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PubMed1978

Flocculation and adsorption of enzymes during growth of a moderate halophile, Micrococcus varians var. Halophilus.

Flocculation of a moderate halophile, Micrococcus varians ATCC 2197, occurred during growth in complex medium containing 3 M NaCl and a concentration of MgSO4 and KH2PO4 greater than 40 and 14 mM, respectively. Extracellular nuclease activity was absent in the flocculated cultures. Repeated washing of flocs by Mg2+-free Tris buffer containing 3 M NaCl, lowering of pH value of floc suspension below 6.3, or addition of ethylenediaminetetraacetic acid resulted in complete dissociation of the flocs and release of Mg2+ ions as well as nuclease and amylase. Inhibition of extracellular enzyme production accompanied by flocculation appeared to be the result of adsorption of enzyme proteins to surfaces of the flocs, but not of inhibition of biosynthesis. Floc formation could also occur in media containing 18 mM CaCl2 and 3.0 mM KH2PO4, but the Ca flocs were not deflocculated by washing with Ca2+-free buffer, suggesting that the affinity of Ca2+ for cell envelopes was stronger than that of Mg2+. It was also observed that most halophilic Planococcus and Micrococcus flocculated in the presence of MgSO4 and phosphate but halophilic Pseudomonas, Acinetobacter, and Bacillus did not.

Adsorption↗

PubMed1988

Yeast flocculation: competition between nonspecific repulsion and specific bonding in cell adhesion.

Yeast flocculation is governed by the competition between electrostatic repulsion (nonspecific interaction) and polysaccharide-protein bonds (specific interaction). The electrical surface potential, which is mainly due to phosphodiester linkages (of the cell wall phosphomannan), maintains the cells dispersed. Polysaccharides and proteins of the cell surface can readily penetrate the potential barrier and may establish specific bonds. The specific inhibition of flocculation by various mannosyl derivatives suggested that the protein receptor binds to the group Man alpha----3 Man alpha----PO4- ----6 Man alpha----2 Man alpha... of phosphomannan. Calcium, which is required for flocculation, could act as a bridge between the negatively charged groups of phosphomannan and those of the protein receptor. The role of calcium, however, cannot be restricted only to charge neutralization because other divalent cations inhibit flocculation; our results show that cation binding is governed by strong stereochemical constraints. Studies on protein-polysaccharide interactions have shown that electrical charges may remain uncompensated at short distance, but can be stabilized by hydrogen bonds. Calcium could induce a "locked" conformation of the receptor; this conformation is the only one capable of binding phosphomannan strongly enough to make cell adhesion possible.

Calcium↗

PubMed1992

Interaction between flocculent and nonflocculent cells of Saccharomyces cerevisiae.

Interaction between nonflocculent and flocculent cells of Saccharomyces cerevisiae was studied. Adhesion experiments were done using three types of nonflocculent cells and a flocculent one. Two types of nonflocculent cells were obtained from the flocculent strain by changing environmental growth conditions. The integration of nonflocculent cells in the flocs was observed by two different methods: measurement of the sedimentation capacity of mixtures and microscopic observation of stained nonflocculent cells blended with flocculent cells. It was possible to verify that cell-cell interaction corresponds to a true stable binding and not to a simple entrapment inside the floc matrix.

Cell Adhesion↗

PubMed2001

Ethanol-induced cell aggregation (flocculation) and its physiological background in Schizosaccharomyces pombe rive 4-2-1.

Cell aggregation (flocculation) of the yeast Schizosaccharomyces pombe strain RIVE 4-2-1 developed in glucose-containing medium, but only in the presence of ethanol. Cell surface proteins which participated in cell to cell interactions were characterised by the susceptibility of flocculation to different proteolytic enzymes, heat treatment, denaturing and thiol compounds and by the inhibition of flocculation by sugars and derivatives. It was shown that a galactose-specific lectin was involved in this new type of flocculation.

Carbohydrates↗

PubMed2005

Flocculation of Bacillus thuringiensis var. israelensis suspension and its efficacy against mosquito larvae.

