Abstract
The Coccolithoviridae are a group of viruses which infect the marine coccolithophorid microalga Emiliania huxleyi. The Emiliania huxleyi viruses (known as EhVs) described herein have 160- to 180-nm diameter icosahedral structures, have genomes of approximately 400 kbp, and consist of more than 450 predicted coding sequences (CDSs). Here, we describe the genomic features of four newly sequenced coccolithoviruses (EhV-88, EhV-201, EhV-207, and EhV-208) together with their draft genome sequences and their annotations, highlighting the homology and heterogeneity of these genomes to the EhV-86 model reference genome.
GENOME ANNOUNCEMENT
The coccolithoviruses infect Emiliania huxleyi, a globally distributed bloom-forming marine microalga. The abundance of Emiliania huxleyi viruses (EhVs) in natural seawater can typically reach 107 ml−1 in bloom conditions and 108 to 109 ml−1 under laboratory culture (6). Following the full sequencing of the model virus EhV-86 (isolated in 1999 from the English Channel) and the partial sequencing of EhV-163 (isolated from a Norwegian fjord the following year), we have recently undertaken to sequence the remaining English Channel isolates currently contained within the Plymouth Virus Collection (PVC) (1). The draft genomes of EhV-84, EhV-203, and EhV-202 have been described previously (4, 5). Here, we present the draft genomes of the remaining four coccolithoviruses in the PVC: EhV-88, EhV-201, EhV-207, and EhV-208.
EhV-88 was isolated from the English Channel (50°15′N/04°13′W) from a depth of 5 m in 1999, while EhV-201, EhV-207, and EhV-208 were isolated from the English Channel (49°56′N/04°19′W, 50°15′N/04°13′W, and 50°15′N/04°13′W, respectively) from a depth of 2 to 15 m in 2001 (1, 8). Their icosahedral virion structure and morphology are similar to those of other coccolithoviruses and of phycodnaviruses in general (9). Phylogenetic analysis of available major capsid protein (MCP) and DNA pol gene sequences indicates that the closest relatives to EhV-88 are EhV-84 and EhV-86 (4, 7), while EhV-201, EhV-207, and EhV-208 are closely related to EhV-203 (1, 8).
Genome sequencing, finishing, and annotation were performed by the Broad Institute. The genomes were sequenced using the 454 FLX pyrosequencing technology platform (Roche/454, Branford, CT). Library construction and sequencing were performed as previously described (2). General protocols for library construction can be found at http://www.broadinstitute.org/annotation/viral/Phage/Protocols.html. De novo genome assembly of resulting reads was performed using the Newbler v2.3 assembly software package (2). A total of 74,782, 78,268, 33,894, and 85,422 reads were produced and assembled into 8, 7, 16, and 17 contigs, comprising 396,598 bp, 406,701 bp, 420,391 bp, and 409,403 bp, for EhV-88, EhV-201, EhV-207, and EhV-208, respectively. Genes were identified using the Broad Institute's Automated Phage Annotation Protocol (2). Additional gene prediction analysis and functional annotation was performed within the Integrated Microbial Genomes-Expert Review (IMG-ER) platform (3).
General features of the genomes include nucleotide compositions of 40.18%, 40.46%, 40.49%, and 40.42% G+C and 475, 451, 473, and 455 predicted protein coding sequences (CDSs) for EhV-88, EhV-201, EhV-207, and EhV-208, respectively. EhV-201, EhV-207, and EhV-208 have six tRNAs (Arg, Asn, Gln, Glu, Leu, and Lys), while EhV-88 has five (Arg, Asn, Gln, Ile, and Lys). EhV-84 is most similar to the model virus EhV-86, encoding 231 CDSs with identical homologues in the EhV-86 genome. In contrast, EhV-201, EhV-207, and EhV-208 have just 26, 29, and 25 CDSs sharing 100% identity with their EhV-86 homologues, respectively. The majority of CDSs not shared with EhV-86 encode hypothetical proteins of unknown function. Those of predicted function include those encoding glycosyltransferase (EhV-201, EhV-207, and EhV-208), methyltransferase (EhV-88, EhV-207, EhV-208), and RNase (EhV-88 and EhV-201). The genomes of these viruses will provide new insights into coccolithovirus evolution and their coevolution and interaction with Emiliania huxleyi.
Nucleotide sequence accession numbers.
The nucleotide sequence accession numbers for the draft genomes sequences have been deposited in GenBank under accession numbers JF974310, JF974311, JF974317, and JF974318.
ACKNOWLEDGMENTS
This research was funded in part by the Gordon and Betty Moore Foundation through a grant to the Broad Institute (M.R.H.) and through the NERC Oceans 2025 program (M.J.A.). J.I.N. is supported by an NERC studentship, and C.A.W. is supported by a BBSRC Industrial CASE studentship sponsored by PML Applications. H.O. is supported by IGS/CNRS and ANR (grants ANR-09-PCS-GENM-218, ANR-08-BDVA-003).
Samples G3265, G3266, G3249, and G3250 were sequenced, assembled, and annotated at the Broad Institute.
We thank Konstantinos Mavromatis from JGI who assisted with information regarding the IMG/ER platform and the Broad Institute's Genome Sequencing Platform, Finishing Team, and Annotation Team for their efforts to generate the genomic data. Jean Devonshire and the Centre for Bioimaging at Rothamsted provided technical support for transmission electron microscopy.
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