Reference Work Entry

The Prokaryotes

pp 364-402

Symbiotic Associations Between Ciliates and Prokaryotes

  • Hans-Dieter Görtz


Ciliates are frequently colonized by bacteria. This is partly due to the cytology and biology of these highly evolved heterotrophic protozoa (Hausmann and Bradbury, 1996). As phagotrophic predators on microorganisms, they bear a high risk of microbial, namely bacterial, infections: ingested bacteria may resist digestion, escape from the phagosomes, and persist in the cells as endocytobionts. Traditionally, intracellular bacteria in ciliates have been termed “symbionts” (Preer et al., 1974). Phagocytosis appears to be the usual way infectious bacteria enter their host cells. In addition to intracellular bacteria, ectosymbionts may be intimately associated with ciliates. The most intriguing example is certainly the epixenosomes of Euplotidium, which even defend their host against predators (Petroni et al., 2000; see also “Terms in Symbiosis Research”).

The bacterial symbionts of ciliates comprise a variety of bacteria in many unrelated genera of different subgroups of proteoba ...

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