Infection of algae-free Paramecium bursaria with symbiotic Chlorella sp. Isolated from green paramecia : I. Effect of the incubation period

Abstract

The significance of the length of incubation (30 sec to 48 h) of algae-free Paramecium bursaria with symbiotic Chlorella sp. for the success of infection, i.e. the reestablishment of the endosymbiotic algae has been investigated. When algae are brought together with paramecia, they are rapidly taken up by the ciliates. During a 30 sec incubation one ciliate engulfs about 50 chlorellae. A prolongation of the incubation period increases the number of ingested algae. However, the success of infection, determined one and five day(s) after the end of the incubation, is independent from the length of the incubation period and, consequently, does not depend on the number of ingested algae, either: In all experiments about 50% of the Paramecium population becomes infected and one to three algae are primarily enclosed in individual perialgal vacuoles within a ciliate cell. Thus, the endosymbiont population of a Paramecium cell originates on an average from two algae. Since successful infection is restricted only to a part of the Paramecium population and since the number of primarily established endosymbionts does not depend on the number of ingested algae, the success of infection and the formation of perialgal vacuoles seem to be not limited by properties of the algae but by features of the host, the possible nature of which is discussed.