Arch Virol (2002) 147: 1479–1516
Phycodnaviridae – large DNA algal viruses
J. L. Van Etten
, M. V. Graves
, and N. Delaroque
Nebraska Center for Virology and Department of Plant Pathology,
University of Nebraska, Lincoln, Nebraska, U.S.A.
Center for Biotechnology, University of Nebraska, Lincoln, Nebraska, U.S.A.
Department of Biology, University of Konstanz, Konstanz, Germany
Max-Planck-Institut f¨ur Chemische
Okologie, Jena, Germany
Received December 12, 2001; accepted March 6, 2002
Published online May 25, 2002
Summary. Members and prospective members of the family Phycodnaviridae
are large icosahedral, dsDNA (180 to 560 kb) viruses that infect eukaryotic algae.
The genomes of two phycodnaviruses have been sequenced: the 331 kb genome
of Paramecium bursaria chlorella virus (PBCV-1) and more recently, the 336 kb
genome of the Ectocarpus siliculosus virus (EsV-1). EsV-1 has ∼ 231 protein-
encoding genes whereas, the slightly smaller PBCV-1 genome has 11 tRNA genes
and ∼ 375 protein-encoding genes. Surprisingly, the two viruses only have 33
genes in common, of which 17 have no counterparts in the databases. The low
number of homologous genes between the two viruses can probably be attributed
to their different life styles. PBCV-1 is a lytic virus that infects a unicellular,
endosymbiotic freshwater green alga whereas, EsV-1 is a lysogenic virus that
infects a free-living ﬁlamentous marine brown alga. Furthermore, accumulating
evidence indicates that the phycodnaviruses and their genes are ancient, thus
allowing signiﬁcant differences to have evolved. This review brieﬂy describes
some of the biological properties of the phycodnaviruses, focusing on PBCV-1
and EsV-1, and then compares their genomes.
The largest virus genome sequenced to date was described recently, 335,593 bp
from Ectocarpus siliculosus virus (EsV-1) that infects the marine ﬁlamentous
brown alga, E. siliculosus . The EsV-1 genome is ∼ 5 kb larger than the
330,744 bp genome of another algal virus, Paramecium bursaria chlorella virus