Ineffective and non-nodulating mutant strains of Rhizobium japonicum

Abstract

Mutant strains of R. japonicum that were unable to allow the ''Corsoy'' cultivar of soybean to reduce acetylene or fix N2 were isolated. These strains grow as well as the wild type in a variety of media. Mutant strains SM1 and SM2 did not form nodules on the host plant, but they reduced acetylene in the nonsymbiotic assay. Strains SM3 and SM4 produced nodules that did not have the characteristic pink pigment caused by leghemoglobin. The nodules formed by these strains also were small. One mutant strain, SM5, produced large pink nodules. The lesion in this strain may be in the gene that specifies nitrogenase component II.