Rhizobium japonicum mutants induced by gamma rays and some chemical mutagens

Numerous symbiotic mutants of R.japonicum were isolated after UV irradiation or nitrosoguanidine mutagensis. Cultures of R.japonicum GM 377 were irradiated with 0, 25, 50, 75, 100, 150, 175, 200, 250 and 300 krad of gamma-rays. As for chemical mutagensis, cultures were treated with Sodium azide and colchicin at concentration of 1x10-6, 1x10-5, 5x10-5, 1x10-4, 5x10-4, 1x10-3 and 5x10-3 mol. Results revealed that gentamicin at concentration of 24.0 Mg/ml was able to kill all the populations of R.japonicum. Therefore, this concentration was used for mutants selection. However, numerous mutants at different freguencies were identified. The highest percentage of mutant was obtained with Sodium azide at 1x10-4 mol