Interface-mediated death of unconditioned Tetrahymena cells: effect of the medium composition.

We have previously shown that the cell death of Tetrahymena thermophila in low inocula cultures in a chemically-defined medium is not apoptotic. The death is caused by a cell lysis occurring at the medium-air interface and can be prevented by the addition of insulin or Pluronic F-68. Here, we report that cell death can also be caused by the medium. The specific effects of several medium constituents were tested in the presence and absence of an interface. Four of the 19 amino acids (arginine, aspartic acid, glutamic acid, and histidine in millimolar concentration) as well as Ca2+ (68 microM) and Mg2+ (2 mM) and trace metal ions (micromolar concentrations) are all sufficient to induce the interface-mediated death. The effect of the amino acids and the salt ions Ca2+ and Mg2+ can be abolished by the addition of insulin (10(-6) M) or Pluronic F-68 (0.01% w/v), whereas insulin/Pluronic F-68 only postpones the death induced by trace metal ions. On the basis of our findings, a new recipe for a chemically-defined medium has been formulated. Single cells can grow in this medium in the presence of medium-air interface without any supplements.