Isolation and characterization of a single-stranded DNA virus infecting the marine planktonic diatom Chaetoceros sp. (strain TG07-C28)

Diatom dynamics in the ocean represents one of the most interesting research themes for marine ecologists. Recent studies have shown the significance of viruses as potential sources of mortality for diatom populations, as well as the more traditional environmental factors. Here, we report the isolation and characterization of a new single- stranded DNA (ssDNA) virus (Csp05DNAV) that causes lysis in Chaetoceros sp. TG07-C28, isolated from the surface water of Ago Bay, Japan. The virus was isolated from the sediments in Ago Bay, and its infection was both lytic and species-specific. The latent period was estimated to be <24 h. The virion is 32-34 nm in diameter, and accumulates in the nucleus of host cells. Csp05DNAV has a closed circular ssDNA genome, which includes a partially double-stranded region. Partial sequence analysis revealed that the open reading frame of this virus genome was similar to the putative replicase-related proteins of previously reported diatom viruses that harbor a ssDNA genome; specifically, CsalDNAV, CdebDNAV, ClorDNAV, and CtenDNAV. Based on the genome structure, Csp05DNAV is considered to belong to the genus Bacilladnavirus. As both the host and virus were isolated from Ago Bay, the host-virus system probably is ecologically important in the bay. This finding provides basic information towards elucidating diatom dynamics in coastal waters.