Metagenomic Identification of a Nodavirus and a Circular Ssdna
Total Page：16
File Type：pdf, Size：1020Kb
Vol. 105: 237–242, 2013 DISEASES OF AQUATIC ORGANISMS Published September 3 doi: 10.3354/dao02628 Dis Aquat Org FREEREE ACCESSCCESS Metagenomic identification of a nodavirus and a circular ssDNA virus in semi-purified viral nucleic acids from the hepatopancreas of healthy Farfantepenaeus duorarum shrimp Terry Fei Fan Ng1,6,*, Shankar Alavandi2, Arvind Varsani3,4,5, Scott Burghart1, Mya Breitbart1,* 1University of South Florida, College of Marine Science, St. Petersburg, Florida, USA 2Central Institute of Brackishwater Aquaculture, #75, Santhome High Road, RA Puram, Chennai, India 3School of Biological Sciences, University of Canterbury, Christchurch 8140, New Zealand 4Biomolecular Interaction Centre, University of Canterbury, Christchurch 8140, New Zealand 5Electron Microscope Unit, Division of Medical Biochemistry, Department of Clinical Laboratory Sciences, University of Cape Town, Observatory 7700, South Africa 6Present address: Blood Systems Research Institute, San Francisco, California, USA ABSTRACT: Fisheries and aquaculture are impacted sporadically by newly emerged viral dis- eases. In most cases, searches for a causative pathogen only occur after a serious disease has emerged. As random shotgun sequencing (metagenomics) offers opportunities to identify novel viruses preemptively, the method was tested on nucleic acids extracted from the hepatopancreas of 12 healthy northern pink shrimp Farfantepenaeus duorarum captured from the Gulf of Mexico. Among the sequences, a nodavirus (Farfantepenaeus duorarum nodavirus, FdNV) and a virus with similarities to circoviruses and cycloviruses that possess circular single-stranded DNA (ssDNA) genomes, were identified. The FdNV genome sequence was most closely related phylo- genetically to nodaviruses causing white tail disease in Macrobrachium rosenbergii and muscle necrosis disease in Litopenaeus vannamei. While the circular ssDNA virus represents the third to be detected in association with a marine invertebrate, transmission trials are needed to confirm its infectivity for F. duorarum. This study highlights the potential for using metagenomic approaches in fisheries and aquaculture industries to identify new potential pathogens in asymptomatic mar- ine invertebrates, uncharacterized pathogens causing a new disease, or multiple pathogens asso- ciated with disease syndromes. KEY WORDS: Fisheries · Pathogen discovery · Metagenomics · Nodavirus · Circovirus Resale or republication not permitted without written consent of the publisher INTRODUCTION However, aquaculture worldwide has become in - creasingly susceptible to new diseases due mainly to In 2010, global aquaculture of over 600 species movement of live animals, the increased use of high- including finfish, crustaceans, and mollusks pro- density farming systems, and increasing anthro- duced approximately 60 million tons of seafood with pogenic pressures on aquatic ecosystems (FAO 2011). an estimated value of US $119 billion (FAO 2011). With tropical shrimp aquaculture, it has been esti- *Corresponding authors. © Inter-Research 2013 · www.int-res.com Emails: [email protected], [email protected] 238 Dis Aquat Org 105: 237–242, 2013 mated that up to 40% of annual production (>$3 bil- MATERIALS AND METHODS lion) is currently being lost, mainly due to viral dis- eases (Stentiford et al. 2012). Overtly healthy juvenile Farfantepenaeus duo- Although emerging diseases often cause sub - rarum (6−8 g) caught near Tarpon Springs, Florida, stantial economic losses, little effort is generally USA, in the Gulf of Mexico, were transported to the expended on preemptively identifying potential laboratory in aerated buckets. Hepatopancreas tissue pathogens before they cause a problem to aqua- dissected aseptically from 12 shrimp was pooled and culture. This delays development of molecular homogenized in sterile SM buffer (50 mM Tris, 10 mM diagnostic tests for identifying pathogen reservoirs MgSO4, 0.1 M NaCl, pH 7.5) using a Tissumizer (Tek- and vectors, host and geographic ranges, modes mar). Virus particles were purified from filtered of transmission, and genetic relatedness to other homogenate as described previously (Breitbart & pathogens, impeding our understanding of disease Rohwer 2005, Ng et al. 2011a, 2012). Briefly, homo - epidemiology and ability to minimize disease im - genate was clarified by centrifugation at 10 000 × g pacts (Walker & Winton 2010). The reactive (10 min), filtered through a 0.22 µm filter, mixed with approach also neglects the fact that many potential 0.2 volume chloroform for 10 min, and then incu- pathogens have evolved to coexist in symbiosis bated with 2.5 U DNase I and 0.25 U RNase A per µl with particular hosts, with transition to disease