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The University of Oklahoma *

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1134

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Biology

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Dec 6, 2023

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Comparing Escherichia Coli (E. Coli) Population Growth in Different Temperatures Escherichia Coli also known as E. Coli are prokaryotes which have its own set of functions different from animals, however, they are still living creatures and have optimal living spaces in which they prefer just like any other living organism. There are many conditions which causes bacteria to not work at their most optimal like changes in pH, temperature, resources, etc. Too basic or acidic of a pH or too high of a temperature will denature the proteins within the bacteria and cause the proteins and enzyme to not work as well (Ratkowsky, Olley, Ross 2004). In that case the reasoning behind this experiment is to compare the population growth of E. Coli in different temperatures such as 20C, 30C 37C and 40C to see if there is a significant different between the growth populations. E. Coli has an optimum temperature of 37C; therefore, it should have the highest grow (Albrecht 2018). If we can understand the best temperature at which a bacteria can grow, it will help many different professions within their work force to prevent the spread of bacteria. For example, food workers that want to prevent the spread of bacteria to not contaminate their customers. Question & Hypothesis: With previous knowledge about living organisms, we wonder if there are differences within growth in E. Coli within different environmental temperatures. We hypothesize that there will be a significant difference in growth between 20C, 30C, 37C, 40C and with further observation be to observe that 37C is prime temperature at which E. Coli reproduces best at. To start our experiment, everyone’s group was assigned a specific temperature in which we had to observe from. There would be different flasks of E. Coli incubating in different

temperature baths. There would be eight different flasks in total, four of which were our controls that contained just soy broth and the other four would be our experimental flask which contained E. Coli and soy broth. Sets of two flasks, one control and one experimental would each sit in the water bath incubating a specific temperature of 20C, 30C, 37C and 40C for a total of 14 hours, starting at 7:00 and ending at 21:00. When collecting our data, we would first calibrate the spectrophotometer by using a pipet to collect a small amount of the control broth and use that to zero the system. We would then repeat the process of collecting our data by always stirring the flask and then collecting a small amount of the experimental broth and observing the absorbance three times every hour. We collaborated with other groups to collect the full set of data that we needed which was all three samples of each broth at each temperature at each hour. After the readings were completed, we performed a two-way ANOVA. In this lab we compared the absorbance level of E. Coli to determine the difference in population growth in different temperature environments. Table 1 showcases the processed data of our raw data. This processed data contains the averages of absorbance of E. Coli of each test preformed on each temperature. The higher the absorbance the darker the solution, meaning that the growth of the E. Coli is also large. When looking at Table 1, we can see that the average absorbance levels for 37C is larger than the three other temperatures 20C, 30C and 40C. The average absorbance of each test in 37C are 0.18, 0.17 and ,0.17. We can also see that 20C had the least amount of E. Coli growth with 0.11, 0.12 and 0.12 for absorbance. We can also see this trend in Figure 1, where 37C had the highest amount of absorbance with 30C being an extreme close second. Both 20C and 40C were lower in growth, 20C being the lowest. From this we can assume that 20C slowed down the growth of E. Coli whereas, 40C had denatured the bacteria instead. We know this because in the graph you can visually see the absorbance increasing but

then decreasing from 16:00 to 21:00, which represents the death phase in 40C. For 30C and 37C there was also an increase in absorbance and no decrease, meaning that the lag phase kept going throughout all 14 hours. For 20C there was a slight death phase starting at 20:00. As for Table 2, this is the ANOVA two-way test of the averages of absorbance of each test for each temperature. Highlighted yellow is the p-value and we know that if the p-value is less than .05 than the data is significantly significant meaning we fail to reject our hypothesis. In conclusion, our hypothesis was failed to reject. This means that we are rejecting our null hypothesis that there is no difference growth of E. Coli under different temperatures, however, we are accepting our hypothesis that E. Coli does grow at different rates depending on environmental temperature. We can learn that changes in temperature does greatly affect the way bacteria grows, helping future food providers understand that foods that are cooks will be more sterilized and have less bacteria than foods that have been left out at body temperature of 37 C. Food providers can be more conscious about how they store their food to help serve their customers.

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