Abstract
BackgroundThe coral is predominantly composed of the metabolically dependent coral host and the photosynthetic dinoflagellate Symbiodinium sp. The system as a whole interacts with symbiotic eukaryotes, bacteria and viruses. Gemmocystiscylindrus (cf. “type-N” symbiont) belonging to the obligatory parasitic phylum Apicomplexa (Alveolata) is ubiquitous in the Caribbean coral, but its presence in the Great Barrier Reef coral has yet to be documented. Approaches allowing identification of the healthy community from the pathogenic or saprobic organisms are needed for sustainable coral reef monitoring.Methods & Principal FindingsWe investigated the diversity of eukaryotes associated with a common reef-building corals from the southern Great Barrier Reef. We used three tag encoded 454 amplicon pyrosequencing assays targeting eukaryote small-subunit rRNA gene to demonstrate the presence of the apicomplexan type-N and a photosynthetic sister species to Apicomplexa - Chromera velia . Amplicon pyrosequencing revealed presence of the small-subunit rRNA genes of known eukaryotic pathogens ( Cryptosporidium and Cryptococcus ). We therefore conducted bacterial tag encoded amplicon pyrosequencing assay for small-subunit rRNA gene to support effluent exposure of the coral. Bacteria of faecal origin (Enterobacteriales) formed 41% of total sequences in contrast to 0-2% of the coral-associated bacterial communities with and without C . velia , respectively.SignificanceThis is the first time apicomplexan type-N has been detected in the Great Barrier Reef. Eukaryote tag encoded amplicon pyrosequencing assays demonstrate presence of apicomplexan type-N and C. Velia in total coral DNA. The data highlight the need for combined approaches for eukaryotic diversity studies coupled with bacterial community assessment to achieve a more realistic goals of defining the holobiont community and assessing coral disease. With increasing evidence of Apicomplexa in coral reef environments, it is important not only to understand the evolution of these organisms but also identify their potential as pathogens.
Highlights
The coral reef is traditionally defined by the cnidarianSymbiodinium symbiosis [1,2]
Whether G. cylindrus is capable of causing disease is yet to be demonstrated, it has been suggested as a contributing factor in White plague lesions of Caribbean coral [8]
Tissue and mucus from coral samples consisting of the outer 3–4 cm of a branch tip were removed from the skeleton with directed air jets of high pressure air supplied using SCUBA, and slurry was preserved in salt-saturated dimethyl sulfoxide (DMSO) conservation buffer as previously described [2]
Summary
The coral reef is traditionally defined by the cnidarianSymbiodinium symbiosis [1,2]. Apicomplexa has been described as a key eukaryotic phylum in essentially all living vertebrate and invertebrate groups, including reef building coral. It comprises highly successful parasites which cause diseases of human (e.g. malaria, Cryptosporidiosis) and veterinary (e.g. coccidiosis) importance and represent a substantial global economic and healthcare burden [5]. The closest extant group to Apicomplexa (represented by photosynthetic alga - Chromera velia) was isolated and cultured from coral species of the southern Great Barrier Reef [6]. We used three tag encoded 454 amplicon pyrosequencing assays targeting eukaryote small-subunit rRNA gene to demonstrate the presence of the apicomplexan type-N and a photosynthetic sister species to Apicomplexa - Chromera velia. With increasing evidence of Apicomplexa in coral reef environments, it is important to understand the evolution of these organisms and identify their potential as pathogens
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