PERIPLASMIC GLUCANS OF PSEUDOMONAS-SYRINGAE PV SYRINGAE

We report the initial characterization of glucans present in the perip lasmic space of Pseudomonas syringae pv. syringae (strain R32). These compounds were found to be neutral, unsubstituted, and composed solely of glucose. Their size ranges from 6 to 13 glucose units/mol. Linkage studies and nuclear magnetic resonance analyses demonstrated that the glucans are linked by beta-1,2 and beta-1,6 glycosidic bonds. In cont rast to the periplasmic glucans found in other plant pathogenic bacter ia, the glucans of P. syringae pv. syringae are not cyclic but are hig hly branched structures. Acetolysis studies demonstrated that the back bone consists of beta-1,2-linked glucose units to which the branches a re attached by beta-1,6 linkages. These periplasmic glucans were more abundant when the osmolarity of the growth medium was lower. Thus, P. syringae pv. syringae appears to synthesize periplasmic glucans in res ponse to the osmolarity of the medium. The structural characteristics of these glucans are very similar to the membrane-derived oligosacchar ides of Escherichia coli, apart from the neutral character, which cont rasts with the highly anionic E. coli membrane-derived oligosaccharide s.