Y. Tsukii et al., EVIDENCE FOR A VIRAL MACRONUCLEAR ENDOSYMBIONT IN PARAMECIUM-CAUDATUM, The Journal of eukaryotic microbiology, 42(2), 1995, pp. 109-115
Some strains of P. caudatum contain macronuclear inclusion bodies that
are morphologically distinct from bacteria. They vary in number as we
ll as in size in each macronucleus. The inclusion bodies are basically
divided into peripheral and inner areas. The peripheral area consists
of fibrillar proteins of 22-24 nm in thickness, which are specificall
y stained with fast green in 45% acetic acid. On the other hand, chrom
atin-like granules are within the inner area of large inclusion bodies
. The granules within the inner area changed their distribution depend
ing upon the physiological state of their host cells. Transplantation
experiments and crossbreeding analyses revealed that genetic factors r
esponsible for the multiplication of the inclusion bodies can 'infect'
other macronuclei (or cells) via the cytoplasm. These results suggest
that the inclusion bodies are a non-bacterial macronuclear endosymbio
nt, possibly produced by a virus or a virus-like element.