Faculty of Veterinary Science, University of Sydney, Sydney, New South Wales, Australia.
PLoS One. 2013 Sep 30;8(9):e76095. doi: 10.1371/journal.pone.0076095. eCollection 2013.
The 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 FINDINGS: We 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-Chromeravelia. 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.
This 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.
珊瑚主要由代谢依赖的珊瑚宿主和光合作用的甲藻共生体 Symbiodinium sp. 组成。整个系统与共生真核生物、细菌和病毒相互作用。属于专性寄生的 Apicomplexa 门（Alveolata）的 Gemmocystiscylindrus（cf. "type-N" 共生体）在加勒比珊瑚中无处不在，但尚未在大堡礁珊瑚中记录到其存在。为了可持续地监测珊瑚礁，需要从致病性或腐生性生物中识别健康群落的方法。
我们调查了来自大堡礁南部常见造礁珊瑚的相关真核生物多样性。我们使用了三种针对真核生物小亚基 rRNA 基因的标签编码 454 扩增子焦磷酸测序测定法，证明了 Apicomplexa 型-N 和与 Apicomplexa 密切相关的光合姐妹种 Chromeravelia 的存在。扩增子焦磷酸测序揭示了已知真核生物病原体（Cryptosporidium 和 Cryptococcus）的小亚基 rRNA 基因的存在。因此，我们进行了细菌标签编码扩增子焦磷酸测序测定法，以支持珊瑚的污水暴露。粪便来源的细菌（肠杆菌目）形成了总序列的 41%，而与 Chromeravelia 一起或不一起的珊瑚相关细菌群落分别只有 0-2%。
这是首次在大堡礁检测到 Apicomplexa 型-N。真核生物标签编码扩增子焦磷酸测序测定法证明了 Apicomplexa 型-N 和 C. Velia 存在于总珊瑚 DNA 中。这些数据突出表明，需要结合真核生物多样性研究和细菌群落评估的方法，以实现更真实地定义整个共生体群落和评估珊瑚疾病的目标。随着 Apicomplexa 在珊瑚礁环境中越来越多的证据，不仅要了解这些生物的进化，还要确定它们作为病原体的潜力。
