1. Chapter 9 Genetics of Bacteria and Their Viruses: Transduction and phage genetics
Jones and Bartlett Publishers © 2005

2. Transduction
Lytic cycle – the phage attaches to a bacterium then injects its nucleic acid. More copies of the phage are made by the infected bacterium, then the cell lyses to release the new phage particles.
Phage that only have a lytic cycle are called virulent.

3. Phage research has helped scientists understand prokaryotic genetics.
Phage are 1/100 to 1/500th the size of a bacterium.
They can be lytic or lysogenic.
Lytic = virulent.
Lysogenic = prophage.
Temperate phage = do both.

4. Life cycle of a bacteriophage

5. Phage structure

6. Life cycle of bacteriophage T4

7. Assembly of bacteriophage T4

8. Life cycle of the
Lambda phage

9. Generalized transduction of bacterial genes mediated by bacteriophage P1
When a bacteriophage can transfer any bacterial gene, the process is called generalized transduction

10. Transduction can be used for mapping genes at a higher resolution than is possible by conjugation mapping

11. Bacteriophage genetics
Phage progeny generally are identical to their parent (except for mutations).
If two or more phage particles infect a single bacterial cell simultaneously, new phage genotypes can arise.
This is different from eukaryotic recombination in two ways:
The number of participating DNA molecules differs from cell to cell.
Reciprocal recombinants are not always recovered in equal frequencies.

12. Infection of a bacterial lawn by a lytic bacteriophage creates a clear spot (plaque) due to the lysis of bacteria

13. Results of a number of phage crosses can be combined to generate the complete genetic map of a bacteriophage chromosome

14. The genetic map of bacteriophage T4
Bacteriophage T4 chromosome is approximately 167,000 base pairs in size. The chromosome is linear but the genetic map is circular

15. Bacteriophage T4 chromosome is circularly permuted and terminally redundant

16. Mapping of bacteriophage T4 deletion mutants in rapid lysis genes (rII mutants) using overlapping deletions

17. The logic of mapping of rII deletion mutants by crossing to a set of ordered overlapping deletion mutants

18. A high resolution genetic map of the rIIA and rIIB genes showing 2 hot spots of mutation
Each small square in this map represents an independently isolated mutation. A very large number of mutations occur at 2 sites, one in rIIA gene and one in rIIB gene.

19. A genetic map of the bacteriophage  showing the genes and the transcripts

20. Insertion of bacteriophage l into the bacterial chromosome and silencing of the lytic genes creates a lysogenic cell

21. Upon infection, the sticky ends of the bacteriophage l DNA join to make a circular molecule

22. Cleavage sites and reciprocal recombination

23. Overview of l integration into the bacterial chromosome

24. Site-specific recombination is involved in the insertion of bacteriophage l DNA to create a lysogen

25. Maps of the lytic virus and the prophage are circular permutations of each other

26. Abnormal excision of the l prophage transfers bacterial genes to the excised phage and leaves behind phage genes
The “d” in the name of the excised phages (ldgal or ldbio) stands for defective. Phage genes were lost during the pick up of the host genes.