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.
A new form of cell death has been observed. The death occurs at liquid-air interfaces when Tetrahymena cells are grown in a chemically defined medium (CDM) at low inocula. The cells die by lysis at the liquid-air interface (medium surface), which they reach due to negative gravitaxis as well as positive aerotaxis. When the cells are grown in a closed compartment, with no liquid-air interface, the death is not observed, and the cells proliferate. Cloning of cells in CDM is thus possible. The addition of effectors such as NGF (10(-11) M), EGF (10(-10) M), PDGF (10(-10) M), and insulin (10(-7) M) to cells in CDM prevents the surface mediated death. Since detergents/surfactants like SDS (7 x 10(-5) M), NP-40 (2 x 10(-5) M), Tween 80 (10(-4))% w/v), Pluronic F-68 (10(-7) M), and the biosurfactant surfactin (10(-6) M) have the same effect, we suggest that the effectors act by stimulating the cells to exudate surfactant(s) of their own. Furthermore, lyzed cells and exudates from living cells (pre-conditioned medium) prevent the death. In conditions with liquid-air interfaces, certain physical parameters are of great importance for the survival of cells at low inocula. The parameters are the distance to the surface, the temperature, and the inoculum. By increasing the height of the medium, lowering the temperature, and increasing the inoculum of the culture, the survival can be greatly enhanced. There is no evidence for programmed cell death (PCD) or apoptosis.
A new form of cell death has been observed. The death occurs at liquid-air interfaces when Tetrahymena cells are grown in a chemically defined medium (CDM) at low inocula. The cells die by lysis at the liquid-air interface (medium surface), which they reach due to negative gravitaxis as well as positive aerotaxis. When the cells are grown in a closed compartment, with no liquid-air interface, the death is not observed, and the cells proliferate. Cloning of cells in CDM is thus possible. The addition of effectors such as NGF (10(-11) M), EGF (10(-10) M), PDGF (10(-10) M), and insulin (10(-7) M) to cells in CDM prevents the surface mediated death. Since detergents/surfactants like SDS (7 x 10(-5) M), NP-40 (2 x 10(-5) M), Tween 80 (10(-4))% w/v), Pluronic F-68 (10(-7) M), and the biosurfactant surfactin (10(-6) M) have the same effect, we suggest that the effectors act by stimulating the cells to exudate surfactant(s) of their own. Furthermore, lyzed cells and exudates from living cells (pre-conditioned medium) prevent the death. In conditions with liquid-air interfaces, certain physical parameters are of great importance for the survival of cells at low inocula. The parameters are the distance to the surface, the temperature, and the inoculum. By increasing the height of the medium, lowering the temperature, and increasing the inoculum of the culture, the survival can be greatly enhanced. There is no evidence for programmed cell death (PCD) or apoptosis.
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