AME 34:207-218 (2004)  -  doi:10.3354/ame034207

ABSTRACT: HcRNAV, a novel single-stranded RNA (ssRNA) virus specifically infecting the bivalve-killing dinoflagellate Heterocapsa circularisquama, was isolated from the coastal waters of Japan. HcRNAV strains were divided into 2 types based on intra-species host-range tests. The 2 types showed complementary strain-specific infectivity. In the following experiments, typical strains of each type (HcRNAV34 and HcRNAV109), were characterized. Both virus strains were icosahedral, ca. 30 nm in diameter, and harbored a single molecule of ssRNA approximately 4.4 kb in size. Thus, in morphology and nucleic acid type, HcRNAV is distinct from HcV, the previously reported large double-stranded DNA virus infecting H. circularisquama. Virus particles appeared in the cytoplasm of the host cells within 24 h post-infection, and crystalline arrays or unordered aggregations of virus particles were observed. The burst size and latent period were estimated at 3.4 × 10³ to 2.1 × 10⁴ infectious particles cell^-1 and 24 to 48 h, respectively. To our knowledge, this is the first report of a ssRNA virus infecting dinoflagellates that has been isolated and maintained in culture. Although HcRNAV is considered to have some similarities with plant viruses belonging to genera Sobemovirus and Luteovirus, further genomic analysis is required to discuss the detailed classification and nomenclature of HcRNAV. The finding of RNA viruses infecting microalgae such as HaRNAV (Heterosigma akashiwo RNA virus) and HcRNAV emphasizes the diversity of algicidal viral pathogens.

KEY WORDS: Dinoflagellate · Phycovirus · ssRNA viruses · Heterocapsa circularisquama · Algal virus