Characterization of Different Sized Cells of Baker's Yeast

Abstract

Commercial baker's yeast cells were fractionated into small and large sized cells by repeated centrifugation, and characterization of the small cells was carried out by comparison with the original cells. The small cell preparation consists of more than 90% of small sized age 0 cells, whose length of major axis ranged from 2.5 to 4.5 ,ce. There was no significant difference in DNA content and nuclear appearance between the small and original cell preparations. Respiratory activities were also essentially the same, but a marked difference was observed not only in RNA content but in MAR-column chromatograms. The amount of rRNA corresponding to 28S rRNA was greatly decreased in small cells and that of unidentified peak III was increased. The large cells whose length of major axis ranged from 4.5 to 6.5 showed excellent synchrony when placed in a synthetic medium. The situation of small cells in the cell division cycle was discussed.The cell population of a budding yeast is heterogeneous as to its divisional age as a consequence of its mode of reproduction.Some observations were reported on physiological characters of the age 0 cell which has not undergone the first budding yet. For example, initiation of budding from the age 0 virgin cell is always somewhat delayed from the second budding of its mother cell in agar-mounted slide culture (1) ; ascospore formation in the sporulation culture was hardly observed in the age 0 cell (2), etc. On the other hand, commercial product of baker's yeast in Japan always contains about 40% of small sized cells bearing no bud scars which are easily verified by the vital staining with fluorescent Brightener (1). From this point, it can be used as an experimental material suitable for characterization of the age 0 cell, if effective method of fractionation is established.The present paper deals with the method of obtaining small sized age 0 cells from a baker's yeast and some of its physiological characters.15

Increase in Cell Size as a Measure of Growth of Saccharomyces Cerevisiae

“…It was also confirmed that these cells are, without exception, age 0 cells which have not undergone any budding in the past (6).…”

“…Because the cells entering or nearly entering into the stationary phase were employed at the beginning of the culture either in the synchronous culture or in the single-cell culture, definite time called lag period was required up to the 1st budding ; thereafter, however, the cells grew normally and did not require any lag period for the 2nd and 3rd budding of the mother cells (6,29,30).…”

“…The cellular divisional age is defined as the number of budding which the cells had undergone in the past (6).…”

“…The cell suspension was subjected to fractional centrifugation in order to obtain the large-sized cells according to the method described previously and the synchronous culture was conducted employing the large cells as described previously ( 6).…”

“…It was reported previously that a large amount of small-sized cells was contained in the cell mass of a commercial baker's yeast. These small-sized cells existed not only in the cell mass of the commercial products, but in the logarithmically growing cells of baker's yeast (6).…”