What Effect Do
Ultraviolet Rays Have
On Yeast Colony
Growth?
By Katie Schneider
Grade 10
Research
• UV-A light causes tanning, skin aging, and cataracts
• UV-B causes sunburn, skin aging and skin cancer
• UV-C is most effective at killing microorganisms
Research
• UVA radiation causes 2 types of DNA damage:
• cyclobutane pyrimidine dimers
• 6-4 photoproducts
• These 2 types of damage are repaired by nucleotide excision
repair
Research
• In this experiment, the Saccharomyces cerivisiae is genetically
engineered to be DNA-repair-deficient
• The enzymes that normally would repair DNA damage are
knocked out so that the yeast is especially sensitive to UV light
Hypothesis
• If yeast colonies are exposed to UV light for varied amounts of
time, a short amount of UV exposure will aid in yeast
production, but longer exposure will kill the yeast cells
because of the damaging effects of UV light.
Materials
• UV-sensitive yeast
strain purchased from
Carolina Biological
• Sterile dilution tubes
• Sterile toothpicks
• Dextrose (YED)
• Petri dishes
• Sterile distilled water
• Pipettes
• Glass spreading beads
•
•
•
•
•
•
•
•
Disposable gloves
Microwave oven
Permanent marker
Aluminum foil
Stopwatch
Cardboard box
3 UV flashlights
Transparent sticker
with 34 sections
Procedure
• The agar plates were poured by heating sterile YED agar in a
microwave then pouring the agar onto 25 petri dishes
• The master plate was then streaked with yeast
• To determine the optimal serial dilution needed for the experiment,
1:1,000 and 1:10,000 dilutions of a yeast suspension made from the
growth on the master plate were tested
• They showed no growth, so they were tested again, but without UV
exposure
• They again showed no growth, so 1:10 and 1:100 dilutions were
tested
• The 1:10 dilution provided growth that was too dense, so 1:100
dilution was used for actual experimentation
• Plastic test tubes and sterile bulb pipettes were then used to make
the 1:100 serial dilution of the yeast suspension
Procedure
• 2.5 mL of this suspension was pipetted into each petri dish, which was
labeled either exposed or control for 1, 3, 5, or 7 minutes, with 3 trials for
each
• 5 glass beads were placed in each petri dish, which were swirled across
the plate to spread the yeast suspension
• Three holes were made across the middle of a cardboard box, and UV
flashlights emitting light in the 385 nm range were places in the openings
• Three petri dishes at a time were then exposed to the light for their
indicated times
• Controls were covered in aluminum foil before being exposed to the UV
light
• The exposed samples were then covered in aluminum foil, and stored in
an incubator for 2 days at 30°C
• To collect the data, a transparent grid containing 34 sections was placed
over the petri dish
• The number of sections containing yeast growth out of 34 was then
recorded
Procedure
• There were 3 trials for each amount of time for control and
exposed
• Independent variable-the amount of time the yeast was
exposed to UV light
• Dependent variable-the amount of yeast growth
• Control-the yeast not exposed to UV light
• Constants-amount of yeast in each petri dish, size of the petri
dishes
Photos
Data
Number of Sections Showing Yeast Growth out of 34
Trial #
Control
1 min
Exposed Control
1 min
3 min
Exposed Control
3 min
5 min
Exposed Control
5 min
7 min
Exposed
7 min
1
34
34
18
30
34
0
34
34
2
32
30
34
0
26
33
34
0
3
0
34
34
34
34
34
34
34
33
29
21
31
22
34
23
Average 22
Data
Average Yeast Growth
45
Number of Sections with growth out of 34
40
35
30
25
20
15
10
5
0
control 1 min
exposed 1 min
control 3 min
exposed 3 min
control 5 min
Amount of time exposed to UV light
exposed 5 min
control 7 min
exposed 7 min
Sources of Error and
Improvements
• This project should be conducted in the summer so that sunlight can
be used as UV light instead of UV flashlights.
• Also, in this experiment, the data was measured by determining
whether there was growth in each of 34 different sections. Any
growth at all in a designated grid section was considered a positive
result.
• Also, when spreading the yeast suspension with the glass beads, it
ended up being concentrated primarily around the perimeter of the
dishes, so this may have affected the results.
• If this experiment were to be performed again, one should use a
higher serial dilution level, such as 1:1000 instead of 1:100, and an
alternate method for counting the yeast growth should be used that
yields more accurate results.
• Additional trials performed using these changes might result in data
that is more reliable.
Conclusion
• Hypothesis-“a short amount of time will aid in yeast
production, but a longer amount of time will kill the yeast cells
because of the damaging effects of UV light.”
