English: (A) Paramecium bursaria and its symbiotic Chlorella cells. (B) Plaques formed by PBCV-1 on a lawn of Chlorella variabilis. (C) Five-fold averaged cryo-electron micrograph of PBCV-1 reveals a long narrow cylindrical spike structure at one vertex and fibers extending from one unique capsomer per trisymmetron. (D) PBCV-1 attached to the cell wall as viewed by the quick-freeze, deep etch procedure. Note the virions attached to the wall by fibers. (E) Surface view of the PBCV-1 spike structure and fibers. (G) Attachment of PBCV-1 to the algal wall and digestion of the wall at the point of attachment. This occurs within 1–3 minutes postinfection (PI) (H) Virion particles assemble in defined areas in the cytoplasm named virus assembly centers at ~4 hour PI. Note that both DNA containing (dark centers) and empty capsids. (J) Localized lysis of cell plasma membrane and cell wall and release of progeny viruses at ~8 hours PI.