Abstract
The diversity of viruses is influenced by evolutionary mechanisms such as recombination, altered selection pressures associated with host switching and high mutation rates. Small circular viruses, such as nanoviruses of plants and circoviruses of animals, are rapidly evolving viruses that present the opportunity to study these mechanisms. It has been suggested previously that animal circoviruses originated from plant nanoviruses that developed the ability to infect animal hosts1 and are causally associated with immunosuppression in several animal species. We characterized seven small circular ssDNA genomes (TtCV1-TtCV7) amplified from bottlenose dolphin (Tursiops truncatus) skin scrape samples using rolling circle amplification and PCR techniques. The seven TtCV genomes ranged from 1,799 to 1,890 bp in length and showed a wide arrangement of genome organizations, varying in the number and orientation of the open reading frames (ORFs). A consistent feature across the genomes was the presence of a major ORF encoding a putative replicase gene with 32 to 35% homology with the replicase protein of either plant nanoviruses or avian circoviruses, depending on the genome. Bayesian phylogenetic analysis of the replicase gene grouped TtCVs with nanoviruses and circoviruses, further supporting the hypothesis of these viral families sharing a common ancestor. Additionally, recombination signals were detected in three of the TtCV genomes. These results highlight the high diversity of circular ssDNA viral genomes found in bottlenose dolphins and may shed light on important aspects of the evolutionary processes of animal circoviruses. The clinical significance of these viruses remains to be determined.
Acknowledgements
This work was funded by research grant N° N00014-06-1-0250 from the Office of Naval Research to H.N. and research contract N° N66001-08-D-0070 from the Department of Defense to Dr. Pamela Yochem (Hubbs-SeaWorld Research Institute). All sample collection protocols were approved by the University of Florida Institutional Animal Care and Use Committee (IACUC# C233). The authors would like to thank Dr. P. Yochem for her support on this project, including comments on the abstract and presentation. We would also like to thank Jennifer Burchell and Celeste Benham for their assistance in the laboratory.
Reference
1. Gibbs MJ, Weiller GF. 1999. Evidence that a plant virus switched hosts to infect a vertebrate and then recombined with a vertebrate-infecting virus. Proc Natl Acad Sci U.S.A. 96:8022-8027.