Pirsonia guinardiae,gen. et spec. nov.: A parasitic flagellate on the marine diatomGuinardia flaccida with an unusual mode of food uptake

Pirsonia guinardiae gen. et spec. nov. was discovered as a parasite onGuinardia flaccida in the North Sea near List/Sylt during a bloom of this centric planktonic diatom. It is a colourless, small flagellate with an oblique cell apex and two subapically inserting flagella of different length and different orientation. The flagellates attach to a host cell and form an antapical process which pierces the diatom frustule and develops inside into a “trophosome”, consisting of a proximal digestion vacuole and distal pseudopodia which phagocytise host cytoplasm. The main body, the “auxosome”, remains outside the host cell. The trophosome persists for some time after the detachment of the auxosome or its derivatives. There are two types ofPirsonia guinardiae. Type A attaches to the valvae as well as to the girdle region, the auxosome remains flagellated and generally detaches after the feeding process to divide twice (seldom 3 times). Thick-walled (resting?) cysts are formed. Occasionally, a fusion of two sister cells has been observed. Type B attaches only to the valvae; the auxosome lacks flagella; it divides during the feeding process to give rise to a bouquet of 8 to more than 50 daughter cells which become flagellated when they detach. The taxonomical position of the flagellate is discussed. Diagnoses of genus and species are given.     

Copepod Population-Specific Response to a Toxic Diatom Diet

Diatoms are key phytoplankton organisms and one of the main primary producers in aquatic ecosystems. However, many diatom species produce a series of secondary metabolites, collectively termed oxylipins, that disrupt development in the offspring of grazers, such as copepods, that feed on these unicellular algae. We hypothesized that different populations of copepods may deal differently with the same oxylipin-producing diatom diet. Here we provide comparative studies of expression level analyses of selected genes of interest for three Calanus helgolandicus populations (North Sea, Atlantic Ocean and Mediterranean Sea) exposed to the same strain of the oxylipin-producing diatom Skeletonema marinoi using as control algae the flagellate Rhodomonas baltica. Expression levels of detoxification enzymes and stress proteins (e.g. glutathione S-transferase, glutathione synthase, superoxide dismutase, catalase, aldehyde dehydrogenases and heat shock proteins) and proteins involved in apoptosis regulation and cell cycle progression were analyzed in copepods after both 24 and 48 hours of feeding on the diatom or on a control diet. Strong differences occurred among copepod populations, with the Mediterranean population of C. helgolandicus being more susceptible to the toxic diet compared to the others. This study opens new perspectives for understanding copepod population-specific responses to diatom toxins and may help in underpinning the cellular mechanisms underlying copepod toxicity during diatom blooms.     

Responses and structural recovery of periphytic diatom communities after short-term disturbance in some rivers (Hanoi, Vietnam)

Field transfer experiments of periphytic diatom assemblages developed on artificial substrates were set up to assess the responses of those communities to environmental disturbances. The glass slides were positioned for colonization at the relatively unpolluted site (Red, in the Red River) and at the heavily polluted site (TL, in the To Lich River) in the beginning of the experiment. After a period of 2?weeks, the colonized glass slides were concomitantly transferred from the unpolluted Red site to the heavily polluted TL site and to the moderate polluted site (NT₂, in the Nhue River) and, conversely, from the TL site to the Red site, and then to the NT₂ site. The responses and the adapting capacity of periphytic diatom communities to environmental changes were assessed through the cell density, diversity index, species richness, taxonomic composition, and diatom indices after 2 and 4?weeks of transfer periods. For all transfers except for the transfer from the Red to the TL site in which the growth inhibition of diatom cells was found, the diatom density significantly increased until the end of the experiment. Thus, the diatom communities have expressed their pollution tolerance or sensitivities by changing their composition to adapt themselves to environmental changes. Characteristic species of the Red site (Gyrosigma scalproides, Navicula recens) were replaced by Nitzschia palea, Nitzschia umbonata, Aulacoseira granulate typical species of the NT₂ site, in the biofilm transferred from the Red site to the NT₂ site. The relative abundances of typical diatom species of the Red site proliferated in the biofilm transferred from the TL site to the Red site. The replacement of periphytic diatom communities appeared after the transfer from the second week at the different sites. The slow shift of the species towards the typical species at the TL site could result from the organized structure of diatoms within biofilm before the transfer from the Red site to the TL site. The shifts in values of the Index of Specific Polluosensitivity and Diatom Assemblage Index to organic pollution throughout the experiment indicated the clear sensitivity of these indices to water quality changes.     

