# How to isolate plastic degrading bacteria from soil!

## Step 4: My Experiment / Cool Calculations

I did the first part of the experiment over summer between my spring and fall quarter. It was approximately 4 months long and in that time I was able to get plastic weight loss in all four of the columns I tested. Of course the results varied (0.38%, 0.39%, 0.08%, and 2.05 %). I got a significant amount of isolates, but decided to test 19 randomly selected isolates. After four months of waiting I weighed these strips and found that 6/19 isolates I tested showed significant plastic degradation ( 7.59%, 8.10%, 8.15%, 7.51%, 8.60%, 7.28%). Unfortunately I got these results during my final undergraduate days so I was unable to continue the experiment and identify the isolates. However, with the data I obtained I made some very cool calculations, which I will show below.

Plastic is a simple molecule (see image below), it is essentially a huge molecule with a 2 Carbon: 4 Hydrogen ratio.

The weight ratio is     3.98x10^-23g Carbon : 6.68x10^-24g Hydrogen
The ratio in % is        85.6% Carbon :  14.4% Hydrogen
The approximate number of carbon atoms per E.coli cell = 7x10^9 cells
Weight of Carbon in a single cell= 1.40x10^-13g

Using this information the weight of the Carbon atoms lost from the plastic can be calculated. Divide that number by the number of days the experiment took place to get the weight loss per day. And although this is a rough estimate, the weight of the Carbon loss can be translated into the number of microbial cells that grew based on that weight, and then the growth of these cells per day can be calculated as well.    :)

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Cryb3by says: 1 month ago
I was wondering if the % of degradation for the plastic strips may have been affected by the fact that it was being tested in plastic containers. I'm no microbiologist but I was just wondering

Thanks!
BrunoGallas says: 1 year ago
Fantastic!!!
I can barely wait to try this with a class! I'm a undergraduate on physics so I'm not an expert on microbial life nor plastic compounds, but I'll do as you said and then try to analyze the results.
rch121 (author) in reply to BrunoGallas1 year ago
Awesome! I am very excited, I did my best to make the instructions so they could easily be followed. If you have any questions about anything let me know. Also, let me know how the results go, even if you get a different result! Thanks!