Fun with Soil – Elizabeth

Where did you obtain your soil sample?

I got my soil from the path that walks up the right side of the football field behind Alumni Gym. The exact coordinates are Lat 42.816563, Long -73.926441. There was a layer of mulch on top that I moved out of the way and then I dug down about two inches. The soil was moist, but not wet, and dark. There were more ants in the soil than I expected once I got down into it.

Why did you choose this location?

I chose this location because I feel like it hasn’t been disturbed in a while. Most of the bushes in this area are just tended by facilities; not really replanted each year. The soil and the bacteria in it have probably been sitting long enough to have seen competition and (hopefully) some antibiotic production.

Do you expect a lot of isolates? Why or why not?

I expected the least-diluted plates to be covered, so I guess that’s one way to quantify “a lot of isolates.” However, given that its a soil sample and it was under a layer of mulch with at least some exposure to water, there’s probably a fair amount of anaerobic organisms there that we won’t grow at all, so I would expect very few of those isolates.

Have you initial observations supported this?

Yes – when I saw the plates, the ones with 1/100 dilutions were covered. They also looked like the serial dilutions were somewhat successful, as the numbers of colonies on each one decreased (based on rough estimate – I didn’t count them).

What media did you choose? What dilutions?

I chose to work with LB, 10% TSA, and R2A using dilutions of 1/100, 1/1000, and 1/10000. I used the LB as standard and then chose the 10% TSA as a “medium richness” media and the R2A as a bit of a less nutritious media. I thought this range of nutritional value would provide good comparison between plates. My dilution choices were based on our protocol from the test plates (the first lab); we weren’t seeing countable plates until the 1/10000 dilutions, so I made sure to get a 1/10000 plate for each media.

Will you need to redo any?

None of them initially seemed like they needed to be redone. They all had some growth on them and the lowest dilutions seemed countable.

How did your sample differ on the different media?

Honestly, I didn’t look at them too much. For personal reasons, my time in the lab has been limited and I haven’t been able to compare them in detail.

2 thoughts on “Fun with Soil – Elizabeth

  1. After I picked my media for the class, I actually thought the same as you did. I picked general or rich media for my three, but thought that if nothing grew perhaps I should’ve also done a limited nutrient medium. However, all of my plates grew so my choices of LB, 10% TSA, and AC were fine choices.

  2. I know this is nitpicky, but how did you get such accurate GPS coordinates? I tried using the internet on my phone to find my location, but I think because I use an ‘incognito’ mode it said I was in the outskirts of NYC.

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