Abstract
Amebae of Naegleria gruberi may be grown on nutrient agar in association with Aerobacter aerogenes. When transferred from agar to a defined aqueous environment, the amebae transform into flagellates. Conditions are described which favor the synchronous and reproducible conversion of entire populations of amebae into flagellates. Transformation is measured by fixing aliquots of the transforming population and counting the proportion which have completed a specific change. The time course of appearance of flagellates has been analyzed.
At 25°C half of the amebae round up about 55 minutes after suspension, develop visible flagella 6–10 minutes later, and assume a flagellate shape 14–18 minutes after that. The times are reproducible, and more than 90% of the population completes a given change within 25 minutes. The relative rate of transformation is dependent on temperature, but independent of cell population density. The early events of transformation are arrested at 10°C, but at about the time the amebae round up, some critical event occurs after which the appearance and elongation of flagella can continue at the low temperature.
The capacity of Naegleria amebae to transform is stably inherited, and the phenotypic changes occur without change in genotype. In addition, although the flagellates are unstable and revert to amebae, in an aqueous environment these amebae retransform and revert repeatedly until they begin to encyst.