Phycodnaviridae– large DNA algal viruses

Abstract

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 approximately 231 protein-encoding genes whereas, the slightly smaller PBCV-1 genome has 11 tRNA genes and approximately 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.

Viral activation and recruitment of metacaspases in the unicellular coccolithophore, Emiliania huxleyi

“…Taken together, our findings support the late-phase (Ͼ30 h) induction and active recruitment of the host's PCD execution machinery by coccolithoviruses. It is tempting to speculate that this recruitment may represent a conserved strategy among the broad, monophyletic Phycodnaviridae family of giant icosahedral dsDNA viruses infecting eukaryotic phytoplankton (37,38), which encompass the Coccolithovirus. Indeed, virally encoded proteins containing caspase cleavage sequences were also found in the only other Phycodnaviridae genome sequences completed to date, Ectocarpus siliculosus virus (EsV-1) and Paramecium bursaria Chlorella virus 1 (PBCV-1) (Table 1).…”

Paramecium bursaria Chlorella Virus 1 Encodes Two Enzymes Involved in the Biosynthesis of GDP-L-fucose and GDP-D-rhamnose

“…For example, PBCV-1 encodes three enzymes, UDP-glucose dehydrogenase, glucosamine synthase, and hyaluronan synthase, involved in the biosynthesis of the extracellular matrix polysaccharide hyaluronan (8 -10). Other ORFs resemble glycosyltransferases and enzymes involved in the metabolism of nucleotide sugars (2,3). In the present study we characterize two PBCV-1 ORFs, A118R and A295L, that encode proteins that resemble GDP-D-mannose 4,6-dehydratase (GMD) and GDP-4-keto-6-deoxy-D-mannose epimerase/reductase (GMER), respectively.…”

“…The PBCV-1 genome, which has been sequenced, consists of a large (Ͼ330 kb) linear, non-permuted double-stranded DNA with covalently closed hairpin ends (2). Additional features of the virus have been reviewed recently (3). The PBCV-1 major capsid protein, Vp54, located on the viral surface, is one of three glycosylated viral proteins.…”

Quantification of virus genes provides evidence for seed-bank populations of phycodnaviruses in Lake Ontario, Canada

“…Although phytoplankton viruses are diverse in capsid size, and genome size and type, most cultivated algal viruses belong to the family Phycodnaviridae. Phycodnaviruses are nucleo-cytoplasmic large DNA viruses with capsid sizes ranging from 100-220 nm, and genomes ranging in length from 170 to 560 kb (Van Etten and Meints, 1999;Van Etten et al, 2002;Dunigan et al, 2006). The earliest effort to characterize phycodnavirus communities while circumventing difficulties associated with virus cultivation involved designing algal-virus specific (AVS) PCR primers that targeted DNA polymerase (polB) genes .…”