This experiment used spectrophotometry to measure E. coli growth at four different temperatures (27°C, 37°C, 45°C, and 55°C) over the course 75 minutes. The aim was to measure cell numbers by measuring the turbidity of samples inoculated with E. coli. Growth rates and generation times were then obtained using the data collected. It was expected that the E. coli would have the highest growth rate and shortest generation time at 37°C. This temperature is most similar to E. coli’s natural environment, the human intestinal tract. At 37°C, E. coli should spend a substantial amount of time in the exponential phase of bacterial growth, and have a prolonged stationary phase before entering a period of cell death. The E. coli grown at 55°C were expected to show a decreased growth rate and a longer generation time. At this temperature, proteins and other cellular components become denatured and cell lysis occurs. It was expected that E. coli grown at 45°C would have a growth rate and generation time in between that of the 37°C and 55°C samples. At 45°C proteins should not become denatured and most cells will not lyse. The increased heat was predicted to slow cell metabolism and mitosis enough to distinguish a difference in growth rate and generation time compared to the 37°C sample. The last sample, grown at 27°C, was expected to show a lower growth rate and higher generation time compared to the three other samples. At this lower temperature, the metabolic processes of E. coli were predicted to slow significantly, which would reduce the number of new cells forming and increase the generation time by slowing mitosis.
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