Intersyngenic variations in the esterases of bacterized Paramecium aurelia

Abstract

The esterase isozymes were surveyed in bacterized stocks representative of all 14 syngens of Paramecium aurelia by starch gel electrophoresis. The properties of substrate specificity and independent variation of particular isozymes permit the ordering of the differences observed among stocks. Differences can arise from several sources: bacterial variation, intrasyngenic variation, and intersyngenic variation. Bacterial esterases tend to be found in certain zonal areas (see Rowe et al. , 1971) and produce minor stock differences, which are erratic in their distribution. Unlike the situation found in Tetrahymena pyriformis , major intrasyngenic variations are rare in P. aurelia except in syngen 2. This lack of intrasyngenic variation is significant in view of the wide differences in geographic origin and micronuclear chromosome numbers among stocks within a syngen. It suggests that certain esterase genotypes must be under stringent selection within a syngen. The lack of intrasyngenic variation permits assessment of intersyngenic relationships. Syngens differ in a complex way from each other, suggesting that several gene differences may be involved. The syngens can be classified on the basis of their esterases. Syngens which have been shown to be more closely related in terms of cross-mating, breeding systems, and other criteria tend to be more similar in their esterase isozymes. The isozyme technique confirms relationships previously suggested among syngens and offers the promise of eventual assessment of evolutionary distances among syngens. However, establishment of these relationships will be clearer in the absence of bacteria.