Flagellate densities in the sediment surface layer (0-3 mm) were in general 2 to 4 times higher than in the 2 deeper sampled layers (30-33, 60-63 mm). The extraordinary high flagellate densities near Esbjerg (Denmark) were remarkable: 859 X 103 cells in the surface layer in summer and 1100 X 103 cells in the 2 deeper layers during winter. In both seasons, at all depths and all stations most cells (50 to 75%) occurred in the 2 to 5 pm size class. Few flagellates were larger than 10 pm or smaller than 2 pm. Pooled winter and summer data of flagellate densities in the sediment surface layer showed a positive correlation with bacterial production and bacterial specific growth rate, explaining 20 and 30% respectively of the variance. In summer a positive correlation existed between flagellate density and bacterial specific growth rate and grain size, together explaining 53% of the variance. In winter nanoflagellate densities were significantly correlated with bacterial biomass and abundance accounting for 59% and 33%, respectively, of the variance. The data suggest that bacterial biomass/abundance during winter sets llmits to flagellate densities. Increased bacterial production was probably responsible for generally higher summer flagellate densities although grain size could become a limiting factor for flagellate densities in silty sediments during summer

Siliceous structures and silicification in flagellated protists

Abstract: Flagellated protists produce a diverse range of siliceous structures, such as internal and external skeletons, scales, spines, bristles, cell walls, cyst walls, and loricae. The different groups of silica-depositing flagellates, i.e., chrysophytes/synurophytes, choanoflagellates, dinoflagellates, ebriids, silicoflagellates, thaumatomastigids, and the genus Petasaria are reviewed. Brief mention is also given to those algal groups in which silicification is uncommon and rare (i.e., chlorophytes, euglenophytes, haptophytes/prymnesiophytes, xanthophytes/tribophytes), but in which silicified structures nevertheless occur in few flagellate genera. Special attention is given to aspects of morphology and development of the different siliceous structures as well as on aspects of systematics and taxonomy.

Phagotrophic nanoflagellates contribute to occurrence of a-glucosidase and aminopeptidase in marine environments

Abstract: Using fluorogenic substrate analogs, the dynamics of extracellular enzyme activities (EEA) of free and particle-bound a-glucosidase and aminopeptidase were investigated in mixed cultures of marine phagotrophic nanoflagellates and bacteria. Flagellate growth on either live or heatkilled bacteria led to an expression of free aminopeptidase activity with up to 94 % of total EEA found in the dissolved phase. No significant release of free a-glucosidase or free aminopeptidase was found in flagellate-free bacterial cultures. Fed with heat-killed bacteria, flagellates seemed to exhibit both cell wall bound a-glucosidase and aminopeptidase actlv~ties. Flagellate biovolume-specific EEA In flagellate assemblages grown on heat-killed bacteria was similar in magnitude to bacterial biovolumespecific EEA in flagellate-free bacterial cultures. The significance of these results is further discussed according to current theories on enzyme-catalyzed organic matter cycling.

N remineralization in planktonic protozoa

Abstract: Ammonium excretion rates of two marine planktonic protozoa (an oligotrichous ciliate, Strombidium sulcatum, and an aplastidic flagellate, Pseudobodo sp.) both isolated from oligotrophic Mediterranean waters were quantified with heat-killed bacteria as the food source for the protozoans. Ammonium excretion rates ranged from 0.25 to 2 µg N mg DW−1 h−1 for the ciliate and from 2.8 to 8.5 for the phagotrophic flagellate. Maximum excretion rates took place during the early exponential growth phase, suggesting possible covariation of excretion rates with either protozoan body size or their growth rates or metabolic state. Comparison of these excretion and regeneration rates with those obtained in situ for oligotrophic waters (∼0–37 nmol liter−1 h−1) indicates that protozoa may account for >50% of the nutrient recycling in these waters.

