Years ago, the bacteria Agrobacterium tumefaciens was thought to exist anywhere in soil. Later discoveries found that it was associated with plant roots. It is Gram-negative, rod-shaped, aerobic and can easily infect virtually any dicot plant. It was originally thought to have peritrichous flagella, but later understood to have 5-11 circumtrichetal flagella. Optimum growth occurs at 32 C with a trace of manganese and succinate serving as the carbon source.
A. tumefaciens infects the roots of plants at the site of mechanical injury. The injury signals the production of lignin precursors, which in turn induce the vir genes of A. tumefaciens. These genes carry out the transformation process whereby the A. tumefaciens genes are incorporated into the plant’s genome. This transformation causes crown gall disease, which leads to tumor overgrowths on the surface of plant roots. The infection does not result in plant death, merely altered cell function.
A. tumefaciens carries the vir gene on its Ti plasmid. Each gene controls a different aspect of the infection. VirB encodes transmembrane mediators, virE controls single-strand DNA binding, virF affects infection efficiency, and virG contains the transcriptional regulator. Other genes control other aspects of infection, but have not been completely characterized yet. As a result of its ability to manipulate genetic material, A. tumefaciens has been useful in the introduction of exogenous genes into host plant cells.
By far the most interesting aspect of A. tumefaciens is the ability to transfer its genes into the plant’s genome. The infected cells then produce opines, which serve as sources of nitrogen and carbon. A. tumefaciens also contains genes for the catabolism of opines, but these are not transferred to the plant. This allows only the bacteria to digest opines, with a steady non-digested stream manufactured by the plant.
References
The Prokaryotes: a handbook on the biology of bacteria: ecophysiology, isolation, identification, applications / edited by Albert Balows … [et al]. New York: Springer-Verlag, c1992.Anath Das, http://biosci.cbs.umn.edu/BMBB/faculty/Das.A.html.
Transforming Plants Basic Genetic Engineering Techniques, http://www.gene.com/ae/AB/IWT/Transforming Plants.html.
Plant Genetic Engineering: Methodology, http://photoscience.la.asu.edu/photosyn/courses/BIO_343/lecture/geneng.html.
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.
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