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Marine diatoms and dinoflagellates play a variety of key ecosystem roles as important primary producers (diatoms and some dinoflagellates) and grazers (some dinoflagellates). Additionally some are harmful algal bloom (HAB) species and there is widespread concern that HAB species may be increasing accompanied by major negative socio-economic impacts, including threats to human health and marine harvesting1, 2. Using 92,263 samples from the Continuous Plankton Recorder survey, we generated a 50-year (1960–2009) time series of diatom and dinoflagellate occurrence in the northeast Atlantic and North Sea. Dinoflagellates, including both HAB taxa (for example, Prorocentrum spp.) and non-HAB taxa (for example, Ceratium furca), have declined in abundance, particularly since 2006. In contrast, diatom abundance has not shown this decline with some common diatoms, including both HAB (for example, Pseudo-nitzschia spp.) and non-HAB (for example, Thalassiosira spp.) taxa, increasing in abundance. Overall these changes have led to a marked increase in the relative abundance of diatoms versus dinoflagellates. Our analyses, including Granger tests to identify criteria of causality, indicate that this switch is driven by an interaction effect of both increasing sea surface temperatures combined with increasingly windy conditions in summer.

Crustaceans worldwide are infected with alveolate parasites of the genus Hematodinium, causing substantial losses to langoustine and crab fisheries. The distinct seasonality in Hematodinium occurrence in their decapod hosts, as well as unsuccessful attempts at transmission, suggest the existence of life stages outside their benthic crustacean hosts. We used a nested polymerase chain reaction method to detect Hematodinium rDNA in the environment and in potential alternative hosts. Environmental samples from the Clyde Sea, Scotland, were screened during the April release of dinospores and during June and August, when infection prevalence is rare in benthic crustaceans. Hematodinium rDNA was amplified in 15% (14/94) of isolated langoustine larvae, and in 12% (13/111) of crab larvae. In addition, Hematodinium rDNA was present in mixed plankton samples devoid of decapod larvae, but including the 2 μm–10 mm fraction of particulate organic matter in the water column, containing phytoplankton and other zooplankton. These results indicate that Hematodinium occurs in the water column and is harboured by planktonic organisms, including larval stages of the crustacean hosts, when infections are at their lowest in adult hosts.

Predatory protists use chemical recognition to increase feeding efficiency by responding to point sources of prey chemoattractants and through adhering to the cell surface of their prey. In respons ...

International audience; The heterotrophic marine flagellate Oxyrrhis marina, is a popular and tractable model organism, being common in the intertidal environment and relatively straight forward to maintain in the laboratory. In this report, based on our experience of collecting and culturing ~400 isolates, we provide a quantification of how 'easy' O. marina is to locate and isolate from the environment and subsequently maintain in culture. In addition, we provide a brief review of the literature pertaining to O. marina culturing, stressing in particular the broad physiological tolerance and wide diet range of this organism. Finally, in light of the increasing interest in the genetics and genomics of O. marina, and heterotrophic protists more generally, we highlight existing strategies for culturing heterotrophs for '-omic' applications, and summarise our specific culturing approaches, for genomic and proteomic studies of O. marina. In this context, we outline a simplified version of Droop's medium for axenic culturing and offer details on the use of heat-killed Escherichia coli as a simple and robust food source for culturing O. marina in the absence of other eukaryotes and live prokaryotes.

Many "model" protists are maintained in culture and used, experimentally, to answer questions associated with planktonic processes. Given the current interest and rapidly increasing amount of literature on the heterotrophic dinoflagellate Oxyrrhis marina, we present in this special issue a series of focused, interlinked research articles. Being written by experts in their respective fields, the authors have included unpublished data and in all cases have offered a synthesis of data and ideas. Furthermore, we have encouraged cross-paper discourse, emphasizing the interdisciplinary nature of our work and the utility of O. marina to this end; we also offer guidance, both practical and intellectual, on how future research related to O. marina might progress. In this introduction, however, we raise the wider issue of which criteria are required to consider a taxon as a "model species". We then assess the extent to which O. marina can fill this role. In general, we recognize O. marina as a model in three distinct disciplines: ecology, evolution/genomics and biogeography. Of possibly greater importance, we recognize that if O. marina continues to be studied at an escalating rate, there will be a concomitant increase in realized and potential synergies across these fields. © The Author 2010. Published by Oxford University Press. All rights reserved.

