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Chapter4 Heredity and variation of bacteria

Chapter4 Heredity and variation of bacteria. outline. Concepts Genetic materials of bacteria Mechanism of variation. concepts. Heredity Variation Genotypic variation Phenotypic variation. Variation of bacteria. Variation in morphology and structure lose capsule (Pneumococcus) H O

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Chapter4 Heredity and variation of bacteria

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  1. Chapter4Heredity and variation of bacteria

  2. 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 13years, 230 generation • C. diphtheriae b-corynephage, diphtheriae toxin

  6. Variation • Variation in drug resistance • Penicillin resistant strains of staphylococcusaureus • 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. 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. RTF Tn 10 Tn 8 Tn 9 Tn 21 • Phenotypic effects Fertility plasmid,F plasmid coding sex pilus Resistance plasmid, R plasmid resistance transfer factor resistance determinant • 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 • Composition • Nucleic acid • DNA or RNA • Protein • Protection • Infection

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

  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: • 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) • 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 • 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: 10-8-10-6 • 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. Donor Recipient 2 Conjugation Definition: Donor DNA transferred to recipient cell through sex pilus.

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

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

  40. Hfr F- Hfr F- Hfr F- Hfr F- Mechanism of Hfr x F- Crosses

  41. F’ F- F’ F- F’ F’ F’ F’ Mechanism of F’ x F- Crosses

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

  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. gal gal bio bio gal bio gal bio bio gal 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

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