Axenic mass cultivation of the free-living soil amoeba, Acanthamoeba castellanii in a laboratory fermentor

Axenic mass cultivation of Acanthamoeba castellanii in laboratory fermentors (14 l) yielded after 20 days approximately 3 g cells (wet weight). After a short lag phase amoebal cell numbers increased exponentially to a maximum of 3.5×10⁵ cells per ml until cell death occurred after 20 days. Optical density and protein concentrations revealed identical patterns. During amoebal growth only 12–19% of the initially added glucose (100 mM) as sole carbon source was used. Large amounts of ammonia (1 g in 10.5 l culture volume) were excreted into the medium which subsequently raised the pH from 6.6 to 7.7, and from 6.6 to 6.8 in 2 and 20 mM buffered media, respectively. Growth inhibition and cell death could not be explained by a depletion of glucose or oxygen limitations during growth. The production of ammonia had a growth inhibitory effect, however, the sudden termination of the exponential growth phase and cell death could not be explained by the toxic influence of ammonia only.