Microzooplankton are ecologically important grazers of phytoplankton and bacteria in aquatic systems. Inhabiting a three-dimensional realm, the ability of a microzooplankter to detect and respond to infochemical cues from its prey will confer a strong selective advantage. The heterotrophic dinoflagellate Oxyrrhis marina has been repeatedly used to study the effect of infochemicals on foraging success and the results from such investigations have stimulated further research on other microzooplankton. Here, we present a case study that highlights the utility of O. marina for infochemistry research and review current knowledge on its behavioural response to dissolved infochemicals. Through a series of microcapillary assays, we show that 0.1–100 µM source concentrations of the algal secondary metabolite dimethylsulphoniopropionate elicit a motile chemosensory response in O. marina. We outline some of the technical limitations in infochemistry research and provide examples where studies on O. marina resulted in recent progress, before emphasizing the role of the diffusion limited boundary layer or “phycosphere” in chemodetection. The ability of O. marina to detect prey exudates in the phycosphere effectively increases the predator–prey encounter radius and has significant implications to the outcome of encounter rate models. Finally, we introduce a new direction of research that utilizes O. marina as a model microzooplankter to elucidate the function of infochemicals in multi-trophic interactions.

A model was developed to explore patterns of carbon flow through the pelagic food web of Lake Fryxell, Taylor Valley, Antarctica. The goals of this study were to quantify patterns of carbon flow and test hypotheses of top-down versus bottom-up controls on this system. The model included seven trophic groups: bacteria, photosynthetic nanoflagellates (PNAN), heterotrophic nanoflagellates (HNAN), ciliates (bacterial feeding and flagellate feeding), phytoplankton and rotifers (the top predator); all inputs were driven by predatory demands. This system has no insects, vertebrates, crustacea or allochthonous inputs from terrestrial plants. Autotrophs and bacteria contributed ca. 94% of total community biomass, with all other heterotrophic organisms representing

Pony Lake is a saline and hypereutrophic coastal pond located on Cape Royds in the McMurdo Sound area in Antarctica. Previous studies have shown that Pony Lake typically has high concentrations of dissolved organic carbon (DOC) concentrations (e.g., 9.2 mM) associated with dense blooms of a chlorophyte, Chlamydomonas intermedia Chodat. We studied different classes of dissolved organic material (DOM) isolated from Pony Lake on two dates that bracketed the transition from ice-covered to ice-free conditions. We used tangential flow ultrafiltration followed by XAD column chromatography to isolate fulvic acids and transphilic acids in three molecular size ranges. The small and large size fractions (passing through a 10,000-amu filter and being retained by a 100,000-amu filter, respectively) accounted for most of the total DOM and fulvic acid pools, whereas most of the transphilic acid was in the small size fraction. Measurement of molecular weight using high-pressure size exclusion chromatography (HPSEC) showed that the fulvic acid and transphilic acid in the medium and large size fractions had molecular weights corresponding to a range of 1260–1470 amu, and those in the small size fraction had molecular weights of about 1000 amu. The 13C nuclear magnetic resonance (NMR) spectra of both the fulvic and transphilic acids showed a predominance of aliphatic and carbohydrate carbons and were similar among size fractions and between the two dates. Although a large decrease in the DOC concentration occurred during the transition to ice-free conditions (from 7.7 to 2.7 mM), the changes in the DOM fractionation were relatively small. The percentage of the DOM accounted for by transphilic acid increased from 11% to 18%, and the peak in the HPSEC chromatograms corresponding to the smaller molecular weight range decreased for all fulvic acid and transphilic acid fractions. The nitrogen content of all fulvic acid and transphilic acid fractions decreased significantly during the transition and the δ15N values became heavier for all fractions. The only discernible change in the 13C NMR spectra of all the fractions was a decrease in a peak in the region corresponding to amide carbons. These results suggest that preferential loss of N-containing molecules of fulvic acid and transphilic acids occurred in association with the considerable loss of DOM in midsummer.

