Survival and Growth of Tetrahymena thermophila in Media that are Conventionally Used for Piscine and Mammalian Cells

The transfer of Tetrahymena thermophila from normosmotic solutions (~20–80 mOsm/kg H₂O) to hyperosmotic solutions (> 290 mOsm/kg H₂O) was investigated. During the first 24 h of transfer from proteose peptone yeast extract (PPYE) to either 10 mM HEPES or PPYE with added NaCl to give ~300 mOsm/kg H₂O, most ciliates died in HEPES but survived in PPYE. Supplementing hyperosmotic HEPES or PPYE with fetal bovine serum (FBS) enhanced survival. When ciliates were transferred from PPYE to a basal medium for vertebrate cells, L‐15 (~320 mOsm/kg H₂O), only a few survived the first 24 h but many survived when the starting cell density at transfer was high (100,000 cells/ml) or FBS was present. These results suggest that nutrients and/or osmolytes in either PPYE or FBS helped ciliates survive the switch to hyperosmotic solutions. FBS also stimulated T. thermophila growth in normosmotic HEPES and PPYE and in hyperosmotic L‐15. In L‐15 with 10% FBS, the ciliates proliferated for several months and could undergo phagocytosis and bacterivory. These cell culture systems and results can be used to explore how some Tetrahymena species function in hyperosmotic hosts and act as opportunistic pathogens of vertebrates.