Early this week................

This week’s class began with a lecture on the effects of gamma radiation and desiccation (less than 5% humidity) on cells. Both of these can induce double strand DNA breaks and oxidize proteins, etc. in cells affected by these two conditions. It is assumed that survival mechanism for desiccation repair is similar to gamma radiation repair based on past experimentation. Our twenty six strains were irradiated with gamma radiation; each strain had a 0, 3, 6, and 16 kGy sample. We spot plated these samples, five samples per plate of optimal media, on dishes labeled with the kGy, date and strain numbers. After streaking the plates (0, 3, and 6 kGy, 16 kGy was not ready), we parafilmed and placed the plates in the desiccators. The second lab of the week involved spot plating, using the same techniques from Monday’s class, the 16kGy samples. We then streaked strains: 27 through 40, 45, 46, 48, and 49, one strain per plate, on their optimal media containing starch. Each plate was labeled with the date and strain number, parafilmed and placed in the incubator. The last task of the day involved plate counting of un-irradiated LRH-01 serial dilution samples made on 1/21. The first dilution was uncountable (> 300 colonies), the second dilution for all media were countable (30- 300 colonies) and the rest of the plates, with the exception of PCA 10-5 (it is hypothesized that all three plates had been contaminated), were not countable (Geodermatophilaceae from the marine agar and plated them on new marine agar plates. We took six suspected Geodermatophilaceae from the 1/10 PCA and plated them on new 1/10 PCA plates. We then took the plate count numbers and determined the colony forming units per gram. The results of the plates can be summarized as follows: there was good serial dilution technique based on the decreasing colony counts and increasing the dilution (except PCA 10-5 plates),

LRH-1 Marine agar -2 dilution:

LRH-1 Marine agar -3 dilution:

LRH-1 Marine agar -4 dilution:

LRH Marine agar -5 dilution:

each media resulted in different colonies (great diversity between plates) being produced which may be the result of the media inhibiting the growth of certain organisms and stimulating the growth of others (based on the variance of colony colors, shapes, etc.).

LRH-1 PCA agar -2 dilution:


LRH-1 1/100 PCA agar -2 dilution: