Agrobacterium
| Agrobacterium | |
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| Scientific classification | |
| Kingdom: | Bacteria |
| Phylum: | Proteobacteria |
| Class: | Alpha Proteobacteria |
| Order: | Rhizobiales |
| Family: | Rhizobiaceae |
| Genus: | Agrobacterium |
| Type species | |
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Agrobacterium tumefaciens (Smith and Townsend 1907) Conn 1942 |
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| Species | |
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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.
The Agrobacterium genus is quite heterogeneous. Recent taxonomic studies have reclassified all of the Agrobacterium species into new genera, such as Ahrensia, Pseudorhodobacter, Ruegeria, and Stappia, but most species have been controversially reclassified as Rhizobium species.
A. tumefaciens causes crown-gall disease in plants. The disease is characterised by a tumour-like growth or gall on the infected plant, often at the junction between the root and the shoot. Tumors are incited by the conjugative transfer of a DNA segment (T-DNA) from the bacterial tumour-inducing (Ti) plasmid. The closely related species, A. rhizogenes, induces root tumors, and carries the distinct Ri (root-inducing) plasmid. Although the taxonomy of Agrobacterium is currently under revision it can be generalised that 3 biovars exist within the genus, A. tumefaciens, A. rhizogenes, and A. vitis. Strains within A. tumefaciens and A. rhizogenes are known to be able to harbour either a Ti or Ri-plasmid, whilst strains of A. vitis, generally restricted to grapevines, can harbour a Ti-plasmid. Non-Agrobacterium strains have been isolated from environmental samples which harbour a Ri-plasmid whilst laboratory studies have shown that non-Agrobacterium strains can also harbour a Ti-plasmid. Some environmental strains of Agrobacterium possess neither a Ti nor Ri-plasmid. These strains are avirulent.
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