HOMOLOGY BETWEEN THE GENES OF OCTOPINE CATABOLISM OF RHIZOBIUM-MELILOTI A3 AND CORRESPONDING GENES FROM THE TI PLASMID

The ability to catabolize crown-gall opines is found in Agrobacterium tumefaciens and various types of nonagrobacteria. Among the 75 Rhizobium meliloti strains tested in this work, 6 utilized the opines octopine and octopinic acid as the sore carbon and nitrogen source. From a genomic library of one of these six strains, R. meliloti A3, a clone conferring the octopine catabolism (Occ) phenotype was identified and named pJMA. A different Occ clone, which had been obtained from R. meliloti Rm41, did not hybridize with clone pJMA from strain A3. However, some fragments of drone pJMA hybridized to a 20-kilobase KpnI fragment containing the Ti plasmid genes of octopine catabolism (occ genes) from A. tumefaciens 15955. Shorter probes carrying the octopine permease genes or part of the octopine oxidase and ornithine cyclodeaminase genes from A. tumefaciens also hybridized with pJMA. The R. meliloti DNA carried by pJMA was localized to a megaplasmid of the wild-type strain A3. Thus, it appears possible that genes represented on the Occ clone from strain A3 share a common origin with the corresponding genes from the Ti plasmid.