In situ identification and localization of bacteria associated with Gyrodinium instriatum (Gymnodiniales,Dinophyceae) by electron and confocal microscopy |
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Authors: | Elsa Alverca Isabelle Biegala Gabrielle Kennaway Jane Lewis Susana Franca |
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Affiliation: | 1. LME, Instituto Nacional de SauU de Dr Ricardo Jorge, Av. Padre Cruz, 1649-016 Lisbon codex, Portugal;2. Station Biologique de Roscoff, CNRS UPR 9042, Université Pierre et Marie Curie, Place Georges Teissier, BP 74, 29682 Roscoff Cedex, France;3. Phytosciences Research Group, School of Biosciences, University of Westminster, 115 New Cavendish Street, London W1M 8JS, UK |
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Abstract: | The presence of intracellular bacteria in the dinoflagellate Gyrodinium instriatum Freudenthal & Lee has previously been described but the bacterial flora associated with this species has not been characterized. In this study, new results of transmission electron microscopy (TEM) and in situ hybridization using several bacterial group-specific oligonucleotide probes are presented. The long-term association of endocytoplasmic and endonuclear bacteria with G. instriatum has been confirmed. All endonuclear and most of the endocytoplasmic bacteria labelled were identified as belonging to the betaproteobacteria. Large clusters of Cytophaga-Flavobacterium-Bacteroides (CFB) were labelled and observed in the cytoplasm of the dinoflagellate cells, but were absent from the nucleus. Gammaproteobacteria were only observed outside the dinoflagellates. No alphaproteobacteria were detected either free-living or intracellular. Empirical observation of intracellular CFB reflected a degradation process of moribund dinoflagellate cells, whereas the systematic colonization of dinoflagellate nucleoplasm by betaproteobacteria suggested a true symbiotic relationship. Natural colonization may have occurred, perpetuated by vertical transmission of intracellular bacteria to the dinoflagellate daughter cells, via a pool of bacteria sequestered within the nucleus. Dividing bacteria were observed in the nucleus and equilibrium may be maintained by release of endonuclear bacteria to the cytoplasm through nuclear envelope constrictions. |
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Keywords: | confocal microscopy dinoflagellates Gyrodinium instriatum in situ hybridization intracellular bacteria oligonucleotide probes TEM ultrastructure |
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