Formation and Stability of Synaptic Receptor Domains

Neurotransmitter receptor molecules, concentrated in postsynaptic domains along with scaffold and a number of other molecules, are key regulators of signal transmission across synapses. Employing experiment and theory, we develop a quantitative description of synaptic receptor domains in terms of a reaction-diffusion model. We show that interactions between only receptor and scaffold molecules, together with the rapid diffusion of receptors on the cell membrane, are sufficient for the formation and stable characteristic size of synaptic receptor domains. Our work reconciles long-term stability of synaptic receptor domains with rapid turnover and diffusion of individual receptors.Comment: 5 pages, 3 figures, Supplementary Materia

Determination of cell number and size of a population of Pseudomonas fluorescens by image analysis

Image analysis is a very useful technique for counting and sizing bacteria, minimising hum an operati on and providing accurate results in a short inte rval of time. Microscopic observations of a population of Pseudomonas fluo rescens were digitised by a frame grabber and the grabbed images were enhanced by background subtraction and multiplication of two copies. To extract the objects from the background, an appropriate threshold had to be chosen. Full grown single bacterial cells showed to be normally distributed around two mean sizes, one corresponding to standi ng bacteria and the other to lying bac teria. Two Gauss functions were least square fitted to the se data points resulting in the mean area and the standard deviation. The enumeration of single cells was obtai ned from the area of each gauss curve. It was also possible to determ ine the number of single bacteria in aggregates, once the mean project area of a single cell is known. The enumeration was made for each threshold selected. The number of particles coun ted was constant in a large range of threshold. whereas the cell area increases with the threshold ins talled

Obtenção de chips de caju por osmose seguida de fritura.

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Isolation of phages from industrial environments to control biofilms

Resumo de comunicação apresentada em "16th Evergreen Phage Biology Meeting, Olympia", WA, EUA, 7-12 Agosto 2005.Biofilms are frequently in many industrial environments and are responsible for severe negative impacts such as equipment damage, loss in product quality and in economics. For instance in pulp and paper industry, microorganisms together with their exudates and the entangled fibres and filler materials form massive and slimy protusions hanging out from the material surfaces, which interfere with the paper-making process in various steps. Also, in dairy industry, biofilm presence may be responsible for pathogen cross-contamination, product defects such as package bloating, decreased shelf life, and off flavours, odours and textures. The eradication of these biofilms, as reported by several authors, is very difficult due to the nature of biofilm structure and the physiological attributes of biofilm organisms which confer an inherent resistance to biocides. The application of biological agents such as phages as an alternative to the chemical products is an interesting approach that should be studied in more detail. This work aimed the isolation of bacteria and the respective bacteriophages from a pulp and paper mill and from a dairy industry. The focus was given to EPS producing bacteria such as P. fluorescens, Sphingomonas paucimobilis, Staphylococcus sciuri, and Klebsiella oxytoca. Phages were isolated from the industrial effluents and also nearby waste water treatment plants. After phage isolation from each industrial sector, the selection was based on the wider broad of lytic activity and time of bacterial elimination. For each type of industry, a 5 phage cocktail is being developed to be tested in the control the most prevalent biofilm producing bacteria

Real-time quantification of Pseudomonas fluorescens cell removal from glass surfaces due to bacteriophage FS1 application

Aims: To study the efficacy of the lytic phage φS1 in eliminating Pseudomonas fluorescens in the early stage of biofilm formation, using an in situ and real time methodology for cell quantification. Methods and Results: Cell adhesion and phage infection studies were carried out in a parallel plate flow chamber under laminar conditions. Cells were allowed to adhere until reaching 1·7–1·8 × 106 cells cm−2 and phage infection was performed with two different phage concentrations (2 × 109 PFU ml−1 and 1 × 1010 PFU ml−1). Phage concentration clearly affects the speed of infection. The less concentrated phage solution promoted a three times slower rate of cell removal but did not affect the overall percentage of cell removal. In fact, after a longer infection period the less concentrated phage solution reached the same 93% cell removal value. Conclusions: Phages are efficient in the eradication of bacterial cells at the early stage of biofilm formation and their presence at the surface did not allow bacterial recolonization of the surface. Significance and Impact of the Study: To date, no published studies have been made concerning in situ and real time quantification of cell removal from surfaces due to phage action.Fundação para a Ciência e a Tecnologia (FCT

