DUPLICATION OF DNA REGIONS CARRYING REPETITIVE SEQUENCE RS-ALPHA IN BRADYRHIZOBIUM-JAPONICUM-110

RS alpha is a repeated DNB sequence found within the nitrogen-fixation gene cluster of Bradyrhizobium japonicum, a symbiotic nitrogen-fixing bacterium that nodulates soybean. Bradyrhizobium japonicum strain 110 spc4 contains 12 repeats, each located on a separate XhoI DNA restrict ion fragment between 1.2 and 14 kb in length. Although Fix(+) and Fis( -) derivatives of B. japonicum USDA 110 ere first reported more than t wo decades ago, genotypic differentiation, on the basis of RS alpha hy bridization pattern, was reported only recently. Bradyrhizobium japoni cum strain USDA 110 had only single copies of the RS alpha-hybridizing bands, but a particular Fix-derivative, MSDJG1, carried doublers of t wo distinct XhoI fragments that carry RS alpha 3 and RS4 alpha. In thi s study RS alpha hybridization patterns were anal c-sed further in bot h Fis' and Fis-derivatives of strain 110 to test for duplication of th ese particular genomic regions, It was concluded that the duplication, or not, of genetic regions carrying RS alpha 3 and RS alpha 4 in stra in USDA 110 derivatives is unrelated to symbiotic nitrogen-fixation ab ility. Like Fix-MSDJG1, Fis(+) strain 110 derivatives I-110 and MN-110 had duplications of the XhoI DNA restriction fragments carrying RS al pha 3 and RS alpha 4, but Fix-strain 110 derivative L2-110 lacked thes e duplications, Thus, it is new clear that Fix-derivatives MSDJG1 and L2-110 arose via distinct genetic mechanisms, Interestingly, Fis(+) de rivatives of strain 110 from the laboratories of Elkan and Hennecke di ffered in RS hybridization profile.