Role of Wall Phosphomannan in Flocculation of Saccharomyces cerevisiae

Publisher Website
Google Scholar
Abstract
Treatment with 60% HF removed most of the P and small amounts of mannan, glucan and protein from walls of 2 non-flocculent strains (NCYC366 and NCYC1004) and 2 flocculent strains (NCYC1005 and NCYC1063) of S. cerevisiae. Organisms of all strains showed increased flocculating ability following HF treatment. Flocculation of untreated organisms of NCYC1005 and NCYC1063, and of HF-treated organisms of all 4 strains, declined appreciably when they were washed in deionized water, with or without EDTA, and the flocculation was measured in deionized water instead of in 0.05 M-sodium acetate containing Ca2+. Treatment with 1,2-epoxypropane also caused a decrease in the flocculating ability of these organisms. Extracting the lipids from organisms of strains NCYC366 and NCYC1004 had no effect on their flocculating ability, but decreased the flocculating ability of organisms of strains NCYC1005 and NCYC1063. The pH-electrophoretic mobility curves of untreated and HF-treated organisms confirmed the loss of wall phosphate by HF treatment, and indicated that HF treatment had little effect on the content of protein carboxyl groups in the outer wall layers. Mannose at 0.22 M completely prevented floc formation by organisms of strain NCYC1063; but even at 0.33 M, it had very little effect on floc formation by HF-treated organisms of strains NCYC366 and NCYC1063. Organisms of all 4 strains bound fluorescein-conjugated concanavalin A to the same extent after treatment with HF as before, but this treatment led to a greatly diminished binding of fluorescein-conjugated antiserum raised against organisms of strain NCYC366. The results indicate that phosphodiester linkages in yeast-wall mannan are not involved in bridge formation through Ca2+ during floc formation and that this arises principally through carboxyl groups. [Flocculation is the spontaneous aggregation by certain stratus of S. cerevisiae or S. carlsbergensis at the end of a brewery fermentation to form flocs which sediment in the fermentation vessel].