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PubMed1979

Temperature sensitivity of flocculation induction, conjugation and sporulation in fission yeast.

Homothallic cultures of Schizosaccharomyces pombe, anaerobically grown to stationary phase in broth at 32 degrees C, were induced by aeration to flocculate. Flocculation was followed by copulation, conjugation, zygote formation, meiosis and sporulation. Cultures grown to stationary phase at 32 degrees C and then aerated at 37 degrees C did not sporulate. Grown to stationary phase at 37 degrees C, cultures were not immediately inducible when aerated at 32 degrees C. To identify which events in the developmental sequence were thermosensitive, we grew and induced cultures at 32 degrees C and then shifted them at various times to 37 degrees C. We observed the following events to be thermosensitive: development of respiratory sufficiency, readiness (inducibility of a culture within 1 h), flocculation induction, copulation, conjugation and early sporulation (including meiosis). Respiration, flocculation and spore maturation were thermoresistant. Conjugation-induced lysis and postdevelopmental deflocculation were enhanced at 37 degrees C.

Ascomycota↗

PubMed1978

[Use of flocculants for detection of viruses in fluids (author's transl)].

Hydroxide flocs of iron, aluminium, zinc, and tin were tested for their capabilities of virus enrichment in fluids (such as water and liquid foods). The virus used was polio type II att. The flocculation with tin yielded the best results because it gave the highest recovery rates (90%) and good reproducibility. A satisfactory enrichment was also obtained with the flocculation with aluminium- and iron salts. The losses were 31 and 33%. The lowest recovery rates were obtained with nickel- and zinc flocculation (losses: 70 and 77%). The difficulties in filtering the flocs and eluting the virus with 3% beefextract could be overcome by centrifugation and dissolution of aluminium and iron flocs with sodium-potassium-tartrate (average recovery rates 5 and 27%). In addition we tested the flocculation in lemonade as a model fluid loaded with a high content of organic material which usually interfere with the formation of flocs and in consequence the enrichment of viruses. An enrichment of viruses in lemonade was possible only with previously prepared and aged flocs of tin and iron. The loss was 18 and 12% respectively.

Aluminum↗

PubMed1981

Studies on the pathogenesis of ischemic cell injury. VI. Mitochondrial flocculent densities in autolysis.

Flocculent densities in the matrix of mitochondria have become quite important in cell pathology since, when prominent, they indicate irreversible cell injury. The morphology and chemical nature of these flocculent densities have been studied in Kidney after various periods of autolysis in vitro in whole tissue samples and in isolated mitochondria. After 30 to 60 min of ischemia, flocculent densities were seen only occasionally and they were most prominent in samples subjected to mechanical damage during isolation. However, in 2- and 4-h samples numerous densities were seen. The size of the densities increased with time, being about 1,400 A in diameter at 4 h. Densities were also seen in mitochondria isolated in medium containing EDTA. They were seen only in the mitochondrial matrix, and could occasionally be found in condensed mitochondria. Small densities were generally round but larger one varied in shape and often appeared as aggregates of smaller densities. Digestion of the densities from water-soluble glycol methacrylate embedded samples was successful with pronase, but neither acid nor lipid solvents were effective. calcium or inorganic phosphate content of isolated mitochondria did not show an increase parallel to the occurrence of flocculent densities. The results suggest that the densities consist predominantly of protein and are probably formed through denaturation of proteins of the mitochondrial matrix and/or the inner membrane.

Animals↗

PubMed2000

Construction of a flocculent brewer's yeast strain secreting Aspergillus niger beta-galactosidase.

One way of improving heterologous protein production is to use high cell density systems, one of the most attractive being the flocculating yeast production system. Also, lactose is available in large amounts as a waste product from cheese production processes. The construction of flocculent and non-flocculent brewer's yeast strains secreting beta-galactosidase and growing on lactose is presented. A plasmid was constructed coding for an extracellular beta-galactosidase of Aspergillus niger and having, as selective marker, the yeast CUP1 gene conferring resistance to copper. This selective marker allows for the transformation of wild-type yeasts. This work represents an important step towards the study of heterologous protein secretion by flocculent cells.

Aspergillus niger↗

PubMed1986

Calculation of ionic flocculation concentrations for biological membranes bearing ionizable groups.

