RHIZOBIUM-LEGUMINOSARUM CFN42 LIPOPOLYSACCHARIDE ANTIGENIC CHANGES INDUCED BY ENVIRONMENTAL-CONDITIONS

Four monoclonal antibodies were raised against the lipopolysaccharide of Rhizobium leguminosarum bv. phaseoli CFN42 grown in tryptone and ye ast extract. Two of these antibodies reacted relatively weakly with th e lipopolysaccharide of bacteriods of this strain isolated from bean n odules. Growth ex planta of strain CFN42 at low pH, high temperature, low phosphate, or low oxygen concentration also eliminated binding of one or both of these antibodies. Lipopolysaccharide mobility on gel el ectrophoresis and reaction with other monoclonal antibodies and polycl onal antiserum indicated that the antigenic changes detected by these two antibodies did not represent major changes in lipopolysaccharide s tructure. The antigenic changes at low pH were dependent on growth of the bacteria but were independent of nitrogen and carbon sources and t he rich or minimal quality of the medium. The Sym plasmid of this stra in was not required for the changes induced ex planta. Analysis of bac terial mutants inferred to have truncated O-polysaccharides indicated that part, but not all, of the lipopolysaccharide O-polysaccharide por tion was required for binding of these two antibodies. In addition, th is analysis suggested that O-polysaccharide structures more distal to lipid A than the epitopes themselves were required for the modificatio ns at low pH that prevented antibody binding. Two mutants were antigen ically abnormal, even though they had abundant lipopolysaccharides of apparently normal size. One of these two mutants was constitutively un reactive towards three of the antibodies but indistinguishable from th e wild type in symbiotic behavior. The other, whose bacteroids retaine d an epitope normally greatly diminished in bacteroids, was somewhat i mpaired in nodulation frequency and nodule development.