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Bacterial and Viral Genetic Systems

Cholera bacteria. H. pylori. Bacterial and Viral Genetic Systems. Part I Ch. 8. Ebola virus. Outline. Techniques to study bacteria The bacterial genome Plasmids Gene Transfer Mapping bacterial genes Antibiotic resistance Bacterial transformation. Bacterial “in vitro” growth.

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Bacterial and Viral Genetic Systems

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  1. Cholera bacteria H. pylori Bacterial and Viral Genetic Systems Part I Ch. 8 Ebola virus

  2. Outline • Techniques to study bacteria • The bacterial genome • Plasmids • Gene Transfer • Mapping bacterial genes • Antibiotic resistance • Bacterial transformation

  3. Bacterial “in vitro” growth Liquid OR solid agar plates You will do in lab next week

  4. Minimal Growth Media Complete Growth Media For prototrophs For auxtrophs (mutants) Bacterial Growth Bacterial Colony Colonies are “clones”

  5. Mutant bacteria: can be found based on their “food” requirements

  6. Bacterial Genome (normally—there are exceptions) • A circular chromosome • Haploid • Normally compact DNA • NOnuclear membrane: prokaryote—no exception to this rule DNA “escaping” out of damaged cell

  7. Bacterial Plasmids • What are they? • What affect can they have on the bacterial cell? • How did they get inside the cell? 2 plasmids joined together Some plasmids are integrated And some remain independent. Episomes can be either!

  8. Episome • The fertility factor (F factor) is an episome • Controls gene exchange and mating in bacteria

  9. Methods for bacterial gene transfer (in nature) • Conjugation • Transformation • Transduction You will do this in the lab!

  10. Methods for bacterial gene transfer (in nature) DNA transfer is not linked to reproduction in bacteria. • Conjugation: bacteria to bacteria • Transformation: external environment to bug (bacteria) • Transduction: from virus to bug!

  11. Methods for bacterial gene transfer (in nature) • Conjugation: often involves recombination • Transformation: May have recombination • Transduction: May have recombination How do we know?

  12. Experimental evidence to support bacterial recombination MINIMAL MEDIA NO GROWTH ON EITHER PLATE MIX STRAINS SOME GROWTH

  13. Most conjugation transfers requires the “F” factor Sex pilus

  14. Bacterial Recombination • Certain bacterial cells show recombination with “F” factor • These are called High-frequency (Hfr) cells

  15. Hfr cells and stepwise recombination

  16. Hfr cell to a F’ cell • The F factor is cut from the bacterial chromosme and may even carry some bacterial chromosome with it!

  17. Partial diploids • F’ can conjugate with F- cell. • Leads to “partial diploid”= merozygotes • Two copies of some genes

  18. Mapping bacterial genes • Using “interrupted conjugation

  19. Transfer times indicate map distances 10 5 15 20 25 0 lac gal ton azi origin

  20. R Plasmids • Contain genes for antibiotic resistance • Easily spread among unrelated bacteria Fish bacteria E. coli E. coli

  21. Transformation • Uptake of DNA by bacteria from its external environment • May be DNA fragment • Bacterial cell must be “competent” • May recombine with host’s DNA TRANSFORMANTS

  22. Transformation can be also used to map bacterial genes

  23. Note: • You will carry out a bacterial transformation in lab next week; however, there will be some technical differences from what may occur in nature. • I will emphasize these in lab. • Next we complete chapter 8 • Viral genetic systems

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