Lab 7 summary CC-BY-NC

Maintainer: admin

Summary of Lab 7 for BIOL 112 (Winter 2011). Week of Feb 21 2011.

Microbiology II: growth cycle of bacteria; effects of radiation on bacteria.
Genetics: Drosophila practice.

1Growth cycle of bacteria

  • Bacteriophage: viruses that infect bacteria
    • Virus particles: DNA or RNA enclosed in a protein coat
    • Become active only in living cells, reproduce themselves at expense of host
    • Bacteriophage destroy host cell, causing them to burst open (lyse) when released
  • Experiment: mixing T4-infected E. coli with uninfected E. coli, spreading them on an agar plate
    • There will be a dense growth of bacteria except in areas surrounding virus-infected bacteria
    • Clear areas = plaques; where bacteria were killed and lysed by the free parental phage
    • We can then count the number of plaques, and from that get the density of infective phage particles in the original suspension
    • Can also figure out the growth cycle of T4 phage (time taken to infect, reproduce, and be liberated)
  • Procedure:
    • Add some T4 phage suspension to bottle containing E. coli
    • Dilutes the number of free parental phage, and prevents uninfected bacteria from being infected or whatever
    • Vortex, water bath, then add to another bottle
    • Plate onto agar, 5 plates total, after 10, 20, 30, 40, 50 mins in the water bath
  • Results:
    • Control plate has no plaques - no T4
    • Latent period, rise period (due to progeny phase released after bursting, infecting others), lag period
    • Burst size: assume all infected bacteria released progeny phase after 40 mins; ratio of plaques at 40 mins to plaques at 10 mins

2Effects of radiation on bacteria

  • UV light can increase the rate of mutation in bacteria by damaging DNA
  • Some members of the population will be killed, but others will have more mutations than normal
  • Experiment: divide agar plates in quadrants, plate with Serratia exposed to 0, 1, 2, 3 seconds of UV light
    • Think about it, it makes sense
  • Next lab: count the number of colonies in each quadrant, plot number of surviving colonies vs. irradiation time (inactivation curve)
    • Survival rate of bacteria should vary inversely with length of exposure

3Drosophila practice

  • We practice anesthesising flies with fly nap, then discard them into the morgue jar lol
  • Wild-type flies:
    • Brick-red eyes
    • Grey body colour
    • Wings extending beyond posterior end of abdomen
  • Mutant flies:
    • White eyes
    • Same grey body colour
    • Wings shorter than the abdomen
  • Distinguishing males from females:
    • Males have sex combs on forelimbs (impossible to see, really)
    • Males have rounded, solid-coloured posterior ends; females, pointed and more striped
    • Also females usually larger
  • Dead flies have perpendicular wings lol