Variation in virome diversity in wild populations of Penaeus monodon (Fabricius 1798) with emphasis on pathogenic viruses.

Marine animals typically harbor a community of viruses, a number of which are known to cause diseases. In shrimp aquaculture, viral pathogens are the principal causes of major economic losses. However, the composition of the viral load of shrimps in wild population is poorly known. In this study, we explored the viral diversity in the microbiome of wild Penaeus monodon collected from six sites in the Philippines, with a view to detecting pathogenic forms. We employed a metagenomic approach via particle-associated nucleic acid isolation, sequence-independent single primer amplification, and pyrosequencing. Virome analysis of shrimp samples from different sites revealed distinct virome profiles, and hence significant differences in diversity, among the various sites based on number of OTUs, Shannon-Weaver Index, and Inverse Simpson Index. Sequences of key shrimp pathogens were detected such as the white spot syndrome virus (WSSV), and Penaeus stylirostris densovirus (PstDV). However, the patterns of distribution of the pathogenic viruses varied; whereas WSSV was found only in three out of six sites and PstDV were found in all but one site. The results also revealed shrimp-associated viruses that have not yet been observed in P. monodon such as avian virus-like, insect virus-like, plankton virus-like and bacteriophage-like sequences. Despite the diverse array of viruses detected in the study, a large proportion remains unidentified (i.e., similarity to sequences in the database was lower than the threshold required for definitive identification), and therefore could represent unexplored virus sequences and viral genomes in the environment.