Agrobacterium tumefaciens is a bacterium which is responsible for producing crown gall disease, a type of tumorous growth which can occur in many plants. This bacterium can be especially damaging for populations of grape vines, stone fruits, roses, beets, radishes, and nuts. Plants infected with the bacterium will produce distinctive galls, tumors which can grow quite large and which may be located at various regions on the plant. The gall can act to strangle the plant, depriving it of water and nutrients and causing it to become sickly.
This organism is gram negative and rod shaped, and it inhabits the soil in many regions of the world. It often congregates around the roots of plants, trees, and shrubs to take advantage of nutrients which may leak from the root system to sustain itself. As long as a plant remains healthy, Agrobacterium tumefaciens should not be a problem, as the surface layers of the roots will keep the bacteria out.
When a plant is injured, however, it allows the bacteria to enter, setting up an opportunity for the bacteria to colonize and cause crown gall disease. The bacteria themselves are actually not responsible; rather, the tumor is caused by a plasmid produced by the bacteria. This plasmid is known as a tumor inducing (Ti) plasmid, referencing the fact that it carries DNA which will cause tumors to develop. When bacteria are stripped of the Ti plasmid, they are still functional.
For plants infected with Agrobacterium tumefaciens, there may not be much to be done. The plants can be pruned to remove the growth, and measures such as soil sterilization can also help. In some cases, it may be necessary to fully remove plants and their roots and to sterilize the soil to start from scratch. Since it can take several years to bring production up to previous levels, this measure is often avoided, if possible, to cut down on losses caused by infection.
Given that Agrobacterium tumefaciens works by introducing DNA into plants, it should come as no surprise to learn that this bacterium is used in genetic engineering. Researchers who want to introduce new DNA to a population of plants can engineer the plasmid, changing its contents so that it will deliver a payload of desirable DNA which it enters a vulnerable plant. Agrobacterium tumefaciens is used in labs all over the world which do work with transgenic crops, including labs which develop crops for commercial use, such as transgenic corn species.