1. Chapter4 Heredity and variation of bacteria
Xin Gang
Department of microbiology and immunology Shantou University Medical College

2. Genetic materials of bacteria Mechanism of variation
outline
Concepts
Genetic materials of bacteria
Mechanism of variation

3. concepts
Heredity
Variation
Genotypic variation
Phenotypic variation

4. Variation of bacteria Variation in morphology and structure
lose capsule (Pneumococcus)
H O
Lose Spore
L-form

5. Variation Variation in virulence Bovine TB BCG C. diphtheriae
13years, 230 generation
C. diphtheriae
b-corynephage, diphtheriae toxin

6. Variation Variation in drug resistance Variation in colony
Penicillin resistant strains of staphylococcus aureus
Variation in colony
S-R
Variation in enzyme activity
Phenotypic
Genotypic

7. I Genetic materials of bacteria
Chromosomes
Plasmids
Phage
Transposable elements

8. 1 Chromosomes
DNA forms: ds-DNA, circle

9. Rolling-circle pattern of replication
Size
E.coli 1300mm, 4288gene
Rolling-circle pattern of replication

10. 2 Plasmids
Extrachromosomal genetic elements that are capable of autonomous replication.
Small double-stranded DNA molecules, usually circular
exist independently of host chromosome
autonomously replicating (replicon)
may disappear spontaneously or by induction (UV)
incompatibility and compatibility

11. Classification of Plasmids
Transfer properties
Conjugative
40-100kbp
eg. F, R plasmid
Nonconjugative
<15kbp, transfer by mobilization
eg. ColE1 plasmid

12. Phenotypic effects Fertility plasmid,F plasmid coding sex pilus
Resistance plasmid, R plasmid
resistance transfer factor
resistance determinant
Tn 9
Tn 21
Tn 10
Tn 8
RTF
Virulence plasmid
Coliciogenic plismid
R determinant

13. 3 Bacteriophage, phage
T4 bacteriophages infecting E.coli.

14. Bacteriophage (Phage)
Definition
Bacterial virus.
Virus of bacteria, fungi, actinomyces, and spirochete.

15. Composition and Structure
Nucleic acid
DNA or RNA
Protein
Protection
Infection

16. Structure (T4) Head or capsid Tail Head/Capsid Contractile Sheath Tail
Tail Fibers
Base Plate

17. Infection of Host Cells
Attachment
Sheath contraction
Nucleic acid injection

18. Attachment and injection

19. Types of Bacteriophage
Lytic or virulent phage
(e.g., T4)
Lysogenic or temperate phage
(e.g., l)

20. Virulent Phage Lytic or virulent phage
Phage that can only multiply within bacteria and kill the cell by lysis. (e.g., T4)

21. Lytic Phage Multiplication Cycle

22. Lytic cycle Attachment Injection and uncoating Biosynthesis
Eclipse
Early proteins
Phage DNA synthesis
Late proteins
Intracellular accumulation
Maturation and releasing

23. Lysogenic Phage Lysogenic or temperate phage: Prophage
Phage that can either multiply via the lytic cycle or enter a quiescent state in the bacterial cell. (e.g., l)
Prophage
Lysogen,Lysogenic bacterium
Lysogenic conversion

24. Lysogenic phage /temperate phage
Lysogenic bacterium
/lysogen
prophage

25. Lysogenic or phage conversion
Definition: A change in the phenotype of a bacterial cell as a consequence of lysogeny
Modification of Salmonella O antigen
Toxin production by Corynebacterium diphtheriae

26. Lytic versus lysogenic infection by phage Lambda

27. 4 Thransposable element
Concept
Segments of DNA that are able to move around the genome.
Properties
“Random” movement
Jumping genes or movable genes
First discovered in the 1940s by Barbara McClintock during her study on maize genetics.(won the Nobel prize in 1983)

28. Types of Transposon Insertion sequences (IS) Importance
A short sequence of DNA containing only the genes for those enzymes required for its transposition.
Importance
Mutation
Plasmid insertion
IR: inverted repeat

29. Types of Transposon Transposons (Tn) or complex Tn Importance
contain genes other than those required for transposition (eg. Antibiotic resistance or toxin genes)
Importance
Antibiotic resistance

30. II mechanism of variation
Mutation
Gene transfer and recombination

31. i Mutations in bacteria
Changes in DNA sequences
Base substitutions, deletions, insertions, rearrangements
Spontaneous mutation:
Backword mutation or reverse mutation

32. ii Gene transfer and recombination
Transformation
Transduction
Conjugation
Lysogenic conversion
protoplast fusion

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

34. 1 Transformation
Definition: Gene transfer resulting from the uptake of DNA from a donor.
Competence of the recipient (Bacillus, Haemophilus, Neisseria, Streptococcus)

35. Griffith’s transformation experiments

36. Bacterial Transformation
With DNA Fragments

37. 2 Conjugation
Donor
Definition: Donor DNA transferred to recipient cell through sex pilus.
Recipient

38. F plasmid Mechanism of F+ x F- Crosses Pair formation DNA transfer F+
Conjugation bridge
DNA transfer
Origin of transfer
Rolling circle replication F+ F-

39. Physiological States F plasmid
Hfr
Hfr,
high frequency of recombination
Hfr F’
F’ plasmid

40. Mechanism of Hfr x F- Crosses

41. Mechanism of F’ x F- Crosses

42. Resistance plasmid, R plasmid
RTF (resistance transfer factor)
transfer genes
code pili
R determinant (resistance determination )
resistance genes
transponsons
Tn 9
Tn 21
Tn 10
Tn 8
RTF
R determinant

43. 3 Transduction
Definition: Gene transfer from a donor to a recipient by way of a bacteriophage

44. Types of transduction
Generalized - Transduction in which potentially any donor bacterial gene can be transferred
Specialized (restricted) - Transduction in which only certain donor genes can be transferred

45. Generalized transduction
by bacteriophages

46. Generalized Transduction
Infection of Donor
Phage replication and degradation of host DNA
Assembly of phages particles
Release of phage
Infection of recipient
Legitimate recombination

47. specialized transductionby
a temprerate bacteriophage

48. specialized transduction
gal
bio
specialized transduction

49. lysogenic conversion
DNA recombination
protoplast fusion

50. Practical implications
Application in diagnosis, treatment and prevention of infectious diseases
Eg. L-form
PCR
Detection of mutagenicity
Application in genetic engineering

51. The Ames Test for mutagenicity