Transduction

Phages play an important role in the transfer of bacterial genes from one bacterium to another. As briefly discussed in chapter 8, DNA can be transferred from one bacterial cell, the donor, to another, the recipient, by phage in the process called trans-duction. There are two types of transduction. In one type, any bacterial gene can be transferred, a process called generalized transduction. The phages that carry out this process are termed generalized transducing phages. The second type is termed specialized transduction since only a few specific genes can be transferred by the phages, which are specialized transducing phages. ■ transduction, p. 205

Generalized Transduction

Virulent as well as temperate phages can serve as generalized transducing phages. Recall that some phages in their replication life cycle degrade the bacterial chromosome into many fragments at the beginning of a productive infection. These short DNA fragments can be incorporated inadvertently into the phage head in place of phage DNA in the process of phage maturation. Following lysis and release of the phage carrying the bacterial DNA, the phage binds to another bacterial cell and injects the bacterial DNA. Once inside the new host, the DNA from the donor cell can integrate into the recipient cell DNA by homologous recombination. These recipient cells do not lyse but are transduced. Since the genetic information transferred can be any gene of the donor cell, this gene transfer mechanism is called generalized transduction. ■ generalized transduction, p. 206

Why do the transducing virulent phage not lyse the cells they invade? Because the bacterial DNA replaces the phage DNA inside the phage's head, the genetic information necessary for the synthesis of phage-induced proteins is lacking. The phage is termed defective because it lacks the DNA necessary to form complete phage and lyse the recipient cell.

Specialized Transduction

Specialized transduction involves the transfer of only a few specific genes and is carried out only by temperate phages. The most actively studied specialized transducing phage is A, which integrates only at specific sites in the chromosome of E. coli. Lambda transduces specific genes by the following means (figure 13.11).

Table 13.4 Phage

Features of Interactions of Phage with Host Cells

Type of Interaction Type of Nucleic Acid*

Result of Interaction

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