A NOVEL CELL-SURFACE POLYSACCHARIDE IN PSEUDOMONAS-PUTIDA WCS358, WHICH SHARES CHARACTERISTICS WITH ESCHERICHIA-COLI K ANTIGENS, IS NOT INVOLVED IN ROOT COLONIZATION

Previously we have shown that flagella and the O-specific polysacchari de of lipopolysaccharide play a role in colonization of the potato roo t by plant growth-promoting Pseudomonas strains WCS374 and WCS358. In this paper, we describe a novel cell surface-exposed structure in Pseu domonas putida WCS358 examined with a specific monoclonal antibody, Th is cell surface structure appeared to be a polysaccharide, which was a ccessible to the monoclonal antibody at the outer cell surface, Furthe r study revealed that it does not contain 2-keto-3-deoxyoctonate, hept ose, or lipid A, indicating that it is not a second type of lipopolysa ccharide. Instead, the polysaccharide shared some characteristics with K antigen described for Escherichia coli, From a series of 49 differe nt soil bacteria tested, only one other potato plant growth-promoting Pseudomonas strain reacted positively with the monoclonal antibody, Mu tant cells lacking the novel antigen were efficiently isolated by an e nrichment method involving magnetic antibodies, Mutant strains defecti ve in the novel antigen contained normal lipopolysaccharide, One of th ese mutants was affected in neither its ability to adhere to sterile p otato root pieces nor its ability to colonize potato roots, We conclud e that the bacterial cell surface of P. putida WCS358 contains at leas t two different polysaccharide structures, These are the O-specific po lysaccharide of lipopolysaccharide, which is relevant for potato root colonization, and the novel polysaccharide, which is not involved in a dhesion to or colonization of the potato root.