Flocculation Ability Research Articles

Effect of cultural and nutritional conditions on the control of flocculation expression in Saccharomyces cerevisiae.

The effect of cultural (temperature and pH) and nutritional conditions (nitrogen and carbon source) on the flocculation expression of three strains was studied. The strains' flocculation ability was determined by placing the cells in a stationary phase of growth in standard flocculation conditions. The flocculation ability of strain NCYC 1195, recently classified in the literature as the NewFlo phenotype, was more sensitive to growth temperature than Flo1 phenotype strains (NCYC 869 and NRRL Y265). The initial pH of the culture medium did not affect the flocculation ability of Flo1 phenotype strains but in the case of strain NCYC 1195 flocculation was repressed when the initial pH of the culture medium was below 3.5. Flocculation in strain NCYC 1195 was also repressed in defined culture medium; this inhibition was not related to a deficiency in any particular nitrogen source, but rather to the poor buffering capacity of the defined medium. All strains showed strong flocculation when grown in glucose, but were nonflocculent in glycerol. It was clearly demonstrated that the phenotypic expression of flocculation could be induced or repressed by changing cultural and nutritional conditions. Two distinct behaviours were also displayed with regard to the effect of the cultural conditions upon flocculation, namely the effect of pH. These different behaviours can be used to distinguish the two flocculation phenotypes.

Isolation and partial purification of mannose-specific agglutinin from brewer's yeast involved in flocculation.

Yeast cell-agglutinating activity, designated agglutinin (possible lectin), was isolated from cell walls of both non-flocculent and flocculent brewer's yeast cells. Agglutinin-mediated aggregation of yeast cells in a manner similar to flocculation with respect to specific mannose-sensitivity, pH-dependence and calcium-dependence. Agglutinating activity was found to be heat-stable and protease-insensitive. Furthermore, addition of agglutinin to flocculent cells strongly stimulated the flocculation ability of the cells, whereas addition to non-flocculent cells rendered these cells weakly flocculent. Agglutinin was found to be released from flocculent cells during the course of a flocculation assay, but not from non-flocculent cells. Presence of mannose during the assay inhibited release of agglutinin. Our results suggest that (i) mannose-specific agglutinin is continuously synthesized during growth of brewer's yeast cells, (ii) agglutinin is present in cell walls of non-flocculent cells but is unable to bind its ligand on other cells, and (iii) the ability of yeast cells to flocculate in a flocculation assay depends, among other factors, on release of agglutinin from the cells. A 10-kDa polypeptide might represent one form of agglutinin.

Purification and partial characterization of a flocculin from brewer's yeast.

Analysis of a shear supernatant from flocculent, "fimbriated" Saccharomyces cerevisiae brewer's yeast cells revealed the presence of a protein involved in flocculation of the yeast cells and therefore designated a flocculin. The molecular mass of the flocculin was estimated to be over 300 kDa, as judged from sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Gel permeation chromatography of the flocculin yielded an aggregate with an apparent molecular weight of > 2,000. The flocculin was found to be protease sensitive, and the sequence of its 16 N-terminal amino acids revealed at least 69% identity with the predicted N terminus of the putative protein encoded by the flocculation gene FLO1. The flocculin was isolated from flocculent S. cerevisiae cells, whereas only a low amount of flocculin, if any, could be isolated from nonflocculent cells. The flocculin was found to stimulate the flocculation ability of flocculent yeast cells without displaying lectinlike activity (that is, the ability to agglutinate yeast cells).

Cell surface hydrophobicity and flocculence in Saccharomyces cerevisiae wine yeasts

Cell surface hydrophobicity (CSH) of 18 flocculent strains of Saccharomyces cerevisiae was studied. The CSH was estimated by hydrophobic microsphere attachment assay (HMA) and by microbial adhesion to hydrocarbons assay (MATH). The MATH showed that all the different flocculent strains were hydrophobic, varying only in the degree of CSH. Conversely, some strains proved to be hydrophilic with HMA. Treatment of flocculent cells with proteolytic enzymes caused a dramatic decrease in the CSH in all the strains, changing their affinity from that for hydrocarbons to that for water. Such treatment did not abolish the flocculation ability of several strains. Reversible change of flocculation-dispersion by the addition of EDTA caused an increase in CSH. These data led to the conclusion that the CSH character is not always closely related to flocculation ability, demonstrating once more that flocculation is mediated by different mechanisms.

