ISOLATION AND CHARACTERIZATION OF THE SYMBIOTIC PHENOTYPE OF ANTIBIOTIC-RESISTANT MUTANTS OF FRANKIA FROM RHAMNACEAE

Induced rifampicin-resistant mutants of Frankia were isolated by treat ment of spores from strain ChI1 with 2 mg/ml of nitrosoguanidine. The mutagenic treatment was followed by growth for 72 h on non-selective m edium to allow the expression of the mutation, before plating on selec tive medium. Spontaneous rifampicin-resistant mutants were isolated fr om strain ReI4 and chloramphenicol-resistant mutants were derived from strains ReI6 and TtI42. The mutants grew in medium containing up to 2 0 mu g/ml of antibiotics. They showed similar morphology and growth pa ttern compared with their parent strains. However, they exhibited diff erences in symbiotic properties, such as infectivity and nitrogenase a ctivity, from their parent strains.