Agrobacterium

Agrobacterium is a genus of Gram-negative bacteria established by H. J. Conn that uses horizontal gene transfer to cause tumors in plants. Agrobacterium tumefaciens is the most commonly studied species in this genus. Agrobacterium is well known for its ability to transfer DNA between itself and plants, and for this reason it has become an important tool for genetic engineering.

==Nomenclatural history== Leading up to the 1990s, the genus Agrobacterium was used as a wastebasket taxon. With the advent of 16S sequencing, many Agrobacterium species (especially the marine species) were reassigned to genera such as Ahrensia, Pseudorhodobacter, Ruegeria, and Stappia. The remaining Agrobacterium species were assigned to three biovars: biovar 1 (Agrobacterium tumefaciens), biovar 2 (Agrobacterium rhizogenes), and biovar 3 (Agrobacterium vitis). In the early 2000s, Agrobacterium was synonymized with the genus Rhizobium. This move proved to be controversial. The debate was finally resolved when the genus Agrobacterium was reinstated after it was demonstrated that it was phylogenetically distinct from Rhizobium and that Agrobacterium species were unified by a unique synapomorphy: the presence of the protelomerase gene, telA, which causes all members of the genus to have a linear chromid. By this time, however, the three Agrobacterium biovars had become defunct; biovar 1 remained with Agrobacterium, biovar 2 was renamed Rhizobium rhizogenes, and biovar 3 was renamed Allorhizobium vitis.