SUMMARY: Using an enrichment procedure, mutant strains of were isolated that lacked the ability to utilize octopine as a nitrogen 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. It is concluded that 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, whereas the avirulent strains failed to show such transport. All the virulent mutants induced tumours containing octopine. The results are discussed in relation to the hypothesis that the genes which code for the octopine synthesizing enzymes in the tumour are of bacterial origin.


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