Notes cover lecture 6A, 6B and 6C videos of M118L course at University of California, Irvine. Covers concepts like evolution of bacteria, the Luria and Delbruck (1943) experiment, and bacterial growth phases.
Lecture 6 (covers videos A, B, & C) Abbreviations:
Tuesday, February 9, 2021 8:09 PM Ex. = for example,
b/w = between
b/c = because
w/ = with
w/o = without
• Evolution: heritable change in a pop over time, driven by selective pressure. Steps to
v. = versus
INC = increase
evolution:
Imagine mutations only arose in the presence of stress. Which of the following would be true?
• Mutation: change in DNA that leads to expression of different RNA/protein and thus The freq of AR bacteria would INC. Stress from antibiotics would cause selection for bacteria
that are resistant over time.
different phenotype.
To measure factor: use immunostain-- will stain factor and show where localization is.
• Selection: pressure from the environment that makes that phenotype advantageous. Non-repairing antibiotic and antibiotic group. -> Comparing antibiotics means is one antibiotic
better than the other…
No-antibiotic control group measures effectiveness of antibiotic. Clonogenic assay used to
• Mutations occur all the time, but w/o selection we rarely see them appear in populations measure repair.
BLES assay: identify DSB-damage repair.
(selection poses trends).
Soil bacteria that come into contact with antibiotic-treated manure give way to higher frequencies of
antibiotic-resistance in said bacteria than soil bacteria exposed to antibiotic-free manure. (Antibiotics
• Luria and Delbruck, 1943: tested different mutation models to determine which is will be more metabolically active when tested against non-antibiotic manure; other sources of
selective pressure in manure, like nitrogen???)
correct.
○ Induced mutation model: determined that a beneficial *random* mutation only
arises in the presence of stress.
○ Spontaneous mutation model: beneficial mutations occur randomly at any time. ->
mutations can happen early-- can be passed down to progeny. CORRECT
MODEL!
• Presence of jackpot phenotype (half of colony possess mutation) indicates
spontaneous mutation.
• Why are bacteria good models for examining evolution? Small, fast replication time,
cheap to grow, and genomes are easier to manipulate.
• CFU/ml: Colony-Forming Units per milliliter; measures how many cells actually grow
into a colony, viewed on a plate. CFU > OD for cell growth.
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