Exocellular

Frere JM et al (1975) Kinetics of interactions between the exocellular DD-carboxypeptidase-transpeptidase from Streptomyces R61 and (3-lactam antibiotics. Eur J Biochem 57 343-351... 

Enzymes most frequently proposed to fruit juices producers are pectinases coming from Aspergillus. Pectinases are exocellular enzymes and are the main activities produced among numerous side activities type hemicellulases, glycosidases. The Table 1 gives the spectrum of enzymatic activities contained in three commercial preparations A, B and C. 

Most polymers used in oil field operations and resource recovery are synthetic. The man-made materials in common use are polyO-amidoethylene) ( = polyacrylamide ), poly( 1-amidoethylene-r-( sodium 1-carboxylatoethylene ) ( = partially hydrolyzed polyacrylamide ), poly(l-amidoethylene-r-( sodium 1-(2-methylprop-1N-yl-1-sulfonate)amidoethylene) (AMPS-acrylamide copolymer), and xanthan gum. Xanthan gum is a synthetic because no one finds a pool or river contaminated with Xanthomonas compestris that experiences the right sequence of solute to naturally produce the exocellular gum polymer. A fermenter is a man made object, a tree is not. 

Polysaccharide formation may be endocellular, exocellular or capsular. The polysaccharide is usually a normal metabolic product, frequently a major product. Isolation and purification of a bacterial polysaccharide generally involve continued precipitations from a buffered solution, together with electrodialysis or ultrafiltration. 

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. 

Smarda, J. and Smajs, D. (1998). Colicins - exocellular lethal proteins of Escherichia coli, Folia Microbiol. (Praha), 43, 563-582. 

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... 

Environmental Potential of the Trichoderma Exocellular Enzyme System... 

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. 

CA 67, 75047n(J967) [Gelled expl compns contg a Xanthomonas hydrophilic colloid mixed with aq soln of inorganic nitrate (such as AN) and borax are described. Xanthomonas is a hydrophilic, exocellular, high-mo 1-wt colloid prepd by culture fermentation by... 

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. 

The increased use of tanks for the storage of raw milk on the farm between pickups has introduced the danger of potential off-flavor development caused by lipases that are produced by certain microorganisms (psychrotrophs) at low temperatures. The exocellular lipases of psychrotrophic bacteria are extremely heat resistant, and although the microorganisms are killed, the enzymes survive pasteurization and sterilization temperatures. Rancidity may become noticeable when cell counts exceed 106 or 107/ml. Downey (1975) has summarized the potential contribution of enzymes to the lipolysis of milk (Table 5.1). 

Heat-Resistant Lipases. The heat-resistant lipases and proteinases and their effects on the quality of dairy products have been reviewed (Cogan 1977, 1980). Several reports have linked the lipases from bacteria with the off-flavor development of market milk (Richter 1981 Shipe et al. 1980A Barnard 1979B). The microflora developing in holding tanks at 4°C [and presumably in market milk stored at 40°F (Richter 1981)] may produce exocellular lipases and proteases that may survive ordinary pasteurization and sterilization temperatures. Rancidity of the cheese and gelation of UHT milk appear to be the major defects caused by the heat-resistant enzymes. 

Microorganisms found in the microflora from holding tanks belong primarily to the genera Pseudomonas, Alcaligenes, Enterobacter, and Achromobacter. However, Pseudomonas predominates, and isolates from bulk milk show much more lipolytic and proteolytic activity than other psychrotrophs isolated (Stewart et al. 1975). Bacterial exocellular lipases have an optimum pH of 8.75, a relative optimum temperature at 37°C, and an absolute optimum temperature at 50°C (Driessen and Stadhouders 1974B). Kishonti (1975) reported two optimum temperatures at 30° and 55°C, respectively. 

Gripon, J. C. and Debest, B. 1976. Electrophoretic studies of the exocellular proteolytic system of Penicillium roqueforti. Lait 56, 423-438. (French)... 

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

Formation of L-guluronic acid, a component of the alginic acid-like polysaccharide produced by P. aeruginosa and Azotobacter vinelandii, requires special comment. In this case, a polymer built from /3-(l- 4)-linked D-mannosyluronic acid residues serves as an intermediate in the biosynthesis.204,205 Part of the D-mannosyluronic acid residues in the polymer is subjected to an epimerization at C-5 catalyzed by an exocellular enzyme of the micro-organism,205-207 producing a polysaccharide composed of structural blocks that contain only D-mannosyluronic acid or only l-gulosyluronic acid residues, as well %s some having both. The mechanism of the epimerization remains unclear. 

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. 

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