Protistology 2 (1) 63–67 (2001)
Possible new intranuclear symbionts of Paramecium caudatum
Andrew Vishnyakov, Maria Rautian and Natalja Lebedeva
Biological Research Institute of St.-Petersburg State University, St.Petersburg, Russia Summary
Intranuclear bacteria inhabiting macronucleus of Paramecium caudatum isolated from three populations from North America and
Eastern Europe were studied. Interference contrast and electron microscopy was used to describe symbiont morphology. Symbiotic bacteria
from such distant populations are rather similar. They are rod-shaped with 1-2 mm length and 0.3-0.4
mm diameter; cell wall is typical for gram-negative bacteria; membrane vesicles
on the surface of some bacteria indicate the secretion of some periplasm material into the nucleus. According to the in situ hybridization
with group-specific probes, these symbionts belong to a-Proteobacteria subdivision. The proposal of
a-Proteobacteria advantages for intracellular and intranuclear life are discussed.
Key words: intranuclear symbiosis, Paramecium, a-Proteobacteria, macronucleus
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