Induced cell surface hydrophobicity influences flocculation of brewer's yeast in a flocculation assay

Recently, we found that initiation of flocculence of brewer's yeast during growth in defined medium or during fermentation in wort coincided with an increase in cell surface hydrophobicity (CSH) [G. Smit, M.H. Straver, B.J.J. Lugtenberg and J.W. Kijne, Appl. Environ. Microbiol., 58 (1992) 3709-3714; M.H. Straver, G. Smit and J.W. Kijne, Yeast, 9 (1993) 527-532]. Remarkably, this increased level of CSH of flocculent yeast cells was lost during the course of the in vitro flocculation assay used. We tested the effects of presence of calcium and sugars, pH, agitation and incubation time in the assay on CSH and flocculence of cells. The presence of calcium in the incubation solution appeared to be essential for cells to lose induced CSH while the presence of mannose in the assay was found to inhibit specifically loss of induced CSH. Furthermore, induced CSH was lost only after agitation by whirlmixing and after incubation of the cells at a pH permitting flocculation. In all cases, loss of induced CSH coincided with a significant increase in flocculation ability of the cells. Nevertheless, presence of the developmentally-regulated hydrophobic component in the cell suspension was necessary for flocculation. The appearance and loss of induced CSH of flocculent cells were found to be correlated with appearance and loss, respectively, of fimbriae-like structures on the cell surface. The presence of, specifically, mannose during incubation in the assay inhibited the loss of these structures. We hypothesize that (i) the induced hydrophobic factor is associated with and/or identical to the fimbriae, (ii) this factor has lectin-like activity or acts as a lectin ligand, and (iii) binding of the lectin results in cross-linking of fimbriae, which enables simultaneous loss of both induced CSH and fimbriae from the cell surface after whirlmixing.

Water-in-crude oil emulsions from the Norwegian continental shelf 8. Surfactant and macromolecular destabilization

Water-in-crude oil emulsions based on different crude oils from the Norwegian Continental Shelf have been prepared, characterized and destabilized. The destabilization was undertaken with ionic and non-ionic surfactants (Aerosol OT and Triton N-42), fluorinated surfactants and different polymers like polyethylene glycols and polyacrylates of varying molecular masses. The surfactants investigated seem to destabilize according to an interfacial replacement of the indigenous membrane. This is also revealed by interfacial tension measurements. The flocculation ability of the polymers was characterized by means of UV absorbance measurements on Al 2O 3 suspensions in decane. There is not a single correlation between flocculation efficiency and destabilization of the emulsion systems. Model water-in-oil emulsions stabilized by either interfacially active crude oil fractions or by tetraoxyethylene nonylphenol ether were investigated in parallel.

Determinants of flocculence of brewer's yeast during fermentation in wort.

Ability of Saccharomyces cerevisiae MPY3 cells to flocculate during fermentation in wort was found to be triggered after growth limitation by oxygen shortage and to coincide with a sharp increase in cell surface hydrophobicity of the cells. Presence of oxygen in the pitching wort influenced final cell number, flocculence of the cells and cell surface hydrophobicity. Flocculation ability of cells grown in air-depleted pitching wort was hampered, concomitant with a decrease in final cell number and in final cell surface hydrophobicity. Addition of ergosterol and Tween 80 to air-depleted wort restored normal growth of the cells as well as flocculation ability and the increase in cell surface hydrophobicity. The same parameters increased in value after addition of ergosterol and Tween 80 to a fermentation with air-saturated pitching wort. Hydrophobicity of a non-flocculent mutant of S. cerevisiae strain MPY3, fermenting in air-saturated pitching wort, did not increase at cell division arrest. These results support the hypothesis that cell surface hydrophobicity is a major determinant for yeast cells to become flocculent, and suggest that shortage of sterols and unsaturated fatty acids precedes flocculence under brewing conditions.

