Sensitivity to Paramecin in Paramecium aurelia in Relation to Stock, Serotype, and Mating Type

Abstract

The existence of a correlation between the serotype of a stock in P. aurelia and its sensitivity to the paramecin of killer stock 51 of variety 4 has been demonstrated by the following facts. Different serotypes of the three stocks tested (stock 31 of variety 8 and stocks 51-sensitive and 29 of variety 4) differ in the level of their sensitivity to paramecin, the differences being consistent in sign, but varying in amount. Corresponding (though not necessarily identical) serotypes in different stocks may exhibit very different degrees of Pn-sensitivity. Marked differences in sensitivity may distinguish corresponding serotypes that reveal as yet no serologic differences. There is a consistent increase of about 50% in Pn-sensitivity of a clone of animals of the Pn-sensitive stock 51 after its transformation from serotype A to serotype B. When the two mating types of a stock are of the same serotype, they show about the same level of sensitivity to paramecin. The preceding relations are sufficient to account for the variations in relations of Pn-sensitivity previously reported for different stocks. They also provide an explanation for apparent but false induction of acquired resistance by exposure to paramecin. The basis of serotypic difference in sensitivity is still unknown, but preliminary observations suggest that it is in part caused by differences in rate of intake of paramecin and in part by differences in probability of death from acquired paramecin. Some possible ways in which serotype differences could be correlated with differences in Pn-sensitivity are discussed.