GENERATION OF CONJUGATIVE PLASMIDS IN STR AINS CIAM0701 AND CIAM0710 OF RHIZOBIUM-GALEGAE UPON INTRODUCTION OF THE SUICIDE VECTOR PSUP2111

The ''suicide'' vector pSUP2111, containing transposon Tn5, the mob si te of plasmid RP4 and gene nifH of Rhizobium meliloti, was introduced into strains CIAM0701 and CIAM0710 of R. galegae. As a result of cross es of transconjugants of R. galegae carrying transposon Tn5 with aviru lent mutants of R. meliloti and Agrobacterium, recipient cells acquire d Tn5-marked conjugative plasmids; no such plasmids were discovered in donor strains. Occurrence of such plasmids in Nod(-)-mutants of nodul e bacteria of alfalfa restored virulence in four transconjugants out o f thirteen tested. One of these was able to accomplish nitrogen fixati on in symbiosis with alfalfa and formed inactive nodules in Galega ori entalis. Two transconjugants failed to develop symbiosis with G. orien talis. Of eighteen transconjugants of Agrobacterium, six generated nod ules (active in one case) in Medicago sativa, and two formed inactive nodules in G. orientalis.