Bacillus thuringiensis ssp. israelensis (Bti) is increasingly used as an ecologically friendly anti-mosquito agent. The bacterium cells undergo fermentation in dilute suspensions; before practical use, therefore it is necessary to concentrate the suspensions. Aggregation by polymers is a powerful tool with which to regulate the stability of suspensions. Typically, polymers at low concentrations destabilize and at high concentrations stabilize colloidal systems. Bti suspensions can be flocculated efficiently by either cationic or anionic polyelectrolytes. Cationic polyelectolytes were found to be the most efficient flocculants for bacterial suspensions. It was shown that the degree of toxicity of the flocculated Bti suspensions for biting mosquito larvae was in the same range than in non-flocculated suspension.

Animals↗

PubMed2006

Reducing diarrhoea in Guatemalan children: randomized controlled trial of flocculant-disinfectant for drinking-water.

OBJECTIVE: To examine the effect of a new point-of-use treatment for drinking-water, a commercially developed flocculant-disinfectant, on the prevalence of diarrhoea in children. METHODS: We conducted a randomized controlled trial among 514 rural Guatemalan households, divided into 42 neighbourhood clusters, for 13 weeks, from 4 November 2002 through 31 January 2003. Clusters assigned to water treatment with the flocculant-disinfectant were compared with those using their usual water-handling practices. The longitudinal prevalence of diarrhoea was calculated as the proportion of total days with diarrhoea divided by the total number of days of observation. The prevalence of diarrhoea was compared using the Wilcoxon rank-sum test. FINDINGS: The 1702 people in households receiving the disinfectant had a prevalence of diarrhoea that was 40% lower than that among the 1699 people using standard water-handling practices (0.9% versus 1.5%; P = 0.001). In households using the flocculant-disinfectant, children < 1 year of age had a 39% lower prevalence of diarrhoea than those in households using their standard practices (3.7% versus 6.0%; P = 0.005). CONCLUSION: In settings where families rarely treat drinking-water, we introduced a novel flocculant-disinfectant that reduced the longitudinal prevalence of diarrhoea, especially among children aged < 1 year, among whom diarrhoea has been strongly associated with mortality. Successful introduction and use of this product could contribute to preventing diarrhoeal disease globally.

Adolescent↗

PubMed2002

Pre-selection of flocculants by the LUMiFuge separation analyser 114.

This paper reports on lab-scale investigations in relation to pre-selection of flocculants for sludge dewatering with decanter centrifuges. Results obtained were compared with CST-measurements and discussed in relation to findings under field conditions. Experiments were carried out with sewage sludges of different origin and characteristics and a number of commercial flocculants. Kinetics of sedimentation and clarification were measured as well as the compression behaviour and shear sensitivity of sludge sediments. To measure flocculant performance stability against intensive shearing, total solids in the sludge cake obtained and dewaterability of the sludge cake during the first 20-50 s of centrifugation were compared. A screening test procedure was developed. Efficient flocculants should produce high residual total solids and good initial compressibility. Lab-scale investigations deliver more reliable results if the dynamic behaviour of the sludge under centrifugal acceleration is also investigated. The separation analyser LUMiFuge 114 can provide results about the compression behaviour of sludges in the range between 10 and 100 s. So far no other method or device is known which can deliver such results.

Centrifugation↗

PubMed2002

[Sequencing and analysis of flocculation gene(FLO1G)].

The sequence of the flocculation gene (FLO1G) was determined. The result of sequcencing showed that: the cloned gene contains a large open reading frame (ORF) of 3936 bp and encodes for a protein of 1312 amino acid. According to the result of homologous analysis, the cloned gene is homologous to FLO1 but with 675 bp deletion in the ORF region. The missing part belongs to one of the four repeated sequence family of FLO1. Since the cloned DNA fragment can trigger strong flocculence to non-flocculent strain S. cerevisiae YS58, we concluded that the missing part is not the crutical part for the flocculent ability of the gene.

Amino Acid Sequence↗

PubMed1953

Problems of antivenene standardization revealed by the flocculation reaction.