1. Temporal and spatial variation in planktonic abundance, biomass and composition were determined in Lake Hoare (McMurdo Dry Valleys, Antarctica) over two summer seasons (1996–97 and 1997–98). 2. Phototrophic nanoflagellates (PNAN) dominated planktonic biomass, with a mean monthly biomass ranging between 27.3 and 40.4 lg C L)1. The deep chlorophyll maximum was mainly composed of cryptophytes (>87% of total PNAN biomass) and varied in depth between 6 and 12 m. 3. Maximum bacterial concentration was 11.8 · 105 cells mL)1. Bacterial abundance showed relatively little temporal variation, with the exception of a drop in numbers that occurred in late November of both years studied. 4. Ciliates were the most successful heterotrophic protozoan group, with a mean monthly biomass (1.2–3.2 lg C L)1) being typically at least double that of heterotrophic nanoflagellate (HNAN) biomass (0.1–0.7 lg C L)1). 5. Microbial processes within this lake appear to be dominated by bottom up control. The relative importance of allochthonous inputs into the lake (from the ice-cover and stream flow) and autochthonous recycling (by microzooplankton regeneration) are considered. 6. Results from a horizontal transect indicate that the permanence of the main sample hole may have enhanced planktonic biomass over a relatively small spatial scale.

Plankton abundance and biomass were investigated in five lakes of the McMurdo Dry Valleys, Antarctica: Lakes Bonney, Fryxell, Joyce, Hoare and Miers. Despite plankton communities being dominated by organisms

Nitrate loading to coastal waters has increased over recent decades while silicon loading has remained relatively constant or decreased. As the N:Si ratio in coastal waters shifts due to these anthropogenic influences, silicate limitation of diatom biomass may become a feature of the biogeochemistry in coastal waters especially in regions of reduced exchange. Two sets of nutrient enrichment mesocosm experiments were conducted in successive years using a natural planktonic assemblage obtained from the Trondheimsfjord, Norway. The inorganic nutrient concentrations at the start of the experiments were manipulated to give a variety of N:Si concentrations at ratios representative of current and possible future values, should N loading continue. In June 1999 experiments were conducted with a gradient of inorganic N:Si ratios (1:2, 1:1, 2:1, 4:1) to investigate the influence of low and high N:Si ratio conditions and to determine the conditions that would generate Si limitation of diatom growth. In June 2000, based on 1999 data, highly replicated experiments were conducted at N:Si ratios of 1:1 and 4:1 which were expected to result in N and Si limitation of diatom growth, respectively; statistical differences in cellular composition were recorded. N limitation of diatom biomass increase was observed under the three lowest N:Si ratios: particulate carbon (C) accumulation continued to occur following N exhaustion resulting in an increase in the organic C:N ratio. Silicate limitation of diatom biomass increase only occurred at the highest N:Si ratio of 4:1. Silicate exhaustion was followed by continued nitrate uptake for several days, at a slower rate than previously. The resulting increase in organic N was accompanied by an increase in organic C such that the C:N ratio of the organic material at the highest N:Si ratio failed to increase to the extent observed under the N limited conditions. Statistically significant differences in chlorophyll-a yield per unit nitrate, C:chlorophyll-a ratios, C:N ratio and diatom cell yield per unit nitrate or Si were observed in Si compared to N limited conditions. All mesocosms became dominated numerically and in terms of biomass by the diatom Skeletonema costatum. The potential implications of changing N and Si regimes in coastal waters are discussed.

