First assessment of viral diversity across corals from the central Red Sea suggests abundant association with Baculoviridae

Abstract

Coral reefs are among the most diverse marine ecosystems, but they are threatened by climate change. The foundation of reef ecosystems is the coral holobiont or metaorganism that consists of the coral animal host, photosynthetic microalgae, bacteria, and viruses (among other organisms). While microalgae provide the energy for corals to build the massive three-dimensional skeletons, bacteria support functions related to metabolism, immunity, and environmental adaptation. Conversely, the function of viruses is less well understood. Although viruses were previously associated with coral disease and bleaching, we are missing an overall understanding of the diversity and identity of viruses associated with corals, in particular for understudied areas such as the Red Sea. Here we characterized coral-associated viral community composition using a large metagenomic and metatransciptomic dataset covering > 1 billion sequences across > 100 coral samples collected from 14 different coral species in the central Red Sea. The viral sequence portion shows that coral species significantly differ from each other, but the most abundant viral families were consistently present. Notably, we found a pervasive abundance of Baculoviridae in metagenomes. In contrast, Polydnaviridae were the most abundant viruses in metatranscriptomes, highlighting that the combined approach of metagenomics and metatranscriptomics is informative with regard to deciphering viral diversity and activity. Our study provides a first comprehensive description of viruses associated with Red Sea corals. In line with previous studies, we confirm the presence of Baculoviridae, Polydnaviridae, Phycodnaviridae, Mimiviridae, and Herpesviridae, which may be considered viral families that are globally and commonly associated with corals. The reason for the pervasive abundance of Baculoviridae in Red Sea corals at present remains unknown, but it is tempting to speculate that the association is related to the uniquely warm and salty environment of the Red Sea.