Abstract
The non-cosmopolitan distribution of viruses creates a potential for invasive species to arise, when non-native organisms invade and spread into new habitats. Ballast water used to maintain a ship's stability is one of the most important vectors for transporting these non-native species to new ecosystems. Relatively little attention has been paid to viral invasions via ships' ballast water compared to macroorganisms due to technical challenges in detecting the wide range of viruses. The goals of our work are to understand the taxonomic diversity and functional potential of the ballast water virome and examine the effect of ballast water on virome structure in local harbor waters using metagenomics. Viral DNA and RNA were simultaneously extracted and amplified for metagenomic sequencing library using Illumina HiSeq 2500 platform.1 This yielded over 550 million paired-end reads of 100 base pairs in length. The viromes of ballast and harbor waters were dominated by double-stranded DNA viruses belonging to three families of bacteriophages (Myo-, Podo-, and Siphoviridae) (84.3%). The rest of the metagenome sequences were distributed across ten viral families, which were composed of one double-stranded RNA viral family (Totiviridae) (0.1%), four single-stranded DNA viral families (Circo-, Gemini-, Micro-, and Parvoviridae) (8.5%), and five single-stranded RNA viral families (Dicistro-, Levivi-, Noda-, Seco-, and Tombusviridae) (5.5%).
The following fish and animal viruses were discovered. The majority of assigned contigs were identified as epizootic haematopoietic necrosis virus (EHNV), a member of the genus Ranavirus in the family Iridoviridae with the type species, Frog Virus 3. EHNV is a large dsDNA virus with broad host and geographic ranges an important cause of mortality in rainbow trout and redfin perch. Viral nervous necrosis virus (VNNV), a member of the genus Betanodavirus in the family Nodaviridae, is a small +ssRNA virus with low host specificity and infects more than 40 species of freshwater and marine fish worldwide. The koi herpesvirus (KHV), a member of the genus Cyprinivirus in the family Alloherpesviridae, was present. KHV is a dsDNA virus with a morphology typical of herpesviruses. It causes a contagious and acute viraemia in common carp (Cyprinus carpio), resulting in explosive losses and in ornamental subspecies, the koi carp. It first appeared in Israel and spread rapidly to other parts of the world, including North America, and has become the most dramatic examples of an emerging disease of fish (Hedrick et al. 2000). One of the ballast water viromes had Macrobrachium rosenbergii nodavirus (MrNV), a member of the genus Alphanodavirus in the family Nodaviridae, the only viral pathogen of shrimp detected in this study, a small +ssRNA virus. It causes white tail disease throughout the world in freshwater shrimp, Macrobrachium rosenbergii, which is the most favored species for farming. More work is needed to understand the viruses of aquatic animals, eventually to prevent potential viral invasions via ships' ballast water.
Acknowledgements
This study was supported by the National Science Foundation, Partnerships for International Research and Education (OISE-0530174). We would like to thank Cordell H. Manz in WDNR for help in sampling ballast water; Qingpeng Zhang at MSU for fruitful discussions on this paper; and John Johnson at MSU, High Performance Computing Center for bioinformatics supports.
* Presenting author
Literature Cited
1. Aw TG, Howe A, Rose JB. Metagenomic approaches for direct and cell culture evaluation of the virological quality of wastewater. J Virol Methods. 2015:in press.