Flocculence of Saccharomyces cerevisiae cells is induced by nutrient limitation, with cell surface hydrophobicity as a major determinant.

Initiation of flocculation ability of Saccharomyces cerevisiae MPY1 cells was observed at the moment the cells stop dividing because of nitrogen limitation. A shift in concentration of the limiting nutrient resulted in a corresponding shift in cell division and initiation of flocculence. Other limitations also led to initiation of flocculence, with magnesium limitation as the exception. Magnesium-limited S. cerevisiae cells did not flocculate at any stage of growth. Cell surface hydrophobicity was found to be strongly correlated with the ability of the yeast cells to flocculate. Hydrophobicity sharply increased at the end of the logarithmic growth phase, shortly before initiation of flocculation ability. Treatments of cells which resulted in a decrease in hydrophobicity also yielded a decrease in flocculation ability. Similarly, the presence of polycations increased both hydrophobicity and the ability to flocculate. Magnesium-limited cells were found to be strongly affected in cell surface hydrophobicity. A proteinaceous cell surface factor(s) was identified as a flocculin. This heat-stable component had a strong emulsifying activity, and appears to be involved in both cell surface hydrophobicity and in flocculation ability of the yeast cells.

Syntheses of Anionic Surfactants Having Two Polyfluoroalkyl Chains and Their Flocculation Ability for Dispersed Magnetite Particles in Water

Abstract Four anionic surfactants having two polyfluoroalkyl chains in a molecule, sodium salt of bis(1H,1H,2H,2H-heptadecafluorodecyl) 2-sulfosuccinate, CF3(CF2)7(CH2)2OCOCH2CH(SO3Na)COO(CH2)2(CF2)7CF3, sodium salt of bis(1H,1H,9H-hexadecafruorononyl) 2-sulfosuccinate, H(CF2)8CH2OCOCH2CH(SO3Na)COOCH2(CF2)8H, sodium salt of bis(1H,1H,7H-dodecafluoroheptyl) 2-sulfosuccinate, H(CF2)6CH2OCOCH2CH(SO3Na)COOCH2(CF2)6H and sodium salt of bis(1H,1H,5H-octafluoropentyl) 2-sulfosuccinate, H(CF2)4CH2OCOCH2CH(SO3Na)COOCH2(CF2)4H, were prepared from maleic anhydride, the corresponding alcohols having a polyfluoroalkyl chain and sodium hydrogensulfite. The flocculation and redispersion abilities of these surfactants against dispersed magnetite particles in water have been examined in comparison with other four anionic surfactants having a single polyfluoroalkyl chain in a molecule; sodium pentadecafluorooctanoate, CF3(CF2)6COONa, sodium 9H-hexadecafluorononanoate, H(CF2)8COONa, sodium 7H-dodecafluoroheptanoate, H(CF2)6COONa, and sodium 5H-octafluoropentanoate, H(CF2)4COONa. These abilities were estimated by measurement of the contact angle against water using pelleted surface-modified magnetite. The abilities of the surfactants having two polyfluoroalkyl chains against flocculation-redispersion were superior to those of the surfactants having one polyfluoroalkyl chain. Especially, sodium salt of bis(1H,1H,2H,2H-heptadecafluorodecyl) 2-sulfosuccinate was the most effective surface active agent for these abilities.

Influence of aeration and glucose concentration in the flocculation ofSaccharomyces cerevisiae

The influence of glucose concentration and aeration rate on the flocculation ability ofSaccharomyces cerevisiae was studied. A low aeration rate exerted a positive effect on flocculation whereas a high aeration inhibited this phenomenon. A positive effect was achieved with a high glucose concentration. By controlling both of these factors it was possible to modulate the flocculation expression of this strain.

