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Characterization of a large DNA virus (BV-PW1) infecting the heterotrophic marine nanoflagellate cafeteria sp. St. John, Tanya Marie

Abstract

A virus (designated BV-PW1) infecting the marine heterotrophic nanoflagellate Cafeteria sp. was purified and characterized. The most successful strategy for purification of the virus particles was ultracentrifugation of culture lysates followed by sucrose-gradient purification to remove contaminating bacteria and bacteriophage. The virus particles are icosahedral, roughly 230 to 300 nm in diameter and contain at least 2 major polypeptides (55 kDa and 65 kDa) and -30 minor polypeptides. It possesses a dsDNA genome >100 kbp with a predicted G + C content of -34%. Sequence analysis of 279 amino acids at the N-terminus of a putative protein revealed the presence of the first 3 conserved motifs that delineate the helicase/NTPase superfamily II, including the NTP hydrolysis motifs GxGKT/S and DExH/D. A phylogenetic tree based on the aminoacid sequence of this region indicates the putative helicase of BV-PW1 is most similar to that of ASFV of the Asfaviridae, however, this branch also falls within the Iridoviridae clade. At this time there is not enough information to classify BV-PW1 within a particular virus family. The virus infecting the nanoflagellate described in this study has several properties in common with a group of other large nucleocytoplasmic DNA viruses, such as the poxviruses, the asfaviruses, the iridoviruses and the phycodnaviruses.

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