Microbiology 3302 Lecture

helllo! my name is Agrobacterium tumefaciens. People knows as Gram negative soil bacterium. they recognize me for my form. I am kind of rod shaped alphaproteobacterium of the family Rhizobiaceae, which includes the nitrogen fixing legumes symbionts. I can cause trouble to plants and also crown call disease( the formation of tumor). Scientists names me Rhizobium radiobacter. I can tell you plants affected by me  are a big concern for agricultural industries.  this table is like my ID. take a look at it!

Scientific classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Alphaproteobacteria
Order: Rhizobiales
Family: Rhizobiaceae
Genus: Agrobacterium
Species: A. tumefaciens

A. rhizogenes, & A. vitris and I  are the only known bacterial pathogens that invade plans by transferring their DNA to the plant, hence they have evolved as a major tool for plant genetic engineering. There are many different biological processes involved in this inter-kingdom DNA transfer, such as intercellular signalling, cell-to-cell DNA transport and DNA integration into the host cell nucleus (Tzfira & Citovsky, 2000).  I require anaerobic respiration.

Nowadays i dont only destroy but i am useful in transgenic plant production that need to find an effective vector system to successfully integrate the gene of interest into the correct area of the plant genome. it happens because genetic modification of the plant occurs as a result of the integration to the plant genome of a specific fragment of DNA, termed the T-DNA, or Transfer DNA, which originates from the bacterial Ti (tumor inducing) plasmid. Expression of these genes leads to the formation of Opines; specific oligosaccharides used purely by A. tumefaciensas a source of carbon.

The entire process is regulated and controlled by a set of genes known as Vir genes, which are activated by the detection of wounded plant phenolic compounds. The transfer process can be divided into 2 steps; the bacterial cellstep and the plant cell step (Tinland, 1996).

Vir Genes and their Function

Vir Gene Function
Vir A, Vir G Sense phenolic compounds from wounded plant cells and induce expression
of other virulence genes
VirD2 Endonuclease; cuts T-DNA at right border to initiate T-strand synthesis
Vir D1 Topiosomerase; Helps Vir D2 to recognise and cleave within the 25bp
border sequence
Vir D2 Covalently attaches to the 5I end of the T-strand, thus forming the
T-DNA Complex. Also guides the T-DNA complex through the nuclear pores
Vir C Binds to the ‘overdrive’ region to promote high efficiency T-strand
Synthesis
Vir E2 Binds to T-strand protecting it from nuclease attack, and intercalates
with lipids to form channels in the plant membranes through which the
T-complex passes
Vir E1 Acts as a chaperone which stabilises Vir E2 in the Agrobacterium
Vir B & Vir D4 Assemble into a secretion system which spans the inner and outer bacterial
membranes. Required for Export of the T-complex and Vir E2 into the
plant cell

Economically, A. tumefaciens is a serious pathogen of walnuts, grape vines, stone fruits, nut trees, sugar beets, horse radish and rhubarb.

REFERENCES:

http://en.wikipedia.org/wiki/Agrobacterium_tumefaciens

http://arabidopsis.info/students/agrobacterium/introduction.html

http://archive.bio.ed.ac.uk/jdeacon/microbes/crown.htm

Microbiology 10th edition Turtura

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