Bacterial cellulose allomorphs

Fig. 2 X-ray diffractograms of the allomorphs in cellulose in II family by the reflection method. A II, mercerized bacterial cellulose, B IVu prepared from A through IIIn (C), C IIIn prepared from A. The treatments were carried out under stretching.

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.

This structure is completely different from the 2D structure of the spherulite composed of fibrous bacterial cellulose. TEM observations demonstrated that the negative-type spherulites are composed of thin crystal plates approximately 8 nm thick, in which the cellulose chains are aligned vertically to the plate, having a cellulose 1 allomorph. These high-order structures of cellulose are formed only via the polymerization of j8-CF. 

Current data suggest that cellulose biosynthesis is a bacterial invention and that eukaryotes acquired the process via multiple lateral gene transfers. Bacteria and eukaryota have independently evolved regulatory mechanisms and molecular structures to utilize the p-1,4-homopolymer synthesized by the catalytic activity of homologous cellulose synthase enzymes. The differences in accessory enzymes probably reflect not only convergent evolution to produce a cellulose I crystalline allomorph, but also inventions of alternative products such as cellulose II, noncrystalline cellulose, or nematic ordered cellulose. 

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