1. The Genetics of Bacteria and Their Viruses8
The Genetics of Bacteria and Their Viruses

2. Plasmids
Plasmids are circular DNA molecules which replicate independently of the bacterial chromosome
Plasmids often carry antibiotic resistance genes transferred to recipient cells by transformation
Plasmids are used in genetic engineering as gene transfer vectors

3. Conjugation
Conjugation = process in which DNA is transferred from bacterial donor cell (F+) to a recipient cell (F-) by cell-to-cell contact
F (fertility) factor = plasmid transferred by conjugation
F factor = episome = genetic element that can insert into chromosome or replicate as circular plasmid

5. Transposable Elements
Transposable elements = DNA sequences present in multiple copies which are capable of movement within the genome
Insertion (IS) elements = mobile elements contain transposase = enzyme catalyzes IS element transfer
Transposons = IS elements which contain bacterial genes

6. Transposable Elements
Transposons can insert into plasmids which can be transferred to recipient cells by conjugation
Transposable elements are flanked by inverted repeats and often contain multiple antibiotic resistance genes= R plasmids

8. Bacterial Genetics Types of bacterial mutants:
Antibiotic-resistant mutants
Nutritional mutants: wildtype=prototroph
mutant=auxotroph which cannot grow in minimal media providing basic nutrients only
carbon-source mutants=cannot use some carbon sources

9. Bacterial Transformation
Recipient cells acquire genes from DNA outside the cell
DNA is taken up by cell and often recombines with genes on bacterial chromosome
Bacterial transformation showed that DNA is the genetic material
Transformation may alter phenotype of recipient cells

10. Cotransformation of Linked Genes
Donor DNA which contains genes located close together are often transferred as a unit to recipient cell = cotransformation
The greater the distance between genes the less likely they will be transferred as a unit to recipient cell
Cotransformation is used to map gene order

12. Hfr Hfr (high frequency recombination) exchange
between donor cells F+ and
few cells where F factor
integrated into bacterial
chromosomes
Recombination inserts Hfr genes into chromosome

14. Chromosome Mapping
Time-of-Entry mapping = method of mapping genes by Hfr X F- matings using interrupted mating technique
A plot of time (minutes) versus # of recombinants is used to map genes as transfer order map
Circular genetic map of E. coli shows map distances of genes in minutes

16. Transduction
Transduction = bacterial DNA fragment is transferred from one bacterial cell to another by a virus (phage) containing bacterial DNA = transducing phage
Generalized transducing phage = transfers DNA derived from any part of the bacterial chromosome

18. Transduction
Phage P1 cuts bacterial chromosome into pieces and can package bacterial DNA into phage particles
Transducing particle will insert ‘transduced” bacterial genes into recipient cell by infection
Transduced genes may be inserted into recipient chromosome by homologous recombination

19. Transduction
Specialized transducing phage = particles contain phage and bacterial genes from a specific point of bacterial chromosome
Cotransduction can be used to demonstrate linkage between bacterial genes
Frequency of cotransduction is a measurement of linkage

21. Transduction
Specialized transducing phages transduce bacterial genes at the site of prophage insertion into the bacterial chromosome
Transduction of bacterial genes occurs by aberrant excision of viral DNA which results in the incorporation of bacterial genes into phage chromosome

22. Temperate Bacteriophages
Temperate bacteriophages have two life cycles: lytic cycle=infection which results in production of progeny phage and bacterial cell lysis and lysogeny = non-productive viral infection results in insertion of viral DNA into bacterial chromosome
Viral DNA integration= site-specific insertion into bacterial chromosome

23. Lysogenic Bacteriohages
In the lysogenic cycle, the viral DNA integrated into the bacterial chromosome is called a prophage
Lysogen=bacterial cell containing integrated prophage
Integration is catalyzed by a viral enzyme= integrase which carries out site- specific recombination between the virus and bacterial cell

25. Lysogenic Bacteria
Prophage induction= excision of prophage from bacterial chromosome and entry to lytic cycle
Prophage induction results from damage to the bacterial chromosome by chemicals or radiation
Excisionase=viral enzyme which removes prophage by site-specific recombination