Enhancement of cellulose production by expression of sucrose synthase in Acetobacter xylinum

Higher plants efficiently conserve energy ATP in cellulose biosynthesis by expression of sucrose synthase, in which the high free energy between gluco se and fructose in sucrose can be conserved and used for the synthesis of U DP-glucose. A mixture of sucrose synthase and bacterial cellulose synthase proceeded to form UDP-glucose from sucrose plus UDP and to synthesize 1,4-b eta-glucan from the sugar nucleotide, The mutant sucrose synthase, which mi mics phosphorylated sucrose synthase, enhanced the reaction efficiency (V-m ax/K-m) on 1,4-beta-glucan synthesis, in which the incorporation of glucose from sucrose was increased at low concentrations of UDP, Because UDP forme d after glucosyl transfer can be directly recycled with sucrose synthase, U DP-glucose formed appears to show high turnover with cellulose synthase in the coupled reaction, The expression of sucrose synthase in Acetobacter xyl inum not only changed sucrose metabolism but also enhanced cellulose produc tion, in which UDP-glucose was efficiently formed from sucrose, Although th e level of UDP-glucose in the transformant with mutant sucrose synthase cDN A was only 1.6-fold higher than that in plasmid-free cells, the level of UD P was markedly decreased in the transformant, The results show that sucrose synthase serves to channel carbon directly from sucrose to cellulose and r ecycles UDP, which prevents UDP build-up in cellulose biosynthesis.