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(2001). Selective influence of filter-feeding benthic bivalves (Corbicula sp., Mytilus sp.) on planktonic ciliates. SIL Proceedings, 1922-2010: Vol. 27, No. 6, pp. 3315-3318.

The influence of prey characteristics such as motility and size as well as of predator characteristics such as satiation and preculturing diet on the feeding process of interception feeding heterotrophic nanoflagellates was investigated. Three species of gram-negative bacteria, one species of gram-positive bacteria, two species of cyanobacteria (Synechococcus) and inert latex particles were fed as prey particles for three species of heterotrophic nanoflagellates (Spumella, Ochromonas, Cafeteria). Ingestion rates depended on the satiation of the flagellates and especially on the filling status of the food vacuoles. In addition, the ingestion rates depended on the characteristics of the food particle and were modified by pre-culturing the flagellates on either Pseudomonas putida or Bacillus subtilis. Digestion was found to be particle-specific. Cyanobacteria were excreted a few minutes after ingestion whereas heterotrophic bacteria were stored and digested in the food vacuoles. The spectrum of ingested particles is not identical to that of digested particles and thus neither the diet of the flagellates nor their impact on bacterial communities can be calculated simply from food vacuole content. "Selective digestion" could be shown to be an important selection mechanism concerning natural food particles. The digestion strategies of Cafeteria on the one hand and Spumella and Ochromonas on the other hand may be an important factor to explain protozoan species composition and succession in the field. In addition to bacterial abundance and grazing pressure by metazooplankton, the bacterial speciescomposition as well as biochemical variations within bacterial species may influence protozoan species composition and abundance.

1. Taxonomic composition and abundance of heterotrophic flagellates (HF) were studied in 55 lakes with different trophy in northern Germany using a live-counting technique. 2. Mean abundances and biomasses of HF ranged from 169 cells L−1 and 22 μg L−1 in mesotrophic lakes to 2439 cells mL–1 and 475 μg L−1 in hypertrophic lakes, respectively. Highest values were generally observed in spring, but mesotrophic lakes showed maximum values in early summer. 3. The taxonomic composition of HF was not significantly influenced by lake trophy and season. The major fraction of HF consisted of chrysomonads and Protista incertae sedis; other important groups were choanoflagellates and bicosoecids. The size distribution of HF changed with lake trophy and season, with a higher proportion of large HF (> 10 μm) in hypertrophic lakes and in spring, respectively. 4. Correlation analyses revealed a strong negative impact of cladocerans on total HF biomass and especially on large HF. Ciliates and large bacteria (> 10 μm) were strongly positively correlated with HF biomass; small bacteria (

A method based on the live-staining (DAPI, FITC, DTAF) of heterotrophic flagellates was developed. These fluorescently labelled flagellates (FLF, different species) were offered as living prey in grazing experiments. The ingested differentially labelled flagellates could easily be identified in food vacuoles of protists by using the epifluorescence microscopy. We tested the method by using a filter-feeding ciliate (Euplotes vannus) and a heterotrophic dinoflagellate (Oxyrrhis marina) as predators of FLF. The food selectivity regarding different species of heterotrophic (Cafeteria, Bodo, Spumella, Oxyrrhis) and autotrophic (Chlamydomonas) flagellates was estimated from food vacuole contents of protists. Both protistan predators showed a preference for large flagellates. Grazing rates of Euplotes and Oxyrrhis on heterotrophic flagellates ranged between 2-53 flagellates per ciliate and hour and 1-31 flagellates and flagellate and hour, respectively. The method was proofed to be very useful for the quantification of trophic interactions among protists using epifluorescence microscopy, it can also be applied for studies by laser scanning microscopy and should be applicable for investigation by flow cytometry.

1. The taxonomic composition, abundance and biomass of heterotrophic protists (ciliates, heterotrophic flagellates (HF), rhizopods and actinopods) in the sediment and water column of shallow inlets of the Southern Baltic was studied under a variety of environmental conditions during 1996-1997. A shallow, highly eutrophic station and a deeper, less eutrophic station were compared. 2. Community biomass ranged from 0.12 to 0.34 μg C cm -3 in the water column and from 1.5 to 105 μg C cm -3 in the sediment. Heterotrophic protists dominated zooplankton biomass at both stations (73% and 84% mean contribution), while they were of minor importance within the zoobenthos. Expressed per unit area, benthic biomass contributed a significant part (44% and 49%) to the total heterotrophic protistan community at both stations. 3. Although the methodology for counting ciliates and HF was focussed on a high taxonomic resolution, the results reveal some general trends in the distribution of heterotrophic protists: protozooplankton biomass was dominated by flagellates (80% mean biomass contribution) at the shallow station and by ciliates (73% mean biomass contribution) at the deep station. In the benthos at both stations, ciliates were the dominant protozoans, followed by the hitherto little-studied rhizopods (25% and 35% mean biomass contribution) and flagellates. 4. The degree of benthic-pelagic coupling differed between taxonomic groups. Benthic and pelagic communities of ciliates showed little taxonomic overlap. In contrast, many heterotrophic flagellate species were found both in the benthos and in the pelagic. These benthic-pelagic species contributed significantly to the biomass of HF in the water column. The planktonic rhizopod community consisted of a subset of those species found in the benthos. 5. The abundance of benthic and pelagic protists was positively correlated at the shallow station, but taxonomic data indicate that the direct exchange between benthic and pelagic communities was only partly responsible.

