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PubMed2000

Flocculation Kinetics and Cluster Morphology in Illite/NaCl Suspensions.

Using static and dynamic light-scattering techniques, we investigated the flocculation of geologic specimen illite and soil illite colloids suspended in NaCl solution at pH 8. Our results show that the two universality classes proposed by Lin and co-workers to characterize the diffusion and reaction-limited régimes of cluster-cluster flocculation do not apply to illite colloids, which have nonspherical morphology. Static light-scattering measurements yielded mass fractal dimensions for the soil illite clusters that were significantly above those required by universality. Those for specimen illite were influenced by the initial colloid concentration, suggesting that cluster restructuring had occurred during flocculation. Dynamic light-scattering measurements revealed a significant departure from linear growth of the mean cluster size with time, as required by universality in the diffusion-limited régime, and, for specimen illite, an oscillatory dependence of the mean cluster radius on time was observed in the transition from diffusion-limited to reaction-limited flocculation. Overall, the morphology, interactions, and restructuring of primary particles are believed to be responsible for the departure from universality in the flocculation behavior of the illite colloids. Copyright 2000 Academic Press.

Journal Article↗

PubMed2002

Depletion flocculation of latex dispersion in ionic micellar systems.

The flocculation behavior of anionic and cationic latex dispersions induced by addition of ionic surfactants with different polarities (SDS and cetyltrimethylammonium bromide (CTAB)) have been evaluated by rheological measurements. It was found that in identical polar surfactant systems with particle surfaces of SDS + anionic lattices and CTAB + cationic lattices, a weak and reversible flocculation has been observed in a limited concentration region of surfactant, which was analyzed as a repletion flocculation induced by the volume-restriction effect of the surfactant micelles. On the other hand, in oppositely charged surfactant systems (SDS + cationic lattices and CTAB + anionic lattices), the particles were flocculated strongly in a low surfactant concentration region, which will be based on the charge neutralization and hydrophobic effects from the adsorbed surfactant molecules. After the particles stabilized by the electrostatic repulsion of adsorbed surfactant layers, the system viscosity shows a weak maximum again in a limited concentration region. This weak maximum was influenced by the shear rate and has a complete reversible character, which means that this weak flocculation will be due to the depletion effect from the free micelles after saturated adsorption.

Journal Article↗

PubMed1996

Molecular cloning and analysis of the dominant flocculation gene FLO8 from Saccharomyces cerevisiae.

A flocculation gene was cloned from a Saccharomyces cerevisiae ATCC60715 genomic library, known to contain the FLO8 gene, on the basis of its ability to confer a flocculation phenotype on a nonflocculent strain. From a total of 11 130 clones, four clones sharing the several restriction fragments were isolated, suggesting that these were derived from the same locus. The results of integration mapping and disruption of the cloned gene indicated that this gene was the FLO8 gene. After disruption of the FLO8 gene, the strain lost its ability to flocculate. The DNA sequence of the FLO8 gene was determined. This gene includes a 2187-bp open reading frame that encodes a 729-amino acid protein. Computer analysis indicated that the FLO8 gene has a significant degree of homology with a S. cerevisiae chromosome V DNA sequence, but no homology with the FLO1 gene. The hydrophobicity profile of the putative FLO8 gene product did not indicate the presence of any significantly hydrophobic regions. Southern analysis of the FLO8 gene present in various yeast strains indicated that the FLO8 gene is highly conserved in yeast strains having a variety of flocculation phenotypes and genotypes. Northern analysis revealed that the level of FLO1 gene transcription is dependent on the rate of transcription of the FLO8 gene. These results suggest that the FLO8 gene mediates flocculation via transcriptional activation of the FLO1 gene.

Amino Acid Sequence↗

PubMed1996

Flocculation of humic substances with metal ions as followed by capillary zone electrophoresis.

