Down-regulation of the expression of PKC1 and SRB1/PSA1/VIG9, two genes involved in cell wall integrity in Saccharomyces cerevisiae, causes flocculation. (1/113)

The cell wall integrity determinants PKC1 and SRB1/PSA1/VIG9 of Saccharomyces cerevisiae were expressed under the control of the tightly regulated promoter pMET3. Substitution of the cell-cycle-regulated SRB1/PSA1 native promoter with pMET3 led to faster cell growth, larger cell volumes, and a twofold reduction of the steady-state SRB1/PSA1 mRNA level. In addition, the new pattern of expression of SRB1/PSA1 resulted in a dominant flocculation phenotype at all phases of batch growth. By contrast, expression of PKC1 from pMET3 increased the flocculation capacity of cells only at stationary phase. Methionine-mediated repression of either PSA1/SRB1 or PKC1 resulted in enhanced cell clumping. Cells in which both these genes had been replaced with their respective pMET3-regulated cassettes were highly flocculent under both expression and repression conditions. These results suggest that greater exposure of flocculin on the cell surface, caused by either cell wall distortion (through depletion of Pkc1p) or aberrant regulation of mannosylation (through constitutive production of Srb1p), results in an increased flocculation ability.  (+info)

Role of wall phosphomannan in flocculation of Saccharomyces cerevisiae. (2/113)

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.  (+info)

Involvement of outer-membrane proteins in the aggregation of Azospirillum brasilense. (3/113)

A bioassay was developed to investigate biological factors involved in the aggregation of Azospirillum brasilense strain Cd. Cells were grown for 24 h under aggregation-inducing and non-aggregation-inducing conditions (high and low C:N, respectively) and sonicated for 20 s. The cells were washed by centrifugation and resuspended in potassium phosphate buffer containing the two types of sonication extract. A greater extent of aggregation and higher flocculation were observed after 2-3 h incubation in the presence of sonicates from cells grown at high C:N (H-cells) compared to cells grown at low C:N. Flocculation did not occur after incubation of these cells in phosphate buffer. Boiled or proteinase K-treated sonicates originating from H-cells had lower aggregation-inducing capacity. After fractionation of the crude sonicate, both the outer-membrane protein (OMP) and the total membrane (mostly OMP) fractions possessed relatively high aggregation specific activities. The aggregation-inducing capacity of the OMP fraction strongly correlated with its protein concentration in the bioassay. Treatment of this fraction with proteinase K also decreased its aggregation-inducing activity. These findings suggest that OMPs are involved in the aggregation process of cells of A. brasilense.  (+info)

Flocculation of hyphae is associated with a deletion in the putative CaHK1 two-component histidine kinase gene from Candida albicans. (4/113)

In Candida albicans, three putative histidine kinase genes have been described thus far, including CaSLN1, CaNIK1/COS1 and CaHK1. The encoded proteins for C. albicans, CaSln1p and CaNik1p, which are similar to Sln1p from Saccharomyces cerevisiae and Nik-1 from Neurospora crassa, seem to function in osmoregulation and morphogenesis, respectively. Recently, the isolation of CaHK1, a putative histidine kinase gene from C. albicans has been reported. In addition to the histidine and aspartyl domains located at its C-terminus as previously described, it is shown here that the N-terminal domain of Cahk1p contains a P-loop motif and a sequence which shows significant homology with the seven C-terminal domains of serine/threonine kinases. The Ser/Thr-homologous domains of Cahk1p could, in fact, correspond to its sensor sequence. CaHK1 has been mapped to chromosome 2 and gene deletion studies were undertaken to understand its function. Deltacahk1 mutants are phenotypically different from any other histidine kinase mutants thus far described either in C. albicans or in any other yeast or filamentous fungus. This study demonstrates that deltacahk1 mutants flocculate extensively in a gene-dosage-dependent manner under conditions which induce germ-tube formation, such as growth in medium 199 (pH 7.5). The flocculation occurs by an interaction along the hyphal surfaces, probably because of the altered expression of one or more hyphal-cell-surface components in the deltacahk1 mutants. These results indicate that CaHK1 could be involved in regulating their expression.  (+info)