In order to study the effect of the nitrogen:silicon (N:Si) ratio on temperate microplankton food webs, mesocosm experiments were conducted in Trondheim (Norway) using two different ratios (molar ratios of 1:1 and 4:1). With the exception of diatoms, the increase in abundance of all microbial groups [phototrophic nanoflagellates, autotrophic dinflagellates, bacteria, heterotrophic nanoflagellates (HNAN), heterotrophic microflagellates and ciliates] was significantly greater in the high N:Si treatment. Midway through the experiment, HNAN biovolume exceeded that of bacteria in the high N:Si treatment, indicating strong top-down grazing control. Heterotrophic microflagellate biovolume exceeded ciliate biovolume under both nutrient regimes. However, heterotrophic plankton failed to respond rapidly to increased diatom biomass. The heterotrophic:autotrophic biovolume ratio remained

Nutrient manipulation experiments were conducted on a natural planktonic community in outdoor mesocosms. Inorganic nitrogen (N) and silicon (Si) were added to achieve N[ratio ]Si ratios of 1[ratio ]1 and 4[ratio ]1. Total particulate carbon (PC) biomass of the microbial assemblage was determined by elemental analysis. Cell volume measurements by microscope on individual components of the community (bacteria, diatoms, photosynthetic nanoflagellates, heterotrophic nanoflagellates, dinoflagellates and ciliates) were also made. We applied published C[ratio ]volume relationships to determine the volume estimated C content (CBV) of these microbial groups and hence of the total assemblage. The total CBV and total PC were compared to test the applicability of C[ratio ]volume relationships under different nutrient regimes both before and after nutrient exhaustion. For initial N[ratio ]Si ratios of 1[ratio ]1, prior to nutrient exhaustion, the relationship between CBV and PC was linear with a gradient of approximately 1, (0.99±0.06), indicating that the published C[ratio ]volume relationships accurately predicted the C content of the microbial assemblage. For N[ratio ]Si ratios of 4[ratio ]1, a linear relationship was again evident between CBV and PC (slope: 1.36±0.08). However, statistical comparison using a general linear model indicated that the gradient of this relationship differed significantly from that when the N[ratio ]Si ratio was 1[ratio ]1, and hence CBV overestimated elemental C. For both N[ratio ]Si ratios, subsequent to nutrient exhaustion (N or Si), and hence when the diatom fraction of the microbial assemblage was in yield-limited post-exponential phase, the two measures of biomass were not well correlated. This indicated that measured cytoplasmic cell volume was a poor indicator of C biomass within the microbial assemblage in nutrient-deplete conditions.

1. Lake Fryxell, situated in the McMurdo Dry Valleys, Antarctica, offers the opportunity to study microbial loop processes in the absence of crustacean zooplankton and other higher organisms. This is the first study of Lake Fryxell to provide detailed temporal and vertical variations of microbial loop organisms. 2. Protozoan communities are concentrated around the chemocline (9–10 m) in Lake Fryxell. Phototrophic nanoflagellates (PNAN), heterotrophic nanoflagellates (HNAN) and ciliates formed deep maxima of 14 580, 694 and 58 cells mL−1 respectively. Although abundance and biomass at the chemocline was high, diversity of protozoa was low, Plagiocampa accounting for> 80% of the total ciliate biomass. 3. In the mixolimnion (4.5–8 m), protozoa were less abundant, but more diverse, with 24 ciliate morphotypes being identified within this region of the water column. Inter-annual variability of protozoan biomass and abundance was greater in the mixolimnion than at the chemocline due to more variable nutrient and prey concentrations. 4. Physicochemical gradients in Lake Fryxell were very stable because the perennial ice cover reduced wind driven currents. As a consequence, ciliate species occurred in distinct depth strata, Monodinium being most abundant directly beneath the ice cover, Askenasia having maximum abundance at 8 m and Plagiocampa dominating ciliate biomass at the chemocline. The lack of vertical mixing reduced seasonal successions of PNAN and ciliate species. Three cryptophyte species dominated the PNAN community at all times (>79% of total biomass).

