Effect of Temperature on Growth, Cell Size, and Free Amino Acid Pool of the Thermophilic Ciliate Cyclidium citriullus

SYNOPSIS. A clone of Cyclidium citrullus , adapted to growth at 18, 27, 37, 43, and 46 C had an optimum at 43 C, with 6.5 divisions/day. Transfer of cells previously grown at 43 or 46 C to 18 C resulted in death of most of the cells, transfer to 27 C increased the lag period, and transfer from 18 C to 37 or 46 C was followed faster division. All cells died at 48 C; some divided before death. At the temperatures employed maximum cell sizes (length and width) were achieved in the early log phase. At 43 C, however, the early log phase cells were smaller. Quantitative and qualitative differences in the free amino acids in the cells were found in ciliates grown at 18, 43, and 46 C; the highest amount/cell was found at 18 C, and the lowest at 43 C. High concentration of proline was noted only at 18 C.