Isolation and characterization of a new type of chlorovirus that infects an endosymbiotic Chlorella strain of the heliozoon Acanthocystis turfacea.

A novel virus, named Acanthocystis turfacea Chlorella virus (ATCV), that infects endosymbiotic Chlorella algae of the heliozoon Acanthocystis turfacea was isolated from freshwater samples. Electron microscopic analysis of ATCV revealed that the viral capsid has a distinct icosahedral shape with a diameter of 140-190 nm. Filamentous structures extending from some of the virus vertices, which may aid attachment of the virus to host cells, were also observed. The capsid is made up of one major coat protein of about 50 kDa and contains a large dsDNA genome. ATCV is a member of the genus Chlorovirus, which belongs to the family Phycodnaviridae, a group of large, icosahedral, dsDNA-containing viruses that infect algae and are ubiquitous in natural environments. However, ATCV is clearly distinct from the prototype Chlorovirus, Paramecium bursaria Chlorella virus (PBCV-1), in some aspects of its genome structure and gene content and therefore must be regarded as a member of a new group of Chlorella viruses.