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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 Being written by experts in their respective fields, the authors have included unpublished data and in all cases have offered a synthesis of data and ideas.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.

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

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.