Modeling of orthokinetic flocculation of Saccharomyces cerevisiae.

This study examined the flocculation behavior of two Saccharomyces cerevisiae strains expressing either Flo1 (LCC1209) genotype or NewFlo (LCC125) phenotype in a laminar flow field by measurement of the fundamental flocculation parameter, the orthokinetic capture coefficient. This orthokinetic capture coefficient was measured as a function of shear rate (5.95-223 s(-1)) and temperature (5-45 degrees C). The capture coefficients of these suspensions were directly proportional to the inverse of shear rate, and exhibited an increase as the temperature was increased to 45 degrees C. The capture coefficient of pronase-treated cells was also measured over similar shear rate and temperature range. A theory, which predicts capture coefficient values due to zymolectin interactions, was simplified from that developed by Long et al. [Biophys. J. 76: (1999) 1112]. This new modified theory uses estimates of: (1) cell wall densities of zymolectins and carbohydrate ligands; (2) cell wall collision contact area; and (3) the forward rate coefficient of binding to predict theoretical capture coefficients. A second model that involves both zymolectin interactions and DLVO forces was used to describe the phenomenon of yeast flocculation at intermediate shear ranges, to explain yeast flocculation in laminar flow.     

Depletion flocculation and depletion stabilization of erythrocytes.

At dextran (Mw approximately 500,000) concentrations from 2 to approximately 10%, suspensions of normal human erythrocytes flocculate in small convex agglutinates. At dextran concentrations greater than 10%, the erythrocytes resegregate in a stable monodisperse suspension. At all these dextran concentrations, the erythrocytes are coated with considerable amounts of dextran. It can be argued that at dextran concentrations from 2 to 10%, as well as at dextran concentrations greater than 10%, there is a thin layer, which is depleted of dextran, between the dextran layer adsorbed onto the erythrocytes and the bulk dextran solution. It can also be shown that there is a repulsive interaction between the two layers of dextran: one adsorbed and one free. When the adsorbed dextran layer is the most concentrated, stability must ensue, and when the dextran in free solution is the most concentrated, flocculation should occur. Below 7% dextran, the concentration of free dextran is higher than the adsorbed concentration; above 10% dextran that situation is reversed. These data correlate well with the depletion flocculation predicted for the lower concentration and the depletion stabilization predicted for the higher dextran concentration.     

The relationship of acid-soluble glycogen to yeast flocculation.

A relationship between yeast flocculation and intracellular acid-soluble glycogen has been established which has been substantiated using flocculation mutants (mutants with altered capacities to flocculate) as well as a normal strain of Saccharomyces carlsbergensis. Sound evidence exists to implicate physiological differences in carbohydrate metabolism (glycogen storage) to this physical property of brewing significance.     

Role of wall phosphomannan in flocculation of Saccharomyces cerevisiae.

Treatment with 60% hydrofluoric acid (HF) removed most of the phosphorus and small amounts of mannan, glucan and protein from walls of two non-flocculent strains (NCYC366 and NCYC1004) and two flocculent strains (NCYC1005 and NCYC1063) of Saccharomyces 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 four 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. 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 four 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 of fluorescein-conjugated antiserum raised against organisms of strain NCYC366. The results indicate that phosphodiester linkages in yeast-wall mannan are not involved in bride formation through Ca2+ during floc formation and that this arises principally through carboxyl groups.     

Ethanol stimulates the flocculation of Zymomonas mobilis

When flocculating cells of Zymomonas mobilis were put in contact with increasing concentrations of ethanol, flocculation was intensified. The settling velocity increased 5.3-fold when the ethanol concentration rose from 0 to 12% v/v. Additionally, the percentage of free-cells diminished considerably (from 33 to 10%), denoting an increase on the extent of flocculation. The stress provoked by ethanol possibly leads to the activation of genes responsible for aggregation.     

Ferric chloride flocculation for nonflocculating beef extract preparations.

The addition of 2.5 mM ferric chloride to 0.5% beef extract solution at pH 3.5 was found to be highly efficient in the recovery of seeded poliovirus type 1 (Sabin) or indigenous viruses from environmental samples. This method was extremely useful to reconcentrate viruses from beef extract solutions that did not flocculate at pH 3.5.     

Repression and induction of flocculation interactions in Saccharomyces cerevisiae.

The biological control of flocculation interactions by factors related to growth under different conditions of aeration was documented with a new assay for flocculence. The degree of flocculence expressed in a genetically defined Saccharomyces cerevisiae strain (FLO1/FLO1 ade1/ade1) remained constant during aerobic growth but varied with aeration. Flocculence was repressed in anaerobically growing cells but was induced in stationary cells or cells returned to aerobic growth. Repression was correlated with the selective inactivation of cell surface lectin-like components. The changes in flocculence were accompanied by changes in 16 extractable proteins separated by electrophoresis; however, a clear correlation between specific protein bands and flocculence could not be established. The study clearly demonstrated that the phenotypic expression of FLO1 could be reproducibly manipulated for experimental purposes by aeration alone.     

Exopolymer production and flocculation by zoogloea mp6.

Flocculation by Zoogloea MP6 was accompanied by the production of a mucopolysaccharide exopolymer. Polymer formation was initiated in mid-logarithmic growth phase, and the quantity produced appeared to be influenced by the level of carbon and nitrogen in the culture medium.     

Exopolymer production and flocculation by zoogloea mp6.

Flocculation by Zoogloea MP6 was accompanied by the production of a mucopolysaccharide exopolymer. Polymer formation was initiated in mid-logarithmic growth phase, and the quantity produced appeared to be influenced by the level of carbon and nitrogen in the culture medium.