Class: BE-210
Group: W3
Members: Alyssa Abo, Jeremy Cohen, Pear Musikabhumma, Keng Hao Shi
Date: April 30, 1997
Full Text

Abstract:
Single-cell organisms, such as bacteria, are capable of rapid adoption to their environment and fast reproduction. The study of such cells growing under various environmental conditions helps to establish the basic principles and techniques used for cell culture and biotechnological processes.

The objective of this project was to determine the growth of E. Coli cells under the influence of heat shocks. The hypothesis tested was as follows:
E. Coli’s growth rate at 37oC before heat shock would be the same as that of the base curve at 37 degC. After the first heat shock, the temperature was increased from 37 degC to 45 degC. It was hypothesized that the bacteria would readjust its growth rate to match that of the 45oC base curve. There may be a small lag phase shortly after the heat shock, but the hypothesis predicted the new growth rate would quickly reach that of the 45 degC base curve. The project further predicted that after the second heat shock, where the temperature decreased from 45 degC to 37 degC, the cells would attempt to readjust their growth rate again. However, due to the possible formation of special proteins or organic molecules during the faster growth phase at 45 degC, the bacteria would not be able to fully recover; thus, the growth rate at 37 degC will be some value in the range from that of 45oC to that of 37 degC.

The temperature factor was the control element in the series of experiments. The exponential growth rate observed 37 degC was 0.0173 with a standard error of 0.00055 cell/min. The growth rate obtained at 45 degC was 0.0286 with a standard error of 0.00215 cell/min.

The heat step function chosen was the 37-45-37 degC temperature change. The experiment was carried out and produced a growth curve in which the exponential growth rates differed for the various temperatures. One of the observed results contradicted the project’s hypothesis. Thus, the experiment was repeated two more times. The results obtained in the following experiments supported the initial hypothesis and suggested unknown factors which led to some of the unexpected results.

When the surrounding temperature changed from low to high, the cells quickly adapted to the surroundings and matched their growth rate to that of the higher temperature. Once the cells adapted to the high temperature surrounding, the system was heat shocked to a lower temperature; however, this did not restore the cell growth rate back to that of the lower temperature. A potential explanation for this finding is that the cells produced excess organic materials during the growth phase at the higher temperature which effected the heat shock to a lower temperature.