The flocculation concentrations in the DLVO theory of colloid stability have previously been calculated under conditions of constant plate potential or constant plate charge. These boundary conditions are not appropriate in the case of biological membranes bearing ionizable surface groups. In this case the surfaces undergo charge regulation as they approach each other and both the surface charge and potential vary. In this paper a numerical method is used to calculate the ionic flocculation concentrations for the two membranes undergoing surface charge regulation. It is shown that the flocculation concentration lies between that for constant charge and that for constant potential. Flocculation concentrations are calculated as a function of the surface density of ionizable groups and are shown to be dependent on both the pKa of the surface groups and the bulk pH of the solution.

Electrochemistry↗

PubMed1989

Extracellular product of Nocardia amarae induces bacterial cell flocculation.

The fact that Nocardia amarae YK1 produced a bacterial flocculation-inducing substance (designated as FIX) was discovered. FIX had a function of flocculating proliferous cells. FIX-induced flocculation was inhibited by making cells resting, but not completely by adding chloramphenicol. FIX worked widely on Gram-positive to -negative bacteria. In the presence of FIX, Achromobacter cycloclastus IAM1013, Acinetobacter calcoaceticus IAM1517, Bacillus subtilis IAM1069, Escherichia coli C600-1, E. coli IAM1239, Flavobacterium lutescens IAM1667, Klebsiella pneumoniae IAM1102, Micrococcus luteus IAM1313 and Pseudomonas putida IAM1002 formed flocs. B. cereus IAM1029, however, exhibited no flocculation.

Agglutination↗

PubMed2005

Association-induced polymer bridging by poly(ethylene oxide)-cofactor flocculation systems.

Poly(ethylene oxide) (PEO) is used in papermaking, water purification and mineral flotation as a flocculating agent. Despite the fact that PEO does not adsorb on cellulose and bleached lignin, and only poorly on calcium carbonate, it can nevertheless be used to deposit colloidal pigments on pulp fibers. PEO by itself is inefficient, but it can be made to work in combination with another compound, usually referred to as a cofactor or an enhancer. The cofactor associates with PEO and the association complex acts as an efficient bridging agent. There are two classes of cofactor: those who cause PEO to cluster and those that do not. In general PEO association-clusters are more efficient flocculating agents than non-clustered PEO. The PEO dissolution procedure has an important effect on the PEO flocculation efficiency. Before reaching thermodynamic equilibrium, PEO is in an entangled state. Cofactors that cluster PEO are likely to maintain PEO in an entangled state and, like the association-clusters, these entanglements are more efficient flocculation agents than well-dispersed PEO. Salt also affects the PEO-cofactor association. For most cofactors, salt is needed to induce the association. Calcium ions can act as bridging agents between association complexes, especially those containing carboxyl groups, thus promoting the formation of association-clusters.

Adsorption↗

PubMed2004

Flocculation and reflocculation of clay suspension by different polymer systems under turbulent conditions.

The focused beam reflectance measurement (FBRM), also known as scanning laser microscopy (SLM), was used as a real-time monitor to study the flocculation and reflocculation of clay suspensions under different shear conditions in the presence of single polymer, dual polymer, microparticle and poly(ethylene oxide)/phenolformaldehyde (PEO/PFR) flocculation systems. For initial flocculation, the high molecular weight PEO and cationic polyacrylamide (CPAM) produced larger flocs than others. However, reflocculation of clay suspensions formed by these non- or low-charged polymers was insignificant after the initial flocs were broken under high shear force. In contrast, high charge density polymers, such as poly(diallyldimethylammonium chloride) (PDADMAC), do not form large initial flocs, but they showed significant reflocculation ability under a continuous shear condition. It is concluded that high flocculation can be obtained by effective polymer bridging, but high reflocculation can only be induced by high electrostatic attractive forces between suspended particles.

Journal Article↗

PubMed2005

Flocculation, deflocculation, and ions migration in latex suspensions.

We have studied the dynamics of the flocculation of poly(styrene-butadiene-acrylic acid) latex suspensions. These suspensions were flocculated by the addition of Ca2+ ions at high concentrations of latex particles. Using diffusing wave spectroscopy and dynamic single light scattering after dilution, we have observed--depending on the pH and on the Ca2+ concentration--several scenarios for flocculation including successive flocculation and deflocculation. This complex behavior reveals that the Ca2+ migration within the shell of the latex is slow in acidic solvent but fast in basic solvent.

Journal Article↗

PubMed2003

Viscosity of emulsions: influence of flocculation.

