The role of viruses in coral health and disease

Abstract

Metagenomic and electron microscopy studies confirm that the coral microbiome contains a rich diversity and abundance of viruses. While there have been no definitive tests of disease causation by viruses in corals, viruses have been implicated as coral pathogens in a number of studies. Growing evidence also indicates that latent viral infections can compromise the algal symbionts under environmental stress and may be involved in the coral bleaching response. Conversely, bacteriophages and archaeal phage viruses are abundant in the microbiome of healthy corals and are likely to be involved in complex ecological networks, genetic material transfer and selective co-evolution within the surface mucus layers and tissues. The relative importance of viral control of bacterial and archaeal populations is unknown, but they are almost certain to be exerting some level of control on the composition and maintenance of the coral microbiome. While rapid leaps in the capability to detect viruses have been made due to advances in metagenomics and bioinformatics, these approaches need now to be integrated with in vitro culture and challenge experiments to assess the functional roles of viruses in health and disease, and it is imperative that interactions with other members of the coral microbiome are taken into account when assessing disease causation.

Sequence analysis of malacoherpesvirus proteins: Pan-herpesvirus capsid module and replication enzymes with an ancient connection to “Megavirales”

“…Putative herpesvirus-like isolated from other aquatic Metazoa, such as two species of stony corals and wild-caught Hydra sp., have been reported (Vega Thurber et al, 2008;Grasis et al, 2014;Correa et al, 2016). Caution has been advised in interpreting these results (Houldcroft and Breuer, 2015;Wood-Charlson et al, 2015;Sweet and Bythell, 2016), and our reanalysis of the three publicly available short sequences from these studies annotated as fragments of anthozoan herpesvirus DNA suggests that they are in fact of bacterial and fungal provenance (Additional File 6). The existence of herpesviruses of coelenterates is nevertheless likely, given that particles with herpesvirus-like morphology have been observed in coral Acropora (Correa et al, 2016).…”

Increased Algal Symbiont Density Reduces Host Immunity in a Threatened Caribbean Coral Species, Orbicella faveolata

“…Toll-like receptor signaling, inflammation, and antiviral responses comprise a large portion of the innate immune responses of scleractinian corals (Mydlarz et al, 2016). Furthermore, these three pathways play important roles in defense against the three major types of cnidarian pathogen: bacterial (Libro et al, 2013;Libro and Vollmer, 2016;Brennan et al, 2017), fungal (Mydlarz et al, 2008), and viral (Soffer et al, 2014;Sweet and Bythell, 2017). O. faveolata has a complete TLR-NF-kB signaling pathway which is responsive to bacterial LPS (Williams et al, 2018); inflammation plays a role in response of the octocoral Gorgonia ventilina to Aspergillus sydowii (Mydlarz et al, 2008) and in the response of Acropora cervicornis to white band disease (Libro et al, 2013;Libro and Vollmer, 2016); antiviral responses may also be an important component of A. cervicornis response to white band disease (Libro and Vollmer, 2016).…”

Corals and Their Microbiomes Are Differentially Affected by Exposure to Elevated Nutrients and a Natural Thermal Anomaly

“…These phages are crucial in shaping the coral microbiome and controlling microbial populations. Phages serve as a lytic barrier against potential pathogens (Sweet and Bythell, 2017) and have been described as non-host-derived immunity (Barr et al, 2013). The viral order Caudivirales has consistently been found in coral viromes (Wood-Charlson et al, 2015;Vega Thurber et al, 2017;Weynberg et al, 2017), with its top three families being Siphoviridae, Podoviridae, and Myoviridae.…”