Antigenic Change in the Lipopolysaccharide of Rhizobium ef/iCFN42 Induced by Exudates of Phaseolus vulgaris. K. Dale Noel. Department of Biology, Marquette University, Milwaukee, Wl 53233, USA. Dominik M. Duelli (1), HongTao (1), and Nicholas J. Brewin (2). (1) Department of Biology, Marquette University, Milwaukee, Wl 53233, USA; (2) John Innes Institute, Norwich NR4 7UH, UK. MPMI 9:180-186. Accepted 27 December 1995, Copyright 1996 The American Phytopathological Society.

Growth of Rhizobium etli CE3 in the presence of exudates from Phaseolus vulgaris resulted in a modified lipopolysaccharide (LPS) that no longer reacted with monoclonal antibody JIM28. However, the overall LPS structure appeared not to be greatly altered, as revealed by unchanged mobility in gel electrophoresis and partial or unaltered reactivity with other antibodies. Activity that triggered LPS antigenic conversion was exuded from both seeds and roots, but reactivity with one of the antibodies indicated that the resulting alterations were not identical. Antibody binding to the LPS decreased as a function of the concentration of exudate present during growth of the bacteria. The antigenic change did not occur if purified LPS or nongrowing bacteria were incubated with the exudates. Exudate-induced LPS modification did not require the Sym plasmid.