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Chapter4 Heredity and variation of bacteria

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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 transduction
by 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

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