How Plasmid/Virus Integrate Into The Bacterial Genome + Recombination

Generalised Transduction

Snustad. Simmons. Jenkins: principles of genetics (575.1 SNU)
The above book covers bacteria and virus pretty well although it may be a bit extensive. For those who wants to know more, you can seek out this book in the library =)

To answer a question that was posed this morning Wed 12/9 (notes is not wrong but probably unclear).

Transduction:

1) Generalised - the phage can transfer any segment of the bacterium genome to another bacterium.
2) Specialised – only restricted segments of the bacterial genome is transferred (those close to the integration site)


Generalised Transduction

From the above diagram and notes:
a defective phage is one that contains bacterial DNA and no phage DNA.

At the end of the lytic cycle, viral DNA is being packed into the phage and so are some of the bacterial chromosome fragments. This packing error will give rise to some phages with viral DNA and others with only bacterial DNA. Size of the bacterial fragments will vary.
Since this defective phage does not contain viral DNA, (after adsorption and injection of the bacterial fragments into a new bacteria cell) no new bacteriophage is synthesized in the recipient bacterial cell.

Specialised Transduction

There is the lysogenic state and en face with an induction event, the excision of prophage is erroneous, removing a phage genome with some of its genetic material replaced by (particular) bacterial genetic material. The recombinant viral DNA that is produced this way is usually defective because some of its own genetic material is left behind.

This new circularized recombinant genome can still undergo replication because its origin of replication is intact and the DNA polymerase is non-discriminating  so you can get many of such DNA.

However, when the recombinant DNA is packaged within a capsid and the transducing particle injected it into a new bacterial cell, since part of the viral genome has been deleted, no progency virus can be formed in this bacterium because the necessary (viral) enzymes are not present*.
Recombination can take place as in diagram or there is integration of the DNA due to a common gene.


*this may be dependent on the site where the viral genome is cut, whether genes are removed. But usually they are and thus rendering the virus defective.





Specialised transduction


Examples of recombination close-up



Integration requires one-point




Recombination requires two-points





Diagram showing integration of F plasmid into bacterial chromosome.
Correct and Incorrect excision of F plasmid.