Buoyant density variation during the cell cycle of Saccharomyces cerevisiae

Abstract

Cell buoyant densities of the budding yeast Saccharomyces cerevisiae were determined for rapidly growing asynchronous and synchronous cultures by equilibrium sedimentation in Percoll gradients. The average cell density in exponentially growing cultures was 1.1126 g/ml, with a range of density variation of 0.010 g/ml. Densities were highest for cells with buds about one-fourth the diameter of their mother cells and lowest when bud diameters were about the same as their mother cells. In synchronous cultures inoculated from the least-dense cells, there was no observable perturbation of cell growth: cell numbers increased without lag, and the doubling time (66 min) was the same as that for the parent culture. Starting from a low value at the beginning of the cycle, cell buoyant density oscillated between a maximum density near midcycle (0.4 generations) and a minimum near the end of the cycle (0.9 generations). The pattern of cyclic variation of buoyant density was quantitatively determined from density measurements for five cell classes, which were categorized by bud diameter. The observed variation in buoyant density during the cell cycle of S. cerevisiae contrasts sharply with the constancy in buoyant density observed for cells of Escherichia coli, Chinese hamster cells, and three murine cell lines. Recent reports have indicated that the buoyant density of bacterial cells measured by equilibrium density banding in gradients of Percoll or similar colloids is constant both at different stages of the cell cycle (4, 6) and at widely different cell growth rates (6; unpublished observations). Buoyant densities of mammalian cells are also independent of the phase of the cell cycle (M.

Theoretical and conceptual derivation of threshold phenomena and metabolic switching models in a chemostat system

“…In our model, the resultant affinity (  only varies slightly with the culture conditions, which can be regarded as reasonable (Kubitschek et al, 1983;Kubitschek et al, 1984;Baldwin and Kubitschek, 1984). In addition, other studies in several experimental situations supported the influence of biomass on substrate affinity (Contois, 1959;Roques, 1982).…”

Cyclic AMP mediates the cell cycle dynamics of energy metabolism in Saccharomyces cerevisiae

“…In contrast, when relating cAMP to dry mass a high level is observed during G 1 and a significant decrease before the cells start budding. As the variation in cell density is quite low at high growth rates (<1% wet weight) (Baldwin and Kubitschek, 1984) due to small changes in storage carbohydrate content (Silljé et al , 1997), cell dry mass can be assumed to correlate fairly well with cell volume. Thus, the intracellular cAMP concentration can indeed be expected to decline before S phase begins, possibly relieving the PKA‐mediated repression of CLN1 and CLN2 transcription (Baroni et al , 1994; Tokiwa et al , 1994).…”

“…A convenient estimate of mean cellular volume for modelling purposes can be obtained by measuring cell dry weight (DW) in asynchronous cultures (Theobald et al , 1997; Vaseghi et al , 2001) where the population distribution is fairly constant, and thus also the mean cell density. However, this is no longer true when analysing synchronous cultures because the cell density is known to fluctuate during the cell cycle (Hartwell, 1970; Baldwin and Kubitschek, 1984). Here the cell density varies mainly due to periodic accumulation and breakdown of trehalose and glycogen, which is especially pronounced at low growth rates (Woldringh et al , 1993; Duboc, 1996; Silljé et al , 1997).…”

Field‐Flow Fractionation as Analytical Technique for the Characterization of Dry Yeast: Correlation with Wine Fermentation Activity

“…In addition to the size, density can also explain the Intec Red profile. Thus, Baldwin et al (23) indicated that yeast cells suffer a variation of the density during the cell cycle and cells with small buds showed the highest values. The lowest density was found when bud diameter coincided with the mother cell diameter.…”