Factors Regulating the Encystment Enhancing Activity (EEA) of Acanthamoeba castellanii

Abstract

An extracellular encystment enhancing activity (EEA) greatly stimulates cyst formation by Acanthamoeba castellanii under several different conditions. The activity appears when conditions are suboptimal for growth. EEA does not induce encystment by itself, but enhances differentiation initiated by other factors. EEA titres and their relationship to differentiation are described for encystment induced by: (1) berenil; (2) glucose starvation; and (3) total nutrient starvation. Extracellular EEA was required for maximum encystment by low density cultures in ( I ) and (2), but not in (3). It was required during the period of visible cyst wall formation rather than for earlier events in encystment. The effectiveness of EEA was reduced under some conditions by spontaneous changes in cellular sensitivity, and by extracellular inhibitors.

Ultrastructure of cyst differentiation in parasitic protozoa

“…The specific conditions that initiate the encystation processes are diverse. In the reptilian parasite E. invadens (Vazquezdelara-Cisneros and Arroyo-Begovich 1984; Sánchez et al 1994) and in the free living amoeba A. castellanii (Byers 1979;Akins et al 1985), the lack of nutrients induces these amoebas to encyst in vitro, while in the human parasite G. lamblia, depletion of cholesterol is the stimulus that initiates the process (Luján et al 1996a). Cyst walls are produced by exocytosis of materials.…”