Ciliate grazing on <Emphasis Type="Italic">Nitrosomonas europaea</Emphasis> and <Emphasis Type="Italic">Nitrospira</Emphasis><Emphasis Type="Italic">moscoviensis</Emphasis>: Is selectivity a factor for the nitrogen cycle in natural aquatic systems?

Ciliated protists are important predators of bacteria in many aquatic habitats, including sediments. Since, many biochemical transformations within the nitrogen cycle are performed by bacteria, ciliates could have an indirect impact on the nitrogen cycle through selective grazing on nitrogen-transforming bacteria. As a case study, we examined ciliate grazing on nitrifying bacteria of the genera Nitrosomonas and Nitrospira. All experiments were designed as in vitro-experiments with cultures of different bacteria and ciliate species. The nitrifying bacteria used in our experiments were Nitrosomonas europaea [Winogradsky 1892] and Nitrospira moscoviensis [Ehrich 2001]. The ciliates comprised of four species that are known as efficient bacterivores and common members of the protist community in aquatic systems: Paramecium aurelia [Müller 1773], Euplotes octocarinatus [Carter 1972], Tetrahymena pyriformis [Ehrenberg 1830] and Cyclidium glaucoma [Müller 1786]. Our experimental approach, using a combination of DAPI and FISH staining, was successful in allowing the observation of ingestion of specific bacteria and their detection within ciliate food vacuoles. However, the ciliates in this study showed no significant selective grazing. No food preferences for a any bacterial taxon or any size class or morphotype were detected. Correlation with time between ciliate abundance and bacterial abundance or biovolume, using log transformed growth rates of ciliates and bacteria, showed no significant results. On the bacterial side, neither an active defence mechanism of the nitrifying bacteria against ciliate grazing, such as changes in morphology, nor competition for resources were observed. These results suggest that in our in vitro-experiments grazing by ciliates has no influence on abundance and growth of nitrifying bacteria and nitrification.     

Brandtia ciliaticola gen. et sp. nov. (Chlorellaceae,Trebouxiophyceae) a common symbiotic green coccoid of various ciliate species

Many freshwater protists harbor unicellular green algae within their cells and these host‐symbiont relationships slowly are becoming better understood. Recently, we reported that several ciliate species shared a single species of symbiotic algae. Nonetheless, the algae from different host ciliates were each distinguishable by their different genotypes, and these host‐algal genotype combinations remained unchanged throughout a 15‐month period of sampling from natural populations. The same algal species had been reported as the shared symbiont of several ciliates from a remote lake. Consequently, this alga appears to play a key role in ciliate‐algae symbioses. In the present study, we successfully isolated the algae from ciliate cells and established unialgal cultures. This species is herein named Brandtia ciliaticola gen. et sp. nov. and has typical ‘Chlorella‐like’ morphology, being a spherical autosporic coccoid with a single chloroplast containing a pyrenoid. The alga belongs to the Chlorella‐clade in Chlorellaceae (Trebouxiophyceae), but it is not strongly connected to any of the other genera in this group. In addition to this phylogenetic distinctiveness, a unique compensatory base change in the SSU rRNA gene is decisive in distinguishing this genus. Sequences of SSU‐ITS (internal transcribed spacer) rDNA for each isolate were compared to those obtained previously from the same host ciliate. Consistent algal genotypes were recovered from each host, which strongly suggests that B. ciliaticola has established a persistent symbiosis in each ciliate species.     

Microplankton Patchiness in the Northwest Altantic Ocean

Plankton samples were collected in the Northwest Atlantic on the Grand Banks of Newfoundland in August 1976 and on Flemish Cap in March 1977. The samples were taken using a Hardy Continuous Plankton Recorder towed at a depth of 9.1 m. On the Grand Banks the following species were found: Ceratium arcticum (Ehrenberg), C. longipes (Ehrenberg), C. lineatum (Ehrenberg), C. macroceros (Ehrenberg), C. fusus (Ehrenberg). C. tripos (Müller) and Ceratium spp. Other microplankton found in the samples included Radiolaria, Globigerina humilis (Brady), and the tintinnid ciliates Tintinnopsis cylindrica (Daday) and Tintinnopsis spp. In the samples from Flemish Cap only a single species of diatom was found in small numbers. The paucity of individuals in these samples is most probably related to the season of the survey, winter. The population density of C. arcticum had a patchiness with a length scale on the order of 10⁴ m. The plankton tow on the Grand Banks was parallel to the north-south axis of the Labrador Current. This patchiness scale on the order of 10⁴ m may reflect a meandering of the Labrador Current.     