Evidence of interference of Asterionella formosa with the feeding of Bosmina longirostris: a field study in a south Andes lake

Intensive sampling of a small temperate lake of the Araucanian region (Argentina), revealed changes in the demography of Bosmina longirostris when the diatom Asterionella formosa density increased (to 54 000 cells ml^–1). Bosmina population behaviour in the field was consistent with the idea that large numbers of Asterionella caused its starvation. Individuals were actually colourless and fecundity dropped to zero, as was evident when Asterionella reached 99.4% of total phytoplankton biovolume. Since cyanophytes, as a whole, are scarce in these lakes, we propose that the flagellate/diatom ratio has a direct effect on cladoceran demography.     

Comparison of diatom community structure from epilithon and fish guts: implications for inferring past changes in water quality

The sampling skills of three common European fish species (Barbus barbus, Chondrostoma nasus and Squalius cephalus) were tested to assess their potential as biomonitors of past changes in river water quality through the analysis of diatoms in fish guts. The study was performed on three rivers with different chemical and physical conditions. Comparison of similarity indices revealed low diatom assemblage resemblance between epilithic samples and samples collected from fish guts at the same locality. In contrast, a mixed-effect linear model identified significant differences between locations through comparison of diatom-based water quality indices. Among fish species, diatom indices calculated from gut samples of B. barbus and C. nasus were in most cases not significantly different from those from epilithic samples while those from S. cephalus were often significantly different. The results of the study demonstrate that diatom analysis of fish guts provides a clear distinction between eutrophic and hypereutrophic rivers. Finer nutrient variations within hypereutrophic conditions were also found to be significant for some diatom indices. In this context, choice of appropriate diatom water quality index proved to be crucial in maximizing the sensitivity of the method.     

Utilization of dissolved organic phosphorus by different groups of phytoplankton taxa

The utilization of nine dissolved organic phosphorus (DOP) compounds by five bloom-causing phytoplankton species was studied under batch culture conditions. The DOP compounds included were adenosine 5-triphosphate (ATP), adenosine 5-monophosphate (AMP), cytidine 5-monophosphate (CMP), guanosine 5-monophosphate (GMP), uridine 5-monophosphate (UMP), glucose-6-phosphate (G6P), sodium glycerophosphate (GYP), 4-nitrophenyl phosphate (NPP), and triethyl phosphate (TEP), and the phytoplankton taxa were Skeletonema costatum, Prorocentrum micans, Alexandrium tamarense, Chattonella marina, and Heterosigma akashiwo. The four flagellate taxa, P. micans, A. tamarense, C. marina, and H. akashiwo, grew well under various DOP regimes. P. micans and C. marina were the most capable of using DOP compounds, sustaining better growth on a majority of nucleotides (ATP, AMP, CMP, GMP, and UMP) and phosphomonoesters (G6P and GYP) than in inorganic phosphorus (P) controls. A. tamarense and H. akashiwo showed equivalent growth in most organic and inorganic P cultures, while the diatom species, S. costatum, could only utilize AMP and GMP. Furthermore, A. tamarense and C. marina could endure N, P-depleted conditions. Among the nine DOP compounds tested, the nucleotide compounds had the highest nutritional value for algal cell growth, while TEP could not sustain growth as the sole source of P. These results suggest that enhanced DOP utilization and the endurance of nutrient-limitation by harmful flagellate taxa offer their competitive advantages, which may account for the frequent occurrence of their blooms in coastal waters.     

