What Effect Do Ultraviolet Rays Have On Yeast Colony Growth?

1. What Effect Do Ultraviolet Rays Have On Yeast Colony Growth? By Katie Schneider Grade 10

2. 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

3. Research • UVA radiation causes 2 types of DNA damage: • cyclobutanepyrimidine dimers • 6-4 photoproducts • These 2 types of damage are repaired by nucleotide excision repair

4. 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

5. 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.

6. 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

7. 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

8. 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

9. 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 petridishes

10. Photos

11. Data

12. Data

13. 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.

14. 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.

15. 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-light-on-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-fair-projects/‌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-israel-watertreatment&SingleRecord=True • Ultraviolet (UV) Radiation. (2010, August 17). Retrieved from http://www.fda.gov/‌Radiation-EmittingProducts/‌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