Bacteria Genomes - AGROBACTERIUM TUMEFACIENS

A. tumefaciens is a Gram-negative , non-sporing, motile, rod-shaped bacterium, closely related to Rhizobium which forms nitrogen-fixing nodules on clover and other leguminous plants. Strains of Agrobacterium are classified in three biovars based on their utilisation of different carbohydrates and other biochemical tests. The unique mode of action of A. tumefaciens has enabled this bacterium to be used as a tool in plant breeding. Any desired genes, such as insecticidal toxin genes or herbicide-resistance genes, can be engineered into the bacterial DNA and thereby inserted into the plant genome. The use of Agrobacterium not only shortens the conventional plant breeding process, but also allows entirely new (non-plant) genes to be engineered into crops.

A. tumefaciens is found commonly on and around root surfaces - the region termed the rhizosphere - where it seems to survive by using nutrients that leak from the root tissues. It infects only through wound sites, either naturally occurring or caused by transplanting of seedlings and nursery stock. It is the causative agent of Crown Gall disease (hairy root disease).

The 5.67-megabase genome of the plant pathogen A. tumefaciens C58 consists of a circular chromosome, a linear chromosome, and two plasmids. Extensive orthology and nucleotide colinearity between the genomes of A. tumefaciens and the plant symbiont Sinorhizobium meliloti suggest a recent evolutionary divergence. Their similarities include metabolic, transport, and regulatory systems that promote survival in the highly competitive rhizosphere; differences are apparent in their genome structure and virulence gene complement. Availability of the A. tumefaciens sequence will facilitate investigations into the molecular basis of pathogenesis and the evolutionary divergence of pathogenic and symbiotic lifestyles.

References:

http://helios.bto.ed.ac.uk/bto/microbes/crown.htm
http://commtechlab.msu.edu/sites/dlc-me/zoo/microbes/agrobacterium.html
Science 294 (5550):2317-23 (2001)