Correlation between streptomycin resistance and symbiotic properties of Rhizobium. I. Conversion of spheroplastizing, effective R. trifolii strain B1 to avirulent rods with changed phage and antibiotic patterns after mutation to high level of streptomycin resistance.

Rhizobium trifolii strain B1, which is infective and fixes nitrogen during symbiosis with clover plants, shows a peculiar property to undergo morphological change during growth, i.e. rods are changing into spheroplast-like forms. Moreover, it failed to grow at 38 degrees. It was found that mutation to high level of streptomycin resistance (above 1000 microgram per/ml) caused loss of this property. Further studies showed that simultaneously with the changes in streptomycin resistance other features of this strain were also changed: infectivity for clover plants, sensitivity to high temperature, phages and antibiotics. Mutation to low level of streptomycin resistance did not change the above mentioned features of the strain B1.