Humic and fulvic acids from various sources have been shown to give different electropherograms by capillary zone electrophoresis (CZE), depending on the pH of the electrolyte. This CZE work is extended here through investigations involving the titration of humic and fulvic acids with Fe(III) and Cu(II) cations. As increasing amounts of these cations were added to the humic substances (HUS), flocculation of metal-humic complexes occurred. This is believed to be caused by binding of the metal cations with negative carboxyl and phenolic sites on the HUS, resulting in a decrease of the repulsive forces that keep the HUS in a conformation more suitable for water solubility. The flocculated complexes were separated from the supernatant by centrifugation, and the supernatants were characterized as to total organic carbon (TOC) content, molecular weight (MW) using gel permeation chromatography, and average electrophoretic mobility (AEM) using CZE. The extent of flocculation correlated with both TOC and quantitative CZE measurements. The MW of the HUS remaining in solution actually decreased, presumably because of precipitation of larger molecules as they became insoluble because of reactions with the metals. Humic acids showed total precipitation of TOC with both metals at a concentration equivalent to their measured acidity. CZE demonstrated that certain fulvic acid fractions (low molecular weight phenolic acids) remained in solution even at high metal concentrations. In summary, changes in electrophoretic behavior of the soluble HUS could be related to changes in charge-to-mass ratios (charge densities) of both humic and fulvic acids with increasing metal cation concentration (neutralization). The copper treated HUS showed changes in their electrophoretic behavior even at low metal concentrations before flocculation, whereas the iron treated HUS flocculated uniformally over the range of added iron without significant changes in AEM. Thus these changes in CZE patterns illustrate different specific binding sites of the HUS for each metal.

Journal Article↗

PubMed2005

Characteristics of Flo11-dependent flocculation in Saccharomyces cerevisiae.

The FLO11-encoded flocculin is required for a variety of important phenotypes in Saccharomyces cerevisiae, including flocculation, adhesion to agar and plastic, invasive growth, pseudohyphae formation and biofilm development. We present evidence that Flo11p belongs to the Flo1-type class of flocculins rather than to the NewFlo class. Both Flo1-type and NewFlo yeast flocculation are inhibited by mannose. NewFlo flocculation, however, is also inhibited by several other carbohydrates including glucose, maltose and sucrose. These differences have in at least one case been shown to reflect differences in the structure of the carbohydrate-binding site of the flocculins. We report that Flo11p-dependent flocculation is inhibited by mannose, but not by glucose, maltose or sucrose. Furthermore, Flo11p contains a peptide sequence highly similar to one that has been shown to characterise Flo1-type flocculins. Further characterisation of the properties of Flo11p-dependent flocculation revealed that it is dependent on calcium, occurs only at cell densities greater than 1 x 10(8) ml(-1), and only occurs at acidic pH.

Amino Acid Sequence↗

PubMed2004

Mathematical modeling of polymer-induced flocculation by charge neutralization.

A detailed mathematical model for flocculation of colloidal suspensions in presence of salts and polymers is described and validated. In former case, the classical DLVO theory, which accounts for relevant variables such as pH and salt concentration, is incorporated into a geometrically sectioned discrete population balance model. For processes involving polymers, flocculation via simple charge neutralization is modeled using a modified DLVO theory in which the effect of adsorbed polymer layers on van der Waals attraction is included. The fractal dimension of aggregates is obtained by dynamic scaling of experimental data for time evolution of mean aggregate size. The particle surface potential is assumed to be approximately equal to the zeta potential. The model predictions are in close agreement with experimental results for flocculation of colloidal hematite suspensions in the presence of KCl and polyacrylic acid at different concentrations. In particular, given values of model parameters, e.g., Hamaker constant, fractal dimension, surface potential, and thickness of adsorbed polymer layer, the model can realistically describe the kinetics of flocculation by a simple charge neutralization mechanism and track the evolution of floc size distribution. Representative examples of sensitivity of the flocculation model to perturbations in surface potential and fractal dimension and to modification in the DLVO theory for polymer-coated particles are included.

Journal Article↗

PubMed1996

Flocculation of dissolved Pb, Cu, Zn and Mn during estuarine mixing of river water with the Caspian Sea.

This is the first study of the flocculation of dissolved Pb, Cu, Zn and Mn during mixing of river water with the largest lake in the world (the Caspian Sea). Flocculation of dissolved metals was investigated on a series of mixtures with salinities ranging from 3.2 to 7.4 per thousand. The flocculation rates {Cu (74%) > Pb (61%) > Mn (58%) > Zn (34%)} are indicative of the non-conservative behavior of metals during estuarine mixing. Statistical analysis indicates that the flocculation of Pb and Mn is governed by salinity. The flocculation rates reveal that the overall metal pollution loads may decline by about 57% during estuarine mixing.

Journal Article↗

PubMed1997

Sexual co-flocculation by heterothallic cells of the fission yeast Schizosaccharomyces pombe modulated by medium constituents.

