The phage infects the cell by “injecting” its genome, which directs the synthesis of new phage.
The phage are released by lysis of the hostges, （烈性噬菌体） including T2
– When these phage with bacterial genes is packaged in their infect cells, the bacterial DNA can have two fates. (1) Most of the time, there is abortive transduction (流产转导). ----The DNA is neither replicated nor integrated into the genome. Why ?
(2) A small proportion of the time (less than 5-10% of the time) the bacterial DNA is integrated into the genome of this host. Complete transduction occurs, involving a double cross-over. Transduction can be used to map closely linked genes.
Generalized transduction – Transfer of random portions of host genomic DNA by bacteriophages during the lytic cycle of virulent or temperate phages.
Any part of the bacterial genome can be transferred.
are made, and the
bacterial chromosome is
broken down into pieces.
Donor bacterial
DNA
Recipient bacterial
DNA
3 Occasionally during phage assembly,
pieces of bacterial DNA are packaged in a phage capsid. Then the donor cell lyses and releases phage particles containing bacterial DNA.
Recipient cell
4 A phage carrying bacterial
DNA infects a new host cell, the recipient cell.
Recombinant cell
5 Recombinant can occur,
producing a recombinant cell with a genotype different from both the donor and recipient cells.
Transduction
Sometimes, segments of the host genome are transferred by phage. This process is generalized transduction transduction(普 遍性转导)
Does the transduction form a partial diploid ？
Transduction
• Transduction is the transfer of bacterial genes in phage particles.
– When phages lyse cells, the bacterial genome is usually degraded. Sometimes, fragments of the bacterial genome similar in size to the phage genome will be packaged into phage particles.
Phage Represent the Third Mechanism
Bacteria can also exchange genes by the process of transduction( 转导), which involves the exchange of genes through phage(噬菌体).
Generalized transduction
Recombinant
Phage protein coat
Bacterial chromosome
Bacterial DNA
Phage DNA
1 A phage infects the
donor bacterial
cell.
2 Phage DNA and proteins
The phage genome directs the synthesis of new phage. These phage are released, lysing （裂 解）the host.
The Lytic Cycle (溶菌周期)
The lytic cycle is a general phage life cycle.
Phage (also called
bacteriophage)
are
viruses that infect bacteria.
Bacteriophage
This shows the DNA phage T4.
A small set of genes are encoded by DNA that is “injected” into the host.