Question

3. (5pts)Deinococcusradioduransisafree-living,hardybacteriumthatcansurvivehigh amounts of gamma radiation and other harsh environmental conditions (it has earned the nickname of “Conan the Bacterium”!). A researcher was investigating the possibility of utilizing Deinococcus radiodurans to perform in situ bioremediation of radioactive waste. The first step was to determine the highest level of gamma radiation it could tolerate while maintaining its optimal growth rate. She inoculated D. radiodurans into 3 flasks of media and incubated them at 32oC with shaking. Once the cells entered log phase, the cultures were either not irradiated (flask 1) or radiated continuously at the indicated gray levels (flasks 2 and 3). The turbidity (optical density, OD600) of all flasks was measured at time points, T1 and T2. Here is the data she recorded:

Based on this data, what is the highest level of gamma radiation at which Deinococcus radiodurans could sustain its optimal (non-irradiated) growth rate? SHOW YOUR WORK.

Flask	Radiation (kGy h-1)	OD600 (T1)	OD600 (T2)
1	0	0.055	0.45
2	20	0.015	0.051
3	40	0.19	0.48

Answer 1

Deinococcus radiodurans is an extremophilic gram positive bacteria, which is outgrown by most other bacteria and its number is enhanced only during harsh conditions when other bacteria are reduced. Here the experiment shows an inetresting set of values obtained at different radiation levels, the control flask ( (1) not radiated) one has a turbidity at T1 as 0.055 and at T2 0.45 at OD600. that is the normal growth pattern when not radiated. whereas at 20 kGy/h the cell turbidity reduced to 0.015 and 0.051 at T1 and T2 respectively. This indicates a slight decrease in the growth pattern of the organism but represents their resistance as well. In the higher radiation (40kGy/h) the growth is shown higher than the normal or control rate of the organism which can be a reading that has to be avoided from the calculation as we know that radiations do effect the normal growth pattern. ( the resistance to dessication is one of the parameter for resistance to radiations).

So, here 20 kGy/h can be considered highest level of gamma radiation at which it could sustain its optimal growth rate.