Cyclic organization of the carbohydrate metabolism in Sinorhizobium meliloti

The pathways of polysaccharide biosynthesis were investigated in cells of S inorhizobium meliloti (strain Su47) using a stable isotope approach. The is otopic labeling of the periplasmic beta-1,2-glucans synthesized from glucos e labeled at various positions evidenced the involvement of catabolic pathw ays, namely the pentose-phosphate and Entner-Doudoroff. pathways, into the early steps of polysaccharide synthesis, The exopolysaccharides produced at the same time had a labeling pattern similar to that of the beta-glucans, indicating similar early steps for both polysaccharides. The results emphas ized a cyclic organization of the carbohydrate metabolism in S. meliloti, i n which the carbons of the initial hexose were allowed to re-enter the cata bolic pathways many times. The metabolic incidences of such metabolic topol ogy are discussed.