Where did you obtain your soil sample?

My soil sample was collected under a tree on the North side of the Rugby field at Union. I dug down underneath a layer of mulch to reach the soil, which was held together by lots of roots. It was a dark, damp soil and contained wood chips from the relatively fresh mulch above.

Why did you choose this location?

Before inauguration, I saw groundskeepers putting fresh mulch around the trees and bushes around campus. I figured these frequently cared for soils might contain diverse microbe populations because of the recent layers of material deposited upon them. Part of the reason I was attracted to this soil was because its dark color reminded me of topsoil which I think of as being fertile with rich microbial life.

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

Hopefully some. It is encouraging that Penicillin-resembling molds grew on my PDA plates because if this antibiotic producing fungus lives in the soil, then possibly microbes that produce antibiotics will be selected for. The dark colour of the soil leaves me hoping for diverse microbial life some of which could be antibiotic producing. However, the fact that it was damp implies that some anaerobic microbes most likely were present, and I don’t expect these will grow on the plates much.  

Have you initial observations supported this?

Yes, lots of diverse colonies grew even though plates were mostly filled with one or two predominant types of colonies. PDA plates grew mold, R2A plates grew swarmers and mycoides, and LB plates grew big white colonies, but all plates had some unique colonies and even ones with rings of no growth around them indicating inhibition of other colonies. One small white colony with a distinctive texture on an R2A plate showed clear inhibition of a larger colony, but didn’t seem to inhibit another smaller colony nearby. I patched any colony that seemed to show inhibition and also any colony that looked unique, so hopefully some of these patched colonies turn out to be antibiotic producers. I calculated 170 cfu’s per gram from the 10^-3 dilution sample.

What media did you choose? How did you sample differ on the different media?

I chose PDA, R2A and LB because I wanted to use less nutritious media in addition to LB. In PDA and R2A, my dilutions were 10^0, 10^-1, and 10^-2, while in LB my dilutions were 10^-1, 10^-2, and 10^-3 because I didn’t want the LB plates to be too crowded nor the less nutritious plates to lack growth. Plates with higher dilutions showed less growth, but seemed more diverse – for example the 10^-3 dilution for the LB was the most diverse plate I had. The distinctions between dilutions blurred with time – by 6 days of growth all plates had a lot going on. PDA plates grew SERIOUS mold which resembled Penicillin producing molds. I even had to seal these plates up so I couldn’t patch much from these. This mold probably grew because of the mulch content in the soil. The R2A plates were overrun by small pinpoint colonies and swarmers, but this was less apparent in the most dilute sample. These also showed mycoides. LB plates were the most diverse and less dominated by only one or two types of colonies (although a large white type of bacteria enjoyed growth). 170 cfu/g in largest dilution. Most varied pigments showed up in LB – orange, brown, white, yellow. LB had the most colonies yielding inhibition.

What dilutions? (see above)

Will you need to redo any?

All plates had too many colonies to count, except LB at 10^-3 dilution which was also the most diverse plate. Thus, I plated two of each media at this dilution in hopes that I will be able to get CFU counts and more inhibiting colonies. At two days growth, R2A was more diverse than LB or PDA – interesting! Also, each plate (regardless media) showed around 40 colonies at 2 days growth.