Evaluation of Acidic Heteropolysaccharide Structures in Rhizobium leguminosarum Biovars Altered in Nodulation Genes and Host Range. Guy Orgambide. Department of Microbiology, Michigan State University, East Lansing 48824 U.S.A. Saleela Philip-Hollingsworth, Lucette Cargill, and Frank Dazzo. Department of Microbiology, Michigan State University, East Lansing 48824 U.S.A. MPMI 5:484-488. Accepted 29 July 1992. Copyright 1992 The American Phytopathological Society.

¹H-NMR spectroscopy showed that the extracellular heterpolysaccharides (EPS) from derivatives of Rhizobium leguminosarum bv. trifolii ANU843 altered in pSym nod composition or function (transposon insertions, deletion of pSym, induction by flavone, and introduction of cloned pSym nod regions from ANU843 and R. l. bv. viciae 248 on recombinant plasmids into the pSym-cured background of ANU843) differed only in 3-hydroxybutyrate stoichiometry per octaglycosyl unit. This change in EPS was likely to be an indirect effect of altered growth during expression of pSym nod genes in the presence of the flavone. No modifications were found in EPS made by R. l. bv. phaseoli 8002 when its resident pSym was deleted or replaced with pSym from R. l. bv. viciae 248, or with a derivative of this pSym lacking the host-specific nodulation genes nodFELMNTO. Thus, although certain O-acyl noncarbohydrate substitutions in EPS are affected by pSym nod genes (including the ones that determine host range) in certain backgrounds of R. leguminosarum, this change does not occur universally among all strains of R. leguminosarum. We conclude that the structure of the acidic EPS does not control host-specific nodulation of white clover, hairy vetch, and beans for the strains of R. leguminosarum tested here.