Bacteriophage - "eaters of bacteria"

1. Bacteriophage - "eaters of bacteria"

2. Life cycle of a Temperate Bacteriophage

3. Phage plaques on a lawn of bacteria

4. Cells resistant to infection a. Lysogens - prevent further infection b. Restriction/modification systems c. Cells that do not contain the receptor mutants arise 1/106

5. Schematic of the appearance of 10 TonRE. coli cells Expected distribution of TonR if resistance is “induced” by exposure to phage - Lamarckism Expected distribution of TonR if resistance is from a spontaneous mutation - Clonal theory

7. 200 Balls 40 Boxes Avg = 200/40 = 5 = m Some boxes get more Some boxes get less Used the Poisson Equation to Examine Results pn - probability or fraction of events that will occur n times, if an average of m events occurs per interval. Fraction with 0 (n) balls = p0 = (50/0!) X e-5 = 0.0067 The number of boxes will be 0.0067 X 40 = 0.2 (or zero). Fraction with 5 balls = p5 = (55/5!) X e-5 = 0.175 The number of boxes will be 0.175 X 40 = 7

8. Calculate mutation rate: p0 - The fraction of cells with no mutation m - average a - mutation rate N - number of cells/sample m = a X N p0 = (m0/0!)e-m = e-m and so p0 = e-aN p0 = e-aN can rewritten as a = (-ln p0)/N 11 of 20 cultures produced no mutants so p0 = 11/20 = 0.55 N is number of cells per plate = 0.2 X108 so a = (-ln 0.55)/(0.2 X 108) = 3 X 10-8 mutations per cell

9. Demonstrated directly by replica plating- Lederbergs (1952)

10. Fine Structure Gene Mapping - Benzer (1961) Genes are discrete units - Beads on String Only get assortment (recombination) between genes

11. Can detect reversion to WT. Can screen 109 organisms Different phenotypes of T4 phage on different strains T4 Phage Strain E. coli B E. coli K rII- Large round No plaques rII+ Small, ragged Small, ragged

12. Phage co-infection experiment

13. Mapping distances with crosses

14. or Determine the order of the mutants Where is C in relation to A and B?

15. Determine the order of the mutants Where is C in relation to A and B?

16. More Crosses

17. More Crosses

18. 0.4 Crosses between deletions

19. Mapping mutations with crosses to deletions

20. Complementation vs Recombination

21. cis-trans Test

22. Investigating the reading frame

23. Determining the reading frame - Crick (1961) Frameshift mutations and suppressors Used acridine to make mutations and suppressors

24. Determining the reading frame - Crick (1961) Frame shift mutations and suppressors How would you distinguish between a revertant and suppressor? How would you isolate the suppressor away from the original mutation?