Accumulation of DNA fragments in aging Paramecium tetraurelia in axenic and nonaxenic media.

The accumulation of DNA fragments in aging Paramecium tetraurelia after 15 days (or approximately 60 generations) of clonal growth in both axenic and nonaxenic media was assayed by alkaline elution assay. This sensitive technique permits measurement of single-strand breaks in double-stranded DNA. The results obtained indicate that P. tetraurelia aged in axenic medium accumulate more apurinic/apyrimidinic lesions, strand breaks, or single-strand gaps than do P. tetraurelia aged in nonaxenic medium. This implies that cells grown in axenic medium have a shorter lifespan than do cells grown in nonaxenic medium. The accumulation of DNA fragments may be the basic mechanism of aging in P. tetraurelia.