Morphological diversity of virus-like particles within the surface microlayer of scleractinian corals

Abstract

Transmission electron microscopy was employed to determine the morphological diversity of virus-like particles (VLPs) associated with the coral surface microlayer (CSM) of Acropora muricata and Porites spp. from the Great Barrier Reef, Australia. VLPs were assigned to one of 17 sub-groups within 5 major morphological groups including tailed bacteriophages, polyhedral, filamentous and lemon-shaped VLPs. Polyhedral VLPs in the 30 to 60 nm size class dominated the CSM of A. muricata and Porites spp., comprising 29.4 and 26.9 % of total VLPs, respectively. Tailed bacteriophages comprised <6 % of total VLPs within the CSM of both A. muricata and Porites spp. Filamentous VLPs (FVLPs) of varying lengths and widths accounted for up to 19.9 % of total CSM VLPs, with no significant difference between the CSM samples and overlying water. Unique VLPs, which could not be classified into any known viral morphological group, accounted for 1.2 to 11.7 % of total VLPs within the CSM and were absent from overlying water. While some exchange of VLPs likely occurred between the CSM and overlying water, our results suggest that the majority of CSM morphotypes were specific to the CSM micro-niche. The similarity of many of these VLPs to previously described viruses suggests that a range of potential hosts exist in the CSM, including bacteria, archaea, cyanobacteria, fungi, algae (possibly including zooxanthellae) and the coral animal. Research on coral-microbial interactions and their role in coral health and functioning is in its infancy and the present study provides important information on the largely unstudied viral component of the coral microbiota. © Inter-Research 2007.