FLOW-CYTOMETRY AND CELL SORTING FOR YEAST VIABILITY ASSESSMENT AND CELL SELECTION

Yeast suspensions were analysed by flow cytometry after dye staining f or determination of total and Viable cell densities. Results were comp arable to traditional colony counting and, in addition, provided furth er information on the percentage of total cells that were viable. The flow cytometric methods provided results within 20 min whereas colony counts were not available until 36 h. We evaluated a number of fluores cent dyes: ChemChrome Y (CY), oxonol (Ox), propidium iodide (PI), Fung olight and rhodamine 123, for accurate determination of viability of i ndustrial yeast cultures and freshly re-hydrated high activity dried y east (HADY). PI, Ox and CY gave the most conclusive live/dead discrimi nation and were the simplest to use. Culturing after dye staining and cell sorting demonstrated that the yeast remained viable after cell so rting and incubation with PI, CY or Ox. The methods, therefore, permit physical selection of individual yeast cells from populations of mixe d viability. Sorting demonstrated that PI stained non-culturable cells whilst CY stained culturable cells. Analysis of yeast stained simulta neously with CY and PI or with Ox and PI demonstrated that PI and CY a ssays were in mutual agreement with respect to viability assessments. The Ox assay was in agreement with CY and PI for live/heat-killed mixt ures. However, for re-hydrated HADY, Ox stained a significantly (P les s than or equal to 0.05) higher proportion of cells than did PI. (C) 1 998 John Wiley & Sons, Ltd.