Studies on transformation in Naegleria gruberi: effects of ions and bacterial suspensions

The presence of electolytes inhibited the transformation of Naegleria gruberi from amoeba to flagellate, the molarity required varying with the salt used, namely 80 mM NaCl, 90 mM KCl, 50 mM CaCl2 or 60 mM MgCl2. Non-electrolytes also prevented this transformation at 250 mM for either sucrose or glucose, and this is known to be an osmotic effect. That the effect of ionic solutions was different was demonstrated by varying the time at which the environemnt was changed from distilled water to salt solution. Experiments with suspensions of either living or heat-killed bacteria in distilled water, together with the supernatants obtained when bacteria were removed by centrifugation, showed that the inhibition of transformation which occurred in bacterial suspensions was not due to any factors produced by the bacteria and present in solution. It appeared that this inhibition was brought about by the physical presence of the bacteria, either living or heat-killed, and some possible interpretations of this 'contact' phenomenon are discussed.