Bacterial cellulose origin

Figures 8 and 9 show solid state 13q nmr spectra of the allomorphs in the I family prepared from ramie and those in the II family prepared from Fortisan. The signal of Cl for IIIj- and IVj did not show enough resolution to split into peaks though there was a shoulder at about 105 ppm. For all allomorphs in the I family, the chemical shifts of the Cl signal ranged from 106.5 to 107.0 ppm and their half-widths were 250 Hz. The Cl signals for the II family were all split into two peaks at 106 and 108.5 ppm. The half-widths were 320, 330 and 290 Hz, for II, HIn and IVj-j, respectively. Larger widths were observed for the cellulose II family. The values of the chemical shift and half-width were averages of values measured for the samples with the various origins, except for the Valonia and bacterial celluloses, which had substaintially different values.

Kai et al. (31) have reported that nascent microfibrils of bacterial cellulose were transformed into cellulose II with 10 3% NaOH aq. Solution or 86 vol % acetone aq. solution. They examined them with electron microscopy and diffraction. The microfibrils transformed into II with the acetone solution did not show any morphological change, retained the microfibrillar state of the original material, and had uniformly thin width and long lengths. The result is not consistent with a mechanism based on change from "parallel chain" to "antiparallel chains" during the transformation from I to II. 

The existence of an ordered structure in cellulose is shown conclusively by wide-angle x-ray diffraction (WAXD) and electron diffraction studies (3). The diffraction patterns exhibit reasonably well-definid reflections for which unit cells have been defined. There are four basic recognized crystalline modifications, namely, cellulose I, II, III and IV. By the WAXD method as proposed by Hermans (4,5) it has been found that native celluloses of different biological origin vary in crystallinity over wide limits, from A0% in bacterial cellulose to 60 in cotton cellulose and 70 in Valonia cellulose. 

At similar hydrolysis conditions, dimensions of the CNP depend on the origin of cellulose feedstock. In general, CNP derived from terrestrial plants (herbs, shrubs, crops, wood, bast fibers, cotton, etc.) have smaller sizes compared to those derived from other sources (tunicate, algae, and bacterial cellulose) this is in agreement with the lateral size of elementary crystallites (Habibi et al., 2010 Hanley et al., 1992 loelovich, 2014b Li and Ragauskas, 2011). 

Although the chemical structure of bacterial cellulose is identical to that of any other vegetable-based counterpart, its fibrous morphology (Fig. 1.20), as obtained directly in its biotechnological production, is unique and consequently the properties associated with this original material are also peculiar and promise very interesting applications. Details about this futuristic biopolymer are given in Chapter 17. 

The structural characteristics of bacterial cellulose are directly related to two factors, namely (1) the origin of the strain, which determines the la/ip ratio and (2) the culture medium composition that influences the chain size. Such characteristics determine the degree of crystallinity of bacterial cellulose and consequently, their physicochemical properties. Structural modifications can be accomplished in a post-production step, since it is possible to functionalize the hydroxyl groups (—OH) by methylation [13], esterification [14], sulphonation [13], nitration [13], deoxyamination [15], etc. 

In a recent original contribution to this topic. Brown and Laborie [41] prepared finely dispersed nanocomposites of bacterial cellulose in poly(ethylene oxide) by introducing the latter polymer in the former growth mediura This integrated manufacturing approach opens a novel promising route to fibre-reinforced nanocomposites based on bacterial cellulose. 

Conserved U motifs originally identified in bacterial cellulose synthases were used to identify the higher plant enzymes, which also contain a conserved zinc-binding domain (ZnBD) specific to the eukaryotic enzymes (Saxena et al. 1995). 

Both bacterial and native plant cellulose (so called cellulose I) coexist in two crystal modifications a (triclinic) and p (monoclinic). The difference consists in the H-bonding systems and in the conformation of neighboring cellulose chains. The la/lp ratio depends on the origin of the cellulose [13]. 

The role of CBMs may not be entirely passive, although thermodynamics ensure that any interaction has to be stoichiometric rather than catalytic. An isolated CBM 2a, originally from a Cellulomonas fimi endoglucanase, formed the usual (3-sandwich, but, in solution, when unconstrained by an attached catalytic domain, dimerised." This CBM liberated small particles from cotton linters but not bacterial microcrystalline cellulose the same behaviour was shown by the holoenzyme which had been inactivated with the appropriate Withers inactivator." " However, another CBM 2a, from Cellvibrio japonicus, was rigorously shown to act only by increasing substrate proximity." ... 

The kind of polysaccharides that are isolated from different bacteria are as follows Alginate, a linear copolymer with (l-4)-linked p-D-mannuronate and its a-L-guluronate residues that is produced by two bacterial genera Pseudomonas species and Azotobacter vinelandii [4]. Bacterial alginates are useful for the production of micro- or nanostructures suitable for medical applications. Cellulose, a p (1—>4) linked D-glucose unit obtained from Acetobacter xylinum. Cellulose of plant origin is usually impure as it contains... 

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