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Changes in bacterial traits

Changes in bacterial traits. Caused by: Changes in environmental conditions (only phenotypic changes) Changes in the genetic codes 1- Intermicrobial exchange 2- Mutations (point mutations, insertions, deletions). Intermicrobial exchange. Transformation

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Changes in bacterial traits

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  1. Changes in bacterial traits Caused by: • Changes in environmental conditions (only phenotypic changes) • Changes in the genetic codes 1- Intermicrobial exchange 2- Mutations (point mutations, insertions, deletions)

  2. Intermicrobial exchange • Transformation (Capturing DNA from solution) • Transduction (Phage-mediated) • Conjugation (Bacterial Sex)

  3. Original Transformation Exp.F. Griffith (1928) using pneumococci

  4. DNA-Mediated Transformation

  5. DNA-Mediated Transformation

  6. Intermicrobial exchanges by vectors

  7. Characteristics of genetic vectors • must be capable of carrying a significant piece of donor DNA • must be readily accepted by the host • plasmids – small, well characterized, easy to manipulate & can be transferred into appropriate host cells through transformation • bacteriophages – have the natural ability to inject their DNA into bacterial hosts through transduction

  8. Transduction(madiated by phage)

  9. Microbe Library, American Society for Microbiology www.microbelibrary.org

  10. Lytic versus Lysogenic

  11. Generalized Transduction

  12. Generalized Transduction

  13. 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.

  14. Transduction(specialized)

  15. gal gal bio bio gal bio gal bio bio gal Specialized Transduction(Lysogenic Phage)

  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

  18. Donor Recipient Conjugation • 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 • Lacks an F factor

  19. Conjugation • Significance • Gram - bacteria • Antibiotic resistance • Gram + bacteria • Production of adhesive material by donor cells

  20. Conjugation

  21. Conjugation: Sex or F Pilus

  22. Plasmids

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

  24. Classification of Plasmids • Transfer properties • Conjugative • Nonconjugative • Phenotypic effects • Fertility • Bacteriocinogenic plasmid (or encoding some other toxins) • Resistance plasmid (R factors)

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

  26. Self-Transmissible R Plasmid

  27. Conjugation: F Plasmid Transfer

  28. Conjugation

  29. Hfr F+ F+ andHFr cells Integrated (Hfr) (High Frequency of Recombination)

  30. F’ Hfr Hfr and F’ cells

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

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

  33. Transposable Genetic Elements • Definition: Segments of DNA that are able to move from one location to another (across the genome or from one genome to another) • Properties • “Random” movement • Transposase • Transposition may be accompanied by duplication

  34. IS Resistance Gene(s) IS IS Resistance Gene(s) IS Types of Transposable Genetic Elements • Transposons (Tn)/ Insertion elements (IS) • Definition: Elements that carry other genes in addition to those involved in transposition • Nomenclature - Tn10, IS6110 • Structure • Composite Tns • Importance • Antibiotic resistance • Epidemiology and evolutionary studies

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