Flow cytometric monitoring of rhodamine 123 and a cyanine dye uptake by yeast during cider fermentation

Flow cytometry of rhodamine 123- or cyanine-stained cider yeast shows that the capacity for mitochondrial uptake of these cationic dyes is lost early in the fermentation. Survival of prolonged anaerobiosis (for at least 22 days) at high ethanol concentrations (at least 11% v/v) during cider fermentation does not require the maintenance of a measurable inner mitochondrial transmembrane electrochemical potential. Confocal laser scanning microscopy of yeasts after exposure to either of the cationic dyes confirms the lack of mitochondrial development and inability of the fermentative organisms to take up the fluorophores. Aeration of samples taken from the fermentation vessels restores the ultrastructure and the dye uptake capacity of the yeasts. This indicates that the changes are reversible, and that the organisms have retained their viability.