An ssDNA virus infecting archaea: a new lineage of viruses with a membrane envelope

Authors

  • Maija K. Pietilä,

    1. Institute of Biotechnology and Department of Biological and Environmental Sciences, Viikinkaari 5, 00014 University of Helsinki, Helsinki, Finland.
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  • Elina Roine,

    Corresponding author
    1. Institute of Biotechnology and Department of Biological and Environmental Sciences, Viikinkaari 5, 00014 University of Helsinki, Helsinki, Finland.
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  • Lars Paulin,

    1. Institute of Biotechnology, DNA Sequencing and Genomics Laboratory, Viikinkaari 4, 00014 University of Helsinki, Helsinki, Finland.
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  • Nisse Kalkkinen,

    1. Institute of Biotechnology, Protein Chemistry Research Group, Viikinkaari 1, 00014 University of Helsinki, Finland.
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  • Dennis H. Bamford

    1. Institute of Biotechnology and Department of Biological and Environmental Sciences, Viikinkaari 5, 00014 University of Helsinki, Helsinki, Finland.
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*E-mail elina.roine@helsinki.fi; Tel. (+358) 9 191 590102; Fax (+358) 9 191 590098.

Summary

Archaeal organisms are generally known as diverse extremophiles, but they play a crucial role also in moderate environments. So far, only about 50 archaeal viruses have been described in some detail. Despite this, unusual viral morphotypes within this group have been reported. Interestingly, all isolated archaeal viruses have a double-stranded DNA (dsDNA) genome. To further characterize the diversity of archaeal viruses, we screened highly saline water samples for archaea and their viruses. Here, we describe a new haloarchaeal virus, Halorubrum pleomorphic virus 1 (HRPV-1) that was isolated from a solar saltern and infects an indigenous host belonging to the genus Halorubrum. Infection does not cause cell lysis, but slightly retards growth of the host and results in high replication of the virus. The sequenced genome (7048 nucleotides) of HRPV-1 is single-stranded DNA (ssDNA), which makes HRPV-1 the first characterized archaeal virus that does not have a dsDNA genome. In spite of this, similarities to another archaeal virus were observed. Two major structural proteins were recognized in protein analyses, and by lipid analyses it was shown that the virion contains a membrane. Electron microscopy studies indicate that the enveloped virion is pleomorphic (approximately 44 × 55 nm). HRPV-1 virion may represent commonly used virion architecture, and it seems that structure-based virus lineages may be extended to non-icosahedral viruses.

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