Abstract
For amoebae of Naegleria gruberi NEG-M growing in an axenic medium, one component of the medium, yeast extract, controls whether phenotypic transformation into flagellates occurs. Fractionation of the yeast extract yielded two components that control transformation: electrolytes and an unidentified Factor. Electrolytes prevent transformation if present above a certain concentration. For NaCl and KCl, for example, the critical concentration is 0.08 M. The effect is not specific to particular ions, nor is it due simply to ionic strength. Osmotic pressure produced by nonpenetrating nonelectrolytes like sucrose can also inhibit transformation, but the effect of electrolytes is not due solely to osmotic pressure. The unidentified Factor, a small molecule, probably aromatic (adsorbs reversibly to charcoal), can prevent transformation at a concentration that does not increase the osmotic pressure of the solution, and that is estimated to be not more than 0.001 M. The action of Factor in controlling transformation is much potentiated by electrolytes, such that a combination of one-eighth the electrolyte concentration needed to prevent transformation with one-fourth the Factor concentration completely prevents transformation. The synergistic action with Factor is not specific to a particular ion, but there are differences. For example, Na+ is much more effective than Cs+. Factor and osmotic pressure do not act synergistically. Amoebae grown in the presence of extra Factor adapt to it, and will transform in concentrations of Factor and of electrolyte that prevent transformation of unadapted cells. These adapted cells also can transform in regular growth medium. It is concluded that Factor and electrolytes are involved in the normal control of transformation of these axenic Naegleria. The results provide a starting point for studying early events in this cell differentiation.