Germinal aging in Tetrahymena thermophila.

The manifestations of germinal aging in the ciliate Tetrahymena thermophila include death of the cells at conjugation and macronuclear retention in which the normal replacement of the old macronucleus by a new one fails to occur. Available data suggest that methods of routine maintenance that reduce the number of fissions may delay aging. Differences in breeding performance following maintenance for 1-5 years in axenic peptone broth vs. bacterized Cerophyl were not significant; those following maintenance at different temperatures were significant. The analysis of several hundred crosses is consistent with a random mutational basis for aging in the micronucleus and does not support the hypothesis of an age-correlated program in which the rate of deterioration increases with time. Following routine cultural maintenance for as long as 9-11 years, some lines show no deficiencies in their ability to produce viable progeny, and sublines of the same clone frequently differ significantly in their breeding performance. Moreover, breeding degeneration occurs at constant, but different, rates in different inbred strains.