Results are presented from a study into the effects of scuba diving on water column structure in perennially ice-covered Lake Fryxell, Antarctica. General theoretical predictions are compared with results, which assess potential impacts from diving activities on water quality parameters related to disruptions to water column stability and dissolved gas concentrations. Potential mechanisms of water column disturbance are considered including: (1) mixing due to diver motion, (2) mixing by diver-exhaled bubble plumes and (3) changes of water column gas concentrations due to dissolution of diver-exhaled gases. Data (temperature, dissolved oxygen, specific conductance, pH, dissolved organic carbon, salinity) were collected from two control holes and one dive hole immediately before and 2.5 d after dive activities. Variability in measured parameters did not differ significantly between sampling sites either before or after diving; and differences between control holes and dive hole observations, on a depth-by-depth basis, were within the range of expected statistical fluctuations. Pre- and post-dive virus-like particle, bacterial, ciliate, photo- and heterotrophic flagellate densities also did not differ significantly. An apparent lack of long-term trends indicative of water column destabilization over the past 18 ys of diving is discussed, along with recent evidence for deep mixing in this lake. Although all potentially affected parameters have not been considered, theoretical model results and an analysis of field data suggest that diving impacts on physicochemical properties and microbial distributions in a closed-basin, ice-covered lake occur at spatiotemporal scales other than those considered in this study.

1. The ingestion rates of planktonic, mixotrophic cryptophytes in two perennially ice-covered Antarctic lakes in the McMurdo Dry Valleys, were investigated during the summer of 1997–1998. 2. In Lake Fryxell, which is meromictic, ingestion rates increased with depth in November and were highest in a cryptophyte maximum close to the chemocline. In Lake Hoare, which is unstratified and freshwater, there was no significant difference in ingestion rates with depth. In both lakes, the highest ingestion rates occurred in early summer, decreasing in December and January. Ingestion rates varied between 0.2 bacteria cell−1 h−1 and 3.6 bacteria cell−1 h−1. 3. During November, mixotrophic cryptophytes removed up to 13% of bacterial biomass day−1 and had a greater grazing impact than heterotrophic nanoflagellates (HNAN). As summer progressed, the grazing impact of cryptophytes and HNAN became similar. 4. The maximum depth of cryptophytes in Lake Fryxell was predated by a population of the ciliate Plagiocampa. Plagiocampa had an ingestion rate of 0.13–0.19 cryptophytes cell−1 h−1. The grazing impact on the cryptophyte community was insignificant. However, the ciliate appeared to be indulging in temporary mixotrophy, sequestering the cryptophytes for a number of weeks before digesting them. 5. It is suggested that mixotrophy is an important survival strategy in the extreme lake ecosystems of the McMurdo Dry Valleys.

It is timely to evaluate the role of protozoa as model organisms given their diversity, abundance and versatility as well as the economic and ethical pressures placed on animal-based experimentation. We first define the term model organism and then examine through examples why protozoa make good models. Our examples reflect major issues including evolution, ecology, population and community biology, disease, the role of organelles, ageing, space travel, toxicity and teaching. We conclude by recognising that although protozoa may in some cases not completely mimic tissue- or whole-animal-level processes, they are extremely flexible and their use should be embraced. Finally, we offer advice on obtaining emergent model protozoa.

Crustaceans worldwide are infected with alveolate parasites of the genus Hematodinium, causing substantial losses to langoustine and crab fisheries. The distinct seasonality in Hematodinium occurrence in their decapod hosts, as well as unsuccessful attempts at transmission, suggest the existence of life stages outside their benthic crustacean hosts. We used a nested polymerase chain reaction method to detect Hematodinium rDNA in the environment and in potential alternative hosts. Environmental samples from the Clyde Sea, Scotland, were screened during the April release of dinospores and during June and August, when infection prevalence is rare in benthic crustaceans. Hematodinium rDNA was amplified in 15% (14/94) of isolated langoustine larvae, and in 12% (13/111) of crab larvae. In addition, Hematodinium rDNA was present in mixed plankton samples devoid of decapod larvae, but including the 2 μm-10 mm fraction of particulate organic matter in the water column, containing phytoplankton and other zooplankton. These results indicate that Hematodinium occurs in the water column and is harboured by planktonic organisms, including larval stages of the crustacean hosts, when infections are at their lowest in adult hosts.

