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Proteomic response of Stylophora pistillata endosymbionts to moderate ‘bleaching’ stress

We present the proteomic response of Symbiodinium sp. endosymbionts from the coral Stylophora pistillata of the central Great Barrier Reef to moderate conditions of thermal 'bleaching' stress, with and without trace metal limitation. Using quantitative high throughput proteomics, we identified 8098 MS/MS events relating to individual peptides from the endosymbiont-enriched fraction. These included 109 peptides meeting stringent criteria for quantification of which only 26 showed significant change in our experimental treatments ; 12/26 increased expression in response to thermal stress with little difference affected by iron limitation. Surprisingly, there were no significant increase in antioxidant or heat stress proteins ; those induced to higher expression were generally involved in protein biosynthesis. An outstanding exception was a massive 114-fold increase of a viral replication protein indicating that thermal stress may substantially increase viral load and thereby contribute to the aetiology of coral bleaching and disease. In the absence of a sequenced genome for Symbiodinium or other dinoflagellates, this proteome reveals a plethora of proteins potentially involved in microbial-host interactions. This includes photosystem proteins, DNA repair enzymes, antioxidant enzymes, metabolic redox enzymes, heat shock proteins, globin hemoproteins, proteins of nitrogen fixation and metabolism, and a wide range of viral proteins associated with these endosymbiont-enriched samples. Also present were 21 unusual peptide/protein toxins thought to originate from either microbial consorts or contamination by coral nematocysts. Of particular interest are the proteins of apoptosis, vesicular transport and endo/exocytosis, which we shall discuss in the context with processes of coral bleaching.

Coral Stylophora pistillata; proteomic response of Symbiodinium sp. endosymbionts; thermal 'bleaching' stress; quantitative high throughput proteomics

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