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Nero , L. C. (Illinois Institute of Technology, Chicago), Mae G. Tarver, and L. R. Hedrick . Growth of Acanthamoeba castellani with the yeast Torulopsis famata . J. Bacteriol. 87: 220–225. 1964.— Acanthamoeba castellani and Torulopsis famata cells were cultured together for 10 days at three different temperatures: 18, 25, and 32 C. In the 18- and 25-C series, the yeast population reached a peak within 3 to 5 days and then declined for the next 5 days. This decrease in yeast population corresponded with an increase in the development of amoebae, which first appeared as vegetative cells and later transformed themselves into cysts. The changes in population were determined by counts in a hemocytometer. The vegetative amoeba population seldom exceeded 4 × 10 7 cells per bottle culture, but the encysted population approached 16 × 10 7 cysts per bottle culture within 10 days of incubation. The amoebae actively ingested the yeasts and used these cells as their principal source of energy. At 18 C each amoeba consumed 70 yeast cells per day; at 25 C each amoeba ingested 35 yeast cells per day. In the 32-C series, both the yeast and the amoebae had slow growth rates. The development of cysts corresponded with the growth of the yeast population without the rapid increase in yeast population prior to the growth of the amoebic cells.