Cephalodella edax. sp. nov. A rotifer parasitic in the motile colonial alga Uroglena volvox Ehrenberg

A monogonont rotifer found parasitizing colonies of the motile alga Uroglena volvox Ehrenberg in two north English lakes is described as a new species. Diagnostic taxonomic details are given together with remarks on other rotifers known to occur in motile colonies of algae.     

Grazing of ciliates on blue–green algae: Effects of ciliate encystment and related phenomena

Grazing of the ciliate Colpoda steinii on the blue–green alga Anacystis nidulans has been studied in batch and chemostat type laboratory cultures. Growth of the populations, grazing of the ciliates on the algae, hydrodynamic washout of the populations (in chemostat cultures), encystment of Colpoda, and transfer of cysts from the liquid culture to the vessel wall and their attachment thereto were all found to have significant effects on the dynamics of this system. In addition, reinoculation of the liquid with ciliates excysted from the wall and with algae detached from the wall may be important. The interaction of all of these processes produces quite complex dynamical phenomena which at present cannot be predicted by a model. The results obtained differ from those found earlier for feeding of ciliates or slime mold amoebas on bacteria in that steady states of coexistence, rather than sustained oscillations, were exhibited by the present system.     

Feeding by ciliates on two harmful algal bloom species, Prymnesium parvum and Prorocentrum minimum

We have focused on ciliates as potential grazers on toxic phytoplankton because they are major herbivores in aquatic food webs. Ciliates may exert top down control on toxic phytoplankton blooms, potentially suppressing or shortening the duration of harmful algal blooms (HABs). We measured the growth rates of several ciliate species on uni-algal and mixed diets of both HAB and non-HAB algae. The tintinnids Favella ehrenbergii, Eutintinnus pectinis and Metacylis angulata and the non-loricate ciliates Strombidinopsis sp. and Strombidium conicum were isolated from Long Island Sound (LIS), and fed HAB species including the prymnesiophyte Prymnesium parvum (strain 97-20-01) and the dinoflagellate Prorocentrum minimum (strains Exuv and JA 98-01). Ciliates were fed algal prey from cultures at various growth phases and at varying concentrations. We observed no harmful effects of P. minimum (Exuv) on any of the ciliates. However in a comparison of strains, P. minimum (Exuv) supported high growth rates, whereas P. minimum (JA 98-01) supported only nominal growth. P. parvum was acutely toxic to ciliates at high concentrations (2×10⁴–3×10⁴ cells ml⁻¹). At low concentrations (5×10³–1×10⁴ cells ml⁻¹), or in culture filtrate, ciliates survived for at least several hours. In mixed diet experiments, as long as a non-toxic alga was available, ciliates survived and at times grew well at concentrations of P. parvum (5×10²–3×10⁴ cells ml⁻¹) that would otherwise have killed them. The present study suggests that prior to the onset of toxicity and bloom formation ciliates may exert grazing pressure on these HAB species, potentially contributing to the suppression or decline of P. minimum and P. parvum blooms.     

Isolation and identification of herbivorous ciliates from contaminated microalgal cultures

Ciliates are a common but understudied group of grazers that can invade microalgal cultures. To estimate the potential impact of ciliates on microalgal culture productivity, the identification of species that can invade these cultures is essential. Furthermore, isolation of these herbivorous ciliates allows to use them in experiments that investigate the impact of ciliate grazing on the productivity of microalgal cultures. The main aims of this study were to isolate and identify ciliates that invade cultures of the freshwater microalgae Chlorella and Chlamydomonas, and to establish a live collection of these ciliates for usage in future experiments. To this end, we optimized a method for isolating ciliates from contaminated microalgal cultures and we developed a new PCR primer set for amplifying the partial 18S rDNA of ciliates belonging to the classes Spirotrichea, Oligohymenophorea and Colpodea. As a result, we isolated 11 ciliates from microalgal enrichment cultures inoculated with non-sterile dust and various freshwater sources. Of these 11 species, 7 were found to be feeding on Chlamydomonas. Ciliate species that fed on Chlorella could not be isolated in this study. Ciliate species feeding on Chlamydomonas were identified based on a combination of morphological observations and molecular analyses of partial 18S rDNA sequences.     

