Identification of different daughter and parent subpopulations in an asynchronously growing Saccharomyces cerevisiae population.

Under all growth conditions, a growing Saccharomyces cerevisiae yeast population is extremely heterogeneous, since individual cells differ in their cell size; this is due to their position in the cell division cycle and their genealogical age. To gain insight into the structure of a growing yeast population, we used a recently developed flow cytometric approach which enables, in asynchronously growing S. cerevisiae populations, tagging of both the cell age and the protein content of individual cells. This approach enabled the identification of daughter cells belonging to different cell cycle positions (i.e. newborn, G1, S + G2 + M + G1*, and dividing), thus yielding information about the relative fraction in the whole population, cell size and variability. More limited information could be obtained for the parent subpopulation; however, we were able to identify and characterize the dividing parent cells. The coefficient of variation (CV) of the protein content distribution for the dividing parents (27) was much higher than the CV of dividing daughters (18). Further findings obtained indicated a large overlap between the cell protein content distributions of daughter and parent cells as well as between the protein content of cells of the same subpopulation but belonging to different stages of the cell division cycle. The analysis of these differences enables a better understanding of the complex structure of an asynchronously growing yeast population.