Bacteriophage "eaters of bacteria"

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Bacteriophage - "eaters of bacteria"
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Life cycle of a Temperate Bacteriophage
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Phage plaques on a lawn of bacteria
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Cells resistant to infection a. Lysogens -
prevent further infection b. Restriction/modifica
tion systems c. Cells that do not contain the
receptor mutants arise 1/106
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Schematic of the appearance of 10 TonR E. 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
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(No Transcript)
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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
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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
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Demonstrated directly by replica plating-
Lederbergs (1952)
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Fine Structure Gene Mapping - Benzer (1961)
Genes are discrete units - Beads on String Only
get assortment (recombination) between genes
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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
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Phage co-infection experiment
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Mapping distances with crosses
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Determine the order of the mutants
Where is C in relation to A and B?
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Determine the order of the mutants
Where is C in relation to A and B?
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More Crosses
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More Crosses
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Crosses between deletions
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Mapping mutations with crosses to deletions
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Complementation vs Recombination
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cis-trans Test
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Investigating the reading frame
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Determining the reading frame - Crick
(1961) Frameshift mutations and
suppressors Used acridine to make mutations and
suppressors
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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?