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Research into causative agents underlying coral disease have focused primarily on bacteria, whereas potential roles of viruses have been largely unaddressed. Bacteriophages may contribute to diseases through the lysogenic introduction of virulence genes into bacteria, or prevent diseases through lysis of bacterial pathogens. To identify candidate phages that may influence the pathogenicity of black band disease (BBD), communities of bacteria (16S rRNA) and T4-bacteriophages (gp23) were simultaneously profiled with amplicon sequencing among BBD-lesions and healthy-coral-tissue of Montipora hispida, as well as seawater (study site: the central Great Barrier Reef). Bacterial community compositions were distinct among BBD-lesions, healthy coral tissue and seawater samples, as observed in previous studies. Surprisingly, however, viral beta diversities based on both operational taxonomic unit (OTU)-compositions and overall viral community compositions of assigned taxa did not differ statistically between the BBD-lesions and healthy coral tissue. Nonetheless, relative abundances of three bacteriophage OTUs, affiliated to Cyanophage PRSM6 and Prochlorococcus phages P-SSM2, were significantly higher in BBD-lesions than in healthy tissue. These OTUs associated with BBD samples suggest the presence of bacteriophages that infect members of the cyanobacteria-dominated BBD community, and thus have potential roles in BBD pathogenicity., (© 2018 Society for Applied Microbiology and John Wiley & Sons Ltd.)

Recent metagenomic analyses have revealed a high diversity of viruses in the pelagic ocean and uncovered clear habitat-specific viral distribution patterns. Conversely, similar insights into the composition, host specificity and function of viruses associated with marine organisms have been limited by challenges associated with sampling and computational analysis. Here, we performed targeted viromic analysis of six coral reef invertebrate species and their surrounding seawater to deliver taxonomic and functional profiles of viruses associated with reef organisms. Sponges and corals' host species-specific viral assemblages with low sequence identity to known viral genomes. While core viral genes involved in capsid formation, tail structure and infection mechanisms were observed across all reef samples, auxiliary genes including those involved in herbicide resistance and viral pathogenesis pathways such as host immune suppression were differentially enriched in reef hosts. Utilising a novel OTU based assessment, we also show a prevalence of dsDNA viruses belonging to the Mimiviridae, Caudovirales and Phycodnaviridae in reef environments and further highlight the abundance of ssDNA viruses belonging to the Circoviridae, Parvoviridae, Bidnaviridae and Microviridae in reef invertebrates. These insights into coral reef viruses provide an important framework for future research into how viruses contribute to the health and evolution of reef organisms., (© 2018 Commonwealth of Australia. Environmental Microbiology © 2018 Society for Applied Microbiology and John Wiley & Sons Ltd.)

Reef-building corals form close associations with organisms from all three domains of life and therefore have many potential viral hosts. Yet knowledge of viral communities associated with corals is barely explored. This complexity presents a number of challenges in terms of the metagenomic assessments of coral viral communities and requires specialized methods for purification and amplification of viral nucleic acids, as well as virome annotation. In this minireview, we conduct a meta-analysis of the limited number of existing coral virome studies, as well as available coral transcriptome and metagenome data, to identify trends and potential complications inherent in different methods. The analysis shows that the method used for viral nucleic acid isolation drastically affects the observed viral assemblage and interpretation of the results. Further, the small number of viral reference genomes available, coupled with short sequence read lengths might cause errors in virus identification. Despite these limitations and potential biases, the data show that viral communities associated with corals are diverse, with double- and single-stranded DNA and RNA viruses. The identified viruses are dominated by double-stranded DNA-tailed bacteriophages, but there are also viruses that infect eukaryote hosts, likely the endosymbiotic dinoflagellates, Symbiodinium spp., host coral and other eukaryotes in close association., (© 2015 The Authors. Environmental Microbiology published by Society for Applied Microbiology and John Wiley & Sons Ltd.)

Recognition is an important stage in the establishment of highly specific mutualistic associations. Yet, for the majority of symbioses, very few of the mechanisms involved in recognition and specificity are known. In this study, we provide evidence for a recognition mechanism at the onset of symbiosis between larvae of the coral Fungia scutaria and their endosymbiotic dinoflagellate algae. This recognition step occurs during initial cellular contact between the symbiotic partners through a lectin/glycan interaction. We determined that an intact algal cell surface was required for successful infection of F. scutaria larvae. Modification of the algal cell surface by enzymatic digestion with trypsin or N-glycosidase significantly reduced infection success, and implicated algal cell surface glycans in recognition. Using flow cytometry, alpha-mannose/alpha-glucose and alpha-galactose residues were identified as potential recognition ligands on the algal cell surface. Finally, inhibition of these cell surface glycans significantly reduced infection of F. scutaria larvae by the algae. These data provide evidence that the algal cell surface contains glycan ligands, such as alpha-mannose/alpha-glucose and alpha-galactose, which play a role in recognition during initial contact at the onset of symbiosis with F. scutaria larvae.