Optimal Growth Conditions and Generation Time for E. coli

Optimal Growth Conditions and Generation Time for E. coli
Introduction
The goals of these exercises were to determine the optimal growing condition and the generation time of E. coli.
Materials and Methods Please refer to the lab manual for a complete list of materials.
To determine the optimal growth condition for E. coli, we had to test the environmental factors that could affect the growth. We tested the relative growth of E. coli in the presence and in the absence of oxygen. The results showed that it can grow with and without oxygen but grows better in an oxygenated environment. We tested the affects of temperature on the relative growth; 4-8 degrees Celsius, 22.5 degrees Celsius, 37 degrees Celsius, and 55 degrees Celsius. The results showed that the optimal growth temperature for E. coli is 37 degrees Celsius. We then tested the affects of pH using a pH of 3, 7.2, and 10. The results for the optimal condition was 7.2 pH. The last test we ran was with osmolality. We had a TSA with .9%, 2%, and 10% NaCl. Our results concluded that .9% and 2% were optimal growth condition for osmolality in growing E. coli. With these results we were able to conclude that the optimal growing condition for E. coli is an oxygenated environment in 37 degrees Celsius, with a pH of 7.2 and an osmolality of .9% or 2% NaCl.
To determine the generation time of E. coli we distributed the bacteria into a flask of actively growing broth cultures. We kept this flask at the optimal growing conditions for E. coli to grow. We took the initial absorbance and transmittance and then allowed the E. coli to grow. Periodically we took samples of the culture and recorded the absorbance and transmittance data. We then used this data to create a graph. Using the graph we were able to determine the generation time for E. coli.
Results
Please refer to the worksheet. On the worksheet attached to this paper is the information and results of the tests we took over the environmental factors that could affect the growth of the bacteria, E. coli. It lists what we tested and the relative growth on a scale of 0 – 4, with 0 being no growth and 4 being heavy growth. It also states our conclusion on each of the tests run. On the back of the worksheet there is a chart listing the growth curve data at optimal growth conditions. We listed the time, minutes from 0, absorbance, and transmittance. Please refer to the graph. On the graph we have absorbance on one side and transmittance on the other, both versus time. We plotted the points and drew a line showing the growth curve. I have two blue dashed lines showing the log phase on the growth curve and two red dashed line sets showing the determination of generation time. The space between the two red sets is the generation time for E. coli. I have a legend on the right showing which dots on the graph are which and which lines are which. The title of chart is Growth Curve for E. coli and I have units for each axis.
Discussion
The goals of these exercises were to determine the optimal growing condition and the generation time of E. coli. With the tests we ran we determined that the optimal growing conditions for E. coli are an oxygenated environment in 37 degrees Celsius, with a pH of 7.2 and an osmolality of .9% or 2% NaCl. E. coli is naturally found in the intestines and colon in human beings but the growth conditions we came up with in the lab are similar to the conditions found in nature. The generation time for E. coli that I found with my data during the log phase and in optimal growth conditions is around 90 minutes. While graphing the data points of absorbance and transmittance on the graph I noticed the inverse relationship between the two sets. The absorbance of the E. coli goes up with time while the transmittance goes down with time. Once they reach the end of the log phase both absorbance and transmittance seem to steady off and stay at the same number from then on.