Lab 7 summary

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