Nitrogen Fixation Mutants of the Actinobacterium Frankia Casuarinae CcI3.

Frankia is a representative genus of nitrogen-fixing (N-fixing) actinobacteria; however, the molecular mechanisms underlying various phenomena such as the differentiation of a N fixation-specific structure (vesicle) and the regulation of N fixation (nif) genes, have yet to be elucidated in detail. In the present study, we screened hyphal fragments of Frankia casuarinae that were mutagenized by 1-methyl-3-nitro-1-nitrosoguanidine or gamma rays, and isolated 49 candidate N fixation mutants. Twelve of these mutants were selected for further study, and their abilities to grow in NH-deficient (N-) liquid media and their rates of acetylene reduction activities were evaluated.