Colloidal and Dissolved Organic Matter Excreted by a Mixotrophic Flagellate during Bacterivory and Autotrophy

Abstract: Excretion of dissolved and colloidal organic carbon by a mixotrophic flagellate, the chrysophyte Poterioochromonas malhamensis, was studied. Flagellates were incubated either with 14C-labeled bacteria or with inorganic 14C, in order to compare organic exudates originating from primary production with exudates originating from ingested bacteria. Colloids of >0.02 μm constituted a larger fraction of the exudates originating from ingested bacteria, compared with exudates derived from primary production. Flagellate feeding on bacteria specifically labeled in different cell components was compared. Cell wall components gave rise to less colloidal organic carbon than did other cell constituents. To investigate the degradability of flagellate 14C-exudates, they were added to lake water and mineralization to 14CO2 was monitored. Bacterially derived exudates were more recalcitrant than exudates originating from photosynthesis. The results support the hypothesis that bacterial utilization of labile organic compounds, followed by flagellate bacterivory and exudation, results in a transformation of labile organic matter into more recalcitrant forms.

Rates and Ratios of Nitrogen and Phosphorus Released by a Bacterivorous Flagellate.

Abstract: Rates and elemental ratios of nutrient released by a bacterivorous flagellate (Spumella sp.) were examined during the exponential and stationary growth phases of the flagellate. Two types of an isolated bacterium were used as prey : one was phosphorus-rich (C: N : P molar ratio=59 : 13: 1) and the other was phosphoruspoor (C: N : P=79: 17: 1). Specific release rates by the flagellate of ammonium, dissolved inorganic and organic phosphorus (DIP and DOP) were much higher during the exponential growth phase than during the stationary one. Ammonium and DIP release rates in the experiment using the P-rich bacterium (Experiment 1) were not so remarkably different from those using the P-poor bacterium (Experiment 2) during both phases. However, DOP release rates were much higher in Experiment 1 than in Experiment 2 during both phases. Ratios of ammonium released to total dissolved phosphorus released were significantly lower in Experiment 1 than those in Experiment 2 during both phases. Further, these ratios were higher than bacterial N : P ratios in both experiments. N : P ratios of nutrients released by the flagellate could have been determined by bacterial N : P ratios, but the release appeared more efficient for nitrogen than for phosphorus.

Significance of the Virus-Rich 2-200 nm Size Fraction of Seawater for Heterotrophic Flagellates: I. Impact on Growth

Abstract: . The effect of artificially changing the concentration of naturally occurring free virus-like particles (VLPs) on growth of marine heterotrophic flagellates was tested in batch cultures using ultrafiltration technology. This manipulation influenced the course of flagellate growth markedly. During 1 week of incubation the growth of 4 tested flagellate strains (Oxyrrhis marina, Paraphysomonas imperforata, Petalomonas cantuscygni, Pteridomonas danica) was strongly favoured after increasing the VLP concentration. Bacteria, however, were repressed in these treatments beyond 50 h. In cultures with natural seawater microbiota, we both reduced and enriched the concentration of VLPs. In these cultures, reduction of material in the virus-rich 2–200 nm size fraction led to a strong positive growth response of heterotrophic flagellates. In VLP-enriched treatments of natural seawater microbiota a tendency toward growth stimulation was also found, although this was not significant. Enrichment with VLPs caused no recognizable mortality either in cultured flagellate strains or in naturally occurring flagellate communities. However, it is suggested that a highly bioactive component must be present in the virus-rich 2–200 nm size fraction. Virus-like particles are discussed as possible candidates influencing heterotrophic flagellate community successions.

Colloidal andDissolved Organic Matter Excreted byaMixotrophic Flagellate during Bacterivory andAutotrophy

