PHAGE SUSCEPTIBILITY AND PLASMID PROFILE ANALYSIS OF SINORHIZOBIUM-FREDII

This is the first report identifying bacteriophages and documenting me gaplasmids of Sinorhizobium fredii. Plasmid DNA content and bacterioph age typing of eighteen strains of S fredii were determined. S. fredii strains fell into ten plasmid profile groups containing 1 to 6 plasmid s, some evidently larger than 1000 MDa. Twenty-three S. fredii lytic p hages were isolated from soil, and they lysed six different S. fredii strains. The host range and plaque morphology of these phages were stu died. Susceptibility to S. fredii phages was examined for S. meliloti; Rhizobium leguminosarum bvs. viceae, trifolii and phaseoli; R, loti; Bradyrhizobium japonicum; B. elkanii and Bradyrhizobium sp. (Arachis). Several phages that originally lysed S. fredii strain USDA 206 also l ysed strains of all three S. fredii serogroups described originally by Sadowsky et al. Phages that infected S. fredii strains USDA 191 and U SDA 257 were highly specific and lysed only serogroup 193 strains. S. meliloti strains L5-30 and USDA 1005 were lysed by three of the phages that lysed S. fredii strain USDA 217. No other Rhizobium or Bradyrhiz obium strain tested was susceptible to lysis by any of the S. fredii p hages. The present investigation indicates that phage susceptibility i n conjunction with plasmid profile analysis may provide a rapid method for identification and characterization of strains of S. fredii.