RHIZOBIUM EXTRACELLULAR STRUCTURES IN THE SYMBIOSIS

The extracellular and surface polysaccharides produced by Rhizobium sp ecies constitute a composite macromolecular interface between the bact erial cell and its environment. Several of these polysaccharides are i nvolved in the complex series of interactions leading to the establish ment of an effective Rhizobium-legume symbiosis. Extracellular heterop olysaccharides (EPSs) are found in culture supernatants, while capsula r polysaccharides adhere to the cell surface. Cyclic (1-2)-beta-D gluc an is a periplasmic oligosaccharide that has also been found in the cu lture supernatants of some strains. The lipopolysaccharides (LPSs), wh ich form part of the outer membrane and contain the O-somatic antigens , comprise the other major group of extracellular polysaccharides. In this review we will describe the major Rhizobium extracellular structu res and their role in symbiosis with leguminous plants.