Science Buddies: "Ask an Expert"

I have a science competition (first one I’m going to) for school and I need to come up with an experiment.

1. Mark agar plate in 2 halves. Swab agar plate with E. Coli bacteria. Rotate and swab 2 more times.
2.Use an index card and cover half of the plate.
3. Place under uv lights for 30 seconds.
4. Incubate overnight.
5. Check the next day for any remaining bacteria colonies
6.Use cotton swab and swab one colony of bacteria over another half of a new agar plate.
7. Repeat all previous steps 5 times.

This is just a rough draft if a procedure but do you guys think this will be any good or show any success at all?

Thanks

I’m in 8th grade btw.

I would expect your experiment to show the effect of UV radiation killing bacteria, in other words, there should be many fewer surviving colonies on the part of the plate that was exposed to UV radiation, if your radiation dose was sufficient.

I doubt the experiment would show UV resistance develop in five rounds of selection. UV radiation disrupts DNA, and that is something the bacteria can't easily protect themselves from. The bacterial cells have mechanisms for repairing damaged DNA, and you would likely be selecting for strains with very active / improved versions of those mechanisms, if you tuned your UV dose suitably for that (don't kill them all). Other than that, the bacterial cells can't keep the radiation out, the way they can keep out e.g. some antibacterial drugs.

The way these types of experiments are typically done in the lab is to not streak the plate, but to suspend the bacteria in a small volume of sterile buffer solution or growth medium, and then pipetting that solution onto the plate, and spreading it evenly using a sterile spreader. With a suitable number of bacteria in your suspension, you can get nicely separated individual colonies (each originating from a single cell) on the plate, and those colonies can be counted. That way you should be able to quantify the effect of UV, e.g. count, say, 200 colonies growing on a plate that was not exposed to UV, but only 5 colonies on a plate that was UV-irradiated, using the same amount of the same suspension, and for a given UV dose.

Here's one experiment you could start with before attempting selection for resistance: find the UV dose (seconds of exposure from your UV source, or whatever you're using) that will kill half of the E. coli on a plate, compared to a non-exposed control plate. You would need to experiment to find a suitable dilution of the bacterial suspension: too much bacteria, and your plates will be too full to count individual colonies, too little and you won't see anything.