Infection of Alga-Free Paramecium bursaria with Strains of Chlorella, Scenedesmus, and a Yeast

SYNOPSIS. Twenty‐one different stocks of Paramecittm bursaria, belonging t o 4 separate varieties (syngens), whose endosymbiotic chorellae had been removed, were tested for reinfection by several strains of Chorella, some previously isolated from P. bursaria, and others free‐living. In addition, infection of P. bursaria by a single strain of the green alga Scenedesmus sp., and an unidentified strain of yeast was attempted. Most combinations involving Chlorella yielded infected paramecia, and all those with Scenedesmus or the yeast did so. The failures with Chlorella were attributed to low infectibility of the stocks of Paramecium concerned, rather than to inability of the Chlorella to survive inside the paramecia. Little evidence was found that the strains of P. bursaria differed genetically in ability to maintain the symbiotic organisms.