• The results support the hypothesis
• Because of the high standard deviation, however, the results
may not be reliable.
• This experiment has relevance to the world today because UV
light is a major cause of skin cancer, and extended exposure
can be extremely detrimental to skin health.
• Other experiments regarding UV light could be conducted
testing the strength of UV at different times of day, during
different seasons, or for longer periods of time.
References
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Cells and DNA. (2011, October 17). Retrieved from http://ghr.nlm.nih.gov/handbook/basics?show=all#gene
Clancy, S. (2008). DNA Damage & Repair: Mechanisms for Maintaining DNA
Integrity. Retrieved from Nature Education database.
Deoxyribonucleic Acid (DNA). (2011, March 23). Retrieved from http://www.genome.gov/25520880
DNA damage from deamination and depurination [illustration]. (n.d.). Retrieved from Science Online database.
Genetic Engineering. (2011, May 23). Retrieved from
http://www.fda.gov/AnimalVeterinary/DevelopmentApprovalProcess/GeneticEngineering/default.htm
Goodman, B., MA. (2011, October 6). UVA Radiation May Cause DNA Damage in Skin. Retrieved from
http://www.webmd.com/healthy-beauty/news/20111006/uva-radiation-may-cause-dna-damage-in-skin
Highland, J. (n.d.). The Effects of UV Light on Yeast. Retrieved from http://www.livestrong.com/article/252729-the-effects-of-uv-lighton-yeast/
Hockberger, P. E. (2002). History of Ultraviolet Photobiology. Retrieved from Department of Physiology, Feinberg School of Medicine,
Northwestern University website: http://www.photobiology.info/Hockberger.html
Kirkland, K., PhD. (2007). Infrared and Ultraviolet. In Light and Optics (pp. 106-109). New York: Facts On File, Inc.
Liu, S., & Usinger, L. (n.d.). All About Agar. Retrieved from http://www.sciencebuddies.org/science-fairprojects/project_ideas/MicroBio_Agar.shtml
MacNeal, R. J., MD. (2007, August). Overview of Sunlight and Skin Damage. Retrieved from Merck website:
http://www.merckmanuals.com/home/skin_disorders/sunlight_and_skin_damage/overview_of_sunlight_and_skin_damage.html
Maczulak, A. (n.d.). Saccharomyces. In Encyclopedia of Microbiology. Retrieved from
http://www.fofweb.com/activelink2.asp?ItemID=WE40&SID=5&iPin=EMBIO0159&SingleRecord=True
Tanner, F. W., & Ryder, E. (1923, May). Action of Ultraviolet Light on Yeast-Like Fungi. Botanical Gazette, 75(3), 309. Retrieved from
http://www.jstor.org/pss/2470221
Twyman, R. (2002, August 28). What are ‘model organisms’? Retrieved from http://genome.wellcome.ac.uk/doc_wtd020803.html
Ultraviolet radiation and human health. (2009, December). Retrieved from World Health Organization database.
Ultraviolet treatment for water suggested. (2010). Biofouling. Retrieved from
http://www.fofweb.com/activelink2.asp?ItemID=WE40&SID=5&iPin=UPI-1-20100422-140951-bc-israelwatertreatment&SingleRecord=True
Ultraviolet (UV) Radiation. (2010, August 17). Retrieved from http://www.fda.gov/RadiationEmittingProducts/RadiationEmittingProductsandProcedures/Tanning/ucm116425.htm
Whyte, D. B. (2009, December 4). Exploring DNA Damage: What Effect Do Ultraviolet Rays Have on Yeast Colony Growth? .
Wyman, B., & Stevenson, H. L. (n.d.). Ultraviolet radiation–A range (UV-A). In The Facts On File Dictionary of Environmental Science,
Third Edition. Retrieved from http://www.fofweb.com/activelink2.asp?ItemID=WE40&SID=5&iPin=DEST4675&SingleRecord=True
Wyman, B., & Stevenson, H. L. (n.d.). Ultraviolet radiation–B range (UV-B). In The Facts On File Dictionary of Environmental Science,
Third Edition. Retrieved from http://www.fofweb.com/activelink2.asp?ItemID=WE40&SID=5&iPin=DEST4676&SingleRecord=True
Wyman, B., & Stevenson, H. L. (n.d.). Ultraviolet radiation–C range (UV-C). In The Facts On File Dictionary of Environmental Science,
Third Edition. Retrieved from http://www.fofweb.com/activelink2.asp?ItemID=WE40&SID=5&iPin=DEST4677&SingleRecord=True