High resolution video-microscopy was used to observe grazing patterns of the heterotrophic nanoflagellates Cafeteria roenbergensis, Bodo saltans, Spumella sp., and Ochromonas sp. Spumella and Ochromonas enclose food particles with pseudopodia while Cafeteria and Bodo engulf particles by invagination of the cell surface. The following parameters of the feeding process were quantified: frequency of flagellar beating, speed of particles in different positions of the feeding current, food size selection, feeding rate, and the time budget for the handling of particles. The mean handling times differed between 94 s for Cafeteria and 4 s for Ochromonas for ingested particles. Handling times for ingested particles were significantly longer than for non-captured particles. Long handling times were calculated to be disadvantageous only for flagellates which propel a high water volume per hour (esp. Ochromonas) or live in a bacteria-rich environment. Our model calculations may provide a reasonable theoretical explanation for a concentration-dependent behavioural variability of the feeding strategy of different heterotrophic nanoflagellates (HNF) species.

Summary In order to assess the quantitative importance and community structure of benthic rhizopods in brackish lagoons of the southern Baltic Sea, their abundance, biovolume, and taxonomic composition were studied by using a liquid cultivation method. Seasonal dynamics in the superficial sediment of station Bak (Hiddensee Island) were investigated during eleven sampling campaigns between March and November 1996. Additional samples from three sediment layers were taken at two other stations. Rhizopod abundances at station Bak ranged from 2,800-10,900 cells cm-3. A seasonal trend with a summer maximum and minima in early spring and late autumn was observed. 46 morphotypes of rhizopods were found, 27 of which were identified to species. Gymnamoebia and Schizopyrenida always dominated the rhizopod community numerically, whereas testate and naked filose rhizopods sometimes contributed the major part to community biovolume. Typical marine and freshwater rhizopods coexisted in the study area. In addition to bacterivorous forms, high contributions of herbivores and omnivores were found. Our results suggest that the hitherto little-studied rhizopods are a major component of benthic protistan communities of shallow coastal waters. The high contributions of herbivorous and omnivorous forms to the rhizopod community indicate a complex trophic role of rhizopods within the benthic microbial food web.

The structure of a benthic microbial food web and its seasonal changes were studied in the shallow brackish waters of the island of Hiddensee, northeastern Germany, at two sites in close proximity by monthly or bimonthly sampling from July 1995 to June 1996. Abundance and biomass of phototrophic and non-phototrophic bacteria, heterotrophic flagellates (HF) and ciliates as well as the biomass of microphytobenthos were determined in the upper 0.3 cm sediment layer. Abundance of organisms showed strong positive correlation with water temperature, with the exception of the bacteria. Non-phototrophic bacterial numbers ranged from 7 × 108 to 6.7 × 109 cells cm−3 and phototrophic bacterial abundance from 4 × 107 to 2.7 × 108. Heterotrophic protist abundance ranged from 8 × 103 to 104 × 103 ind cm−3 for HF and from 39 to 747 ind cm−3 for ciliates. The biomass partitioning demonstrated the primary importance of non-phototrophic bacteria (min. 0.83, max. 84.87 μg C cm−3), followed by the microphytobenthos (min. 1.32, max. 50.93 μg C cm−3). The heterotrophic protists contributed roughly the same fraction to the total microbial biomass, with the biomass of the HF being slightly higher (HF 0.23 to 1.76 μg C cm−3, ciliates 0.04 to 1.17 μg C cm−3). Taxonomic classification of the benthic HF revealed the euglenids to be the most important group in terms of abundance and biomass, followed by thaumatomastigids and kinetoplastids. Other important groups were apusomonads, cercomonads, pedinellids and cryptomonads. The structure of the HF assemblage showed strong seasonal changes with euglenids being the most abundant taxa in summer, while apusomonads and thaumatomastigids were predominant in winter. Similar to the pelagic microbial food web, benthic picophototrophic bacteria were occasionally abundant, and the feeding modes of heterotrophic protists exhibited a great variety (predominantly omnivores, bacterivores, herbivores or predators). Filter-feeding HF were of little importance. Contrary to the pelagic environment, a top-down control on total benthic bacterial numbers by HF seemed unlikely at the studied stations which were characterised by muddy sand.

Even though bacterivorous flagellates have been recognized as being able to structure the bacterial community, their behavioral basis for food selection is hardly known. We investigated the feeding behavior of the filter-feeding choanoflagellate Monosiga ovata and the raptorial-feeding kinetoplastid flagellate Rhynchomonas nasuta feeding on a bacterial community dominated by Pseudomonas putida and compared it to that of interception-feeding flagellates. M. ovata handles several food particles simultaneously. In contrast, R. nasuta handles only 1 particle at a time. The han- dling time for 1 prey particle is in the range of 3.7 s for R. nasuta but more than 300 s for M. ovata. The speed of food particles within the feeding current of M. ovata was only 9.3 ± 5.7 µm s -1 but due to the large surface of the collar the filtered water volume was 6.4 nl h -1 and therefore comparable to that of interception-feeding flagellates of a similar size. Bacteria ingested by M. ovata were signifi- cantly smaller compared to the bacteria in the medium (p = 0.001). Size selection of food particles occurs during the processing of food items. This is in contrast to raptorial-feeding R. nasuta, which shows passive food size selection for bigger particles during the contact phase. Attachment of bacte- ria proved to be an efficient protection mechanism, defending them from being grazed by flagellates. There are significant species-specific differences in the processing of food particles which explain the coexistence of various bacterivorous nanoflagellates in the size range of 3 to 5 µm and indicate the existence of specific predation pressure on different bacteria.

