UNAFFECTED NODULATION AND NITROGEN-FIXATION IN CARBOHYDRATE PLEIOTROPIC MUTANTS OF RHIZOBIUM-MELILOTI

Pleiotropic mutants were isolated from Rhizobium meliloti M5N1 with the resistance transposon Tn5. They failed to use carbohydrates as carbon source, but not dicarboxylic acids. Diauxic growth properties of the wild type and uptake assays in both M5N1 and a mutant strain 2.10 showed that the mutant was affected in the active transport of sugars. Exogenous cyclic AMP failed to affect the phenotype of the mutant, and a relatively high frequency of reversion was observed. This suggests that the mutant 2.10 was probably altered in a crp-like gene. However, its symbiotic properties remained unaffected. Thus, symbiosis does not depend on sugar utilization.