Metabolic Analysis of Adaptation to Short-Term Changes in Culture Conditions of the Marine Diatom Thalassiosira pseudonana

This report describes the metabolic and lipidomic profiling of 97 low-molecular weight compounds from the primary metabolism and 124 lipid compounds of the diatom Thalassiosira pseudonana. The metabolic profiles were created for diatoms perturbed for 24 hours with four different treatments: (I) removal of nitrogen, (II) lower iron concentration, (III) addition of sea salt, (IV) addition of carbonate to their growth media. Our results show that as early as 24 hours after nitrogen depletion significant qualitative and quantitative change in lipid composition as well as in the primary metabolism of Thalassiosira pseudonana occurs. So we can observe the accumulation of several storage lipids, namely triacylglycerides, and TCA cycle intermediates, of which citric acid increases more than 10-fold. These changes are positively correlated with expression of TCA enzymes genes. Next to the TCA cycle intermediates and storage lipid changes, we have observed decrease in N-containing lipids and primary metabolites such as amino acids. As a measure of counteracting nitrogen starvation, we have observed elevated expression levels of nitrogen uptake and amino acid biosynthetic genes. This indicates that diatoms can fast and efficiently adapt to changing environment by altering the metabolic fluxes and metabolite abundances. Especially, the accumulation of proline and the decrease of dimethylsulfoniopropionate suggest that the proline is the main osmoprotectant for the diatom in nitrogen rich conditions.     

Flagellate Predation on a Bacterial Model Community: Interplay of Size-Selective Grazing, Specific Bacterial Cell Size, and Bacterial Community Composition

The influence of grazing by the bacterivorous nanoflagellate Ochromonas sp. strain DS on the taxonomic and morphological structures of a complex bacterial community was studied in one-stage chemostat experiments. A bacterial community, consisting of at least 30 different strains, was fed with a complex carbon source under conditions of low growth rate (0.5 day⁻¹ when nongrazed) and low substrate concentration (9 mg liter⁻¹). Before and after the introduction of the predator, the bacterial community composition was studied by in situ techniques (immunofluorescence microscopy and fluorescent in situ hybridization), as well as by cultivation on agar media. The cell sizes of nonspecifically stained and immunofluorescently labeled bacteria were measured by image analysis. Grazing by the flagellate caused a bidirectional change in the morphological structure of the community. Medium-size bacterial cells, which dominated the nongrazed community, were largely replaced by smaller cells, as well as by cells contained in large multicellular flocs. Cell morphological changes were combined with community taxonomic changes. After introduction of the flagellate, the dominating strains with medium-size cells were largely replaced by single-celled strains with smaller cells on the one hand and, on the other hand, by Pseudomonas sp. strain MWH1, which formed the large, floc-like forms. We assume that size-selective grazing was the major force controlling both the morphological and the taxonomic structures of the model community.     

The periparturient rise in fecal egg counts in three strains of Florida native ewes and its value in predicting resistance of lambs to Haemonchus contortus

The periparturient rise in fecal egg counts in three strains of Florida Native ewes and its value in predicting resistance of lambs to Haemonchus contortus. International Journal for Parasitology16: 185–189. Significant (P < 0.05) differences in the magnitude of the periparturient rise in fecal egg counts (PPR) occurred in ewes of three strains of Florida Native sheep. Non-lambing ewes (n = 12) and lactating University strain ewes (n = 31), a strain selected over a 26-year period for parasite resistance by survival at pasture without anthelmintic treatment, had lower fecal egg counts than ewes of either Maxcy strain (n= 17), a commercial strain treated regularly with anthelmintics, or Backlinie strain (n = 16), a strain of Florida Native sheep that had some crossbreeding to Hampshire and Suffolk in their genotype and were regularly treated with anthelmintics. Whereas both Maxcy and Backlinie ewes showed a pronounced PPR, none occurred in non-lambing ewes (n=12) and the slight rise in fecal egg counts observed in University ewes was not significantly different from that of the non-lambing ewes. Backlinie ewes having twin lambs (n = 5) had a higher PPR than Backlinie ewes with single lambs (n = 11) or Maxcy ewes with single lambs (n = 15), but all three groups had higher PPRs than University ewes with single lambs (n = 27). No differences occurred in fecal egg counts of non-lambing ewes regardless of strain. Six weeks after weaning fecal egg counts of all ewes were uniformly low regardless of strain or prior lactation status.Ram lambs born to these ewes showed no significant strain differences in Haemonchus contortus burdens after experimental infection, deworming with levamisole and reinfection, although University lambs (n= 13) had lowest mean worm burdens at necropsy (2437) followed by Maxcy lambs (n= 12, mean =3106) and Backlinie lambs (n= 13, mean =3670). There was no significant correlation between worm burdens in these lambs and the magnitude of the PPR in their dams. Eight to 16 weeks after turn out to a common parasite-infested pasture ewe lambs (n = 13) born to University ewes had lower fecal egg counts than similar ewe lambs (n=8) born to Backlinie ewes. Prior to this time differences were not significant and egg counts were generally low. The magnitude of the PPR in their dams was not significantly correlated with fecal egg counts or PCVs of individual ewe lambs.     