Spargelpflanzen (Asparagus officinalis L.), die in der Saatzucht Moringen und in der Saatzucht Aschersleben der Sudwestdeutschen Saatzucht Dr. H. R. Spath, Rastatt, zur generativen bzw. vegetativen Vermehrung verwendet werden, wurden auf Virusbefall getestet. Die Testung erfolgte durch mechanische Inokulation von Chenopodium quinoa Willd.‐Pflanzen. Die Ergebnisse zeigten, das sowohl in mehrjahrigen Spargelpflanzen als auch in Spargeljungpflanzen aus der in vitro‐Kultur die relative Viruskonzentration des Spargel‐Virus 1 (asparagus virus 1 potyvius, AV‐1) in Abhangigkeit vom Sprostyp, Zeitpunkt der Testung und Genotyp unterschiedlich war. “Langtriebe”; von Spargeljungpflanzen zeigten geringere relative Viruskonzentrationen und waren haufiger “virusfrei”; als “Kurztriebe”;. Bei Jungpflanzen und mehrjahrigen Spargelpflanzen lag die relative Viruskonzentration im Marz deutlich unter der im Juli. Der Spargelklon 1007 ('Eposs'?) zeigte zu beiden Zeitpunkten eine deutlich hohere relative Viruskonzentration als d...

Summary The trophic role of ciliates in microbial food webs has often been considered to be either bacterivore, herbivore or predatory. In general, single species have been assigned to only one trophic level, although early publications have already pointed to omnivorous feeding in many different groups of ciliates. However, the knowledge on the quantitative aspects of ciliate food preferences is scarce up to now. The aim of this study was to quantify food selectivity with the help of different fluorescently labeled potential prey organisms offered to the omnivorous filter-feeding ciliate Stylonychia mytilus as a model organism. Different fluorescently labeled bacteria (FLB) and algae (FLA), and inert fluorescent particles (FP) were offered in feeding experiments and evaluated with the help of epifluorescence microscopy. In addition, different live-stained fluorescent ciliates (FLCi) were offered as living prey. A vital staining method for obtaining FLCi is described. The results of this study showed a selective ingestion of different ciliates as well as a clear selection between different algae. Bacteria and FP were ingested, but negatively selected. There was a variability in the food preference regarding different-sized cells by Stylonychia mytilus indicating ontogenetic differences in feeding habits. Young daughter cells were not able to ingest the largest prey items. Feeding rates of Stylonychia were highest during the first twenty minutes of the experiments and reached a plateau after 60 min. Capture efficiency for ciliate prey was 70% at the beginning and declined to a value of about 30% after 30 min. Such behavioural patterns may significantly overestimate feeding rates of ciliates determined by short-term experiments. Food concentration was shown to have strong effects on ciliate ingestion rates leading to a clearly detectable functional response. Various factors influencing the feeding behaviour of filter-feeding ciliates and their significance in grazing experiments are discussed.

Auf Grund von Versuchsergebnissen werden Erkenntnisse zur Prufung und Bewertung der Resistenz von Mais (Zea mays L.) gegen das Maisverzwergungsmosaik‐Virus (maize dwarf mosaic potyvirus, MDMV) und das Zuckerrohrmosaik‐Virus (sugarcane mosaic potyvirus, SCMV) mitgeteilt. Die Resistenzprufung von 53 verschiedenen Mais‐Linien erfolgte mit jeweils 25 Pflanzen, die zweimal mit definierten Isolaten beider Viren mechanisch inokuliert wurden. Die Bewertung der Resistenz erfolgte durch die Ermittlung des Befallsgrades (BG), der Symptomstarke (Boniturnoten, BN), des Befallsindex (BI) sowie des Resistenzgrades (RG). Die Inokulationsmethode erwies sich auf Grund der BG anfalliger Linien als zuverlassig. Die Reaktionen der unterschiedlichen Genotypen liesen erkennen, das in dem Zuchtmaterial sowohl absolute oder qualitative als auch relative oder quantitative Virusresistenz vorgelegen hat. Zum erstgenannten Resistenztyp zahlen Pflanzen, die trotz wiederholter Inokulation symptomlos und virusfrei geblieben sind. Dem zw...

The trophic interactions between viruses, bacteria and protists play a crucial role in structuring microbial communities and regulating nutrient and organic matter flux. Here, we show that the impact on viral density by heterotrophic flagellates is related to their feeding behaviour (feeding on sedimented particles - Thaumatomonas coloniensis, filter feeding of suspended particles - Salpingoeca sp., and actively searching raptorial feeding - Goniomonas truncata). Phage MS2 was co-incubated with flagellates and the natural bacterial and viral community originating from the same groundwater habitats where the flagellates were isolated. Three complementary assays, i.e. flow cytometry, qPCR and plaque assay, were used for enumeration of total viruses, total MS2 phages, and free and infectious MS2, respectively, to provide insights into the grazing mechanisms of the flagellates on viruses. Phage MS2 was actively removed by the suspension feeders T. coloniensis and Salpingoeca sp. in contrast with the actively raptoriale grazer G. truncata. The decline of viral titre was demonstrated to be caused by ingestion rather than random absorption by both qPCR and locating protein fluorescently labelled MS2 inside the flagellates. Further, we indicate that phages can be used as a minor carbon source for flagellates. Collectively, these data demonstrate that eliminating viruses can be an important function of protists in microbial food webs, carbon cycling and potentially water quality control.

