Exopolysaccharide-deficient mutants of Rhizobium meliloti that form ineffective nodules

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 82; no. 18; pp. 6231 - 6235
• Main Authors: Leigh, J.A, Signer, E.R, Walker, G.C
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences of the United States of America 01.09.1985; National Acad Sciences
• Subjects: Bacteria; Bacteriology; Bacteriophages; Biological and medical sciences; DNA, Recombinant; FIJACION DEL NITROGENO; FIXATION DE L'AZOTE; Fluorescence; FORMATION DE NODOSITES; Fundamental and applied biological sciences. Psychology; Genetics; Glycine max - microbiology; Infections; Microbiology; MUTANT; MUTANTES; MUTANTS; Mutation; NITROGEN FIXATION; NODULACION; Nodules; Phenotypes; Plasmids; POLISACARIDOS; POLYHOLOSIDE; POLYSACCHARIDES; Polysaccharides, Bacterial - genetics; Protons; RHIZOBIUM; Rhizobium - genetics; Rhizobium - physiology; Root hairs; ROOT NODULATION; Symbiosis; Rhizobium meliloti; Nodulation; Polyoside; Bacteria; Rhizobiaceae; Mutation; Defectivity; Extracellular; Nodule
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.82.18.6231

By screening with the fluorescent stain Calcofluor, we have isolated 26 independent transposon Tn5 insertion mutants of Rhizobium meliloti that are deficient in the production of a known extracellular polysaccharide (Exo-). The mutants belonged to six distinct genetic groups based on the ability of their Exo-phenotype to be complemented by different recombinant plasmids from a R. meliloti clone bank. With few exceptions, all of the mutants formed ineffective (non-nitrogen-fixing) nodules on alfalfa. For all but one group, the complementing plasmids restored effective nodulation. These results establish a firm and extensive correlation between the ability of Rhizobium to produce a particular polysaccharide and symbiotic proficiency. The ineffective nodules appeared to contain no bacteroids and to form without shepherds' crooks or infection threads; this symbiotic phenotype matches that described for a set of independently isolated mutants that belong phenotypically and genetically to the group B exopolysaccharide mutants described previously [Finan et al. (1985) Cell 40, 869-877]. Apparently the exopolysaccharide, although not required for nodule formation, is involved in wild-type nodule invasion.