Xylans bacterial

Many pioneer structural investigations were carried out in other groups of polysaccharides, notably on inulin, on the xylan from esparto, on the mannan from yeast and on a series of bacterial polysaccharides amongst the latter were included somatic and lipoid-bound polysaccharides from M. tuberculosis. Noteworthy also was the work on the dextran produced by strains of Leuconostoc, which is showing grqat promise as a blood plasma substitute. 

Other polysaccharides whose solutions yield liquid crystalline phases include the bacterial polysaccharide xylan and the extracellular fungal polysaccharide produced by schizophyllum commune... 

Number of (1 — 3)-/3-D-Xylan-decomposing Marine Bacterial Strains Possessing (1 — 3)- and (1 —> 4)-/J-D-Xylanase Activity14 ... 

The thermophilic and alkalophilic bacterial strain Bacillus circulans D1 used in this study was isolated in a previous work [20], Stock cultures were maintained in a complex medium containing xylan as carbon source [21], with the addition of agar (15.0 g/L). 

The basic mechanism is a disproportionation. Thus a disaccharide, such as sucrose, could give a triose and a free monosaccharide. Synthesis of a levan (i.e. a fructan) would be accompanied by the release of glucose, while the production of a dextran (i.e. a glucan) would liberate free fructose. By repeated transglycosylations of this type polymers arise. A similar mechanism occurs in the production of some plant fructans, but it is otherwise very rare in eukaryotes. Bacterial levans are usually much larger than their eukaryotic counterparts and other polymers produced in the same way include bacterial arabinans, xylans, galactans and glucans. 

Specific gravity of dry CNP is about 1.57—1.59 g/cm tapped density can be 0.25—0.30 g/cm and bulk density 0.1—0.2 g/cm. The nanoparticles isolated from cotton cellulose, bacterial cellulose, and tunicate are usually chemically pure, while CNP from herbs, shmbs, bast fibers, crops, wood pulps, and some other sources may contain residual xylan and lignin. 

The presence of feruloyl esterase activity was first detected in culture filtrates of Streptomyces olivochromogenes grown on oats spelt xylan and wheat bran (iJ) and have subsequently been found in a number of bacterial and fungal... 

Bacterial cellulose (BC) is frequently studied in order to clarify the mechanism for biosynthesis of cellulose (Tokoh et al. 2002a). Details of mechanisms for biopolymerization and simultaneous crystallization in long parallel rows of extended chains are understood fairly well. As an example of the nature of such studies, effects of pectin and xylan medium on the crystallite morphology have been demonstrated (Tokoh et al. 2002b). 

Iwata et al. (27) observed by X-ray analysis that out of different glucans, xylans and galactans, it was indeed the mannans that showed the highest affinity towards bacterial cellulose. The sorption mechanism of different hemicelluloses is, moreover, not necessarily the same. Uhlin et al (28) found that bacterial cellulose crystallized in a different form in the presence of wood hemicelluloses than in their absence (Ip, rather than Iq). Furthermore, xylans and mannans seemed to interact with cellulose in different ways - xylans co-crystallized with cellulose producing defects in the crystalline structure, while mannans mainly decreased the crystallite size and thus also the over all degree of crystallinity. Xylan and mannan chains have been shown to undergo different conformational transitions upon sorption (29). The mannans were able to form a two-fold helix and lay down on the cellulose chain quite nicely and seemed to interact with two cellulose chains, while xylan took on a three-fold molecular axis and could, therefore, not sorb as efficiently. Larsson et al (30) showed through solid-state NMR analysis that xylans can, anyhow, interact directly with cellulose surfaces. Tetramers were the smallest polymers to sorb onto cellulose surfaces (29). 

In this preliminary study, extracted willow xylan was not immediately available for use in blending studies. As a result, native, partially acetylated birch xylan and a synthetically acetylated elm xylan were obtained from the sample collection of Professor T. E. Timell, an emeritus faculty member at our institution. Blends of these polymers with cellulose esters and bacterial polyesters were typically prepared by mbcing solutions of the respective polymers dissolved in either dimethylformamide (DMF) or water followed by evaporation in a vacuum oven at 10S°C yielding a thin film. A thermoplastic bacterial co-polyester (poly(hydroxybutyrate)) containing 30% hydroxyvalerate content) was purchased from the Aldrich Chemical Company (cat. no. 28,248-0). The glass transition temperature (Tg) of each polymer and blend was determined using a TA Instruments 2920 differential scanning calorimetry (DSC) instrument. 

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