The polar regions offer the opportunity to study possible diversification processes of spatially and temporally separated populations. We focused our study on similar morphotypes/species (e. g. species with the same morphology) of heterotrophic flagellates and ciliates originating from both, Antarctic and Arctic waters: 38 populations of six choanoflagellate morphospecies (Acanthocorbis unguiculata, Helgoeca nana, Diaphanoeca grandis, Savillea micropora, Stephanoeca apheles, Salpingoeca tuba), four other flagellate morphospecies (Cafeteria roenbergensis, Podomonas magma, Procryptobia sorokini, Protaspis sp.) and three ciliate morphospecies (Holosticha sp., Uronema marinum, Pseudocohnilembus persalinus). We analysed similarities and differences regarding their genotypes (SSU rDNA) and for several species regarding morphotypes and autecology (temperature and salinity tolerance). Most of the investigated polar protists were psychrophilic and showed a high salinity tolerance. Morphologically well defined acanthoecid choanoflagellates isolated from both poles showed the lowest intraspecific diversity (< 0.5% p-distance). No intragenomic polymorphism of SSU rDNA within one individual and among clones from one population occurred. The way of dispersal for acanthoecid choanoflagellates still remains unclear. Even under extreme stress none of the examined cultures formed cysts. Single cell PCR appeared to be an appropriate method to investigate species not available as monoclonal cultures. As a prerequisite for barcoding, acanthoecid choanoflagellate species have a very low intraspecific variability regarding SSU rDNA. There was a clear correlation between autecological, morphological and molecular data sets, which may help interpreting molecular data from clone libraries or next generation sequencing.

Stability and persistence of populations is of great interest for management and conservation purposes. Spatial dynamics can have a crucial role in population stability via synchronization, and beneficial and detrimental effects on population persistence have been shown. Despite a theoretical understanding of synchronization, empirical data on synchrony of populations are restricted to systems that do not display the full spectrum of complex dynamics that may occur in nature (that is, chaos or quasiperiodicity). Here we show in experiments that the qualitative form of dynamic behaviour of chaotic and periodic oscillating communities did not change when unidirectionally coupled to oscillating driver communities. Driver and response populations were phase locked in cyclic communities, whereas chaotic communities showed only short periods of statistical coherencies. Our study provides the first empirical analysis of synchronization of chaotic communities and shows that the likelihood for chaos is not lowered in spatially explicit systems but that cyclic and chaotic systems differ in synchronization. published

The seasonal changes of the abundance and biomass of protozooplankton were investigated by a live-counting technique in the mesoeutrophic Lake Neumuhler See. In addition, the biomass of metazoans and phytoplankton was studied. During the annual cycle, the percentage contribution of the different protozoan groups changed significantly. Ciliates dominated the biomass in late spring, summer and autumn, heterotrophic nanoflagellates (

Knowledge of the spatial scales of diversity is necessary to evaluate the mechanisms driving biodiversity and biogeography in the vast but poorly understood deep sea. The community structure of kinetoplastids, an important group of microbial eukaryotes belonging to the Euglenozoa, from all abyssal plains of the South Atlantic and two areas of the eastern Mediterranean was studied using partial small subunit ribosomal DNA gene clone libraries. A total of 1364 clones from 10 different regions were retrieved. The analysis revealed statistically not distinguishable communities from both the South-East Atlantic (Angola and Guinea Basin) and the South-West Atlantic (Angola and Brazil Basin) at spatial scales of 1000–3000 km, whereas all other communities were significantly differentiated from one another. It seems likely that multiple processes operate at the same time to shape communities of deep-sea kinetoplastids. Nevertheless, constant and homogenous environmental conditions over large spatial scales at abyssal depths, together with high dispersal capabilities of microbial eukaryotes, maintain best the results of statistically indistinguishable communities at larger spatial scales.

Here we present a new approach to quantify food-web interactions within semi-natural biofilms by combining the establishment of biofilms from natural rivers in flow cells with video microscopy. In a first application of this approach, we focused on the surface-gliding heterotrophic flagellates (HF) Neobodo designis, Rhynchomonas nasuta and Planomonas sp. It was shown that the three HF generally ingested single biofilm-associated bacteria whereas bacteria within microcolonies were attacked but not ingested. However, grazing strategies differed considerably. While the kinetoplastids N. designis and R. nasuta displayed long search and short handling times, Planomonas sp. showed the opposite grazing characteristics. The latter behaviour resulted in a high relative predation success of 80% (precent of attacked prey ingested), whereas the relative predation success of the two kinetoplastids was only 20%. However, the two contrasting strategies resulted in similar ingestion rates for Planomonas sp. and N. designis of 0.5 to 0.6 ingestions flagellates(-1) minute(-1), respectively. Our results showed distinct differences in the feeding behaviour of three flagellates having similar life forms and provide direct evidence that microcolony formation in biofilms protects bacteria from grazing by HF in situ. The new approach provides individual-based insights into the complex food web interactions within biofilms.