Reproduction of an inbred strain of Culex pipiens prevented by loss of Wolbachia pipientis

The development time for an autogenous strain of Culex pipiens was prolonged after the mosquitoes were “cured” of their symbiotic Wolbachia pipients with tetracycline. Eggs produced by aposymbiotic females caged with either aposymbiotic or normal males failed to hatch. Neither growth rate nor reproduction was improved by feeding the larvae a commensal flagellate, bovine blood cells, or adenylic acid.     

Dr Han L. Golterman,a Limnologist: a tribute on the occasion of his 65th birthday and retirement

The green algae D. tertiolecta, the flagellate I. galbana and the diatom C. gracilis were grown in batch cultures. The organisms were analysed for lipid class composition at the logarithmic and stationary growth phases using the Chromarod-Iatroscan thin layer chromatography with flame ionization detection (TLC-FID) system.There were major differences in lipid class production among the organisms investigated, but few differences in lipid class distribution between log phase and stationary phase cultures of D. tertiolecta and I. galbana. C. gracilis displayed the general trend exhibited in diatom metabolism, which can be characterized by an increase in triacylglycerol synthesis in situations of stress.     

Fecal Bacterial Community Changes Associated with Isoflavone Metabolites in Postmenopausal Women after Soy Bar Consumption

Soy isoflavones and their metabolism by intestinal microbiota have gained attention because of potential health benefits, such as the alleviation of estrogen/hormone-related conditions in postmenopausal women, associated with some of these compounds. However, overall changes in gut bacterial community structure and composition in response to addition of soy isoflavones to diets and their association with excreted isoflavone metabolites in postmenopausal women has not been studied. The aim of this study was to determine fecal bacterial community changes in 17 postmenopausal women after a week of diet supplementation with soy bars containing isoflavones, and to determine correlations between microbial community changes and excreted isoflavone metabolites. Using DGGE profiles of PCR amplified 16S rRNA genes (V3 region) to compare microbial communities in fecal samples collected one week before and one week during soy supplementation revealed significant differences (ANOSIM p<0.03) before and after soy supplementation in all subjects. However, between subjects comparisons showed high inter-individual variation that resulted in clustering of profiles by subjects. Urinary excretion of isoflavone (daidzein) metabolites indicated four subjects were equol producers and all subjects produced O-desmethylangolensin (ODMA). Comparison of relative proportions of 16S rRNA genes from 454 pyrosequencing of the last fecal samples of each treatment session revealed significant increases in average proportions of Bifidobacterium after soy consumption, and Bifidobacterium and Eubacterium were significantly greater in equol vs non-S-(-)equol producers. This is the first in vivo study using pyrosequencing to characterize significant differences in fecal community structure and composition in postmenopausal women after a week of soy diet-supplementation, and relate these changes to differences in soy isoflavones and isoflavone metabolites.

Trial Registration

Clinicaltrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00244907","term_id":"NCT00244907"}}NCT00244907     

Yellow water in La Jolla Bay,California, July 1980. II. suppression of zooplankton grazing

Experiments were conducted to determine how much grazing pressure adult females of Calanus pacificus Brodsky, a dominant planktonic herbivore in local waters, exerted upon a bloom of the dino- flagellate, Gymnodinium flavum Kofoid & Swezy, in the waters off La Jolla in July, 1980. One set of females was presented with water collected from the chlorophyll maximum, and a second set was presented with Thalassiosira weissflogii Grunow, which is readily ingested by Calanus. Filtration rates upon the diatom were significantly higher (8.4 ml · copepod^?1 · h^?1) than upon the dinoflagellate (0.30 ml · copepod^?1 · h^?1). Calanus did not exert a significant grazing pressure upon the dinoflagellate bloom. Gut content analyses support this conclusion. The persistence of the bloom was probably due, in part, to the avoidance of Gymnodinium flavum by copepod grazers and to the consequent lack of grazing pressure.     

