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The bacterial cellulose produced in an agitated culture (Ag-BC) showed the highest emulsion-stabilizing effect among the examined cellulosic materials. It was clarified that a mechanical barrier and a scaffolding structure composed of fine fibrils of bacterial cellulose interrupted the coalescence of oil droplets to stabilize the emulsion without reducing the interfacial tension as occurred with sorbitan monolaurate. Since Ag-BC consists of thinner fibrils and smaller floes than any other cellulosic material, Ag-BC would cover a larger surface area of the oil droplet as a mechanical barrier. The emulsion containing Ag-BC was stable against the addition of salt, and changes in pH and temperature in comparison with xanthan gum and sorbitan monolaurate. This stability would have been due to the stability of the mechanical barrier and a scaffolding structure composed of stable crystalline cellulose. In contrast, instability in the conformation of xanthan gum and a reduction in the interfacial tension of the surfactant would lead to instability of the emulsion.

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Higher plants efficiently conserve energy ATP in cellulose biosynthesis by expression of sucrose synthase, in which the high free energy between glucose and fructose in sucrose can be conserved and used for the synthesis of UDP-glucose. A mixture of sucrose synthase and bacterial cellulose synthase proceeded to form UDP-glucose from sucrose plus UDP and to synthesize 1,4-␤-glucan from the sugar nucleotide. The mutant sucrose synthase, which mimics phosphorylated sucrose synthase, enhanced the reaction efficiency (V max ͞K m ) on 1,4-␤-glucan synthesis, in which the incorporation of glucose from sucrose was increased at low concentrations of UDP. Because UDP formed after glucosyl transfer can be directly recycled with sucrose synthase, UDPglucose formed appears to show high turnover with cellulose synthase in the coupled reaction. The expression of sucrose synthase in Acetobacter xylinum not only changed sucrose metabolism but also enhanced cellulose production, in which UDP-glucose was efficiently formed from sucrose. Although the level of UDP-glucose in the transformant with mutant sucrose synthase cDNA was only 1.6-fold higher than that in plasmid-free cells, the level of UDP was markedly decreased in the transformant. The results show that sucrose synthase serves to channel carbon directly from sucrose to cellulose and recycles UDP, which prevents UDP build-up in cellulose biosynthesis.

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