Cercomonads are important components of microbial food webs in soils and aquatic sediments. Here, we investigated the general morphology, behaviour, life cycle and 18S rDNA phylogeny of cercomonad cultures from a German grassland soil habitat. We describe ten new species including two new genera from 23 strains. Three Cercomonas, two Eocercomonas and three Paracercomonas species are described. Based on large phylogenetic distance and distinct morphology, we erect two novel clade B genera near the root of the cercomonad tree. Nucleocercomonas nov. gen. bears a number of characters unusual for cercomonads: Its anterior flagellum is extremely long, it mostly does not glide, and in its most frequent life stage the cell body does not attach to the substratum, but produces unattached pseudopodia. Furthermore, it has a unique nucleus with a peripheral nucleolus that attaches to the nuclear envelope opposite the basal body connection. Metabolomonas nov. gen. is extremely metabolic. It is characterized by a very high beating frequency of the anterior flagellum, fast gliding, rapid changes in shape and strong cytoplasmic streams. A new genus Brevimastigomonas is erected for the previously described species Paracercomonas anaerobica. The general morphology of cercomonad species often does not correspond with their phylogenetic position: closely related species may have a very different morphology.

This article has been withdrawn.

Microdiaphanosoma arcuatum Wenzel, 1953 is a world-wide distributed ciliate, recorded mainly in soil samples, which we have also identified in ground water samples from South Africa. This ciliate has been frequently overlooked or not determined due to its small size, ∼12 μm. The genus Microdiaphanosoma is nowadays included in the class Colpodea, order Bryometopida, family Kreyellidae. The first complete small subunit (SSU) rDNA gene sequence of this ciliate was obtained from a South African isolate. Phylogenetic analysis including available SSU rDNA sequences from another Colpodea species in the GenBank strongly supported the position of M. arcuatum within the order Cyrtolophosidida instead of the order Bryometopida. The analysis also suggested a sister relationship between this species and species from the family Cyrtolophosididae.

During 1989 and 1990 the carbon dynamics in the shallow eutrophic Lake Muggelsee (Berlin) were investigated by analysing the seasonal succession of phytoplankton, metazooplankton, protozooplankton and bacteria. Size fractionated algal primary production and exudation were measured as well as bacterial production in order to calculate the amount of carbon covering the bacterial carbon demand by primary production. The impact of bacterivorous protozoans and metazoans was estimated by comparison of the calculated feeding rate and the bacterial production. Our results show a shift within the metabolic interactions of the microbial food web from winter/spring to summer, indicating a high significance of the protozooplankton as a regulator on bacteria during the colder season, whereas from early summer the influence of metazooplankton dominated by cladocerans was evident in this eutrophic lake.

Annual changes of rotifers, copepods, cladocerans, the ciliate Epistylis rotans, and larvae of Dreissena polymorpha were analysed for the period 1908–1990. Though food resources increased 6–10 fold in the course of eutrophication, only rotifers and Epistylis increased accordingly. Probably as a result of increased predation pressure crustaceans increased only twice. The seasonal pattern of metazoans and protozoans (flagellates, sarcodines, ciliates) were analysed for 12 and 3 years, resp. During winter and spring, large heterotrophic flagellates and ciliates dominated the zooplankton and were responsible for a pronounced - formerly underestimated - grazing pressure on phytoplankton. In early summer, metazoan filter-feeders were often able to cause a significant reduction of phyto- and protozooplankton. However, during some years, phytoplankton declined in the absence of a pronounced grazing pressure. Field data and experiments revealed that predators were able to regulate the density of cladocerans in early summer (mainly cyclopoids) and summer (mainly Leptodora, smelt and fish juveniles).

We describe three new orders of filosan Cercozoa, five new deep-branching genera, eight new species of Thaumatomonas, Reckertia, Spongomonas, Rhogostoma, Agitata, Neoheteromita and Paracercomonas, sequence their 18S rDNA, and construct 18S rDNA trees for 148 Cercozoa. Our phylogeny indicates that Filosa were ancestrally gliding flagellates; non-flagellate filose amoebae evolved from them five times independently. The new genera are more closely related to environmental DNA sequences than cultured organisms. Tremula longifila, a zooflagellate glider on both flagella (unlike other Cercozoa), is the most divergent filosan (Tremulida ord. n.). Micrometopion nutans is a eukaryote-eating gliding zooflagellate like Metopion and Metromonas. Minimassisteria diva is a widespread trimorphic marine amoeboflagellate granofilosan. Peregrinia clavideferens, a non-testate, scale-bearing, filose amoeba, branches deeply in Thaumatomonadida, which are probably sisters to Spongomonadida. Nudifila producta is a filose amoeboflagellate related to Clautriavia and Marimonadida (ord. n., e.g. Pseudopirsonia, Auranticordis). We substantially revise Imbricatea, now including Spongomonadida, and Thecofilosea to include Phaeodaria. Thecofilosea and Imbricatea and Thecofilosea are sisters, both arguably ancestrally rigid gliding flagellates with ventral pseudopod-emitting grooves. Scale-free Ovulinata parva is sister to Paulinella, so imbricate silica scales can be lost. Internal hollow silica skeletons evolved twice in Thecofilosea (Ebriida, Phaeodaria) or were multiply lost. Protaspa replaces preoccupied ‘Protaspis’.

