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LECTURE 9: GENETICS OF BACTERIA & THEIR VIRUSES II

LECTURE 9: GENETICS OF BACTERIA & THEIR VIRUSES II. bacterial conjugation (rev) bacterial transformation bacteriophage genetics. BACTERIAL CONJUGATION. interrupted-mating selective markers donor is str s recipient is str r origin of replication transferred first

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LECTURE 9: GENETICS OF BACTERIA & THEIR VIRUSES II

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  1. LECTURE 9: GENETICS OF BACTERIA & THEIR VIRUSES II • bacterial conjugation (rev) • bacterial transformation • bacteriophage genetics

  2. BACTERIAL CONJUGATION • interrupted-mating • selective markers • donor is strs • recipient is strr • origin of replication transferred first • 1st transferred markers most frequent in exconjugants

  3. BACTERIAL CONJUGATION • bias in recovery of markers • gradient of transfer used fordetermination of gene orderonly

  4. Schaum’s Outlines – Genetics 3rd Ed., CH12, pp. 321 – 325 4th Ed., CH10, pp. 349 – 355

  5. BACTERIAL CONJUGATION • exogenote enters cell ... merozygote = partial diploid • single recombination event (3x, 5x, ...) nonviable • double recombination event (4x, 6x, ...) viable

  6. BACTERIAL CONJUGATION • bias in recovery of markers • gradient of transfer used fordetermination of gene orderonly •  to determine map distances, select late marker to ensure transfer of all relevant genes ... high resolution mapping

  7. BACTERIAL CONJUGATION • high-resolution mapping by recombinant frequency

  8. Schaum’s Outlines – Genetics 3rd Ed., CH12, pp. 321 – 325 4th Ed., CH10, pp. 349 – 355

  9. TRANSFORMATION IN BACTERIA • conversion of one genotype to another by uptake of exogenous DNA • transformation principle – demonstrated that DNA was responsible for inherited differences in polysaccharide character of S. pneumoniae (CH8)

  10. TRANSFORMATION IN BACTERIA • extracted DNA (in an experiment) breaks at random • co-transformation of 2 tightly linked donor genes is more likely than 2 distant donor genes • cells must be made competent to enable DNA entry • detergents • electrical fields

  11. TRANSFORMATION IN BACTERIA • dependent on concentration of DNA in the medium

  12. TRANSFORMATION IN BACTERIA • DNA must enter and recombine into the host

  13. TRANSFORMATION IN BACTERIA • practice question, p. 237, #18

  14. BACTERIOPHAGE GENETICS • bacteriophage = eaters of bacteria • T-phages well studied; T-even and T-odd

  15. BACTERIOPHAGE GENETICS • bacteriophage = eaters of bacteria • T-phages well studied; T-even and T-odd

  16. BACTERIOPHAGE GENETICS

  17. BACTERIOPHAGE GENETICS • lysis = breaking of cell wall and release of phage particles • bacteriophage lytic cycle ...

  18. BACTERIOPHAGE GENETICS • phage plaques on a lawn of bacteria • 1 plaque forming unit PFU = 1 phage particle • plaque morphology • host range

  19. BACTERIOPHAGE GENETICS • phage cross: h– r+x h+ r– • h+infect strain 1 • h–infect strains 1 & 2 • r+ slow lysis, small plaques • r– slow lysis, large plaques

  20. BACTERIOPHAGE GENETICS • lawn of 2 E. coli strains – 1 immune to h+phage

  21. BACTERIOPHAGE GENETICS • phage cross: h– r+x h+ r– • h+clowdy • h–clear • r+ small • r– large • RF = [h+ r++ h– r–] TOTAL

  22. TRANSDUCTION IN BACTERIA • alternative life cycles of temperate bacteriophage

  23. TRANSDUCTION IN BACTERIA • generalized transduction… random incorporation • lytic cycle, non-integrated phage

  24. thr leu azi TRANSDUCTION IN BACTERIA • co-transduction • donor leu+ thr+ azir recipient leu– thr– azis

  25. TRANSDUCTION IN BACTERIA • genetic map of the purB  cysB region in E. coli

  26. TRANSDUCTION IN BACTERIA • phage integration

  27. TRANSDUCTION IN BACTERIA • specialized transduction… non- random incorporation • lysogenic cycle, integrated phage

  28. TRANSDUCTION IN BACTERIA • specialized transduction… non- random incorporation • lysogenic cycle, integrated phage

  29. TRANSDUCTION IN BACTERIA • transduction: phage acquire host genes and transfer them to other bacterial cells • generalized transduction: transfers any host gene; and occurs when phage randomly packagehost DNA • specialized transduction: faulty separation of prophage (phage incorporated into host genome); new phage contains adjacent host genes only

  30. GENETIC MAPS IN BACTERIA • E. coli linkage map (minutes)

  31. GENETIC MAPS IN BACTERIA • 5 minutes of the E. coli linkage map

  32. GENETIC MAPS IN BACTERIA • correlated genetic and physical maps in E. coli

  33. SUMMARY: RECOMBINATION IN BACTERIA

  34. BACTERIAL CONJUGATION AND RECOMBINATION MAPPING:PROBLEMS • in Griffiths chapter 5, beginning on page 179, add these questions to those listed at the end of lecture #8… #4, 14, 16-21, 24, 28 (eg. in class)-32 • begin with the solved problems on page 177 if you are having difficulty • look Schaum’s Outline (pp. 358-9) • try Schaum’s Outline questions 10.7 – 10.12

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