Abstract for investigating the mutagenic and germicidal effects of UV Light on E. Coli
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Microbiologists hypothesized that exposure to the sun (UV radiation) increased the rate of skin cancer. To test her hypothesis that UV radiation increased gene mutations, she performed the following experiment. She exposed three (3) cultures of different strains of E. coli to UV light for 24 hours. (UV light is known to cause mutations in the genes of DNA). Three cultures of each E. coli were not treated, serving as controls. The 3 UV-treated bacteria and the 3 untreated cultures were plated/streaked onto Minimal Medium minus Histidine (MM-His) agar plates and Nutrient Agar (NA). (Factoid: MM-His agar is "a bare bones" - limited component medium, containing all the amino acids, EXCEPT Histidine); NA is a complete medium containing all the amino acids). Following incubation at 37 degrees for 24 hours, she observed the growth patterns of the 6 bacteria: Table 1 Bacteria and treatment Growth (+/-) on MM-His Growth on NA 001.A – no treatment + + 002.A – no treatment + + 003.A – no treatment + + 001.B - UV treated + + 005.B - UV treated - + 006.B - UV-treated + + Discuss the results of her experiment. 1. Include in your answer what types of media she used (i.e., selective, differential, other).; 2. Why were these media selected for this experiment?; 3. What was the purpose of plating the untreated cultures?; 4. How can you explain the results for bacterium culture 005.B (why didn't it grow?); 5) What conclusions did you reach and why?
Adi S.
Title: The Effect of UV Light on Bacterial Growth In this experiment, you will evaluate the effect of UV light on bacterial growth. UV light affects growth by interfering with DNA, resulting in the formation of thymine dimers. These dimers are lesions that have consequences on DNA functions, including interference in DNA replication and transcription. UV exposure can have lethal effects on bacterial cells, leading to a decrease in their multiplication. The control of bacteria using UV light forms the basis for a method of growth control. There are common mechanisms for repair, including both light and dark repair mechanisms, for UV-induced DNA damage. The details of these repair mechanisms will be discussed in the lab. Cultures of Serratia marcescens and Bacillus cereus will be used in this experiment. The procedure is as follows: 1. Label each plate with the bacteria name and the time (in seconds) of UV exposure. Divide the bottom of the plate into halves, labeling one part as "exposed" and the other part as "control." 2. The exposed part is the area that will be irradiated under the UV source, while the control part will be covered with an index card to block UV radiation. 3. Dip a sterile cotton swab into the appropriate culture tube and swab the agar surface of the plate, making sure to cover the entire area evenly. 4. Dispose of the swab in the appropriate biohazard bag. 5. Repeat the above steps with the other bacteria. 6. Remove the cover of the first plate and place an index card over the part of the plate that will not be irradiated (the control area). Place the plate under the UV lamp for the designated time. 7. Make sure to keep the other plates covered during exposure and place them in a safe location.
Josee P.
Discuss in details the possible reasons for any observed differences in a colony, morphology and the biochemical characteristic of the control as compare to the UV treatment for the different used in this organism.
Suman K.
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