Highly selective extermination of diatom blooms causing labor-discoloration by using habitual viruses.

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Within the four years research project, six novel diatom viruses(RsRNAV, CsNIV, CtenRNAV, CdebDNAV, CsfrRNAV, CcflDNAV) were successfully isolated and characterized. All are icosahedral viruses<40nm in diameter ; their genomes are either single-stranded DNA(ssDNA) or ssRNA. The genomes of the ssRNA viruses are linear and 3'-polyadenylated ; they have two open reading frames- a replicase polyprotein gene and a structural polyprotein gene. They showed considerable similarities to plant- or insect-infecting picomaviruses. On the other hand, CsNIV and CcflDNAV genomes are assumed to consist of a single molecule of covalently closed circular ssDNA as well as a segment of linear ssDNA. It is noticeable that the unknown genome structure was discovered in diatom-infecting viruses. Based on BLAST search results and phylogenetic analyses of RdRp domain(RNA-dependent RNA polymerase domain), both the diatom-infecting ssRNA and ssDNA viruses were shown to be novel virus groups that were only very distantly related with known viruses ; besides, significant similarities among viruses were observed within each virus group. Some of the viruses were shown to exist in natural environments at a detectable level(>3.01 infectious units/ml) ; the highest record was 3.1×10^4 infectious units/ml. These data suggest viruses have a certain impact on natural diatom populations. Furthermore, through a laboratory culture experiment, growth of laver was improved by virally inhibiting coexisting diatom proliferation. This result will provide basic data for developing a new method to prevent laver from discoloration. Further study on practical use of these diatom-infecting viruses will be eagerly expected. Due to this research project, encounter between diatomology and virology was successfully realized. We believe that the resultant data are of great value not only from the viewpoint of pure science but also practical applied science.