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Historical Significance

Agrobacterium tumefaciens was originally named Bacterium tumefaciens by Cavara in 1897. In 1907, the name was changed to Phytomonas tumefaciens (Smith & Townsend) Bergey et al.) by E. F. Smith, which was subsequently changed to A. tumefaciens, the taxon name of current use. This organism was first isolated from grapevines in 1897 by Fridiano Cavara at the Laboratorio di Botanica del Recherci Instituto Forestale di Vallom Drosa in Naples, Italy. In 1907, E. F. Smith and C. O. Townsend in the United States isolated the bacterium from chrysanthemum galls.

As interest grew in determining how A. tumefaciens caused crown gall, a large number of A. tumefaciens strains were isolated and characterized. By the late 1940s, it became apparent that a novel tumor-inducing factor or principle was responsible for initiating the crown gall tumor disease. Although various factors including the secretion of phytohormones, the transmission of bacteriophage, and DNA were implicated, the presence of an extrachromosomal element in all virulent strains of A. tumefaciens was discovered. This important discovery led to extensive studies on the extrachromosomal element termed the Ti plasmid (Ti for tumor-inducing). That a specific portion of the Ti plasmid was transferred and incorporated into the genome of the host plant opened the way to incorporate novel genes into plants. Agrobacterium tumefaciens is considered the organism that launched plant genetic engineering.