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Abstract
Saccharomyces cerevisiae was grown in a glucose-limited chemostat at dilution rates equivalent to mass doubling times of 2 to 16 h. Phase contrast microscopy revealed that cultures with mass doubling times greater than 4·5 h contained two sub-populations of cells, phase-dark and phase-light. The latter were shown to be predominantly unbudded daughter cells, which were not proliferating, and had properties similar to those of stationary phase cells in batch culture. Phase-dark cells were equivalent to cells growing exponentially in batch culture. The results suggest that the formation of phase-light cells represents cell cycle specific differentiation into stationary phase. The consequences of this phenomenon for the interpretation of results obtained with S. cerevisiae in the chemostat are discussed.
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