Novel simple synthetic media for inducing sexual co-flocculation in a short time after mixing heterothallic fission-yeast (Schizosaccharomyces pombe) cells of h- and h+ were devised; The most effective of these, mannose synthetic medium (MSM), contains 0.4% mannose as a carbon source in addition to galactose, KH2PO4 (pH4.0) and 4 vitamins. The addition of galactose to the medium suppressed the asexual self-flocculation but rather promoted the sexual co-flocculation. By transferring and mixing h- and h+ cells grown in malt-extract broth plus galactose into MSM, these heterothallic strains were revealed to be sexually ready through a long period of the log to stationary phases. Furthermore, a variety of C sources and NH4Cl at various concentrations in various media were examined for their effects upon sexual co-flocculation, conjugation and sporulation; it was found that the sugar concentration strictly affected the progress of the sequence of sexual reproduction at 26 degrees C but not 30 degrees C and that sexual co-flocculation of the heterothallic strains was induced only under lower concentrations of C and N source than that for the homothallic one.

Ammonium Chloride↗

PubMed1994

Molecular cloning of the gene encoding a highly expressed protein in SFL1 gene-disrupted flocculating yeast.

We identified a yeast gene encoding Flocculent Specific Protein (FSP) produced excessively in the SFL1 gene-disrupted flocculent strain. The sequenced gene encodes a 430 amino acid protein and is mainly composed of multiple repeats of Ser-Asn-Asn-X-Asp-Ser-Tyr-Gly. The FSP gene disruption of the flocculent strain decreased the degree of flocculation, so FSP may be one factor concerned with yeast flocculation. A gene database search indicated that the FSP gene is identical with the DDR48 gene.

Amino Acid Sequence↗

PubMed1978

[Flocculant interaction with native antibiotic solutions. An examination of the mechanism of the process].

Some characteristics of the fermentation broth filtrates, i.e. concentration of the disperse particles and some of their parameters (projected length, area, distribution of the particles along the maximum chord) were determined and estimated after flocculation. It was shown that the floccules were mainly formed as fine colloid admixtures present not only in "turbid", but also in visually transparant solutions. It was found that the mechanism of flocculation was rather complicated and not always similar for different batches of the fermentation broth filtrate: it was, in particular, affected by the electrostatic interactions, the flocculant interaction with inorganic reagents, bridge-forming processes.

Anti-Bacterial Agents↗

PubMed1980

Flocculation effect of xanthan gum in pharmaceutical suspensions.

The particulate structure in suspensions of magnesium carbonate, aluminum hydroxide, calcium carbonate, and zinc oxide was assessed by sedimentation volume studies, measurement of particle size by an electronic particle sizer, and visualization by microscopy. The results of the particle-size measruement did not always agree with results from the other techniques. magnesium carbonate, aluminum hydroxide, and zinc oxide were flocculated in water. The addition of xanthan gum increased flocculation of magnesium carbonate and aluminum hydroxide and apparently caused partial deflocculation of zinc oxide suspensions. Calcium carbonate suspensions were deflocculated in water, and xanthan gum did not significantly change the properties. Studies with sodium chloride showed that flocculation cannot be attributed to changes in double-layer repulsion. Flocculation in the suspensions studied appeared to be consistent with a bridging mechanism.

Aluminum Hydroxide↗

PubMed1987

Flocculation of suspensions containing nonionic surfactants by sorbitol.

Aqueous suspensions of sulfamerazine, salicylamide, and butamben, containing either polysorbate 20 or polysorbate 80 as a wetting agent, were deflocculated. The presence of relatively high concentrations of sorbitol in the suspensions resulted in flocculation due to dehydration of surfactant polyoxyethylene groups (reflected by the cloud point). The critical flocculation concentration of sorbitol was reduced by raising the storage temperature, lowering the surfactant concentration, switching from polysorbate 80 to polysorbate 20, or adding sodium sulfate to the suspension formulation. Both the cloud point and the sorbitol critical flocculation concentration depended on the particular drug that was suspended. Methylparaben lowered the cloud point, suggesting that the choice of preservative could influence the suspension characteristics in certain cases. The various dehydrating influences were additive. By assuming that interparticle repulsion becomes negligible at the cloud point, it was possible to use cloud point curves to estimate the critical flocculation concentration of sorbitol.

Benzocaine↗

PubMed1988

Yeast flocculation: quantification.

Yeast flocculation is an orthokinetic process dependent upon mechanical agitation for all quantitative measurements. From several methods which were assessed, orbital shaking was selected as being the most practical as well as producing the most meaningful results. Quantitative measurements of flocculation were made in terms of minimum agitation threshold, initial rate, extent of flocculation at equilibrium and flocculated particle size at equilibrium. All these parameters were strain dependent. Critical cell density functions were formed if agitation was limiting regardless of how the agitation was imposed, and are unlikely to be related to bond strength.

Colony Count, Microbial↗

PubMed1988

Yeast flocculation: a dynamic equilibrium.