Construction of hybrid yeasts with increased flocculation for white wine manufacture

Abstract Hybrid strains of yeast have been selected that have better flocculating properties for white wine manufacture. The hybridisation of the production winemaking strain 13a (Varna 84) with a Saccharomyces cerevisiae haploid strain carrying the FLO5 mutation resulted in a hybrid with very good flocculation ability. Its fermentation activity was increased using several backcrosses. At the final step two meiotic segregants with mating ability were crossed with the production wine‐manufacturing strain 75b (Sofia 75); hybrids K93 and K97 were obtained. These hybrids showed better flocculation ability and a more rapid fermentation in comparison with the parental strains 13a and 75b. The composition, taste and aroma of wines obtained using hybrids were similar to those produced by parental strains. The treatment of young white wines was easier if constructed hybrid strains were used.

Synergetic flocculation of the bioflocculant fix extracellularly produced by Nocardia amarae.

The fractionation of bioflocculant FIX produced by Nocardia amarae YK1 revealed that the flocculant was a mixture of more than three substances. Although individual fractions did not exhibit the ability of flocculation at pH 5 to 7, synergetic flocculation was observed at pH 7 after mixing the fractions. Infrared spectrophotometry suggested that the chief components of fractions might be peptides. Enzymatic digestion of peptide moiety resulted in disappearance of flocculation activity. One of the ingredients of FIX carried high contents of glycine (25.6%), alanine (13.8%), and serine (12.3%), of which R groups were relatively small.

A biometric study of higher alcohol production in Saccharomyces cerevisiae

A hundred strains of Saccharomyces cerevisiae were examined for the ability to produce higher alcohols. In the strains tested the production of higher alcohols was found to be an individual strain characteristic and, as such, was statistically significant. The characteristics of the strains used (flocculation ability, foaming ability, killer character, and non-H2S production) were found to be uncorrelated to isobutanol and isoamyl alcohol production, whereas the production of high levels of n-propanol was found to be related to inability to produce H2S. This, in turn, suggests a link to methionine biosynthesis.

Dewatering of peat

Peat treated with polymeric flocculants dewaters much faster than untreated peat. The flocculants decrease the number of suspended particles and a more porous bed structure is formed. The consumption of cationic polyelectrolytes mainly depends on the charge density of the polymer and on the pH of the peat (i.e. its surface potential). This indicates that a charge neutralization process is of importance. Anionic polyions do not flocculate the peat to the same extent, i.e. they always leave some suspended solids. However, since they are cheaper, they are of commercial interest. Addition of inorganic ions improves the flocculation ability of the anionic polymers. There are pronounced differences in floc strength and structure using different polyelectrolytes, thus different pressing strategies will be needed to utilize them effectively. Measurements of the water permeability of a peat bed demonstrate that the dewatering rate can be increased a factor 50 by addition of flocculants. By taking into account the colloidal properties of peat and the effect of polymeric flocculants more efficient dewatering processes could be designed.

Wasserlösliche kationisch modifizierte copolymere mit acrylamid

AbstractDie Copolymerisation von Acrylamid mit N‐[3‐(N′‐Diethyl‐N′‐methyl)ammoniumn‐propyl]‐maleinimid‐methylsulfat in Aceton/Wasser‐Gemischen mit Persulfat‐Initiator führt zu pulverförmigen kationischen Polymeren mit hoher Molmasse, die leicht wasserlöslich sind und sehr gute Ausflockungseigenschaften zeigen. Das Copolymere weist praktisch die gleiche Zusammensetzung auf wie das eingesetzte Monomerengemisch. Sowohl die Ausbeute als auch die Molmasse des Copolymeren steigen mit zunehmender Acetonmenge (bis ca. 52 Vol.‐%) im Lösungsmittelgemisch an.