A model has been suggested by Raijinder Pal (J. Colloid Interface Sci. 231 (2000) 168) that describes experimental data on the viscosity of concentrated emulsions reasonably well. To deduce the final equation the author assumed that droplets are covered with a layer of surfactant molecules. This means that the effective volume of a single emulsion droplet is increased by a factor K>1. It has been found that K should vary between 1.166 and 2.070 to fit the experimental data. If the drop radii are around 1 microm (for an estimate) then the drops would be covered with a layer which thickness should range from 550 A (which is 10 times of the size of SDS micelles) to 3570 A. No doubt adsorption of surfactant molecules results in an increase of the effective drop radius but not by that much. We present an alternative theoretical model for description of the viscosity-volume fraction of droplets behavior of emulsions. The model is based on the assumption that clusters of drops (doublets, triplets, and so on) are formed under the influence of colloidal, hydrodynamic interactions and/or applied shear. According to the proposed model clustering determines the volume fraction dependency of the effective viscosity of emulsions. Two limiting cases are considered: a developed flocculation and a low-flocculated emulsion. In the first case the final equation is close to that deduced by Pal; however, the physical meaning of the equation is substantially different. Comparison with available experimental data shows good agreement with the equations deduced in both the cases of a developed flocculation and a low-flocculated emulsion.

Journal Article↗

PubMed2001

Extracellular biopolymeric flocculants. Recent trends and biotechnological importance.

Many microorganisms secrete extracellular biopolymeric flocculants (EBFs) in the culture broth. This work reviews the development of EBF research and applications. Aspects discussed include a comparison of the chemical and biological flocculating agents, isolation of EBF-producing microorganisms, culture conditions, mechanisms of flocculation, the chemical structure of EBFs, and the role of physicochemical factors in the flocculating activity.

Journal Article↗

PubMed1991

Thixotropic phenomenon in flocculated aqueous dispersions of acrylate methacrylate copolymers.

Aqueous gels of two analogous, water-insoluble copolymers A and B have been formed by addition of excess water to concentrated ethanol solutions of the polymers. A and B differed only in their content of cationic groups in a ratio 2:1 (A:B). The gels were converted permanently to fluids (i.e. gel-sol transformation) at high shear rates. Stability of the resulting polymer dispersions depended on the presence and mutual repulsion of the polymer cations. Polymer B dispersions were less stable to the flocculating effect of an electrolyte (sodium chloride). At certain critical concentrations, 0.2 M NaCl (for polymer A), or 0.1 M NaCl (for polymer B) the electrolyte flocculated the otherwise stable dispersions to a gel structure. The electrolyte-flocculated gels were readily redispersed to fluids by shaking but reverted to gels on standing (thixotropic). In contrast the original coacervated gels (without electrolyte) could not be redispersed easily with manual shaking. Lower polymer-polymer interaction in the thixotropic system relates possibly to increases in particle size and irregularity of particle shape during flocculation.

Acrylates↗

PubMed1997

Induction of sexual co-flocculation of heterothallic fission yeast (Schizosaccharomyces pombe) cells by mating pheromones.

Heterothallic fission yeast (Schizosaccharomyces pombe) cells preincubated with sex pheromone, P- or M-factor of the obverse mating-type cells, in mannose synthetic medium (MSM) results in remarkably increased sexual co-flocculation with obverse mating-type cells almost without time lag, i.e., within 10 min. By contrast, comparable flocculation requires over 1 h if untreated control cells are mixed with obverse mating-type cells. The agglutinin of P cells is more inducible than that of M cells. These pheromonal inductions of sexual co-flocculation are inhibited by the addition of cycloheximide or tunicamycin during preincubation but not by chloramphenicol or hydroxyurea. These results demonstrate that, in addition to (a) the repression of cell division (G1 arrest) and (b) the activation of cell wall autolytic processes (mating-specific elongation of cells: formation of their conjugation tubes), mating pheromones of fission yeast have another important role; (c) to induce sexual co-flocculation (agglutinability). Using our experimental system of preincubation with sexual pheromones, we show that M-agglutinin is heat-stable and its induction is inhibited by tunicamycin, but that P-agglutinin is heat-labile and its induction is only partially inhibited by tunicamycin.

Journal Article↗

PubMed2004

Clearance of minute virus of mice by flocculation and microfiltration.

