Intersyngenic variations in the esterases of axenic stocks of Paramecium aurelia

The esterase isozymes were surveyed in axenic stocks of syngens 1, 2, 4, 5, 6, and 8 of Paramecium aurelia by starch gel electrophoresis. In paramecia there appear to be four types of esterases which are clearer in axenic than in bacterized stocks. Each type differs in its substrate specificity and/or its response to the inhibitor eserine sulfate. Minor variations in type D esterases sometimes occur in different extracts of the same stock and may result from changes in the temperature of growth of the cells or growth cycle differences. Differences in the mobility of the A, B, or C (cathodal) types of esterases may occur in different syngens. They also occur for the A and B types among stocks within a syngen, but the frequency is low, except in the case of syngen 2. Since each of the types of esterases varies independently, at least four and possibly more genes appear to specify the esterases in the species complex. Some pairs of syngens vary in their electrophoretic positions for all types of esterases. Other pairs have identical zymograms. This observation suggests that some syngens may differ from each other by as many as four esterase genes, while others may not differ at all. The difference between P. aurelia and Tetrahymena pyriformis in the degree of intrasyngenic variation observed for enzymes is discussed in relation to other types of characters, the organization of the genetic material in the macronucleus, the presence of symbionts, and their breeding systems. It is suggested that enzyme variation is achieved by the action of different selective forces in these two groups of ciliated protozoa.Supported by research grants from the National Institute of General Medical Sciences (GM-15879), U.S. Public Health Service, and from the British Medical Research Council.