Screening of Natural Waters for Viruses Which Infect Chlorella Cells

Abstract

By using a plaque assay with the unicellular green alga Chlorella sp. strain NC64A as a host, viruses were screened from natural pond waters collected in Kyoto and Higashi-Hiroshina, Japan. From some samples tested, two kinds of plaques, large (+ = 6 to 10 mm) and small (4 = 2 to 3 mm), were detected with various frequencies. The frequency of plaques in each of the water sources was seasonal; generally, it reached a peak value (8,000 PFU/ml) in May and gradually decreased to the limit of detection (<1) in November before increasing again in early spring. Electron microscopy revealed that the purified and negatively stained viruses were very large (125 to 200 nm) icosahedral particles. The genome isolated from these particles was always a linear double-stranded DNA of 340 to 370 kbp. Electrophoresis patterns of the DNA fragments produced by digestion with restriction enzymes differed considerably from plaque to plaque, even for plaques from the same water source. However, Southern hybridization showed strong homology among all of the virus DNAs tested, indicating relatedness of those viruses. A possible use of the Chlorella virus assay system to monitor the natural population of algal cells and water quality is discussed.

Chlorella viruses in diverse fresh waters in North East England

“…lb,c). These appeared identical in size and form to published electron micrographs of Chlorella Pbi virus (Reisser et al 1986) and Chlorella NC64A virus (Yamada et a!. 1991).…”

“…However, it appeared that none of the NE England sites contained viruses able to infect the N American Chlorella NC64A (Table 1). This contrasts strongly with fresh waters in N America, China and Japan where Chlorella NC64A viruses are ubiquitous Yamada et al 1991). The non-uniform geographical distribution of Chlorella viruses is compatible with laboratory demonstrations that Pbi viruses do not infect Chlorella NC64A, and vice versa (Reisser et al 1988b(Reisser et al , 1991.…”

Hyaluronan Synthesis in Virus PBCV-1-Infected Chlorella-like Green Algae

“…We considered two other biological functions for the PBCV-1-encoded hyaluronan; these functions are based on our limited knowledge of the natural history of the viruses. Chlorella viruses are ubiquitous in freshwater collected worldwide, and titers as high as 4 ϫ 10 4 infectious viruses/ml of native water have been reported (Van Etten et al, 1985;Yamada et al, 1991). The only known hosts for these viruses are chlorella-like green algae that normally live as hereditary endosymbionts in some isolates of the ciliate Paramecium bursaria.…”

vAL‐1, a novel polysaccharide lyase encoded by chlorovirus CVK2

“…Large icosahedral, dsDNA‐containing viruses that infect certain strains of the unicellular green alga Chlorella (chlorovirus or Chlorella virus; Phycodnaviridae) [1] are ubiquitous in natural environments [2,3]. In a normal lytic cycle, virus particles attach to the surface of host Chlorella cells and degrade the cell wall at the point of attachment; the viral core is then released into the host cytoplasm, leaving an empty capsid on the cell wall [2].…”