Figure 11.

Electron microphotographs of the virus-containing Paramecium bursaria–Chlorella symbiotic system. The chloroviruses are associated with the somatic cortex of the ciliate. Arrowheads mark the tiny hair like fibers, connecting the virus particles to the paramecium plasma membrane. A unique electron-transparent virus vertex is shown with an arrow in Figure 1, Figure 4 and Figure 5. Longitudinal sections of the ciliary pits and virus particles are located in the tight space of a ciliary pit and between the cilia. The ciliary pits are on average only slightly wider than the diameter of the virus particles, and thus the viruses are shielded by the evaginating alveoli sacs. Viruses appear to be attached to the plasma membrane directly by the vertex opposite the unique electron-transparent vertex, or by one of the other vertices and via hair-like fibers. Therefore, the unique vertex of the virus is ready to attach to their host algae when the paramecia are disrupted. (3) Chlorovirus particles attached to the expulsive trichocyst. (2, 6) Virus particles in association with the plasma membrane on the ciliary ridge. Note, that on the enlarged image (6) the side of the capsid appears very close to the membrane. (7) The viral capsid in the ciliary pits and near the entry of the parasomal sac (place of endocytosis), a virus particle attached to the membrane by the tiny hairlike fibers. (8) A virus particle attached to the plasma membrane of the surface and to the cilia. The virus is recognized by the electron dense nucleocapsid and a distinct electron transparent vertex pointed upwards and opposite the vertex attached to the ciliate plasma membrane. A—alveoli; C—cilia; CP—ciliary pits; PM—plasma membrane; PS—parasomal sac; T—trichocyst. Scale bars 200 nm. Published with permission from Yashchenko et al. [227].