The endosymbionts of Paramecium.

Abstract

AbstractProtozoan cells harbor many different types of endosymbionts. They can be viruses, bacteria, algae, fungi, or even defy classification in relation to free-living organisms. A general description of the types is available in Kirby1 and some are shown in Table 1. There has been little interest in these relationships since it seems to be acknowledged that protozoa are different and one can hardly be surprised at such a situation. This short-sighted approach has recently, however, received several setbacks in the elucidation of a complex interaction between “viruses,” bacterial-like endosymbionts and the host cell genome in Paramecium, and the observation that symbionts in other protozoa are “essential” for their long-term laboratory growth, e.g., Amoeba discoides. Furthermore, the fact that these endosymbionts confer phenotypic properties on the cell, e.g., the “killer” property in paramecia or viability in Amoeba, and the observation that certain characters are determined or associated with cytoplas...