Alteration of the Effective Nodulation Properties of a Fast-growing Broad Host Range Rhizobium due to Changes in Exopolysaccharide Synthesis

Abstract

Summary Strain NGR234 is a broad host range Rhizobium which can effectively nodulate a broad spectrum of legumes. Ninety mutants with altered exopolysaccharide production were isolated after strain NGR234 was subjected to transposon Tn5 mutagenesis. These mutants were classified on the basis of their physiological properties into 9 groups. Their symbiotic porperties were tested on four legumes which form spherical (determinate) nodules ( Macroptilium atropurpureum, Desmodium intortum, Desmodium uncinatum and Lablab purpureus ) and on the legume Leucaena leucocephala which forms cylindrical (indeterminate) nodules. On these plants strain NGR234 forms nitrogen-fixing nodules (Nod + Fix + ). The results from the testing of the various mucoid-defective mutants on these plants show that it is possible to alter the synthesis of the surface polysaccharides of strain NGR234 and produce a narrow host range Nod + Fix + Rhizobium .