3rd week of class……

On Monday we restreaked our stock cultures to new plates as they were 2 weeks old. The new plate will be used for setting up tests next week. In addition we transferred each strain to liquid media to determine if the strains grow in liquid media. This is important to know as it will help us prepare a strategy for experimental design of future tests. Dr. Rainey told us that some of the strains are very hydrophobic and so may not grow well or at all in liquid media.

We did serial dilution plating of the same 3 soils samples we plated last week. The samples we plated this time had been exposed to gamma radiation with a total dose of 5kGy. This is to select for ionizing radiation resistant organisms. It is know that members of the genera Geodermatophilus, Blastococcus and Modestobacter are resistant to ionizing radiation as Dr. Rainey isolated some of the strain we are working with from soils he exposed to gamma radiation. We hope that exposing the soils to 5kGy of radiation will reduce the numbers of sensitive organisms and allow the resistant strains to grow and that some of the resistant strains will be strains of the genera we are studying. We just plated the 1/10, 1/100 and 1/1000 dilutions as we expect the numbers to be greatly reduced.

After we did this work in the lab we met with Dr. Rainey in the conference room and he gave us a lecture on the use of ionizing radiation in isolation of interesting organisms. The powerpoint slides that Dr. Rainey talked about are available on the BIOL 4126 Airset page. He also provided us with a paper (via Airset.com) of a paper he published on the topic in Applied and Environmental Microbiology in 2005.


Following the lecture we had a look at our dilution plates from last week when we had plated the soil samples that had not bee irradiated. The results are very interesting in that there are very different looking colonies on the different media. The dilutions are rather similar on each media but the visual diversity is very different. There are many colonies that are orange or pink that could be members of the genera that we are interested in.

On Wednesday this week we did a lot of plate streaking to test the temperature range for growth of our strains. We streaked each strain on a plate of the medium we know it grows best on and incubated the plates at 10, 25, 30, 37 and 42C. The plates will be incubated for 20 days after which we will record the amount of growth present. We did the same for plates that contain 1, 3, 6 and 9 % (w/v) NaCl and incubated them at 25C. For strains that grow on Marine Agar (MA contains ~3% salt already) we used the medium that it grows second best on. For both of these experiments we streaked two strains per plate. We now have hundreds of plates that Dr. Raineya dn Eugene prepared on Tues for the class on Wed.

After the lab work we went into the conference room and as groups went through the papers describing the 3 genera and made a list of possible phenotypic tests that we could do to characterize our strain collections. Dr. Rainey went through a number of these with us and discussed their possible use and answered question we had about the tests. We typed up the list and sent it to Dr. Rainey who will combine them and upload to Airset page.