at 37°C for 3 h. DNA and RNA were extracted from states only occurring after some ecological imbal- purified material using the Qiagen DNeasy Blood & ance promoted by environmental or anthropogenic Tissue Kit and RNeasy Mini Kit, respectively. factors (Walker & Winton 2010). Understanding RNA and DNA were sequenced using cDNA syn- which potential pathogens exist naturally in com- thesis, DNA amplification, cloning, and sequencing mercially important species would thus assist pre- methods described previously (Breitbart & Rohwer paredness for preventing or managing disease 2005, Ng et al. 2011a). Briefly, DNA was amplified us- should a pathogen emerge as a problem. ing Phi29 DNA polymerase (Geno miphi, GE Health- Various methods are available for identifying and care), fragmented and amplified again using a Whole characterizing novel microorganisms. Metagenomic Genome Amplification kit (Sigma-Aldrich). RNA was sequencing of nucleic acids extracted from fluids or converted to cDNA and amplified by PCR using a tissue homogenates filtered or enriched to concen- TransPlex Whole Transcriptome Amplification kit trate and semi-purify virus particles has proved use- (Sigma-Aldrich). Randomly amplified DNA libraries ful in identifying genome sequences of novel viruses were cloned into a TOPO TA vector (Invitrogen) and in humans and various domestic and wild animals transformed into competent cells. Inserts in 50 to 130 (Breitbart et al. 2002, Allander et al. 2005, Delwart clones from the DNA and RNA libraries were ampli- 2007, Victoria et al. 2008, Ng et al. 2009, 2011a,b, fied by PCR using M13 primers, and amplicons >150 bp 2012, Svraka et al. 2010). Once sequence data are were Sanger sequenced, trimmed, and assembled into available, options abound to develop sensitive, spe- contigs applying a match size = 35, minimum match cific, and rapid molecular tests for virus diagnosis percentage = 95% using the SeqMan Pro-assembler and epidemiology. (DNASTAR). Singlets and assembled contigs were Due to the wild shrimp fishery in southern parts of compared to sequences in the GenBank non-redun- the Gulf of Mexico showing signs of being depleted, dant database using BLASTX (Altschul et al. 1990, aquaculture of northern pink shrimp Farfantepe- 1997), leading to the identification of a circovirus-like naeus duorarum has become increasingly important DNA sequence and a nodavirus-like RNA sequence. to the economy of the region (Arreguin-Sanchez et To generate a complete circovirus-like genome se - al. 2008). To avoid disease impacts, pathogen-free quence by inverse PCR (Ng et al. 2009, 2011a), DNA breeding stocks of F. duorarum have also been was amplified randomly using Phi29 DNA poly- sought to support the industry (Samocha et al. 2008). merase (TempliPhi, GE Healthcare) before PCR for To investigate whether viruses might exist in healthy 45 cycles employing the outward facing primers F. duorarum indigenous to the Gulf of Mexico that 5’124-TGA CAT TGG GAT ACC ACT GG143-3’ and could pose a potential risk to aquaculture, random 5’126-TCA AGG ATA CTG CTG CCA TG107-3’. The shotgun sequencing was undertaken on extracts of ~2 kb DNA amplified by PCR was cloned and Sanger hepatopancreas tissue. This led to the identification sequenced by primer walking. of a new nodavirus and a virus with similarities to Amino acid sequences of the circovirus-like repli- circoviruses and cycloviruses that possess circular cation initiator protein (Rep) and nodavirus capsid single-stranded DNA (ssDNA) genomes. protein (Cap) were aligned to various homologues Ng et al.: Metagenomic sequencing of shrimp viruses 239 using MUSCLE (Edgar 2004) with manual editing. lap et al. 2013). Due to their prevalence in the envi- The multiple alignments were used to infer maxi- ronment, it is not unexpected that circular ssDNA mum-likelihood phylogenetic trees using PHYML viruses should be found associated with marine Version 3.0 (Guindon et al. 2010) with approximate organisms. Since the hepatopancreas is a digestive likelihood-ratio test (aLRT) branch support (Anisi- organ of shrimp, and semi-purified viral DNA ex - mova & Gascuel 2006) and an LG model of substitu- tracted from the hepatopancreas tissue was ampli- tion. Mesquite (version 2.75) was used to collapse fied using Phi29 DNA polymerase followed by ran- branches with <60% aLRT branch support. dom PCR, it cannot be discounted that ShrimpCDV represents an ingested environmental contaminant resilient to degradation by the shrimp digestive sys- RESULTS AND DISCUSSION tem. To gain more knowledge regarding the host of ShrimpCDV, molecular screening of wild Farfante- Virus particles were partially purified from a penaeus duorarum needs to be undertaken to verify homo genate of hepatopancreas tissue from 12 wild the presence of this virus in shrimp tissues exclusive Far