Widespread distribution of Chlorella viruses in Japan.

An extensive survey for Chlorella viruses was done across Japan and in nine countries of Asia, Europe, North America, and South America. Of 150 fresh-water samples collected from 77 distinct areas in Japan, 29 showed plaques on a lawn of Chlorella sp. (strain NC64A). Typically, 10 to 1000 PFU/ml of viruses were present at sampling sites located throughout Japan. Viruses were also detected in two samples from Brazil and China but not from other countries where water samples were screened. Several representatives of these viruses including ones isolated from Brazil and China were compared with respect to genome size, genome structure, and protein components. It was found that these viruses should belong to the same virus group consisting of large icosahedral particles with linear dsDNA genomes. Physiological and ecological factors affecting virus distribution are discussed.