Eukaryotic microbial life at abyssal depths remains “uncharted territory” in eukaryotic microbiology. No phylogenetic surveys have focused on the largest benthic environment on this planet, the abyssal plains. Moreover, knowledge of the spatial patterns of deep-sea community structure is scanty, and what little is known originates primarily from morphology-based studies of foraminiferans. Here we report on the great phylogenetic diversity of microbial eukaryotic communities of all 3 abyssal plains of the southeastern Atlantic Ocean---the Angola, Cape, and Guinea Abyssal Plains---from depths of 5,000 m. A high percentage of retrieved clones had no close representatives in genetic databases. Many clones were affiliated with parasitic species. Furthermore, differences between the communities of the Cape Abyssal Plain and the other 2 abyssal plains point to environmental gradients apparently shaping community structure at the landscape level. On a regional scale, local species diversity showed much less variation. Our study provides insight into the community composition of microbial eukaryotes on larger scales from the wide abyssal sea floor realm and marks a direction for more detailed future studies aimed at improving our understanding of deep-sea microbes at the community and ecosystem levels, as well as the ecological principles at play.

Diagnostic signature DNA sequences are important tools for the identification of species. There is an active debate in the literature on the choice of the best markers applicable for a broad range of organisms. Protists have seldom been included in these evaluations. Mitochondrial gene sequences are inappropriate for protists since several groups do not possess mitochondria. Here we studied the application of the large subunit (LSU) rRNA gene fragments (D1-D5) regarding their usefulness to discriminate between a wide range of heterotrophic nanoflagellates. Phylogenetic analyses based on the LSU rRNA fragments showed similar results compared to phylogenetic trees based on the small subunit (SSU) rRNA. The data set indicates the power of the use of the D1-D5 region as a marker for a DNA-based taxonomy. Our results, together with the available sequences in Genbank, form a comprehensive database for unicellular eukaryotes, especially heterotrophic flagellates. It is now possible to assign new sequences to the different groups of heterotrophic flagellates which we have tested for different closely related Cercomonas and Paracercomonas strains from groundwater.

Biofilm-dwelling consumer communities play an important role in the matter flux of many aquatic ecosystems. Due to their poor accessibility, little is as yet known about the regulation of natural biofilms. Here, a new type of flow cell is presented which facilitates both experimental manipulation and live observation of natural, pre-grown biofilms. These flow cells were used to study the dynamics of mature ciliate biofilms in response to supplementation of planktonic bacteria. The results suggest that enhanced ciliate productivity could be quickly transferred to micrometazoans (ciliate grazers), making the effects on the standing stock of the ciliates detectable only for a short time. Likewise, no effect on ciliates appeared when micrometazoan consumers were ab initio abundant. This indicates the importance of ‘top-down’ control of natural ciliate biofilms. The flow cells used here offer great potential for experimentally testing such control mechanisms within naturally cultivated biofilms.

Nine countries are in part or entirely situated within the Rhine catchment—namely, Austria, Belgium, France, Germany, Italy, Liechtenstein, Luxemburg, The Netherlands, and Switzerland. The Rhine ranks ninth among the Eurasian rivers. It is the primary artery of one of the most important economic regions of Europe. The human population of the basin equals 58 million, many of them crowded in large urban areas extending along the river between Rotterdam and Basel. The Rhine provides services for transportation, power generation, industrial production, urban sanitation, drinking water for 25 million people, agriculture, and tourism and is a classic example of a multipurpose waterway. It has greatly influenced the history, culture, and economy of Europe over the last 2000 years. On the other hand, its ecological integrity and biodiversity have been severely affected by human activities, particularly in the last 200 years. This chapter provides a general overview of the Rhine basin and subsequently portrays different aspects of the six morphologically distinct river sections that developed during the genesis of the river. These are: (1) The Alpine Rhine (Alpenrhein) and its tributaries; (2) the High Rhine (Hochrhein); (3) the Upper Rhine (Oberrhein); (4) the Middle Rhine (Mittelrhein); (5) the Lower Rhine (Niederrhein); and (6) the Delta Rhine.

Analysing the results of various authors recent studies in the pelagic region of the Baltic revealed that protozoan biomass is in the same range or even higher than metazooplankton biomass. The dominant groups of planktonic protozoans are heterotrophic pico- and nanoflagellates (various taxonomic groups), large heterotrophic flagellates (mainly dinoflagellates) and ciliates. Regularly the spring bloom of phytoplankton is accompanied by a maximum of protozoan biomass which declines in early summer as a result of intensive grazing pressure by metazooplankton and changing food conditions. The analysis of results from different stations indicated that biomasses of protozoans increase with an increasing degree of eutrophication. Several trophic levels within the microbial web should be added to the traditional view on the pelagic food web of the Baltic. Our knowledge regarding the quantitative aspect of the microbial matter flux of the Baltic is very limited up to now and complex ecological (and taxonomical) studies using standardized methods including all protozoan components are necessary. Protozoans (various trophic groups and levels), besides bacteria, should be viewed as the metabolically most active heterotrophic component in the pelagic region of the Baltic, their activity should increase with an increasing degree of eutrophication.

