Isolation of antibiotic-resistant and antimetabolite-resistant mutants of Frankia strains Eul1c and Cc1.17

Antibiotic-resistant and antimetabolite-resistant mutants of the nitrogen-fixing symbiotic bacterium Frankia were isolated to provide strains with genetic backgrounds amenable to genetic analysis. The lethal and mutagenic effects of ethyl methanesulfonate (EMS) and UV light on four Frankia strains were investigated. UV irradiation or EMS treatment of strain EuIlc cells resulted in the formation of two different colony types: rough and smooth. The smooth colonies were conditional sporulation mutants. In the case of EMS-induced cells of strain Ccl.17, resistance to lincomycin, ampicillin, and 5-fluorouracil occurred at a frequency of 1 x 10(-5), 1 x 10(-5), and 4 x 10(-5), respectively. The lincomycin-resistant mutants produced a yellow-tan pigment that was released into the growth medium. Resistance to tetracycline and lincomycin with EMS-induced cells of strain EuIlc occurred at a frequency of 3.2 x 10(-3) and 4.7 x 10(-4), respectively. These strains will be useful for the development of genetic methods for Frankia.