Anaerobiosis-induced differentiation of Acanthamoeba castellanii

Acanthamoeba castellanii is a free living amoeba ubiquitous in soil and also commonly found in aquatic environments. In waterlogged soils, anoxia is quickly established as the dissolved oxygen is consumed by the organisms present. We were interested in the effects of anoxic conditions upon this organism. Batch cultures degassed with N2 during mid-exponential growth, induced encystation within 12 h of anoxia, and mature cysts were formed within 2-3 days. Excystation (99%) was achieved by subsequent aeration of these cultures after 3-6 days. Anoxia-induced cysts, maintained in anoxic conditions for up to four months, remained viable. Difference spectra, during anaerobiosis, revealed that cytochromes were not]oar, suggesting that the organism retains its respiratory components. The growth rate of trophozoites, grown in a chemostat, was dependent on the concentration of O2 in the head space and glucose uptake increased at lower dissolved O2 tensions. The results obtained suggest that A. castellanii has a complex adaptive strategy enabling it to cope with microaerobic and anoxic conditions which may be experienced in the environment.