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Abortive Transduction

	Abortive Transduction - As discussed before, fusion between Enterobacteria is common but the formation of stable heterokaryons or diploids is not known. This is perhaps due to the difficulty in transferring the entire genome from one cell to another. After conjugation partial zygotes (merozygotes) are formed but these are transient and therefore, are not very suitable for complementation tests. One of the systems available in bacteria to test complementation is "abortive transduction". In this parasexual mechanism, modified temperate bacteriophages act as vectors of small fragments of bacterial DNA, transporting the DNA from a donor cell in which the phage is grown to a recipient strain which the phage can infect.
However, the transduced bacterial segment fails to undergo recombination and replication but remains functional and is transferred during cell division to only one daughter cell. In Salmonella, motility is one of the many characters that can be transduced by the phage P22. When P22 IS grown on a motile donor strain, transducing phages which can infect nonmotile recipient bacteria can be obtained.
Motile transductants can be isolated by plating the infected nonmotile recipients on soft gelatin agar in which the growth of nonmotile organism is confined and compact, while motile cells migrate outwards as they multiply to give an expanding 'flare' of growth. Stocker, Zinder and Lederberg noticed that in addition to flares, sometimes a number of linear trails of isolated colonies leading out from the outer region of confined growth. These trails were explained on the basis that the motility gene transferred through transduction does not participate in recombination, but is functional and capable of conferring motility. When such cells divide only one daughter cell in which the gene is present is able to move away from the parent forming tiny compact colonies.
This process of unilinear inheritance of the transferred gene continues leaving a trail of nonmotile celled colonies until the gene is lost for reasons not well known. Using single cell studies, this mechanism was confirmed as abortive transduction. Later in 1956, Ozeki also observed the same type of phenomenon in' transduction of nutritional characters in Salmonella diagrammatically summarises linear inheritance as it occurs in abortive transduction.

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