This study was conducted to determine if exposure of shrimp, Litopenaeus vannamei, to a commercial anti-vibrio vaccine caused changes in antibacterial and cellular (phagocytosis) defences. Shrimp post-larvae were administered either Vibromax™ vaccine or a blank preparation. Whole body homogenates were prepared before (day 0), during (day 10) and after (day 20) vaccination and incubated with a selection of pathogenic vibrios. Homogenate from day 0 animals showed natural antibacterial activity towards Vibrio anguillarum which was significantly enhanced for bacteria-exposed shrimp at 10 days post-challenge. This effect of the vaccine was short-term in its duration. No antibacterial activity was observed in day 0 shrimp homogenate against Vibrio alginolyticus but it was significantly enhanced for both vaccinated and blank-vaccinated shrimp by day 10. No natural or inducible antibacterial activity was observed against Vibrio harveyi at 0, 10 or 20 days post-challenge. To determine if prior exposure of shrimp to inactivated vibrios results in elevated hemocyte phagocytic activity, juveniles were injected with either a mixture of formalin-inactivated vibrios or saline. Hemocyte monolayers made from these shrimp were overlaid with a 1:1 mix of Bacillus subtilis and these vibrios. Hemocytes from vibrio-exposed animals showed elevated levels of internalised vibrios compared with those from the saline injected group. These studies show selectively enhanced cellular defences of shrimp following ‘vaccination’.

It has long been viewed that invertebrates rely exclusively upon a wide variety of innate mechanisms for protection from disease and parasite invasion and lack any specific acquired immune mechanisms comparable to those of vertebrates. Recent findings, however, suggest certain invertebrates may be able to mount some form of specific immunity, termed ‘specific immune priming’, although the mechanism of this is not fully understood (see Textbox S1). In our initial experiments, either formalin-inactivated Vibrio harveyi or sterile saline were injected into the main body cavity (haemocoel) of juvenile shrimp (Litopenaeus vannamei). Haemocytes (blood cells) from V. harveyi-injected shrimp were collected 7 days later and incubated with a 1∶1 mix of V. harveyi and an unrelated Gram positive bacterium, Bacillus subtilis. Haemocytes from ‘vaccinated’ shrimp showed elevated levels of phagocytosis of V. harveyi, but not B. subtilis, compared with those from saline-injected (non-immunised) animals. The increased phagocytic activity was characterised by a significant increase in the percentage of phagocytic cells. When shrimp were injected with B. subtilis rather than vibrio, there was no significant increase in the phagocytic activity of haemocytes from these animals in comparison to the non-immunised (saline injected) controls. Whole haemolymph (blood) from either ‘immunised’ or non-immunised’ shrimp was shown to display innate humoral antibacterial activity against V. harveyi that was absent against B. subtilis. However, there was no difference in the potency of antibacterial activity between V. harveyi-injected shrimp and control (saline injected) animals showing that ‘vaccination’ has no effect on this component of the shrimp's immune system. These results imply that the cellular immune system of shrimp, particularly phagocytosis, is capable of a degree of specificity and shows the phenomenon of ‘immune priming’ reported by other workers. However, in agreement with other studies, this phenomenon is not universal to all potential pathogens.