Mixed with either of the specific venoms, refined antivenene (anti-Bitis arietans-Naja flava) will show optimal flocculation at a number of different venom: serum ratios. This is the natural consequence of individual antigen-antibody reactions in a heterogeneous system.Toxin may be recovered from floccules formed at three optimal N. flava venom: serum ratios by heating the floccules at 70 degrees C for ten minutes at pH 2. These three immunologically distinct heat-stable toxins have been called the alpha, beta, and gamma toxins of N. flava venom.The flocculation reaction obtained with the viperine venom cannot be interpreted in terms of protective potency.Most venom-antivenene systems fail to conform with the "law of combination in multiple proportions", i.e., they give non-linear titration curves. The shape of such curves, convex towards the dose axis, is readily explained by the simultaneous titration of multiple toxin-antitoxin systems.In the particular case of N. flava venom-antivenene, the titration curve obtained with whole venom is determined by the relative anti-alpha, anti-beta, and anti-gamma contents of the serum. Further study may pave the way to the standardization of the anti-alpha, anti-beta, and anti-gamma potencies of sera, but attempts at standardizing antivenene potency against any venom are futile unless the toxic "make-up" of the venom is understood.The cross-protection afforded by sera produced against either N. flava venom, or the venom of Sepedon haemachates is limited but indicates an antigenic similarity which may be clarified by work in progress.

Flocculation↗

PubMed2004

The scientific basis of flocculator design.

A new guideline for the design of flocculators is proposed. This guideline is to design continuous flow flocculators on the basis of the characteristic reaction time for the loss of one micrometre particles in the suspension. The most commonly used guideline at the present time is that of Camp, but later proposals by Ives and O'Melia expanded the Camp guideline and incorporated more complete knowledge of flocculation. The suggestion here continues that process, by accounting explicitly for the heterodisperse nature of typical suspensions and the multiple collision mechanisms for particles in determining a characteristic reaction time. While the historical guidelines have served the water treatment industry well for reasonably similar size distributions in waters destabilized by precipitating metal hydroxides, the proposed guideline should be more robust in considering other suspensions. In particular, the new guideline can account explicitly for the effects of nanoparticles on flocculation.

Environmental Health↗

PubMedDate not supplied

The influence of charged lipids on the flocculation and coalescence of oil-in-water emulsions. I: Kinetic assessment of emulsion stability.

The influence of various negatively charged lipids on the stability of phospholipid stabilized oil-in-water emulsions in the presence of varying concentrations of calcium chloride was examined by a measurement of the changes in the turbidity of the emulsion over time. The data were described well by the following equation: (Ai - A) = (Ai - A0) exp(-kt) where Ai is the maximum spectrophotometric absorbance achieved in the system, A is the absorbance at time t, A0 is the absorbance at the start of the experiment and k is the flocculation or coalescence rate constant. Plots of k and Ai/A0 vs. concentration of Ca++ provided an indication of the rate and extent of emulsion flocculation/coalescence, respectively. The sodium salts of phosphatidic acid (SPA) and oleic acid (SO) increased the critical flocculation concentration of calcium while sodium phosphatidylinositol (SPI) and sodium phosphatidylserine (SPS) had no effect on the critical flocculation concentration compared to the control emulsion. The addition of all lipid salts increased the rate of flocculation compared to the control emulsion, however, emulsions containing SPI demonstrated the highest values of k. In contrast, emulsions containing SO coalesced to the largest extent, as indicated by large values of Ai/A0. Systems containing charged phosphatides regained some stability in higher concentrations of Ca++ while those containing oleate were comparatively more unstable up to 20 mM Ca++. Based upon the results of the present studies, it appears that phosphatidic acid is the most important fraction of the anionic phosphatides in stabilizing an emulsion in the presence of calcium ion.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug Stability↗

PubMed1988

Kluyveromyces bulgaricus yeast lectins. Isolation of N-acetylglucosamine and galactose-specific lectins: their relation with flocculation.