Interactions between cationic liposomes and bacteria: the physical-chemistry of the bactericidal action. (5/113)

The bactericidal effect of dioctadecyldimethylammonium bromide (DODAB), a liposome forming synthetic amphiphile, is further evaluated for Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa, and Staphylococcus aureus in order to establish susceptibilities of different bacteria species towards DODAB at a fixed viable bacteria concentration (2.5 x 10(7) viable bacteria/mL). For the four species, susceptibility towards DODAB increases from E. coli to S. aureus in the order above. Typically, cell viability decreases to 5% over 1 h of interaction time at DODAB concentrations equal to 50 and 5 microm for E. coli and S. aureus, respectively. At charge neutralization of the bacterial cell, bacteria flocculation by DODAB vesicles is shown to be a diffusion-controlled process. Bacteria flocculation does not yield underestimated counts of colony forming units possibly because dilution procedures done before plating cause deflocculation. The effect of vesicle size on cell viability demonstrates that large vesicles, due to their higher affinity constant for the bacteria (45.20 m(-)) relative to the small vesicles (0.14 m(-)), kill E. coli at smaller DODAB concentrations. For E. coli and S. aureus, simultaneous determination of cell viability and electrophoretic mobility as a function of DODAB concentration yields a very good correlation between cell surface charge and cell viability. Negatively charged cells are 100% viable whereas positively charged cells do not survive. The results show a clear correlation between simple adsorption of entire vesicles generating a positive charge on the cell surfaces and cell death.  (+info)

Layer-by-layer deposition of oppositely charged polyelectrolytes on the surface of condensed DNA particles. (6/113)

DNA can be condensed with an excess of poly-cations in aqueous solutions forming stable particles of submicron size with positive surface charge. This charge surplus can be used to deposit alternating layers of polyanions and polycations on the surface surrounding the core of condensed DNA. Using poly-L-lysine (PLL) and succinylated PLL (SPLL) as polycation and polyanion, respectively, we demonstrated layer-by-layer architecture of the particles. Polyanions with a shorter carboxyl/backbone distance tend to disassemble binary DNA/PLL complexes by displacing DNA while polyanions with a longer carboxyl/backbone distance effectively formed a tertiary complex. The zeta potential of such complexes became negative, indicating effective surface recharging. The charge stoichiometry of the DNA/PLL/SPLL complex was found to be close to 1:1:1, resembling poly-electrolyte complexes layered on macrosurfaces. Recharged particles containing condensed plasmid DNA may find applications as non-viral gene delivery vectors.  (+info)

Enhancement of plant stem growth by flocculation of the antibiotic-producing bacterium, Pseudomonas fluorescens S272, on the roots. (7/113)

The antibiotic-producing bacterium, Pseudomonas fluorescens, is assumed to be important in protecting plants from soilborne diseases. S. fluorescens S272, a hyper-producing strain of pyoluteorin (PT) and 2,4-diacetylphloroglucinol (DG), had previously been isolated from soil. The present paper reported that the growth of water-cultivated Kaiware radish was promoted to 120-140% of its normal level by the coaddition of an S272 culture broth (0.01-1% v/v) and a polysaccharide flocculant (1-100 ppm) from Klebsiella pneumoniae H12. Tight adhesion of S272 cells to the root tissue was microscopically observed. The growth promotion is assumed to have been caused by antibiotic effects for the following two reasons: 1) PT (4 mg/l) and DG (24 mg/l) addition to a radish culture enhanced stem growth to 130% of the normal level; 2) a culture solution containing the S272 culture broth (0.01-1% v/v) markedly inhibited the decomposition of hypersensitive chrysanthemum leaves. A soil-cultivation experiment with Gomphrena globosa under natural conditions also exhibited enhanced stem length (160%) by coaddition of the S272 culture broth and H12 polysaccharide. These results suggest that polysaccharide-enhanced adhesion of P. fluorescens S272 cells might be useful for promoting plant growth through the increased antibiotic effect.  (+info)

Organic flocculation: an efficient second-step concentration method for the detection of viruses in tap water. (8/113)

A method is described for second-step concentration of viruses from water. This method, combined with an adsorption-elution method, yields a mean recovery of about 75%  (+info)