Flocculation of wine yeasts: frequency, differences, and stability of the character

Flocculating ability in yeasts of the genus Saccharomyces which cause the spontaneous fermentation of grape musts is not rare. About 6.8% of isolates are flocculent. The strains show a different degree of flocculation and also variable developmental behaviour. The genetic analysis, carried out immediately after strain isolation and again after 3 years, shows that only flocculating homozygote strains ensure the stability of the flocculation character over time. Flocculation of some strains shows a degree of instability in the expression of the character which is typical of cytoplasmic inheritance.

Flocculation of a Methylomonas sp.: Possible Involvement of a Surface Protein

Chemostat-grown cells of a newly isolated strain of Methylomonas were flocculated by the addition of small amounts of positively charged flocculants. The flocculation ability of the cells was almost completely lost after extracting the cells with 1–5 mm-EDTA, or by reducing pH to below 4·5. Reconstitution of the flocculation ability of EDTA-extracted cells was obtained either by the addition of an excess amount of calcium ions, or by mixing dialysed EDTA extracts with EDTA-extracted cells. The EDTA extract contained mainly proteins. The major protein was purified to homogeneity by gel filtration, and had a molecular size of 65000 Dal and an isoelectric point of 9·0. Immunological techniques indicated that this protein was located on the surface of the bacteria. We, therefore, propose that the surface protein of the Methylomonas sp. is involved in flocculation by positively charged flocculants.

Solubility Tendency of the Associated Colloidal Flocculant and its Flocculation Ability

Solubility Tendency of the Associated Colloidal Flocculant and its Flocculation Ability

Preparation of Polymer Electrolytes Derived from Polyurethaneamine

Polyurethaneamine (PUA) was prepared from N-methyldiethanolamine and hexamethylenediiso-cyanate. A variety of quaternary ammonium salts of PUA (cationic polymer) were prepared from PUA and alkyl bromides of various chain length (C2C12) with a view of obtaining good flocculants. In alkylating PUA with alkyl bromides, it was found that alkylation occured to urethane-N as well as quaternization reaction, and using low molecule of urethane as model compound prepared from ethanol and hexamethylenediisocyanate, alkylation to urethane-N was ascertained by the reaction of urethane and dodecyl bromide. The flocculation ability for aqueous suspension of kaoline was investigated in the relation to the structure of cationic polymers by measuring the sedimentation velocity, sedimentation volume, and turbidity. Cationic polymer obtained from PUA and the higher alkyl bromide showed good flocculation effect. The suitable range of degree of quaternization was 4060%. Cationic polymer was most effective for flocculation with increase of acidity. The most clarity of supernatant gave 40ppm turbidity at the dosage of 50ppm using cationic polymer (degree of quaternization 84.4%) obtained from PUA and dodecyl bromide. Interraction (metachromasia) between methyl orange and cationic site of a number of cationic polymers were examined, and cationic polymers with the higher degree of quaternization derived from the higher alkyl bromides and PUA were shown large metachro-masia. Cationic polymers derived from the higher alkyl bromides showed good flocculating ability which are not inferior that of typical commercial products.

A Fundamental Study of Polyacrylamide with Regard to Paper Making

The investigations of polyacrylamide concerning the paper making have been summarized. The acrylamide has been polymerized by an inverse emulsion polymerization. The modification of polyacrylamide by condensation with acetaldehyde has been studied, and the flocculation ability of the modified polymer has been discussed. For the purpose of obtaining the cationic derivatives, acrylamide has been copolymerized with 2-methyl-N-vinylimidazole. N-Dimethyl a-minoethyl polyacrylamide and polyacrylic hydrazide have also been prepared with the same intention by the polymer analogous substitution of polyacrylamide. The applications of those cationic polymers to the paper making as wet end additives have deen investigated. A complex polyelectrolyte has been prepared by combining the partially hydrolyzed polyacrylamide with polyethyleneimine. The complex polymer has been found to serve as a good flocculation agent and a wet end additive. The graft copolymerizations of acrylamide onto cellulose and petroleum resine have been also mentioned.