Polysaccharide secretion

The mechanisms triggering polysaccharide synthesis by fungi are well understood but the enzymes involved in polysaccharide secretion remain to be identified. Biosynthetic pathways for the production of specific polysaccharides, such as the capsule synthesis in C. neoformans or pullulan by A. pulllulans, have been studied in more detail because of their proven importance for pharmaceutical or food industries, respectively. However, even in those cases, the mechanisms of polymer biosynthesis are far from being understood. 

Mechanisms of secretion in Gram negative bacteria have been elucidated (with either a Wzx-Wzy-dependent pathway or an ABC transporter-dependent pathway [58]) but very little is known in fungi. Even in the rather well-studied A. pullulans, mechanisms of pullulan secretion remain unclear and no secretory enzyme has been identified [59,60]. Yoneda et al. [49] demonstrated only recently that the cryptococcal capsule was synthesized intracellularly and secreted via exocytosis. It is clear from these few examples that the wide diversity of the molecular structures formd in EPS implies a wide variety of synthetic routes, difficult to identify. 

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This group includes a set of anionic polysaccharides secreted by unrelated bacteria. The common theme, however, is that their main chains have the same tetrasaccharide repeat. Although (high acyl) native gellan (42) and (deacylated) gellan (40,41) are linear polymers, welan (43) is a branched polymer in which a monosaccharide side chain is regularly attached to each repeat. Other members of this family, such as S-657 and rhamsan, are also branched, like welan."0... 

Scleroglucan is a polysaccharide secreted by the mycelia of certain microorganisms. It is produced by aerobic fermentation of D-glucose by such microorganisms. Scleroglucan has been proposed as a better alternative to xanthan gum for drilling fluid compositions [666]. 

Dubourdieu, D. (1978). Etude des polysaccharides secretes par Botrytis cinerea dans la baie de raisin. Incidence sur les difficultes de clarification des vins de vendages pourries. These Doctorat de 3eme cycle, Bordeaux. 

Pectin-like material is secreted from suspension tissue culture cells of sycamore and the rate of secretion of these polysaccharides can be measured using radioactive arabinose which is incorporated into arabinogalactans. The addition of Ca increased the steady state rate of secretion within seconds. The stimulation was brought about by an action on the normal mechanism of cell-wall polysaccharide export from the cytoplasm. It seemed therefore that the fusion of the vesicles with the plasmamembrane was a rate-limiting step and is probably a control point. The action of the Ca " " was to increase the rate of fusion at the cell membrane so that there was an immediate increase in the amount of polysaccharide secreted (35). 

Aman, P., McNeil, M., Franzen, L-E., Darvill, A. G. and Albersheim, P, 1981, Structural elucidation, using h.p.l.c.-m.s. and g.l.c.-m.s., of the acidic polysaccharide secreted by rhizobium meliloti strain 1021 Carbohydrate Research 95, 263-282. Amisha Kamal, J. K. and Behere, D. V. Steady-state and picosecond time-resolved fluorescence studies on native and apo seed coat soybean peroxidase. Biochemical Biophysical Research Communication 289, 427-433. 

Dubourdieu D. (1982) Recherches sur les polysaccharides secretes par Botrytis cinerea dans la bale de raisin. Thdse Doctorat University de Bordeaux II. 

It is a polysaccharide secreted by the bacterium Xantftomonas campestris. It is the sodium, potassium, or calcium salt of a high-molecular-weight polysaccharide containing o-glucose, D-mannose, and o-glucuronic acid. It also contains not less than 1.5% of pyruvic acid. It is a cream-colored powder soluble in water [137]. 

Cells adhere to surfaces when attractive forces exist between the cell stuf ace and the substrate of interest. In vivo, cells in animal tissues adhere to the extraceUular matrix, by binding of adhesion receptors in the ceU s membrane to the proteins of the extracellular matrix. Extracellular matrix is an interdigitating network of proteins and polysaccharides secreted by the cells themselves. For successful cultivation of anchorage dependent cells in a microfluidic device, it is necessary to provide means for the cells to attach to the device surface. Some surfaces, such as glass or poly (methyl methacrylate) (PMMA), may be naturally adhesive to certain cell types. It is generally accepted that the natural adhesiveness of these materials comes from their ability to support adsorption of semm proteins added to the culture... 

Xanthan gum is an anionic polysaccharide secreted by certain bacteria which in the dry state does not exhibit a first-order phase transition. In the presence of a small amount of water a glass transition, cold crystallization, melting and a liquid crystal transition are observed. Figure 5.28A presents DSC heating curves of water-xanthan gum systems with various water contents. A 3 mg sample was hermetically sealed in an aluminium sample vessel, cooled from 320 to 150 K at 10 K/min and subsequently heated at 10 K/min. With reference to Section 5.1, the transition temperatures are defined as follows glass transition temperature and melting and crystallization temperatures 7p and, respectively. The... 

Xanthan Xanthan gum is a polysaccharide secreted by the bacterium Xanthomonas campestiis It is composed of pentasaccharide repeat units, comprising glucose, mannose, and glucuronic acid in the molar ratio 2 2 1 In food industry for stabilization and gelling and viscosity control, in oil industry to enhance oil recovery, in the fabrication of tooth pastes and paints... 

G. Ragu n s, R. Christen, J. Gu6zennec, P. Pignet, and G. Barbier, Vibrio diabolicus sp. nov., a new polysaccharide-secreting organism isolated from a deep-sea hydrothermal vent polychete annelid, Alvinellapompejana, Int. J. Syst. Bacteriol, 47,989-995,1997. 

In general, polysaccharide synthesis in fungi includes the following steps carbohydrate synthesis and polymerization, and, in the case of capsular polysaccharides and EPS, polysaccharide secretion to the extracellular environment. 

Alginates, which are also called alginic acids, are anionic linear polysaccharides secreted by brown seaweed and marine algae, including Laminaria hyperborea, Ascophyllum nodosum and Macrocystis pyrifera [3]. 

Xanthan gum is a polysaccharide secreted by certain species of bacteria. It is produced by a pure-culture fermentation of glucose using the bacterium Xanthomonas campestris, reported to be a minor plant pathogen, though the strain used is reportedly nonpathogenic and nontoxic to humans. ... 

Acetan is a bacterial polysaccharide secreted by Acetobacter xylinium... 

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