Morgan Fenoseff
Bio 159
3/9/15
E. Coli Gowth

INTRO

In order for any cell to grow, it needs a source of nutrients; also known as energy. The process in which cells grow and multiply is known as the cell cycle. Once energy is attained within the cell, the cell wall inflates, and the cell begins to expand in size. Similarly, bacteria populations also go through phases of growth. There are four main stages of bacteria growth. (Earl 2014) The first phase is Lag Phase. Cell population remains virtually unchanged in this phase. Most of the growth occurs in the next phase; the Log Phase. During this phase cells are dividing by binary fission, as well as growing in size. Stationary Phase is the third phase. Since exponential growth cannot continue endlessly, they merely stop growing and dividing in this phase. Again, they remain still, hence the name stationary. Finally is the Death Phase. Once the death phase is reached, all of the population is simply terminated. It is only a matter of time before all of the cells die. In this experiment we will look at a specific cell, E. coli, and justify how different energy sources can cause varying growth rates of the cell.

Our hypothesis is that our different energy sources, including glucose, succinate, and no energy, will affect the growth level of the E. coli population in altered ways since they have different levels of carbon. We predict that the E. coli population that is mixed with glucose will grow the most. Glucose has the highest carbon content, therefore we predict the most exponential growth.
METHODS

In this experiment we aimed to determine the growth pattern of E. coli, based on variable energy sources. Our energy sources, which is also the independent variable, included glucose, succinate, no glucose, and no succinate. Each energy source had three replicates, all of which were recorded every thirty minutes during the passage of one day. To place our sample of E. coli into the petri dishes, we used an M9 media. In preparation to perform these tests we made sure that each petri dish had the same amount and it was distributed uniformly.

Measurements were taken with a spectrophotometer and data was recorded regularly throughout the course of the day. We made sure to zero the spectrophotometer, using blanks, before every measurement to ensure an accurate reading. The significance of this step is extreme because if you do not use a blank, to zero out your device, your data will be flawed. These steps were repeated for every measurement until our data set was complete. After collecting our data, we created an Excel spreadsheet to chart the population growth and use a t-test to see if the results were in fact statistically significant. Once the data was charted, we turned our findings into a graph so that our results could be easily understood via visual representation.

RESULTS

We found our data to be very conclusive, and our predictions were indeed correct. The growth of E. coli in the presence of glucose was quite exponential. This E. coli population started at ~0.07 and ended at ~1.33. The growth of the population in succinate was much more subtle, starting around ~0.04 and ending up at about ~0.3. In addition, it followed a more linear pattern then glucose. When we measured growth without the presence of glucose we were shocked to actually find a decrease in size. The E. coli