EXPRESSION OF THE SYMBIOTIC PLASMID FROM RHIZOBIUM-LEGUMINOSARUM BIOVAR TRIFOLII IN SPHINGOBACTERIUM-MULTIVORUM

An inoculant strain of Rhizobium leguminosarum biovar trifolii contain ing a Tn5 marked symbiotic plasmid transferred this plasmid by conjuga tion to Sphingobacterium multivorum, an organism that can be found in soil. The transconjugant bacteria nodulated the roots of white clover (Trifolium repens) seedlings but did not fix atmospheric nitrogen. Mic roscopic examination revealed abnormal nodule structures. Bacteria iso lated from the nodules were shown to be closely related to the recipie nt S. multivorum and Southern blots of genomic digests probed with nod A DNA confirmed that the transconjugants contained symbiotic genes. Th is is the first report of the spontaneous transfer, by conjugation, of a symbiotic plasmid from R. leguminosarum biovar trifolii to S. multi vorum.