Abstract
BackgroundWe performed an environmental study of viruses infecting the symbiotic single-celled algae of Paramecium bursaria (Paramecium bursaria Chlorella virus, PBCV) in Lake Biwa, the largest lake in Japan. The viruses detected were all Chlorella variabilis virus (CvV = NC64A virus). One of them, designated CvV-BW1, was subjected to further characterization.ResultsCvV-BW1 formed small plaques and had a linear DNA genome of 370 kb, as judged by pulsed-field gel electrophoresis. Restriction analysis indicated that CvV-BW1 DNA belongs to group H, one of the most resistant groups among CvV DNAs. Based on a phylogenetic tree constructed using the dnapol gene, CvV was classified into two clades, A and B. CvV-BW1 belonged to clade B, in contrast to all previously identified virus strains of group H that belonged to clade A.ConclusionsWe conclude that CvV-BW1 composes a distinct species within C. variabilis virus.
Highlights
We performed an environmental study of viruses infecting the symbiotic single-celled algae of Paramecium bursaria (Paramecium bursaria Chlorella virus, PBCV) in Lake Biwa, the largest lake in Japan
Studies on HVCV and PBCV have revealed strong host-parasite relationships [[3] and references therein]: HVCVs do not infect P. bursaria symbionts, whereas PBCVs do not infect hydra symbionts; PBCVs collected in the United States infect algal strain NC64A and other U.S P. bursaria symbionts, but they do not infect algal strain Pbi or other European P. bursaria symbionts; PBCVs collected in Europe infect European P. bursaria symbionts but do not infect U.S
Based on a series of taxonomic studies on symbiotic algae, the all P. bursaria collected so far in Japan have been verified as C. variabilis-harboring type [6]
Summary
We performed an environmental study of viruses infecting the symbiotic single-celled algae of Paramecium bursaria (Paramecium bursaria Chlorella virus, PBCV) in Lake Biwa, the largest lake in Japan. Chlorella virus that infects Chlorella-like algae symbiotic with coelenterate Hydra viridis was first discovered in 1981 and designated HVCV (Hydra viridis Chlorella virus) [1]. Another Chlorella virus that infects Chlorella-like algae symbiotic with ciliate Paramecium bursaria was described (Paramecium bursaria Chlorella virus [PBCV]) [2]. Later, another group of viruses that infect Chlorella-like algae symbiotic with heliozoon, Acanthocystis turfacea was described [4]. Note that viruses attack isolated (or released) algae but not algae inhabiting their hosts (i.e., hydra or paramecium)
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