Blog............

This week in class we counted our irradiated soil plates, calculated the colony forming unites per gram of soil, calculated the percent survival rate, took pictures, and chose ten colonies from those plates to restreak onto fresh plates. We had significantly less growth on our irradiated soil plated that were exposed to 5 kGy radiation compared to our unirradiated plates. On our nonirradiated plates we had the most growth and diversity on 1/10 and 1/100 PCA with significant growth up to 10-4. The 1/100 PCA had the highest cfu/g at 2.276 x 104. For our irradiated soil plates we had no growth at all on MA and on PCA we only observed growth on two of the 10-1 plates. Once again the best growth was observed on 1/10 and 1/100 PCA. The most colony forming unites per gram of soil was on the 1/10 PCA at 2.67 x 103. There was less diversity on the irradiated plates which is to be expected since most organisms are sensitive to radiation. Most of the colonies present were pink/orange/peach (see figure below).

We had the greatest percent survival on 1/10 PCA with 18.7% and the lowest on MA with 0%. Overall radiation reduces the number of colonies present as well as the diversity.

We also observed our salt and temperature plates. Surprisingly we had multiple strains that grew very well on 10°C and a couple that grew well on 42°C. We now need to lower and raise the temperatures to conclude the temperature limits in which these organisms can survive. We were not able to record data for strains grown on 1/10 PCA due to contamination of the media. I believe the temperature at which we had the most growth present was 30°C. Not many of our organisms survived on 9% NaCl and only slight growth was observed at 6%. With the exception of a few strains, most of them grew well on both 1% and 3%, with the greatest amount of growth on 1%. In class we also finished streaking our strains onto starch agar that did not get done last week. We also observed our strains in liquid media to check for growth. Growth was present in all the liquid media.

We streaked 10µl of the irradiated liquid soil dilutions onto plates. Finally, we took pictures of our soil plates. Below you can see our 1/10PCA 10-1 plates pre and post irradiation. The colonies present on the unirradiated soil plates were more tan and cream colored while the colonies on the irradiated plate were pink and less plentiful. I believe this is due to the fact that the tan colonies were most likely inhibiting the growth of the pink colonies and once they were killed off by radiation the pink colonies which were radiation resistant were able to grow.

1/10 PCA 10-1 dilution for N97 pre-irradiation:

1/10 PCA 10-1 dilution for N97 post-irradiation (5kGy):