Carbon dioxide: Signal for Excystment of Naegleria gruberi

Abstract

Exposure of cysts of Naegleria gruberi to slightly increased environmental CO2 caused excystment. Excystment was also induced by addition of prollne or by an increase in the cyst population density, but both did so by increasing the amount of CO2 produced by the bacteria (Aerobacter aerogenes) which contaminated the cyst suspensions. Molecular CO2 would seem to be an excellent signal to induce excystment of a phagotrophic soil amoeba since the presence of CO2 would indicate an environment favorable for growth of the amoebae. Once excystment is initiated, it can proceed to completion in atmo-spheric CO2.