International audience; Protists are major consumers of phytoplankton and bacterioplankton in the marine environment, playing a key role in carbon cycling and nutrient regeneration. Consequently, the feeding activities of planktonic protists have been intensively studied. In particular, the dinoflagellate, Oxyrrhis marina, has been used extensively as a model predator in laboratory-based feeding studies. This is predominately because it is easy to culture and manipulate but also because its plasticity in feeding behaviour allows it to represent a broad range of free-living heterotrophic protists. Prey preferences of this versatile, but selective, predator have been well documented. However, our ability to determine the factors driving prey selectivity is limited by a poor understanding of the detailed mechanisms underlying O. marina feeding. Within this study, we explore known aspects of O. marina feeding behaviour and highlight areas that require further research to exploit this species as an effective model protist predator.

We examine the literature on Oxyrrhis marina cell and life cycles, population growthand production. We then provide an overview of what is known regarding aspectsof O. marina growth, indicate where information is needed and suggest ways inwhich this species can and cannot be used as a general model, in this respect.Little is known about the O. marina life cycle; it is even unknown if cells arehaploid, diploid or polyploid, although there is one report that sex occurs byhomothallic isogamy. There is considerable information on the cell cycle, whichwe briefly review and provide a guide to the literature for details. We brieflydiscuss and provide guidance to information on: (i) population cell size distri-butions; (ii) cannibalism; (iii) our first report of “mini-cells” in cultures ( 8 mm)and their possible role in the life cycle; (iv) cysts, and their possible role in the lifeand cell cycles; (v) biotic influences on growth, such as food type and abundance,assimilation efficiency, prey stiochiometry, strain differences, population growthand starvation and nutritional shifts; (vi) abiotic factors that affect growth, such astemperature, salinity, pH, light and turbulence. We then reflect on the conse-quences of interactions between the above factors and review data on populationgrowth of O. marina in the field and laboratory. Finally, we evaluate the use ofO. marina as a model organism to examine cell and life cycles and ecological pro-cesses. Throughout the paper, we suggest areas that need evaluation.KEYWORDS: model organism; dinoflagellate; protozoa; life history; Oxyrrhis

Marine goniomonads have a worldwide distribution but ultrastructural information has not been available so far. An isolate of the heterotrophic marine nanoflagellate Goniomonas (G. aff. amphinema) from North Wales (UK) has been studied, providing information on its morphology and cellular structure using video, electron, laser scanning confocal microscopy (LSCM), and atomic force microscopy. Here, we describe a new feature, a granular area, potentially involved in particle capture and feeding. The binding of the lectin wheat germ agglutinin to the granular area of cells with discharged ejectisomes indicates the adhesive nature of this novel feature. The presence of a microtubular intracellular cytopharynx, apparently also used for feeding, has been revealed by LSCM. The small subunit rRNA gene of the isolate has been sequenced (1,788 bp). Phylogenetic results corroborate significant genetic divergence within the marine members of Goniomonas. This work highlights the need for integrated morphological, ultrastructural, and molecular investigation when describing and studying heterotrophic nanoflagellates.

Phagotrophic protists are diverse and abundant in aquatic and terrestrial environments, making them fundamental to the transfer of matter/energy within their respective food webs. Recognising their grazing impact is essential to evaluate the role of protists in ecosystems, and this includes appreciating prey selectivity. Efforts have been made by groups and individuals to understand selective grazing behaviour by protists: many approaches and perspectives have been pursued, not all of which are compatible. This article, which is not a review, is the product of our discourse on this subject at the SAME 10 meeting. It is the work of individuals, assembled for their breadth of backgrounds, approaches, views, and expertise. Firstly, to communicate ideas and approaches, we develop a framework for selective feeding processes and suggest 6 steps: searching, contact, capture, processing, ingestion, digestion. We then separate study approaches into 2 categories: (1) those examining whole organisms at the community, population, and individual levels, and (2) those examining physiology and molecular attributes. Finally, we explore general problems associated with the field of protistan selective feeding (e.g. linking food selection into food webs and modeling). We do not present all views on any one topic, nor do we cover all topics; instead, we offer opinions and suggest avenues for continued study. Overall, this paper should stimulate further discourse on the subject and provide a roadmap for the future.

