Unidirectional co-stimulation by a non-mating strain of Tetrahymena thermophila.

We report that a fatty acid auxotroph of Tetrahymena thermophila (RH179E1) fails to mate, yet retains the ability to co-stimulate normal cells unidirectionally. Thus, co-stimulation can be analyzed experimentally in the absence of pair formation. We show that the co-stimulation of normal cells of one mating type is sufficient to shorten the waiting period for pair formation of those cells with initiated cells. This is the first evidence that co-stimulation causes a hyperinduction of mating reactivity in T. thermophila, generating in turn a positive feedback mechanism for (presumably) gamone production. Co-stimulation by the variant strain is at a maximum after 3-4 h of exposure when the variant and wild-type cells are at a ratio of 1:1. When mixed with wild-type cells, RH179E1 induces the formation of progeny (at low frequency) which inherit exclusively genetic material of the wild-type cells.