The Endosymbionts of Paramecium

Publisher Website
Google Scholar
Abstract
Protozoan 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 cytoplasmic factors like viruses in other organisms, e.g., Neurospora and yeast, open the door for explanations of many peculiar systems of inheritance in terms of endosymbionts. The work carried out on protozoan endosymbionts may yet provide a model analysis for explaining systems of inheritance in higher organisms. There is still a reluctance, however, among cell biologists in general to accept the possibility that the cells they work with possess symbionts. Finally, the interactions between symbionts and their host cells may provide an interesting analogy for the interaction between the nuclear genome of a cell and organelles like chloroplasts and mitochondria.