Isolation and Characterization of Agrobacterium tumefaciens Mutants Affected in the Utilization of Octopine, Octopinic Acid and Lysopine

Abstract

Using an enrichment procedure, mutant strains of A. tumefaciens were isolated that lacked the ability to utilize octopine as a N source. Of 55 such isolates, 44 were unable to utilize several amino acids; the remaining 11 strains were altered solely in their ability to utilize octopine, octopinic acid and lysopine. Only the latter were plasmid mutations. Among them, there was a high, but no absolute, correlation with avirulence. All strains contained the TI plasmid. All virulent strains showed active transport of octopine when they had previously been grown in medium containing octopine; the avirulent strains failed to show such transport. All the virulent mutants induced tumors [in Kalanchoe daigremontiana] containing octopine. The results are discussed in relation to the hypothesis that the genes which code for the octopine synthesizing enzymes in the tumor are of bacterial origin.