Estimation of “START” in Saccharomyces cerevisiae by Flow Cytometry and Fluorescent Staining of DNA and Cell Protein

Abstract

For industrial fermentations “early events” refer to the immediate response of the culture when added to the substrate. At that time the culture is exposed to a completely new environment leading to a number of cellular events taking place before measurable changes in the substrate are detectable. These events are considered valid indicators of the physiological status of the culture and key events necessary for an optimal fermentation and final product quality. For Saccharomyces cerevisiae as a starter culture “START”, defined as the time when the cells are committed to cell division, is regarded as an important “early event”. “START” is a “point” late in the G1-phase that yeast cells need to pass before they can replicate their DNA (Hartwell, 1994). Much of the current understanding of “START” in Sacch. cerevisiae comes from studies of cells carrying mutations in cell division cycle (CDC) genes (Baroni et al., 1994 and Tokiwa et al., 1994). “START” has been shown to be a series of tightly regulated events that must occur before the cells are committed to mitotic division (Sherlock and Rosamond, 1993). The yeast cell cycle is divided into four different cell cycle phases G1, S, G2 and M-phase. In the G1-phase cells are unbudded with shapes that approximates a prolate spheroid. The cells grow in volume during this phase of the cell cycle. The initiation of the S-phase coincides with bud emergence and during this phase DNA is doubled. When DNA has doubled the cells enter the G2-phase which is the gap between DNA replication and mitosis.