Polysaccharide exocellular

J. Ceming, Exocellular polysaccharides produced by lactic acid bacteria, FEMS Microbiol. Rev., 1 (1990) 113-130. 

Hot water-extractable C accounts for 1-5% of soil organic C (Leinweber et al. 1995 Sparling et al. 1998 Chan and Heenan 1999) and about 50% of this is thought to be present as carbohydrate (Haynes 2005). Because it is usually extracted from air-dried soils much of the pool originates from desiccated microbial cells but it also includes exocellular polysaccharides, root exudates, lysates and humic material (Redl et al. 1990 Leinweber et al. 1995 Sparling et al. 1998). Both hot water extractable C (Sparling et al. 1998 Chan and Heenan 1999) and hot water-extractable carbohydrate (Ball et al. 1996 Haynes and Beare 1997 Debrosz et al. 2002) have been used as indices of soil quality. 

Exhaustion, 9 175-176, 196 of a dye, 9 163 Exhaust mix, 10 37—38 Exhaust releases, industrial, 10 67 Exhaust streams, categories of, 10 67-68 Exit span areas, in thermal design, 13 258 Exocellular bacterial polysaccharide, 13 70 Exocellular polysaccharides, 20 573 Exons, 20 824... 

Tuinier, R., de Kruif, C.G. (1999). Phase separation, creaming, and network formation of oil-in-water emulsions induced by an exocellular polysaccharide. Journal of Colloid and Interface Science, 218, 201-210. 

Weinbreck, F., Nieuwenhuijse, H., Robijn, G.W., de Kruif, C.G. (2003b). Complex formation of whey protein-exocellular polysaccharide EPS B40. Langmuir, 19, 9404-9410. 

Xanthan is the extracellular (exocellular) polysaccharide produced by Xanthomonas campestris. As with other microbial polysaccharides, the characteristics (polymer structure, molecular weight, solution properties) of xanthan preparations are constant and reproducible when a particular strain of the organism is grown under specified conditions, as is done commercially. The characteristics vary, however, with variations in the strain of the organism, the sources of nitrogen and carbon, degree of medium oxygenation, temperature, pH, and concentrations of various mineral elements. 

Exocellular polysaccharides, which are produced by strains of both Gram-positive and Gram-negative bacteria. They include capsular and extracellular (slime) polysaccharides. 

Other monosaccharide components (of bacterial polysaccharides) that are structurally related to D-ribose include D-riburonic acid,232 identified in the exocellular polysaccharide produced by a strain of Rhizobium meliloti, and D-arabinose, frequently present as the furanose, in polysaccharides of mycobacterial cell-wall.233,234 L-Xylose235,236 should probably be included in the group, as it may be derived from D-arabinose through epimerization at C-4. Biosynthesis of these monosaccharides was not investigated. 

Similar enol ethers probably serve as intermediates in another common modification-reaction of monosaccharide units especially characteristic of exocellular polysaccharides, namely, the formation of cyclic acetals of pyruvic acid. 

The term monomeric mechanism will be used for the mechanism depicted in the left-hand part of Scheme 2 (sequence a). In this case, the monosaccharide residues are transferred consecutively from the corresponding glycosyl donors (Z-A or Z -B) onto a membrane-bound glycosyl acceptor. The acceptor is generally a monosaccharide residue, which may be a fragment of an oligosaccharide chain linked to a hydrophobic molecule embedded in a cell membrane. In many instances, the acceptor that is used for assembly of the polymeric chain (Y) is not identical to the final acceptor (X) of the chain, and further transfer of the chain from Y to X, or liberation of the polysaccharide molecule in the case of exocellular polysaccharides, is a necessary step in the biosynthesis. 

Most of the exocellular polysaccharides produced by bacteria are synthesized inside the bacterial cell, with the use of membrane-bound enzymes. Both types of chain assembly were observed for these polymers. In many cases, the mechanism of the assembly remains unidentified, and the nature of the glycosyl acceptors in the process is not clear. 

The material presented in previous sub-sections clearly shows that both of the possible mechanisms of polysaccharide chain-assembly may operate in the biosynthesis of bacterial polysaccharides. There is no clearcut, mechanistic difference in the biosynthesis of O-specific chains of lipopoly-saccharides, exocellular polysaccharides, and carbohydrate chains of Grampositive, cell-wall polymers for every class of polymer, the existence of both mechanisms of chain assembly was demonstrated. 

C3K produces an insoluble exocellular polysaccharide(1). This polysaccharide is entirely composed of D-glucosyl residues which are connected almost exclusively by B-(l- -3)-linkages. This and the similar glucan formed by some strains of Agrobaoterium are named Curdlan because they form irreversibly, resilient gel when heated in water. 

The nuclei of the acellular, slime mold Physarium polycephalum contains a /3-D-gaIactan (d.p. 560) bearing phosphate (2.5%) and sulfate (9.6%) groups. One unit in every 13 is branched, but the main structural-feature is 4-O-substituted D-galactopyranosyl units.121 It resembles the exocellular polysaccharide.122... 

The acidic, exocellular polysaccharide from Tremella mesenterica, isolated by Cetavlon precipitation, has repeating structure 39 with D-... 

Acidic polysaccharides (see Table IV) that contain uronic acid residues are, perhaps, the most prevalent type of exocellular polysaccharide. Often, these acidic biopolymers contain other sugars, including pentoses, hexoses, and heptoses, also found in neutral polysaccharides (see Tables V and VI). In many instances, these polymers possess alkali-labile O-acyl substituents, such as acetic, formic, ma-lonic, pyruvic, and succinic acids. Positively charged biopolymers that contain free amino sugars are rare, but have been found (see Table VII). More often, these amino sugars are N-acylated, generally with acetyl groups. 

It is difficult to state whether formation of exocellular polysaccharides is more prevalent among the bacteria, the yeasts, or the molds. However, with bacteria, polysaccharide formation has been studied the most thoroughly. Several yeasts are known to elaborate exopolysaccharides and are excellent sources thereof. Polysaccharide formation by fungi is less frequently observed. However, species of... 

Microbial, Exocellular Polysaccharides Containing Acidic Sugar Residues... 

Tuinier, R., and Kruif, C.G.d. (1999). Phase behavior of casein micelles-exocellular polysaccharide mixtures experiment and theory. J. Chem. Phys. 110, 9296-9304. 

Fucose has been detected in many fungi. It is formed on hydrolysis of the cell walls of the yeast-like fungi Mucor adventitius, Mucor hiemalis, Mucor javanicus, Mucor plumbeus, Mucor racemosus, Mucor spinosus, and Mucor sylvaticus, and in Rhizopus oryzae, Rhizoptts tamari, Rhizopus tonkiniensis, and Zygorrhyncus vuillemmU. The acidic, exocellular polysaccharide of Mucor racemosus contains L-fucosyl residues. ... 

In certain instances, the exocellular and intracellular polysaccharides of yeasts have been used by taxonomists as an aid in classification of the parent organisms. For example, Lipomyces lipoferus may readily be distinguished from Lipomyces starkeyi by the sugars formed on partial and on complete hydrolysis of their exocellular polysaccharides (see Table VII), a differentiation that is difficult if morphological characteristics and sugar-utilization patterns are used. ... 

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