The application of Lucilia sericata larvae to chronic, infected wounds results in the rapid elimination of infecting microorganisms, including MRSA. Previously, we demonstrated in vitro antibacterial activity of native excretions/secretions (nES) from L. sericata and partially purified two low mass antibacterial compounds with masses of 0.5-10kDa and

Planktonic flagellates and ciliates are the major consumers of phytoplankton and bacterioplankton in aquatic environments, playing a pivotal role in carbon cycling and nutrient regeneration. Despite certain unicellular predators using chemosensory responses to locate and select their prey, the biochemical mechanisms behind prey reception and selection have not been elucidated. Here we identify a Ca(2+)-dependent, mannose-binding lectin on the marine dinoflagellate Oxyrrhis marina, which is used as a feeding receptor for recognizing prey. Blocking the receptor using 20 microM mannose-BSA inhibited ingestion of phytoplankton prey, Isochrysis galbana, by 60%. In prey selection studies, O. marina ingested twice as many 6 mum diameter beads coated with mannose-BSA as those coated with galNac-BSA. When pre-incubated with mannose-BSA, O. marina was no longer able to discriminate between different sugar-coated beads. Thus, these findings reveal molecular mechanisms of protozoan prey recognition. Our results also indicate the functional similarity between cellular recognition used by planktonic protozoa to discriminate between different prey items, and those used by metazoan phagocytic blood cells to recognize invading microorganisms.

Carbohydrate-protein interactions appear to play an important role in the phagocytosis of microbial prey by free-living protozoa. The present study utilizes FITC-labelled plant lectins to investigate the presence and localization of cell surface glycoconjugates on live and fixed planktonic protists (Dunaliella primolecta, Oxyrrhis marina, Goniomonas amphinema, Paraphysomonas vestita and Euplotes vannus). With live flagellate preparations, lectins primarily bound to external cell surfaces, with minimal internal staining observed. In contrast, cell fixation permeabilized cell membranes, allowing lectins to bind to internal structures, such as nuclear membranes and food vacuoles, interfering with the characterization of cell surface glycoconjugates. The method developed to label cell surface sugar moieties of live planktonic protists successfully overcomes the problems associated with fixation, and thus provides a useful protocol for future studies on protistan cell surface carbohydrate characterization.

Laboratory experiments were conducted to study nitrogen (N) regeneration by the heterotrophic marine dinoflagellate Oxyrrhis marina when ingesting phytoplankton prey of two different species and of two alternative carbon:nitrogen (C:N) ratios. Experiments were conducted in the presence of l-methionine sulfoximine (MSX) which acts as a glutamine synthetase inhibitor. Utilisation by phytoplankton of N regenerated by protozoans and other organisms drives secondary production in marine food webs. However, the rapid utilisation of this N by phytoplankton has previously hampered accurate assessment of the efficiency of protozoan N regeneration. This phenomenon is particularly problematic when the phytoplankton are nutrient stressed and most likely to rapidly utilise N. The use of MSX prevented significant utilisation by phytoplankton of protozoan regenerated N. Hence, by removing the normal pathway of N cycling, we were able to determine the N regeneration efficiency (NRE) of the protozoan. The results suggested that predator NRE could be explained in terms of the relative CN stoichiometry of prey and predator. Using a mathematical model we demonstrated that changing the method used to simulate the NRE of the protozoan trophic level has the potential to markedly modify the predicted dynamics of the simulated microbial food web.

Colin Reynolds’ distinguished career began 42 years ago, when, as an undergraduate, he started work on nuisance algae in London reservoirs. Since the publication of his first book, The Ecology of Freshwater Phytoplankton, in 1984 [1], our understanding of planktonic organisms has increased substantially. Indeed, Reynolds acknowledges that many of the assumptions made in his first book no longer hold true. For example, researchers now recognise the crucial role that microbes have in aquatic ecosystems.