Kluyveromyces bulgaricus is a yeast which, upon culture in a calcium-enriched glucose-peptone medium, flocculates. Its flocculation can be reversed by the addition of galactose. In this paper, it is shown that two lectins can be isolated either from the concentrated culture broth or from the supernatant of deflocculated cells suspended in galactose solution. The N-acetylglucosamine-specific lectin, at pH 7.4, agglutinates untreated sheep red blood cells, but agglutinates neither untreated rabbit red blood cells nor glutaraldehyde-fixed sheep or rabbit red blood cells. Conversely, at pH 4.5, this lectin agglutinates glutaraldehyde-fixed sheep red blood cells. The galactose-specific lectin, at pH 7.4, agglutinates both untreated and glutaraldehyde-fixed rabbit red blood cells but does not agglutinate untreated or glutaraldehyde-fixed sheep red blood cells. At pH 4.5, this lectin agglutinates both glutaraldehyde-fixed sheep and rabbit red blood cells and induces flocculation of deflocculated K. bulgaricus cells. In all cases, the agglutination and the flocculation induced by one of these two lectins were inhibited by free or conjugated N-acetyl-D-glucosamine or by free or conjugated D-galactose, respectively. No glycosylhydrolase activity could be detected in the purified lectins.

Acetylglucosamine↗

PubMedDate not supplied

Bioavailability of sulfathiazole from flocculated and deflocculated suspensions and its implications.

Flocculation is commonly used to stabilize pharmaceutical suspensions. Flocculated and deflocculated suspensions of sulfathiazole were administered to healthy human volunteers. Bioavailability from these two types of suspensions was studied from urinary free drug excretion. Bioavailability was significantly lower from flocculated suspensions. The study indicates the necessity of studying all flocculated drug suspensions for bioavailability data.

Biological Availability↗

PubMed1994

[Flocculation of NPH insulin].

In the past decade, human insulins have been substituting animal insulins, offering the advantage of its lesser antigenic capacity. One of the most clinically important problems with human NPH insulins is its tendency to flocculate. We present four diabetic patients who, after using flocculated human NPH insulin, encountered a deterioration in the metabolic control of their diabetes, and in two of them, there were bouts of diabetic Ketoacidosis "without any other apparent causal factors". Among those causes favoring flocculation are movement during transport, high temperatures, and probably leaving the vial open for an excessively long period of time, as with the extraction of multiple doses. Physicians, educators, diabetics, and their relatives should be informed of this phenomenon. Diabetics, especially those who carry insulin with them, should carefully inspect their vials before each injection to detect signs of flocculation.

Adult↗

PubMed1995

The Saccharomyces cerevisiae FLO1 flocculation gene encodes for a cell surface protein.

The sequencing of a 6619 bp region encoding for a flocculation gene previously cloned from a strain defined as FLO5 (Bidard et al., 1994) has revealed that it was a FLO1 gene. The FLO1 gene product has been localized at the cell surface of the yeast cell by immunofluorescent microscopy. The Flo1 protein contains four regions with repeated sequences which account for about 70% of the amino acids of this protein. A functional analysis of the major repeated region has revealed that it plays an important role in determining the flocculation level. A gene disruption experiment has shown that FLO5 strain STX 347-1D contains at least two flocculation genes of the FLO1 type but that they are supposed to be inactive and do not contribute to its flocculation. However, enzyme-linked immunosorbent assays performed on intact cells have revealed that a protein expressed at the cell surface of the FLO5 strain STX 347-1D is antigenically related to Flo1p. A deletion analysis of the 5' region of the FLO1 gene has shown that the expression is submitted to controls which depend on the genetic background of the strain.

Amino Acid Sequence↗

PubMed1998

Computer Simulation of Flocculation Processes: The Roles of Chain Conformation and Chain/Colloid Concentration Ratio in the Aggregate Structures.