STEROLS OF DICTYOCHA FIBULA (CHRYSOPHYCEAE) AND OLISTHODISCUS LUTEUS (RAPHIDOPHYCEAE)1

Sterols from cultured Dictyocha fibula Ehrenberg and Olisthodiscus luteus Carter were extracted and identified for comparison with sterols from other Chromophycota species. Although orientation at C-24 was not absolutely determined, the sterols of Dictyocha, a silicoflagellale, appeared to consist of only 24-methyl-22-dehydrocholesterol and 24-methylenecholesterol, a sterol composition not known in any other alga. This is in keeping with the taxonomic isolation Dictyocha has among algae. On the other hand, Olisthodiscus luteus contained 24-ethylcholesterol, 24-ethylcholestanol, 24-methylcholesterol, and cholesterol. This composition is in accord with sterols of members of the Xanthophyceae and Raphidophyceae.     

Prey preference and consumption capacity of Nephus arcuatus (Coleoptera: Coccinellidae): the influence of prey stage,prey size and feeding experience

This study examined the feeding habits of Nephus arcuatus Kapur (Coleoptera: Coccinellidae), an important predator of mealybugs in south-western Iran. The consumption capacity of male and female N. arcuatus adults was determined by their feeding on eggs, first-instar nymphs, and adult females of two destructive mealybugs, Nipaecoccus viridis (Newstead) and Planococcus citri Risso, over a 24-h period. N arcuatus consumed significantly more first-instar nymphs than eggs, and more eggs than female adults of both prey species. In addition, we also studied the developmental stage prey preference of adults reared on either N. viridis or P. citri and found that the prey preference of females did not change with the developmental stage of the mealybug. Meanwhile, the males reared on either N. viridis or P. citri showed a significant preference for the first-instar nymphs of P. citri over first-instar nymphs of N. viridis, while a preference for the eggs or adult females of these two mealybugs was not observed. This selection of first-instar nymphs by males was not tied to its previous feeding experience. Our findings suggest that prey stage, prey size and previous feeding experience had no effect on the prey selection of N. arcuatus, making it a good candidate for the biological control of mealybugs.     

Inhibition of nitrate and nitrite reduction by 2,4-dinitrophenol in ankistrodesmus

Summary As Kessler (1955, 1959) has shown, nitrite reduction by the green alga, Ankistrodesmus braunii is completely inhibited by 10^-3 m 2,4-dinitrophenol. However, although nitrite accumulates in the medium when cultures are supplied with nitrate and dinitrophenol, the reduction of nitrate is not completely insensitive to the inhibitor.Direct measurements show that 2,4-dinitrophenol inhibits nitrate disappearance from the medium by 65–80%. The degree of inhibition increases when the initial nitrate concentration is decreased.It is suggested that inhibition of nitrate assimilation by dinitrophenol is due to inhibition of an active uptake of nitrate by the cells, and that at high nitrate concentrations, a dinitrophenol-insensitive uptake process increases in importance.     

Biology of Multi Cell Ponds Treating Municipal Wastes

Observations were made over a period of one year on the performance of multi stage stabilization ponds treating domestic waste waters. The unit is composed of Primary anaerobic (P₁) and two consecutive Secondary (P₂) and Tertiary (P₃) facultative ponds. The overall reduction in BOD, bacteria, PO₄, SO₄, NH₃N, Cl⁻ and total solids were 89.4, 99.8, 76.2, 47.7, 79.7, 18.6 and 74.0 percent, respectively. Elimination of H₂S was 84.8% in the final effluents. Chlorella vulgaris was found to be the dominant alga followed by Euglena, Ankistrodesmus, Phacus and Synedra as subdominant forms. 9 species of protozoa have been recorded in the first pond and their number declined in the successive ponds.     

