Clonal lifespans cultured in chemically defined medium and conventional bacterized medium in Paramecium octoaurelia.

The unicellular ciliate, paramecium, reproduces by binary fission, but can not continue to divide unlimitedly without sexual reproduction. We examined the clonal life span of Paramecium octaurelia stock 299 cultured in conventional bacterized medium (BM) and a chemically defined medium (DM). The cells that lived in BM divided 300 times. Although the cells in DM divided more slowly, some cells continued to divide more than 100 times. The mean life span of 90 cell lines cultured in BM was 151 +/- 49 fissions and that of 84 cell lines in DM was 68 +/- 28. When some older cells, which had been cultured in DM, were transferred to BM, most of them showed much longer life spans than those remaining in DM. The results showed that the life spans of cell clones were affected by the culture conditions.