Biosynthesis of curdlan from culture media containing 13C-labeled glucose as the carbon source

13C-Labeled curdlans were biosynthesized by Agrobacterium sp. (ATCC 31749) from culture media containing D-(1-13C)glucose, D-(6-13C)glucose, or D-(2-13C)glucose as the carbon source, and their structures were analyzed by 13C NMR spectroscopy. The labeling was mainly found in the original position, that is, C-1, C-6, or C-2, indicating direct polymerization of introduced glucose. In addition, C-3 in curdlan obtained from D-(1-13C)glucose, C-1 in curdlan obtained from D-(6-13C)glucose, and C-1 and C-3 in curdlan obtained from D-(2-13)glucose were labeled. From analysis of this labeling, the biosynthesis of curdlan was interpreted as involving five routes: (1) direct synthesis from glucose; (2) rearrangement (1-13C-->3-13C); and (3) isomerization (6-13C-->1-13C) of cleaved trioses by the Embden-Meyerhof pathway, followed by neogenesis of glucose and formation of curdlan; (4) from fructose 6-phosphate formed in the pentose cycle (2-13C-->1-13C, 3-13C); and (5) neogenesis of glucose from fragments produced in various pathways of glycolysis. The 13C-labeling at C-6 and C-2 in the starting glucoses is well preserved in the C-6 carbon and the C-1 to C-3 carbons, respectively, in the curdlan produced.