Abstract: Excretion ofdissolved andcolloidal organic carbon byamixotrophic flagellate, thechrysophyte Poterioochromonas malhamensis, wasstudied. Flagellates wereincubated either with14C-labeled bacteria orwith inorganic 14C, inordertocompare organic exudates originating fromprimary production withexudates originating fromingested bacteria. Colloids of>0.02pumconstituted a larger fraction oftheexudates originating fromingested bacteria, compared withexudates derived fromprimary production. Flagellate feeding onbacteria specifically labeled indifferent cell components wascompared. Cellwallcomponents gave risetolesscolloidal organic carbon thandidothercell constituents. Toinvestigate thedegradability of flagellate '4C-exudates, they wereaddedtolakewaterandmineralization to'4Co2wasmonitored. Bacterially derived exudates weremorerecalcitrant thanexudates originating fromphotosynthesis. Theresults support thehypothesis thatbacterial utilization oflabile organic compounds, followed byflagellate bacterivory and exudation, results inatransformation oflabile organic matter intomorerecalcitrant forms. Mostoftheorganic matter inpelagic environments generally exists inthedissolved form. Thus, processes involved inthe dynamics ofdissolved organic matter(DOM;operationally defined asorganic matterthatpasses theporesoffilters, usually of0.2-to0.7-,um poresize[1]) arecrucial toour

Plastid ribosomal protein genes from the nonphotosynthetic flagellate Astasia longa.

Abstract: The plastid genome of the colorless, nonphotosynthetic protist Astasia longa resembles that of the photoautotrophic species Euglena g r a d i s but is only half the size (73 kb instead of 143 kb). A large number of intact ribosomal protein genes, rRNA genes, and tRNA genes have been identified in the 50% of Astasia ptDNA that has been sequenced (Siemeister and Hachtel, 1989; Siemeister et al., 1990a, 1990b). No genes for photosynthetic function have been found except rbcL. A similar loss of photosynthetic genes has occurred from ptDNA of a nonphotosynthetic parasitic flowering plant, Epifagus virginiana (Wolfe et al., 1992). The ptDNA of A. longa is a functional genome, since the large subunit of Rubisco and transcripts of a number of the protein-encoding genes have been detected (Siemeister and Hachtel, 1990). The reduced ptDNA of A. longa must be maintained to express at least one protein with nonphotosynthetic function that is essential for euglenoid flagellates. Here we report on additional genes on the ptDNA of A. longa that encode plastidic ribosomal proteins (Table I). The results corroborate other findings that genes coding for components of the plastid translational apparatus have been specifically retained on the ptDNA of A. longa. We have cloned and sequenced XbaI fragments X6 (4.0 kb) and X 1 1 (2.9 kb) and the 1.5-kb BglII fragment B9 of A. longa ptDNA (for location of these fragments, see Siemeister and Hachtel, 1989). By comparison with the complete sequence of the chloroplast DNA from E. grucilis (EMBL accession No. X70810; Hallick et al., 1993), ribosomal protein genes rpl2, rp120, rp122, rp123, and rpsl9 were identified. rp123 and rpsl9 are split genes in both E. g r a d i s (Christopher et al., 1988) and A. longa. rp123 of A. longa contains two class I11 introns (1 13 and 103 bp in size), whereas three class I11 introns were found in E. gradis rp123 (for classification of introns, see Hallick et al., 1993). Introns 2 and 3 of E. g r a d i s rp123 occur in A. longa rp123 at identical positions, whereas intron 1 is missing in A. longa and exons 1 and 2 of E. gradis rp123 appear to be fused in A. longa. In the rpsl9 gene of both A. longa and E. gracilis, two class I11 introns (101 and 113 bp in A. longa) occur in exactly the same positions. Downstream from the translation stop codons of a11 five ribosomal protein genes, inverted repeat sequences were found that are known to function as efficient RNA processing and stabilizing ele-

A light and transmission electron microscopic study of hexamite capsularis sp. nov.(diplomonadina: hexamitidae) in fish(xenocypris dividi)

Abstract: A diplomonad flagellate Hexamita capsularis spnovfrom the posterior intestine of the fish(Xenocypris dividi)from Liangzi Lake,Hubei Province,is describedThe flagellate was oval,withsmooth surface and homogenous cytoplasm,621±028μm in length,343±048μm in width and with anelliptical capsuleTwo recurrent flagellae arranged between two nuclei ran longitudinally to the posteriorendFibrillar bands connected the accessory organelles of two cytostomal tubes,the body depressed atthe posterior end of the body