Complete genome sequence of a Megalocytivirus (family Iridoviridae) associated with turbot mortality in China

Abstract

Background: Turbot reddish body iridovirus (TRBIV) causes serious systemic diseases with high mortality in the cultured turbot, Scophthalmus maximus. We here sequenced and analyzed the complete genome of TRBIV, which was identified in Shandong province, China.

Results: The genome of TRBIV is a linear double-stranded DNA of 110,104 base pairs, comprising 55% G + C. Total 115 open reading frames were identified, encoding polypeptides ranging from 40 to 1168 amino acids. Amino acid sequences analysis revealed that 39 of the 115 potential gene products of TRBIV show significant homology to other iridovirus proteins. Phylogenetic analysis of conserved genes indicated that TRBIV is closely related to infectious spleen and kidney necrosis virus (ISKNV), rock bream iridovirus (RBIV), orange-spotted grouper iridovirus (OSGIV), and large yellow croaker iridovirus (LYCIV). The results indicated that TRBIV belongs to the genus Megalocytivirus (family Iridoviridae).

Conclusions: The determination of the genome of TRBIV will provide useful information for comparative study of Megalocytivirus and developing strategies to control outbreaks of TRBIV-induced disease.

Figure 1

Organization of the TRBIV genome. Arrows indicate the location, orientation and putative size of each ORF. White arrows represent ORFs with predicted function similar to other organisms, and black arrows represent ORFs with unknown function.

Figure 2

Dot matrix plots comparing the TRBIV genome (vertical axis) with the ISKNV, OSGIV, RBIV genomes, and itself (horizontal axis). The horizontal axes represent (A) the TRBIV genome; (B) the ISKNV genome; (C) the OSGIV genome; and (D) the RBIV genome. The complete genomic sequences were aligned using DS GENE 1.5.

Figure 3

Phylogenetic relationships of iridoviruses obtained using four protein sequence alignments: (A) major capsid protein, (B) ATPase, (C) DNA polymerase, and (D) cytosine DNA methyl transferase. The alignments were carried out using Clustal X 1.83 and the neighbor-joining trees obtained using PHYLIP 3.67 are shown with the statistical support indicating the robustness of the inferred branching pattern as assessed using the bootstrap test. GenBank accession numbers: (A) ATV, YP_003785; CIV, NP_149737; MIV, YP_654586; FV3, YP_031669; ISKNV, NP_612228; LCDV-1, NP_044812; LCDV-C, YP_025102; RBIV, AAT71822; SGIV, AAS18087; GIV, AAV91066; TFV, AAL77814; and OSGIV, AAX82316. (B) ATV, AAP33264; CIV, NP_149538; GIV, AAV91100; FV3, YP_031593; OSGIV, AAX82427; ISKNV, AAL98847; LCDV-1, NP_078656; LCDV-C, YP_073620; SGIV, YP_164229; MIV, YP_654660; TFV, AAL77796; and RBIV, AY532606.1. (C) ATV, YP_003817; CIV, AAD48150; FV3, YP_031639; ISKNV, AAL98743; LCDV-1, NP_078724; LCDV-C, YP_073706; RBIV, AAT71835; SGIV, AAS18143; TFV, AAL77804; OSGIV, AAX82331; and MIV, YP_654692. (D) ATV, YP_003792; FV3, YP_031662; ISKNV, AAL98770; OSGIV, AAX82357; LCDV-1, NP_078617; LCDV-C, YP_025103; RBIV, AAT71861; and TFV, NP_572009.