Four experiments covering different seasons were performed to test the impact of increased benthic and planktonic resource availability on the structure of biofilm-dwelling ciliate communities which were cultivated in river bypass systems. The growth of benthic bacteria was stimulated by the addition of dissolved organic carbon. The enrichment of the planktonic resource was achieved by supplementation with suspended bacteria. It was shown that both resource enrichments can differentially influence abundance and taxonomic structure of ciliate communities. Furthermore, both resources can influence different stages during biofilm colonization. Increased benthic bacterial growth mainly resulted in both an accumulation of primarily grazing-resistant bacterial filaments and in an increase in the number of vagile heterotrophic flagellates. This can stimulate nanophagous ciliates (feeding on flagellates) in addition to the direct stimulation of bacteriovorous ciliates. The effects of the planktonic bacteria enrichments were twofold: They could have been utilized either directly by suspension-feeding ciliates or indirectly through an enhanced growth of suspension-feeding attached heterotrophic flagellates, which were then in turn grazed upon by ciliates. The magnitude of responses of the total ciliate abundance to the two resource enrichments further depended on the background conditions, thereby showing temporarily variable limitations of these resources. Furthermore, the particular taxonomic groups stimulated by one resource type sometimes differed between the experiments, an observation which demonstrates that the response depends on different environmental factors and is not easily predictable based simply on resource type. Taken together, our results emphasize the need of a differentiated view on the effects of resources on complex biofilm-dwelling consumer communities with respect to both the origin of carbon source as well as the particular environmental conditions.

The question of whether deterministic chaos occurs in natural populations has been discussed since the 1970s following the discovery that simple population models can generate chaotic dynamics. Natural populations undergo a diverse mixture of deterministic and stochastic processes that define population dynamics. In most habitats populations are also exposed to changes in biotic and abiotic parameters. Models predict that shifts in ecological parameters may lead to a transition between deterministic chaos, stable equilibria, and limit cycles, yet clear examples from empirical studies are rare. However, such transitions should be considered when discussing the occurrence of chaos in nature because ecological time series are in general short and have large sampling intervals. Here we document short-term transitions in population dynamics to and from chaos in an experimental system. Manipulation of only one experimental parameter (chemostat dilution rate) in a multi-species food web of two bacteria and a bacterivorous ciliate showed that switching between different dynamic behaviors occured with surprising rapidity in the microbial populations. Thus, short periods of chaotic dynamics may easily be overlooked in field observations.

The order Thaumatomonadida includes biflagellated heterotrophic flagellates that form filopodia and typically possess siliceous surface scales. We found thaumatomonads to contribute on average about 5%-10% to flagellate abundance in different benthic habitats. A new species of thaumatomonads, Thaumatomonas coloniensis n. sp., is described on the basis of morphological and molecular biological features. This new species was isolated both from groundwater at Appeldorn near Rees (Germany) and from the Rhine River at Cologne (Germany). We have sequenced the small subunit rRNA (ssu rRNA) gene and a fragment of the large subunit rRNA (lsu rRNA) gene (D3-D5 region) from the isolates of the new species, including the first sequence of a representative of the thaumatomonad genus Gyromitus. In agreement with previous studies, the differences in ribosomal genes of different thaumatomonad species are very small. For understanding the phylogenetic relationships of Thaumatomonadida and to explore their sister group relationships, we have created three sequence data sets (ssu rRNA, partial lsu rRNA, concatenated alignment of both) with the same composition of isolates (from Thaumatomonadida, Euglyphida, Cercomonadidae, and Heteromitidae). According to a Kishino-Hasegawa test, Thaumatomonadida evolved within the Cercozoa as a sister taxon to the Heteromitidae. A possibly close relationship to the Euglyphida, recently grouped together with the Thaumatomonadida in the class Imbricatea/Silicofilosea based on the rRNA data sets was not supported by our analyses.

A new species of acanthoecid choanoflagellate isolated from brackish waters of the Danshui estuary in North Taiwan has a mineralized lorica that consists of two chambers with a total length of 19-36microm. It shares with Diplotheca costata the features of a posterior lorica chamber formed from broad and flattened costal strips and an anterior chamber with spatula-shaped costal strips. The new species has therefore been placed in the same genus and named Diplotheca elongata. A phylogenetic analysis of partial SSU rDNA sequences from Diplotheca costata and D. elongata supports this taxonomic affiliation. This is a large and distinctive choanoflagellate which has not been reported in any previous study, suggesting that it may be an endemic species of restricted distribution.

Climate models predict an increasing frequency of extremely hot summer events in the northern hemisphere for the near future. We hypothesised that microbial grazing by the metazoan macrofauna is an interaction that becomes unbalanced at high temperatures due to the different development of the grazing rates of the metazoans and the growth rates of the microbial community with increasing temperature. In order to test this hypothesis, we performed grazing experiments in which we measured the impact of increasing temperatures on the development of the grazing rates of riverine mussels in relation to the growth rates of a unicellular prey community (a natural heterotrophic flagellate community from a large river). In a first experimental series using Corbicula fluminea as a grazer and under the addition of a carbon source (yeast extract), the increase of the prey's growth rates was considerably stronger than that of the predator's grazing rates when temperatures were increased from 19 to over 25 degrees C. This was also the outcome when the mussels had been acclimatized to warm temperatures. Hereafter, specific experiments with natural river water at temperatures of 25 and 30 degrees C were performed. Again, a strong decrease of the mussels' grazing rates in relation to the flagellate growth rates with increasing temperature occurred for two mussel species (C. fluminea and Dreissena polymorpha). When performing the same experiment using a benthic microbial predator community (biofilms dominated by ciliates) instead of the benthic mussels, an increase of the grazing rates relative to the growth rates with temperature could be observed. Our data suggest that predator-prey interactions (between metazoans and microbes) that are balanced at moderate temperatures could become unbalanced at high temperatures. This could have significant effects on the structure and function of microbial communities in light of the predicted increasing frequency of summer heat waves.