The steady state in yeast flocculation is a dynamic equilibrium between flocculated and dispersed yeast cells. The free cell concentration is directly proportional to the total cell concentration and may be expressed as an equilibrium constant. Increased agitation decreases floc size and equilibrium constant whilst increasing floc-surface area and free-cell concentration. Values of equilibrium constant are influenced by agitation in a complex relationship probably involving the floc-surface area and floc momentum. Inhibition of flocculation by mannose and low pH is reversible and becomes greater with increased agitation. Both these inhibitions appear consistent with a weakening of flocculent bond strength by these inhibitors.

Colony Count, Microbial↗

PubMed2002

Application of fluorescence correlation spectroscopy: a study of flocculation of rigid rod-like biopolymer (schizophyllan) and colloidal particles.

The flocculation between the rod-like biopolymer Schizophyllan and two types of colloidal particles (latex with diameter 40 nm and alumina with diameter 60 nm) has been investigated by means of fluorescence correlation spectroscopy (FCS). The concentration ratio of Schizophyllan/particle q was varied in the range 0.1 approximately 20. Under conditions of pH about 5.7, 1 mmol.L(-1) NaCl, and room temperature (22+/-0.5 degrees C), the particles are strongly charged (alumina particles positively charged, latex negatively), while Schizophyllan is neutral. We observed that Schizophyllan chains flocculate with both types of particles, which suggests that the charge neutralization does not play a decisive role in these interactions. The ratio of fluorescence intensity of one floc over that of one particle, Q(f)/Q(p), and the corresponding hydrodynamic radius (r(h)) of the flocs have been measured. For a Schizophyllan-latex system, Q(f)/Q(p) reached a maximum value of 5 for q=3 indicating that the flocs contained five particles on average. The corresponding value of r(h) was r(h)=455 nm. The flocculation kinetic of latex particles with Schizophyllan was too fast to be measurable by FCS. For the Schizophyllan-alumina system, Q(f)/Q(p) was stable at about 1 in the whole studied range of q but r(h) increased with q suggesting that many Schizophyllan chains are adsorbed on individual particles. The flocculation kinetic of this system was studied by FCS and the obtained results were compatible with those of photon correlation spectroscopy.

Aluminum Oxide↗

PubMed1996

The flocculation of wine yeasts: biochemical and morphological characteristics in Kloeckera apiculata.

The floc-forming ability of flocculent strains of Kloeckera apiculata, isolated from musts, was tested for susceptibility to proteinase and sugar treatments. Three different flocculation phenotypes were discriminated by protease digestion, whereas the inhibition of flocculation by sugars distinguished two definite patterns: one mechanism of flocculation involved a galactose-specific protein and the other a broad-specificity lectin. SEM and TEM observation of the cell surface of two different Kloeckera strains revealed fine fibrils and a diffuse structure at the point of contact in one strain, and thick masses of mucus on the cell wall of the other strain.

Carbohydrates↗

PubMed2002

Flocculent activity of a recombinant protein from Moringa oleifera Lam. seeds.

Seeds of the tropical tree Moringa oleifera contain small storage proteins able to flocculate particles in suspension in water. The cDNA encoding one of these flocculent proteins, MO(2.1), was cloned and the recombinant protein was expressed in Escherichia coli. The flocculent activity of the purified recombinant MO(2.1)was assayed on clays and bacteria using light and confocal microscopy and GFP-overexpressing bacteria. We show that MO(2.1)is able to aggregate montmorillonite clay particles as well as gram-positive and gram-negative bacteria. We discuss the use of recombinant proteins to study flocculating properties and improve water purification processes.

Amino Acid Sequence↗

PubMed2006

Effect of flocculation on performance of arming yeast in direct ethanol fermentation.

In the direct ethanol fermentation of raw starch by arming yeast with alpha-amylase and glucoamylase, it is preferable to use a flocculent yeast because it can be recovered without centrifugation. Three types of arming yeast system, I (nonflocculent), II (mildly flocculent), and III (heavily flocculent), were constructed and their fermentation performances were compared. With an increase in the degree of flocculation, specific ethanol production rate for soluble starch decreased (0.19, 0.17, and 0.12 g g-dry-cell(-1) h(-1) for systems I, II, and III, respectively), but that for raw starch did not decrease as much as expected (0.06, 0.06, and 0.04 g g-dry-cell(-1) h(-1) for systems I, II and III, respectively). Microscopic observation revealed that many starch granules were captured in the yeast flocs in system III during the direct ethanol fermentation of raw starch. It was suggested that the capture of starch granules increases apparent substrate concentration for amylolytic enzymes in arming yeast cell flocs; thus, the specific ethanol production rate of system III was kept at a level comparable to those of the other systems.

Ethanol↗