Bacterial conjugation

Conjugation diagram The F-factor is an episome (a plasmid that can integrate itself into the bacterial chromosome by homologous recombination) with a length of about 100 kb.

[citation needed] Among other genetic information, the F-plasmid carries a tra and trb locus, which together are about 33 kb long and consist of about 40 genes.

The F-pili are extremely resistant to mechanical and thermochemical stress, which guarantees successful conjugation in a variety of environments.

[10] Several proteins coded for in the tra or trb locus seem to open a channel between the bacteria and it is thought that the traD enzyme, located at the base of the pilus, initiates membrane fusion.

A recent report claims to have inhibited conjugation with chemicals that mimic an intermediate step of this second nicking event.

[4] The amount of chromosomal DNA that is transferred depends on how long the two conjugating bacteria remain in contact.

In common laboratory strains of E. coli the transfer of the entire bacterial chromosome takes about 100 minutes.

Because such strains transfer chromosomal genes very efficiently they are called Hfr (high frequency of recombination).

The E. coli genome was originally mapped by interrupted mating experiments in which various Hfr cells in the process of conjugation were sheared from recipients after less than 100 minutes (initially using a Waring blender).

[7][8] Furthermore, in contrast to E. coli Hfr conjugation, in M. smegmatis all regions of the chromosome are transferred with comparable efficiencies.

It has been suggested that in these archaea the conjugation machinery has been fully domesticated for promoting DNA repair through homologous recombination rather than spread of mobile genetic elements.

[14] In addition to the VirB2-like conjugative pilus, the Ced and Ted systems include components for the VirB6-like transmembrane mating pore and the VirB4-like ATPase.

[citation needed] Conjugation is a convenient means for transferring genetic material to a variety of targets.

In plant engineering, Agrobacterium-like conjugation complements other standard vehicles such as tobacco mosaic virus (TMV).

Escherichia coli conjugating using F-pili. These long and robust extracellular appendages serve as physical conduits to translocate DNA. [ 3 ]
Schematic drawing of bacterial conjugation.
1.The insertion sequences (yellow) on both the F factor plasmid and the chromosome have similar sequences, allowing the F factor to insert itself into the genome of the cell. This is called homologous recombination and creates an Hfr (high frequency of recombination) cell. 2.The Hfr cell forms a pilus and attaches to a recipient F- cell. 3.A nick in one strand of the Hfr cell's chromosome is created. 4.DNA begins to be transferred from the Hfr cell to the recipient cell while the second strand of its chromosome is being replicated. 5.The pilus detaches from the recipient cell and retracts. The Hfr cell ideally wants to transfer its entire genome to the recipient cell. However, due to its large size and inability to keep in contact with the recipient cell, it is not able to do so. 6.a. The F- cell remains F- because the entire F factor sequence was not received. Since no homologous recombination occurred, the DNA that was transferred is degraded by enzymes. [ 12 ] b. In very rare cases, the F factor will be completely transferred and the F- cell will become an Hfr cell. [ 4 ]
Agrobacterium tumefaciens gall at the root of Carya illinoensis .