Effects of Lactococcus lactis on Composition of Intestinal Microbiota: Role of Nisin

This study examined the ability of (i) pure nisin, (ii) nisin-producing Lactococcus lactis strain CHCC5826, and (iii) the non-nisin-producing L. lactis strain CHCH2862 to affect the composition of the intestinal microbiota of human flora-associated rats. The presence of both the nisin-producing and the non-nisin-producing L. lactis strains significantly increased the number of Bifidobacterium cells in fecal samples during the first 8 days but decreased the number of enterococci/streptococci in duodenum, ileum, cecum, and colon samples as detected by selective cultivation. No significant changes in the rat fecal microbiota were observed after dosage with nisin. Pearson cluster analysis of denaturing gradient gel electrophoresis profiles of the 16S rRNA genes present in the fecal microbial population revealed that the microbiota of animals dosed with either of the two L. lactis strains were different from that of control animals dosed with saline. However, profiles of the microbiota from animals dosed with nisin did not differ from the controls. The concentrations of nisin estimated by competitive enzyme-linked immunosorbent assay (ELISA) were approximately 10-fold higher in the small intestine and 200-fold higher in feces than the corresponding concentrations estimated by a biological assay. This indicates that nisin was degraded or inactivated in the gastrointestinal tract, since fragments of this bacteriocin are detected by ELISA while an intact molecule is needed to retain biological activity.     

Circadian Plasticity in Photoreceptor Cells Controls Visual Coding Efficiency in Drosophila melanogaster

In the fly Drosophila melanogaster, neuronal plasticity of synaptic terminals in the first optic neuropil, or lamina, depends on early visual experience within a critical period after eclosion [1]. The current study revealed two additional and parallel mechanisms involved in this type of synaptic terminal plasticity. First, an endogenous circadian rhythm causes daily oscillations in the volume of photoreceptor cell terminals. Second, daily visual experience precisely modulates the circadian time course and amplitude of the volume oscillations that the photoreceptor-cell terminals undergo. Both mechanisms are separable in their molecular basis. We suggest that the described neuronal plasticity in Drosophila ensures continuous optimal performance of the visual system over the course of a 24 h-day. Moreover, the sensory system of Drosophila cannot only account for predictable, but also for acute, environmental changes. The volumetric changes in the synaptic terminals of photoreceptor cells are accompanied by circadian and light-induced changes of presynaptic ribbons as well as extensions of epithelial glial cells into the photoreceptor terminals, suggesting that the architecture of the lamina is altered by both visual exposure and the circadian clock. Clock-mutant analysis and the rescue of PER protein rhythmicity exclusively in all R1-6 cells revealed that photoreceptor-cell plasticity is autonomous and sufficient to control visual behavior. The strength of a visually guided behavior, the optomotor turning response, co-varies with synaptic-terminal volume oscillations of photoreceptor cells when elicited at low light levels. Our results show that behaviorally relevant adaptive processing of visual information is performed, in part, at the level of visual input level.     

Ingestion of live filamentous diatoms by the Great Lakes amphipod,Diporeia sp.: a case study of the limited value of gut contents analysis

Individuals of the Great Lakes amphipod, Diporeia sp. (formerly named Pontoporeia hoyi) were collected from a 45-m deep station in southeastern Lake Michigan and isolated in small laboratory feeding vessels at 4 °C, after the animals had voided their guts over a 24-hour period. Over a 20-day period, following introduction of a single ration of live cells of the filamentous diatom, Melosira varians, 9 of 10 animals had ingested this material, and 7 of these 9 individuals had deposited fecal pellets. Subsequent examination of gut contents and fecal pellets showed that although animals had ingested whole algal cells/filaments, little of the material in gut contents or fecal pellets bore any identifiable structural similarity to cells/filaments prior to ingestion. The results suggest that earlier studies of pontoporeiid gut contents may seriously underestimate the importance of algal components in the amphipod's diet and imply that Diporeia sp. growth and production may be more closely linked to primary production than previously thought.     

