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Aquatic Microbial Ecology

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

Isolation and characterization of two distinct types of HcRNAV, a single-stranded RNA virus infecting the bivalve-killing microalga Heterocapsa circularisquama

Yuji Tomaru1, Noriaki Katanozaka2,3, Kensho Nishida1, Yoko Shirai1, Kenji Tarutani1, Mineo Yamaguchi1, Keizo Nagasaki1,*

1National Research Institute of Fisheries and Environment of Inland Sea, 2-17-5 Maruishi, Ohno, Saeki, Hiroshima 739-0452, Japan
2SDS Biotech K.K., 2-1 Midorigahara, Tsukuba, Ibaraki 300-2646, Japan
3Present address: Hitec Co. Ltd., 1-8-30 Tenmabashi, Kita, Osaka 530-6025, Japan
*Corresponding author. Email:

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

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