The flocculation of colloidal particles in the presence of adsorbing polymers is a key process in colloid science, as well as in the chemical and biological regulation of aquatic systems. Polymers can influence important physical properties of colloidal aggregates such as their densities and settling velocities, as well as their chemical properties, affecting the probability that two colloidal particles will stick together when they collide. The presence of polymers usually makes more difficult the application of a coagulation theory to colloidal suspensions and the interpretation of experimental observations. Knowledge of floc structures is a key factor in the understanding of flocculation processes, and simulation may provide useful insights required to interpret the results of experimental studies and elaborate new theoretical models. Although modeling leaves much room for more progress, researchers now find it indispensible from a fundamental point of view and for environmental applications. In this paper, we report a computer simulation study of a two- and three- dimensional model for bridging flocculation between large linear polymer chains and comparatively small colloidal particles. The floc structures are investigated as a function of chain/particle concentration ratio, chain conformation, and space dimension. The values of the sticking probabilities are chosen to emphasize colloid-chain interactions compared to colloid-colloid or chain-chain interactions. The results suggest that the floc morphology is strongly dependent on the chain conformation and to a slight extent on the chain/particle concentration ratio. In particular, colloid interactions with linear rods result in a network characterized by fractal dimensions significantly higher than those obtained on the basis of the Cluster-Cluster Aggregation models of colloids only, or by flocculation of colloids with coiled chains. Copyright 1998 Academic Press.

Journal Article↗

PubMed2001

Analysis of Light Scattering Data on the Calcium Ion Sensitivity of Caseinate Solution Thermodynamics: Relationship to Emulsion Flocculation.

We describe the quantitative interrelation between the thermodynamic parameters of caseinate submicelles in the presence of calcium ions (0-14 mM) in aqueous medium and the capacity of the protein to induce depletion flocculation in oil-in-water emulsions at pH 7.0 and ionic strength 0.05 mol dm(-3). Measurements have been made by static and dynamic multiangle laser light scattering of the weight-average molecular weight, the radius of gyration, the hydrodynamic radius, and the second virial coefficient of caseinate submicelles in aqueous solution. Successive thermodynamic approximations with and without consideration of correlations between caseinate submicelles have been used to calculate the osmotic pressure in caseinate aqueous solutions and the free energy of the depletion interaction between droplets in oil-in-water emulsions stabilized by caseinate. Numerical results from both thermodynamic approximations are in reasonably good agreement with experiment, predicting a pronounced decrease in the strength of the depletion attraction at concentrations of Ca(2+) in the range 4-8 mM (with a minimum value at 8 mM). This correlates well with the great enhancement of stability of these emulsions with respect to flocculation in comparison with systems having no added ionic calcium and emulsions with lower (2 mM) or higher (10 mM) Ca(2+) contents. Nevertheless, the allowance for interactive correlations between caseinate submicelles seems to lead to a better prediction of emulsion flocculation on a qualitative level over the whole range of Ca(2+) concentrations studied (2-14 mM). The calculated pronounced decrease in depletion interaction strength is attributable to marked changes in weight-average molecular weight and mean size of aggregates, and to more positive values of the second virial coefficient of caseinate submicelles with increasing Ca(2+) content. Finally, we discuss the part played by the electrical charge on the protein in determining the overall strength of the flocculation-inducing attractive interactions between droplets. Copyright 2001 Academic Press.

Journal Article↗

PubMed1994

Cloning and analysis of a FLO5 flocculation gene from S. cerevisiae.

A yeast flocculation gene was isolated from a genomic library of an FLO5 strain of S. cerevisiae on the basis of its ability to trigger flocculation in a non-flocculent strain. Characterization of the cloned gene by restriction mapping, Southern analysis, and chromosome mapping have shown that it corresponds to a FLO5 gene previously located on chromosome I and that this gene is related to the already described FLO1 gene. A study of gene expression in different yeast strains has indicated that, while this gene is dominant, its expression can be suppressed in some genetic backgrounds. A Northern-blot analysis has demonstrated that the same 5000-nt transcript was present in an FLO5 and an FLO1 strain. A gene disruption experiment has led to the conclusion that another flocculation gene is present and can be active in the FLO5 strain we used.

Chromosome Mapping↗