Lab 4: Using The Spectrophotometer To Measure The Rate Of Bacterial Cell Division: A Bacterial Population Growth Curve

Lab 4: Using The Spectrophotometer To Measure The Rate Of Bacterial Cell Division: A Bacterial Population Growth Curve

Introduction

            This was a wrap-up of the past lab reports submitted early. This is the chance for everyone to see how well we actually did at growing bacteria. So because bacteria multiply so fast due to binary fission. We are able to grow our own cultures and use them to study a growth pattern. The point of this lab was to follow the growth of a population of E. coli bacteria cells through each and every individual stage of growth they undergo. We measure this by using a spectrophotometer. This machine measures light or absorbance, this can be done by shining light through and measuring the turbidity as the number of cells increase. The point of this is to determine the stages of growth. Starting with the lag phase then reaching the log phase, stationary phase and last is the death phase however the death phase can’t be measured using a spectrophotometer.

            

This is how the graph is suppose to look.

Methods & Materials

            Materials were the usual

·      Lab coat

·      Gloves

·      Quvet

·      Samples that were assigned to you

·      Ethanol

·      Patience

Methods for this lab were pretty straight forward for our end however we also had a helper (Casey) that came in every hour to create the sample we needed for 8 hours straight. For us, we were assigned 3 different time periods for each group that we needed to calculate the light penetration to know the growth rate. We were given mostly the beginning hours therefor we could take samples straight out of the tube and test them. However, for the hours around 6 or so and after, you have to dilute the solution in order to get a more accurate reading. We needed to find the abundance (light penetration) for each test. The work shown below is the results of the groups combined work.

Time (hr)	Absorbance (nm)			Average	Standard Deviation
1	0.007	0.054	0.01	0.023666667	0.021483844
2	0.134	0.117		0.1255	0.0085
3	0.132	0.132	0.378	0.214	0.115965512
4	0.82	0.462	0.775	0.685666667	0.159219625
5	0.456	0.488	0.476	0.473333333	0.013199327
6	0.598	0.386		0.492	0.106
7	0.718	0.744		0.731	0.013
8	0.72	0.86		0.79	0.07
9	1.006	1.126		1.066	0.06
18	1.054	1.154		1.104	0.05

Results:

            

The graph above shows a time vs abundance curve, This graph is to be compared to the graph in the introduction. Our Lag Phase is basically from zero to about the first point on the graph because our bacteria were taken out of a LB broth to be put back into it therefor there was no need for an adjustment period for the. Our Log phase was all the way from the first point to the point at 9 hours. Then of course the hour 9 to hour 18 is our stationary phase. We are unable to show the death stage with a spectrophotometer because even if the bacteria are dead, they still block light.

            Discussion

Due to Binary fission, Cells divide very fast and multiply, thus if you capture light as it passes through a clear quvet as the bacteria grow over time then the water gets cloudy. The water gets darker due to the over populating cells multiplying in the liquid thus blocking the light from passing through. This is why A increases over time.

Like stated above we can look at our graph and see the separate stages that include Log phase was all the way from the first point to the point at 9 hours. Then of course the hour 9 to hour 18 is our stationary phase. We are unable to show the death stage with a spectrophotometer because even if the bacteria are dead, they still block light.

Now using equations for growth rate during the lag phase I got y = 1(1+1)^1 = 4

Then for the log phase we used y = 4(1+1)^8 =1024

And finally we can find the stationary phase which tends to be 0 because its stationary (no food, no growth)

Now if we add antibiotics to the bacteria, the growth will be stunned and decrease however mutations from the bacteria and then overcome the bacteria which in return looks something like

If we added it around 180 min into the medium the absorbance would temporarily stun the growth, then basically starting another curve stacked on top of it. This would look something like