Transduction (genetics)

As transduction of gene transfer between bacteria is called by viruses in genetics. It usually viral, but sometimes bacterial genes are transferred without bacteria are in contact with each other. Infection of target cells with viral vectors is also referred to as transduction, whereby foreign immunity genes using viruses are transmitted.

Transduction in addition to transformation and conjugation one of three ways of the natural gene transfer in prokaryotes.

Non-specific ( general ) transduction

As non-specific or general transduction refers to the transfer of bacterial DNA by a virulent bacteriophage. In phage propagation in the bacterial cell ( lytic cycle ), it may accidentally happen that in a phage rather than the phage DNA a piece of bacterial DNA is incorporated, previously controlled by the phage DNA was cut into fragments. This phage infects another cell, the bacterial DNA is incorporated into the bacterial genome (recombinant ).

Specific (special ) transduction

Tempe pension Phages are viruses whose DNA does not occur after injection into the host cell in the lytic, but occasionally in the lysogenic cycle and a rest phase load (example: bacteriophage lambda). The phage DNA is usually first at a certain point (in the case of Escherichia coli, this is the region att ) integrated into the main chromosome of the host, is an exception with episomal genome, for example, the phage P1. These integrated or annular present phage DNA is referred to as a prophage. The vitality of the host cell is not affected. She multiplies and hence the prophage. The integration of a phage may prove advantageous for the bacterium even as the wearing of the prophage often protects against superinfection of other bacteriophages of the same kind. Deteriorate the environment and threatens the death of the host cell, for example, by UV radiation or chemicals, the phage in the lytic cycle occurs because a dead host is no longer a virus for propagation available. When imprecise excision (excision ) of the prophage from the genome of the host, the phage DNA can take a piece of bacterial DNA randomly and install it in another bacterium. In genetic engineering, one makes use of this property being used to transmit certain regions of DNA from one bacterium to another. While taking the bacteriophage in the excision of DNA segments of the host cell is not targeted, but only with statistical probability. Located on the DNA segment that you wish to transfer from one bacterium to another by transduction, a selectable marker, such as an antibiotic resistance gene, survive in the selection of only the bacteria that get the desired DNA segment and incorporated by homologous recombination.

Experiments of Lederberg, Tatum and Zinder

Norton Zinder and Joshua Lederberg was in 1952 in an experiment with the agent of mouse typhoid, Salmonella typhimurium, the nonspecific transduction prove (1947 had Edward Lawrie Tatum and Lederberg already shown the specific transduction of Escherichia coli): The two legs of a U-tube, the were separated by a filter that is only permeable for particles that are smaller than the bacterial cells were fed with two strains of S. typhimurium.

Strain 1 was a mutant deficient only for the amino acid histidine, strain 2 only for the amino acid tryptophan.

After a few hours of incubation, 1 and 2 bacteria could be detected in addition to representatives of the two tribes that were able to produce both histidine and tryptophan itself. In addition, free bacteriophages ( P22 ) could be in the suspension, which were not present at start of the experiment, were observed.

Since the bacteria could not directly contact each other, conjugation was excluded. Was also excluded a transformation, since no free DNA was found in the two legs of the U- tube. In conclusion, it was found that the bacteriophage had transferred parts of the genome of bacteria of a strain on cells of the other strain.