Interface-mediated death of unconditioned Tetrahymena cells: Effect of themedium 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 d eath is caused by a cell lysis occurring at the medium-air interface and ca n 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 i nterface. Four of the 19 amino acids (arginine, aspartic acid, glutamic aci d, and histidine in millimolar concentration) as well as Ca2+ (68 mu M) and Mg2+ (2 mM) and trace metal ions (micromolar concentrations) are all suffi cient 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 insuli n (10(-6) M) or Pluronic F-68 (0.01% w/v), whereas insulin/Pluronic F-68 on ly postpones the death induced by trace metal ions. On the basis of our fin dings, a new recipe for a chemically-defined medium has been formulated. Si ngle cells can grow in this medium in the presence of medium-air interface without any supplements.