Clearance of minute virus of mice (MVM) from CHO cell suspensions by flocculation and microfiltration has been investigated. MVM is a parvovirus that is recommended by the U.S. Food and Drug Administration for validating clearance of parvoviruses. The feed streams were flocculated using a cationic polyelectrolyte. Virus clearance in excess of 10,000-fold was obtained in the bulk permeate for flocculated feeds streams. However, the level of clearance was only about 10- to 100-fold for unflocculated feed streams. The results suggest that virus clearance involves interactions between the MVM particles, the cationic polyelectrolyte, and the CHO cells present. Validating virus clearance is a major concern in the biotechnology industry. New unit operations are frequently added to the purification train simply to validate virus clearance. However, many of these unit operations are less effective at validating clearance of nonenveloped viruses. Validating clearance of parvoviruses is often particularly problematic as they are nonenveloped and the virus particles are small (18 to 24 nm), making physical removal difficult. The results obtained herein indicate that addition of the cationic polyelectrolyte not only results in significant clearance of MVM but also leads to an increase in permeate flux.

Animals↗

PubMed2004

Extracellular enzyme loss during polyelectrolyte flocculation of cells from fermentation broth.

Association of extracellular protein product with flocculated cells reduces product yield. Here, partitioning of the enzyme subtilisin between the liquid and polyelectrolyte-flocculated and sedimented Bacillus increased as the polymer dosage was increased beyond that necessary to obtain optimum floc character (brain floc) for cell removal by centrifugation. Partitioning to the cell floc is partly physical entrapment at all polymer dosages; however, at higher levels there is also direct interaction between the polyelectrolyte and enzyme. Enzyme loss was not likely due to pH denaturation during the flocculation process because conditions were within the stable pH range of the enzyme. The direct interaction between polyelectrolyte and enzyme was characterized through turbidimetric titrations and partitioning studies. Neither changes in the polymer feed concentration nor the method of polymer addition reduced the enzyme loss at dosages optimal for cell removal.

Bacillus↗

PubMed2001

Negative regulation of filamentous growth and flocculation by Lkh1, a fission yeast LAMMER kinase homolog.

We have isolated a full-length cDNA clone that encodes for a Schizosaccharomyces pombe homolog of the dual-specificity protein kinase of the LAMMER family, lkh1 (lammer kinase homolog). The proposed Lkh1 protein contains 575 amino acids. The lkh1(+) null mutant is viable, but exhibits flocculation upon reaching stationary phase in liquid media and filamentous adhesion growth on solid media. Analysis of the flocculation activity of the lkh1(+) null mutant indicates that asexual aggregation of S. pombe cells into floccules is divalent cation-dependent and galactose-specific. We also demonstrate that the Saccharomyces cerevisiae LAMMER kinase homolog, Kns1, can substitute for the Lkh1 function in S. pombe.

Amino Acid Sequence↗

PubMed1995

Industrial yeast strain improvement: construction of a highly flocculent yeast with a killer character by protoplast fusion.

Conditions were optimized for rapid release and improved regeneration of protoplasts of Saccharomyces cerevisiae NCIM 3458. Rapid protoplast release was also obtained with representatives of several other yeast genera under the modified conditions of treatment. The application of the procedure in construction of a highly flocculent Saccharomyces cerevisiae with a killer character is described. Fusion was effected between UV-killed protoplasts of S. cerevisiae NCIM 3578 with a killer character and live protoplasts of the highly flocculent S. cerevisiae NCIM 3528 in the presence of polyethylene glycol (PEG) 6000. Fusants were selected using benomyl resistance as marker, the killer toxin producer rather than the highly flocculent yeast being resistant to the fungicide at a concentration of 100 micrograms ml-1. Fusants were also characterized by their DNA contents, capacity for ethanolic fermentation of molasses sugar and levels of invertase, alcohol dehydrogenase and pyruvate decarboxylase activities.

Cloning, Molecular↗

PubMed2001

Functional correlation between the nuclear localization of Fht1p and its flocculation and heat tolerance activities in budding yeast Saccharomyces cerevisiae.

Fht1p is involved in the flocculation and heat tolerance machinery of budding yeast Saccharomyces cerevisiae. Despite knowledge of its involvement in those phenotypes, a precise mechanism has yet to be discovered. To this end, we monitored the relationship between subcellular localization of Fht1p and its flocculation or heat tolerance function using newly developed expression vectors with a recombinant green fluorescent protein (GFP; S65T/S147P) of Aequorea victoria added at both the N- and C-terminus of Fht1p. The main fluorescent signal of the GFP tagged with either a wild-type Fht1p or mutants which preserve their flocculation function was detected in the nucleus, whereas signals of functionless mutants were dispersed to the cytoplasm.

Cell Nucleus↗