Selectivity of food bacteria for the growth of anaerobic ciliate Trimyema compressum

The anaerobic ciliate Trimyema compressum was cultivated on various food bacteria. Significant growth was observed when Lactobacillus sp., Escherichia coli, Enterobacter aerogenes, Desulfovibrio vulgaris, Methanoculleus bourgense, or Pelobacter propionicus cells were fed to the ciliates. The highest cell yield which we obtained was ca. 9,000 cells/ml when feeding D. vulgaris. However, no growth of the ciliates was observed on the culture with Clostridium novyi, Propionibacterium sp., Desulfobulbus propionicus, Methanobrevibacter arboriphilicus, Methanobacterium sp., Methanosarcina barkeri, or Methanothrix soehngenii cells. The ciliates produced acetate and methane as major end products in any cultures and small amounts of propionate, butyrate and hydrogen were also detected in some cultures. Physiological studies on the food bacteria which we tested indicated that the growth of T. compressum depended on the bacterial species, but there was no apparent correlation between the digestibility and the basic properties of those bacteria (i.e. size of the bacteria, gram-staining properties, susceptibility to the known lytic enzymes, Archaea or Bacteria).     

Epiphytic protozoans on reed rootlets from Dutch waters

The protozoans attached to the submerged roots of reed (Phragmites australis) in some small waters in Holland were studied during one year. Reed was chosen because it is a very common natural substrate for epiphytically living animals. Marked changes in species abundance and overall population density are reported. Most important quantitatively were the ciliates, especially peritrichs, on which emphasis is laid. Vorticella campanula Ehrenberg, 1831 is found to be the dominant species in spring and summer, other vorticellas being also very numerous. Suctorian populations seem to change strongly within weeks without apparent reason. Small attached flagellates were also common. No stalked Heliozoa or medium-sized flagellates were found. The generalisation of the results and comparisons with the literature are discussed. Zoological Laboratory, University of Amsterdam     

Histological survey of symbionts and other conditions in razor clam Ensis arcuatus (Jeffreys, 1865) (Pharidae) of the coast of Galicia (NW Spain)

Symbionts and abnormal conditions of razor clam Ensis arcuatus were surveyed in three commercially important natural beds of Galician estuaries (NW Spain). Samples of 15-20 E. arcuatus were collected every 2 months from January 2003 until July 2004 and processed for histological examination. Prokaryote-like colonies, renal coccidians, gregarines, Trichodina sp. ciliates, haplosporidian-like plasmodia, turbelaria, trematode metacercariae, cestode-like larvae and basophilic inclusion bodies were observed in razor clam tissues without causing host damage. Bucephalid digenean sporocysts and germinoma were seen in some samples causing moderate or severe damage to the host depending on the intensity of infection and both could be a cause for concern if prevalence reached epizootic levels in Galician E. arcuatus populations. None of the parasites detected is OIE notifiable and, in general, the commercially exploited beds studied seem to be devoid of serious pathogens.     

Effects of food quality on growth and biochemical composition of a calanoid copepod,Argyrodiaptomus furcatus,and its importance as a natural food source for larvae of two tropical fishes

Growth, reproduction and biochemical composition were analyzed for the copepod Argyrodiaptomus furcatus fed on the alga Ankistrodesmus gracilis grown in different media. The ingestion of this copepod by larvae of two species of tropical fishes was also evaluated. The mean peak density of the copepod population was 1369 individuals l^–1 for all four diets used, and the highest was 1387 individuals l^–1 on diet ARV (algae + ration + vitamins). A small copepod, A. furcatus tends to have a short life span. The smallest females did not attain maturity in the shortest time on all diets used. Food quality may play a major role in the dynamics of the biochemical composition of this copepod. Argyrodiaptomus furcatus was a more important food item for larvae of tambaqui (Colossoma macropomum) than of pacu (Piaractus mesopotamicus). However, it made up a large part of the gut contents of larvae of both species.     