Food patch size, food concentration and grazing efficiency of the harpacticoid Paramphiascella fulvofasciata (Crustacea, Copepoda)

Harpacticoid copepods are known as important grazers on primary producers. The underlying factors for their food selectivity and grazing efficiency are however far from well known. For instance, their patchy distribution in the marine environment is well documented but how meiofaunal organisms cope with the spatial distribution/accessibility of the available food resources is less clear.In the present study a laboratory experiment was conducted to test the grazing efficiency of Paramphiascella fulvofasciata (Copepoda, Harpacticoida) on the epipelic diatom Seminavis robusta applied in recipients of different area and in various concentrations. Diatoms were enriched in the stable isotope ¹³C in order to trace food uptake and copepods were left to graze for 4 days.We found that the grazing efficiency of P. fulvofasciata was diatom concentration-dependent. A lower diatom uptake at lower diatom densities illustrated this clear functional response. On the contrary, there was no significant effect of the area per se where the copepods could graze upon. The lack of a significant effect of area is mainly due to the high variability in uptake that was recorded in some treatments. Although P. fulvofasciata is a very motile copepod, known as endobenthic and epibenthic species, it was able to concentrate on food uptake at the bottom of the experimental unit as there was no significant difference in uptake between treatments with different water heights in the units. In addition, it was found that a diatom concentration of about 140 000 cells/cm² favours egg production of P. fulvofasciata.     

Axonal Synapses Utilize Multiple Synaptic Ribbons in the Mammalian Retina

In the mammalian retina, bipolar cells and ganglion cells which stratify in sublamina a of the inner plexiform layer (IPL) show OFF responses to light stimuli while those that stratify in sublamina b show ON responses. This functional relationship between anatomy and physiology is a key principle of retinal organization. However, there are at least three types of retinal neurons, including intrinsically photosensitive retinal ganglion cells (ipRGCs) and dopaminergic amacrine cells, which violate this principle. These cell types have light-driven ON responses, but their dendrites mainly stratify in sublamina a of the IPL, the OFF sublayer. Recent anatomical studies suggested that certain ON cone bipolar cells make axonal or ectopic synapses as they descend through sublamina a, thus providing ON input to cells which stratify in the OFF sublayer. Using immunoelectron microscopy with 3-dimensional reconstruction, we have identified axonal synapses of ON cone bipolar cells in the rabbit retina. Ten calbindin ON cone bipolar axons made en passant ribbon synapses onto amacrine or ganglion dendrites in sublamina a of the IPL. Compared to the ribbon synapses made by bipolar terminals, these axonal ribbon synapses were characterized by a broad postsynaptic element that appeared as a monad and by the presence of multiple short synaptic ribbons. These findings confirm that certain ON cone bipolar cells can provide ON input to amacrine and ganglion cells whose dendrites stratify in the OFF sublayer via axonal synapses. The monadic synapse with multiple ribbons may be a diagnostic feature of the ON cone bipolar axonal synapse in sublamina a. The presence of multiple ribbons and a broad postsynaptic density suggest these structures may be very efficient synapses. We also identified axonal inputs to ipRGCs with the architecture described above.     

Infection of Coscinodiscus spp. by the parasitoid nanoflagellate Pirsonia diadema: II. Selective infection behaviour for host species and individual host cells

The parasitoid nanoflagellate (PNF) Pirsonia diadema is hostspecific for the marine centric diatom Coscinodiscus spp. Experimentsshowed that flagellates significantly prefer C. wailesii overC.granii as host species (interspecific selectivity). This preferencewas independent of light conditions (dark, irradiance of 10and 70 µmol m^–2 s^–1) and temperature (10 and15C). Among unicellular host diatoms, the infection behaviourwas selective for individual cells: already infected C.graniicells were more attractive for further flagellate attachmentthan non-infected cells (intraspecific selectivity). Individualcells (