Seminar Details

Using nanoscale imaging technologies to understand differential susceptibility to coral bacterial infection

Date

03/05/2017

Lecturers

Dr. Emma Gibbin - Laboratory for Biological Geochemistry, Ecole Polytechnique Fédérale de Lausanne, Switzerland

Abstract

Reef-building corals form complex relationships with photosynthesizing dinoflagellates (Symbiodinium sp.) and a consortia of microbial partners. Collectively known as the coral holobiont, the complex signaling and metabolic interactions that occur between the different partners enables corals to thrive in the oligotrophic waters of the tropics. Exposure to above-average seawater temperatures disrupts these relationships and thus, the metabolic interactions that sustain the holobiont, resulting in the expulsion of Symbiodinium and/or the manifestation of disease. Over the past decade, there has been an increase in the prevalence and severity of both episodic bleaching and disease outbreaks. It is perhaps unsurprising that thermally-stressed corals are more susceptible to disease, but it is not clear whether this is due to increased virulence of microbial pathogens or a reduction in the immune response of the coral host. We use the association between Pocillopora damicornis and Vibrio coralliilyticus as a model to address this knowledge gap. A paired experimental design was implemented whereby infected (INF) P. damicornis fragments inoculated with 15N-labeled, DsRed-tagged V. coralliilyticus for two hours, were paired with non-infected, control (CON) fragments. Both INF and CON fragments were exposed to isotopically H13CO3--labeled seawater and photosynthesis-saturating light levels during the experiment. The progression of the infection was monitored in real time using the “Coral-on-a-Chip” microfluidic system. When clear symptoms of disease (the development of lesions, biofilms and/or tissue necrosis) were observed, the experiment was quenched and the samples fixed. Post-fixation, samples were embedded in resin, sectioned and prepared for Nanoscale Secondary Ion Mass Spectrometry (NanoSIMS) imaging, which enabled us to track simultaneously the photosynthetically fixed H13CO3- in the symbiont dinoflagellates and the presence of 15N-labeled pathogens in the coral tissue. In this talk, I will present high-resolution images of the infection process, from the initial innoculation of the coral to the colonization of tissue and the development of disease symptoms, while simultaneously quantifying the reduction in photosynthetic performance of the symbiont dinoflagellates as infection progresses.

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