Quantitative aspects of transformation of virulence in Agrobacterium tumefaciens.

In the last decade, a number of bacterial species were shown to possess the ability to transmit morphological and biochemical characters to deficient strains. Tumor-inducing ability or virulence in crown-gall bacteria is such a biochemical character, and the acquisition of virulence is here taken to be the acquisition by avirulent strains of bacteria of the ability to synthesize a tumor-inducing principle active in a given host (Klein and Tink, 1955). In an earlier paper, (Klein and Klein, 1953) we reported that a bactrin, a culture filtrate, and the deoxyribonucleic acid (DNA) of virulent crown-gall bacteria were each capable of transmitting the property of host-specific virulence to avirulent strains of Agrobacterium tumefaciens. The property of virulence, once acquired, was permanent and it was concluded that crown-gall bacteria are capable of undergoing transformation reactions. Since our first paper appeared, a quantitative bioassay for crown-gall tumor formation was developed. This new test system has been used to reinvestigate and to extend various aspects of the transformation of virulence in crown-gall bacteria.