1. Microbial genetics

2. Mutations in Bacteria Mutations arise in bacterial populations
Induced
Spontaneous
Rare mutations are expressed
Bacteria are haploid
Rapid growth rate
Selective advantage enriches for mutants
Gene transfer occurs in bacteria

3. General Features of Gene Transfer in Bacteria
Unidirectional
Donor to recipient
Donor does not give an entire chromosome
Merozygotes
Gene transfer can occur between species

4. Transformation
Definition: Gene transfer resulting from the uptake of DNA from a donor.
Factors affecting transformation
DNA size and state
Sensitive to nucleases
Competence of the recipient (Bacillus, Haemophilus, Neisseria, Streptococcus)
Competence factors
Induced competence

5. Transformation Steps Significance Uptake of DNA Recombination
Gram +
Gram -
Recombination
Legitimate, homologous or general
recA, recB and recC genes
Significance
Phase variation in Neiseseria
Recombinant DNA technology

6. Transduction
Definition: Gene transfer from a donor to a recipient by way of a bacteriophage
Bacteriophage (phage): A virus that infects bacteria

7. Phage Composition and Structure
Nucleic acid
Genome size
Modified bases
Protein
Protection
Infection
Head/Capsid
Contractile Sheath
Tail
Structure (T4)
Size (80 X 100 nm)
Head or capsid
Tail
Tail Fibers
Base Plate

8. Infection of Host Cells by Phages
Adsorption
Tail fibers
Receptor is LPS for T4
Irreversible attachment
Base plate
Sheath Contraction
Nucleic acid injection
DNA uptake

9. Microbe Library, American Society for Microbiology

10. Types of Bacteriophage
Lytic or virulent – Phage that multiply within the host cell, lyse the cell and release progeny phage (e.g. T4)
Lysogenic or temperate phage: Phage that can either multiply via the lytic cycle or enter a quiescent state in the bacterial cell. (e.g., )
Expression of most phage genes repressed
Prophage – Phage DNA in the quiescent state
Lysogen – Bacteria harboring a prophage

11. Events Leading to Lysogeny
Circularization of the phage chromosome
Cohesive ends
Cohesive Ends
Linear Double Stranded
Opened Circle
Ligase
Closed Circle

12. Transduction
Definition: Gene transfer from a donor to a recipient by way of a bacteriophage
Resistant to environmental nucleases

13. Transduction Types of transduction
Generalized - Transduction in which potentially any donor bacterial gene can be transferred

14. Generalized Transduction
Infection of Donor
Phage replication and degradation of host DNA
Assembly of phages particles
Release of phage
Infection of recipient
Homologous recombination
Potentially any donor gene can be transferred

15. Transduction Types of transduction
Generalized - Transduction in which potentially any dornor bacterial gene can be transferred.
Specialized - Transduction in which only certain donor genes can be transferred

16. Transduction Definition Types of transduction Significance
Common in Gram+ bacteria
Lysogenic (phage) conversion
e.g. Corynebacterium diptheriae toxin
Toxin derived from lysogenic phage

17. Conjugation
Donor
Definition: Gene transfer from a donor to a recipient by direct physical contact between cells
Mating types in bacteria
Donor
F factor (Fertility factor)
F (sex) pilus
Recipient
Recipient
Lacks an F factor

18. Conjugation Significance Gram - bacteria Gram + bacteria
Antibiotic resistance
Exponential increase under selective pressure
Gram + bacteria
Production of adhesive material by donor cells

19. Transposable Genetic Elements
Definition: Segments of DNA that are able to move from one location to another
Properties
“Random” movement
Not capable of self replication (not a replicon)
Transposition mediated by site-specific recombination
Transposase
Transposition may be accompanied by duplication

20. Conjugation Significance Gram - bacteria Gram + bacteria
Antibiotic resistance
Exponential increase under selective pressure
Gram + bacteria
Production of adhesive material by donor cells

21. Transposable Genetic Elements
Definition: Segments of DNA that are able to move from one location to another
Properties
“Random” movement
Not capable of self replication (not a replicon)
Transposition mediated by site-specific recombination
Transposase
Transposition may be accompanied by duplication

22. Types of Transposable Genetic Elements
Insertion sequences (IS)
Definition: Elements that carry no other genes except those involved in transposition
Nomenclature - IS1
Structure (flanking inverted repeats)
Importance
Insertional Mutation
Plasmid insertion
Phase variation
Transposase
ABCDEFG
GFEDCBA

23. Types of Transposable Genetic Elements
Transposons (Tn)
Definition: Elements that carry other genes in addition to those involved in transposition
Nomenclature - Tn10
Structure
Composite Tns IS
Resistance Gene(s)
Importance
Antibiotic resistance

24. Plasmids
Definition: Extrachromosomal genetic elements that are capable of autonomous replication (replicon)
Episome - a plasmid that can integrate into the chromosome

25. Classification of Plasmids
Transfer properties
Conjugative
Nonconjugative
Phenotypic effects
Fertility
Bacteriocinogenic plasmid
Resistance plasmid (R factors)

26. Structure of R Factors RTF R determinant Conjugative plasmid
Tn 9
Tn 21
Tn 10
Tn 8
RTF
R determinant
RTF
Conjugative plasmid
Transfer genes
R determinant
Resistance genes
Transposons