Differential growth rates of Candida utilis mother and daughter cells under phased cultivation

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Abstract
The yeast C. utilis was continuously synchronized by the phased method of cultivation with the N source as the growth-limiting nutrient. The doubling time (phasing period) of cells was 6 h. Both cell number and DNA synthesis showed a characteristic stepwise increase during the phased growth. The time of bud emergence coincided with the time of initiation of DNA synthesis. Size distribution studies combined with microscopic analysis showed that the cells expanded only during the unbudded growth phase. Usually the cells stopped increasing in size about 30 min before bud emergence, and the arrest of the increase in cell volume coincided with the exhaustion of N from the medium. There was no net change in the volume of cells during the bud expansion phase of growth, suggesting that as the bud expanded, the volume of the mother portion of the cell decreased. After division the cells expanded slightly. The post-division expansion of cells, unlike the growth before bud initiation, occurred in the absence of the growth-limiting nutrient. The newly formed daughter cells were smaller than the mother cells and expanded at a faster rate, so that both types of cells reached maximum size at the same time. Possible reasons for the different rates of expansion of mother and daughter cells are discussed.