Effect of food type and concentration on the survival,longevity, and reproduction of Daphnia magna

The freshwater microalgae Ankistrodesmus falcatus and Scenedesmus incrassatulus, at three concentrations (6, 12 and 18 mg l⁻¹ t, dry weight), were tested as diets for Daphnia magna cultured in reconstituted hard water, at 19 ± 1 °C. Effects on survival, and reproductive characteristics were evaluated during a complete life-cycle. Test animals fed with the highest food concentration had the lowest survival, longevity, number of clutches, and average inter-brood times, but the total offspring was similar to that obtained with the lowest food concentration, for the same species of alga. Average longevity ranged from 40 to 85 days, with a minimum of 24 and a maximum of 119 days. The average inter-brood time ranged from 4.2 to 5.8 days, the highest values being observed at the lowest food concentration. The average total offspring was maximum for the intermediate concentrations of both algae. The maximum number of clutches ranged from 9 to 23, with the lowest values being observed at the highest food concentration. Even though both microalgae had similar effects on survival and reproduction, and the greatest differences observed were related to food concentration, it seems that S. incrassalulus is a comparatively better food for D. magna. The most suitable food level should be determined prior to carrying out chronic bioassays, and it is also an important factor in cultures for obtaining neonates for toxicological tests.     

The Effect of Grazing by a Ciliated Protozoan on Phosphorus Limitation of Heterotrophic Bacteria in Batch Culture1

ABSTRACT. The yield of the bacterium Enterobacter aerogenes and the ciliate Colpidium colpoda was dependent on initial phosphorus concentrations in batch cultures containing 125 or 250 mg/liter glutamate and 50–1000 μg/liter phosphorus. For both, yield per unit phosphorus declined at higher phosphorus concentrations. A marked decline in growth rate in bacterial cultures was coincident with the depletion of dissolved phosphorus and the development of rapid orthophosphate turnover times. Colpidium introduced to these cultures consumed about 16,000 bacteria/h/ciliate while multiplying exponentially and relieved phosphorus limitation, as indicated by a longer turnover-time for phosphate. The longer turnover-time was due to the reduction of bacterial numbers; in cultures with ciliates, bacteria appear to be more active in taking up phosphate, and much of the total phosphorus accumulates in ciliates. Ciliates released both inorganic and organic phosphorus, but the organic phosphorus did not accumulate to excess in the cultures to an extent that would indicate that it is less used by bacteria. Although ciliates release enough phosphorus to account for ca. 20% of the bacterial uptake, ciliates appear to behave as phosphorus sinks as much as phosphorus recyclers in these closed systems.     

Monoxenic culture of the anaerobic ciliate Trimyema compressum Lackey

Sapropelic ciliates from anoxic mud samples were enriched and cultivated in monoculture together with natural food bacteria growing on cellulose. The ciliates lacked cytochrome oxidase and contained bluish fluorescent endosymbionts. One of the anaerobic ciliates, Trimyema compressum, contained methanogenic bacteria as was shown by methane formation. During continued cultivation, T. compressum gradually lost its endosymbionts. With SEM microscopy no episymbiotic bacteria could be detected.From enrichment cultures of T. compressum, anaerobic bacteria were isolated in pure culture. One of the strains, a Bacteroides spec., proved capable of serving as food bacteria, thus allowing establishment of monoxenic T. compressum cultures. These cultures exhibited a requirement for sterols as growth factors. The doubling time of this ciliate was 13 h at 28°C. The highest yield obtained was 2100 cells/ml.Dedicated to Holger W. Jannasch on the occasion of his 60th birthday     

Carbon budgets for a phytoplanktivorous fish fed three different unialgal populations

Summary The filter feeding blue tilapia, Tilapia aurea, was fed three different algae. Blue tilapia ingestion of two green algae, Chlamydomonas sp. and Ankistrodesmus falcatus and the filamentous blue-green alga, Anabaena flos-aquae, ranged from 21%–89% of the available cells. There were significant differences in the assimilation of algal carbon by the fish depending on the alga fed; A. flos-aquae was the easiest to assimilate (83%). The fish respired significantly less of the Chlamydomonas sp. ingested carbon (15%). The gross growth efficiency of fishes fed either green alga was not significantly different (22%–24%), but these efficiencies were significantly less than the gross growth efficiency of fish fed A. flos-aquae (46%). The carbon budgets for fish feeding on the green algae were similar to that constructed from the literature for a congener fed a mixed algae diet. However, the assimilation component of the budget for blue tilapia fed A. flos-aquae was 2 times greater than that of the literature budget.