Hey folks, back again with a continuation in the two middle school science experiments of Jack and Katherine. If you’ll recall, Jack was interested in determining which organisms break down and decompose grass the fastest while Katherine wanted to know what was growing on her cell phone. In this post I’ll talk about the procedures for their respective experiments. Keep in mind that both Jack and Katherine did all of the work themselves; Maddie, Bianca, and I were only there to offer suggestions and advice.
In Jack’s experiment, we used the grass that he collected from his yard and washed it all; first in 70% ethanol, then in 15% bleach, then in water. The grass needed to be washed to ensure that any natural microorganisms would not impact the digestion of the grass. Jack then massed a set amount of ”clean” grass on sterile filter paper. The grass and filter paper were then placed on a TSA all-purpose agar and labeled appropriately. Then, 1mL each of the organisms to be tested-already being grown in TSB-were pipetted on top of the grass and filter paper. The role of the filter paper was to force the organisms to use the nutrients present in the grass instead of immediately using the nutrients in the TSA.
Jack also plated all of the organisms on separate TSA plates so that growth could be compared. Negative controls were used for both plates with grass and those without. No microorganisms were added to these plates. The plates were kept out at room temperature to simulate the most accurate conditions for grass to be naturally digested. Jack came back once a week and massed the plates to check the progress of the digestion.
After observing the results for a month, Jack determined that Bacillus subtilis and Pseudomonas aeruginosa digested grass most efficiently.
As for Katherine, she began by using a sterile swab and swabbed both her keypad and the touchscreen on her phone. These were each plated separately and placed in the incubator. After incubation, she had 3-4 different colonies growing on her touchscreen and 2-3 colonies on her keypad. We then streaked for isolation, selecting only one colony from each plate to obtain a pure colony. These were then incubated. After isolation was achieved, we walked Katherine through a Gram stain and found that she had Gram positive staphylococcus on her keypad and Gram negative streptobacillus on her touchscreen.
They both put in a lot of effort on these projects and presented at their middle school science fair. In my next and final post, I’ll discuss how they did. As always, good night and good luck.
