FLOW CYTOMETRIC ASSESSMENT OF CELL STRUCTURAL AND FUNCTIONAL-CHANGES INDUCED BY ACETIC-ACID IN THE YEASTS ZYGOSACCHAROMYCES-BAILII AND SACCHAROMYCES-CEREVISIAE

Flow cytometry (FCM) was used with different viability dyes to assess changes in cell structure and function induced by acetic acid (AA) in populations of Zygosaccharomyces bailii (AA resistant) and Saccharomyc es cerevisiae (AA sensitive). Kinetic changes in esterase activity, in tracellular dye processing, and membrane integrity were monitored, and to detect those changes we used three assays involving fluorescein di acetate hydrolysis, FUN-1 processing, and propidium iodide exclusion, respectively, In S, cerevisiae, the decrease in the ability to process FUN-1 preceded the decrease in esterase activity, and there was loss of cell membrane integrity after incubation with AA, In Z, bailii, wit h higher AA concentrations, there was a similar decrease in the abilit y to process FUN-1, which also preceded the loss of cell membrane inte grity. Changes in esterase activity in this yeast induced by AA treatm ent could not be monitored because the changes occurred independently of the presence of the acid, For control samples (untreated cells kill ed with 10% v/v of AA), the percentages of nonaltered cells as estimat ed by FCM and percentages of viable cells as estimated by colony formi ng unit (CFU) counts were identical, However, for cell samples treated for short periods with 3% (v/v) or less of AA, none of the dyes produ ced FCM results comparable to those produced by CFU counts. (C) 1998 W iley-Liss, Inc.