Cell wall surface properties and flocculence of a Kluyveromyces marxianus strain

Yeast flocculation is under genetic control and is described as a cell wall interaction. This characteristic of yeast cells has been traditionally used in industrial fermentation processes. The surface characteristics of the cell walls are expected to be a determinant factor in the aggregation mechanism. Results confirming this have been reported for Saccharomyces strains. It is important to extend these studies to other genera. Among them, due to its potential industrial interest, Kluyveromyces strains must be considered. In this work are reported results relating cell wall surface properties (hydrophobicity and electrophoretic mobility) with the flocculation ability of a strain of Kluyveromyces marxianus. The effect of proteolytic enzymes, pH, salts and sugars on flocculation was also studied. The results obtained clearly demonstrate that cell wall hydrophobicity is a major determinant in the flocculation ability of the Kluyveromyces marxianus cells.Junta Nacional de Investigação Científica e Tecnológica (JNICT

Physico-chemical surface characterization of a bacterial population isolated from a milking machine

The hydrophobicity of 26 species of bacteria representative of the main genera isolated from a rubber short milk tube, which is a constituent of a cluster from a milking machine, was determined. The materials forming the cluster namely rubber, stainless steel (SS) 316, stainless steel (SS) 304, glass and polymethylmethacrylate (PMMA) were also assayed in terms of hydrophobicity. In relation with the hydrophobicity of bacteria, all the strains of Lactobacillus lactis lactis as well as of Enterococcus faecalis are hydrophobic. Concerning Pseudomonas aeruginosa and Staphylococcus sciuri, some are hydrophobic and others are hydrophilic. All the materials are hydrophobic, being rubber, SS 316 and SS 304 the most hydrophobic surfaces while glass is the less hydrophobic. The free energy of adhesion between the bacteria and the materials in aqueous medium was calculated and used to predict which material of the cluster has a higher ability for biofilm formation and by this way contribute for milk contamination due to the release of bacteria from the deposit. For all the situations studied, adhesion is thermodynamically favourable to SS 316, SS 304 and rubber and less favourable to PMMA and glass.Ministério da Agricultura, do Desenvolvimento Rural e das Pescas (INIAP) - Project AGRO 205

Effect of magnetic hyperthermia on the structure of biofilm and cellular viability of a food spoilage bacterium

This work evaluated the effect of magnetic hyperthermia (MH) on planktonic cells and biofilms of a major food spoilage bacterium Pseudomonas fluorescens and its performance compared to a conventional direct heating (DH) technique. The results showed that MH had a greater and faster bactericidal effect, promoting a significant reduction in cell viability (≥3 Log CFU) in planktonic and biofilm cells, and leading to a complete eradication of planktonic cells at 55 °C (after only ~8 min). Accordingly, when comparing the same final temperatures, MH was more harmful to the integrity of cell membranes than DH, as observed in confocal laser scanning microscope images. Additionally, scanning electron microscope images revealed that exposure to MH had promoted modifications of the bacterial cell surface as well as of the structure of the biofilm. These results present the possibility of using MH out of the biomedical field as a potential disinfection method in food-related environments.This work was partly supported by the European Regional Development Fund (ERDF) under the Northern Regional Operational Programme ON.2-O Novo Norte- for the acquisition of the main equipment used in this research. DR also acknowledges the financial support of the Portuguese Foundation for Science and Technology (FCT) through [grant SFRH/BPD/72632/2010]. The authors are very grateful to Dr Edith Ariza and Dr Claudia Mota for their technical assistance in the SEM studies

Monitoring cell detachment by surfactants in a parallel plate flow chamber

The efficacy of the surfactants SDS and CTAB in detaching P. fluorescens from glass surface was evaluated in a parallel plate flow chamber. This device enables “in situ” determinations of cells detachment following the application of surfactants under well controlled hydrodynamic conditions. The results showed that SDS was able to remove almost all adhering bacteria in a short period of time, whereas CTAB did not promote much cell desorption. On the contrary, this surfactant increased the adhesion strength between cells and glass. Both surfactants promoted different alterations of cell surface properties, which explains their dissimilar effectiveness as cleansing agents.programme SAPIEN