Indications of global climate change and associated unusual temperature fluctuations have become increasingly obvious over the past few decades. Consequently, the relevance of temperature increases for ecological communities and for whole ecosystems is one of the major challenges of current ecological research. One approach to investigating the effects of increasing temperatures on communities is the use of fast-growing microbial communities. Here we introduce a river bypass system in which we tested the effect of temperature increases (0, 2, 4, 6 degrees C above the long-term average) on both the colonization speed and the carrying capacity of biofilm-associated ciliate communities under different seasonal scenarios. We further investigated interactions of temperature and resource availability by cross-manipulations in order to test the hypothesis that temperature-mediated effects will be strongest in environments that are not resource-limited. Strong seasonal differences in both tested parameters occurred under natural conditions (no resource addition), and the effects of temperature increase at a given time were relatively low. However, increasing temperature can significantly accelerate the colonization speed and reduce the carrying capacity in particular seasons. These effects were strongest in winter. Simultaneous manipulation of temperature and of resource availability amplified the response to temperature increase, adumbrating strong interactive control of populations by temperature and resource availability. Our results show that the response of communities to local temperature increases strongly depends on the seasonal setting, the resource availability and the stage of succession (early colonization speed vs. carrying capacity).

The role of protozoans in both pelagic and benthic aquatic food webs has received increasing attention by scientists within the last two decades (e.g. Azam et al. 1983, Alongi 1991, Sherr and Sherr 2000). Protozoans are part of a complex food web, in which they conduct several important functions, such as the control of the bacteria (e.g. Berninger et al. 1991, Arndt et al. 2000) and the enhancement of remineralisation processes (Sherr and Sherr 1984). As main bacterial consumers, protozoans can have a high impact on both the taxonomic and morphologic composition of bacterial communities (e.g. Jurgens and Gude 1994, Jurgens et al. 1997). One defence strategy against protozoan predation is the formation of bacterial colonies and filaments (e.g. Jurgens and Gude 1994, Hahn et al. 2001) possibly also forcing the formation of biofilms.

Heterotrophic flagellates (HF) are known as most important grazers of bacteria in many aquatic ecosystem. HF cannot be treated as a black box since HF generally contain a diverse community of species significantly differing in their feeding behaviour and other ecological properties. Today it seems that the dominant taxonomic groups among heterotrophic nano- and microflagellate communities within different marine, brackish and limnetic pelagic communities (heterokont taxa, dinoflagellates, choanoflagellates, kathablepharids) and benthic communities (euglenids, bodonids, thaumatomonads, apusomonads, cercomonads) are relatively similar. HF among protista incertae sedis, often neglected in ecological studies, are abundant bacterivores in all investigated habitats. Recent studies of flagellate feeding processes indicated that there are significant species-specific differences and individual variability regarding the food uptake and food selection of bacterivorous flagellates: Variability of bacterivory is discussed regarding the prevailing feeding modes, the energy budgets, the considerable importance of slight deviations in the time budgets of feeding phases, the ingestion rates and the feeding microhabitat, respectively. The significant flexibility of the grazing impact of bacterivorous flagellate communities creates a complex top-down pressure on bacteria which should have lead to the evolution of efficient predator avoidance mechanisms in bacteria and should be at least partly responsible for the diversity of present bacteria.

Food selectivity and the mechanisms of food selection were analyzed by video microscopy for three species (Spumella, Ochromonas, Cafeteria) of interception-feeding heterotrophic nanoflagellates. The fate of individual prey particles, either live bacteria and/or inert particles, was recorded during the different stages of the particle-flagellate-interaction, which included capture, ingestion, digestion, and egestion. The experiments revealed species-specific differences and new insights into the underlying mechanisms of particle selection by bacterivorous flagellates. When beads and bacteria were offered simultaneously, both particles were ingested unselectively at similar rates. However, the chrysomonads Spumella and Ochromonas egested the inert beads after a vacuole passage time of only 2-3 min, which resulted in an increasing proportion of bacteria in the food vacuoles. Vacuole passage time for starved flagellates was significantly longer compared to that of exponential-phase flagellates for Spumella and Ochromonas. The bicosoecid Cafeteria stored all ingested particles, beads as well as bacteria, in food vacuoles for more then 30 min. Therefore "selective digestion" is one main mechanism responsible for differential processing of prey particles. This selection mechanism may explain some discrepancies of former experiments using inert particles as bacterial surrogates for measuring bacterivory.

Population dynamics and production of a natural population of Brachionus quadridentatus were studied by regular field sampling at a routine station in the shallow Darss-Zingst estuary (3-7%o salinity), Southern Baltic, for two successive years. Investigations included observations of hatched resting eggs, abundance of amictic and mictic females, egg ratio, resting egg production, and mixis rate. Using egg development times from literature, instantaneous rates of growth, birth and death rates were estimated. Mixis rates increased with increasing productivity. The mean P/B value for the growth seasons was 0.89/d and the corresponding production was 9.0 mg wet weight/dm3a. Significant parasitism by microsporidians was observed during one year when up to 12% of the females were infected during June/July. B. quadridentatus served as a food source for the rotifer Asplanchna girodi, the mysid Neomysis integer, and fish juveniles. Copepods could also be considered as predators. However, on an annual basis predators seemed to be of reduced importance and the population dynamics were governed mainly by autoregulative processes.