The enrichment protocol was successful in isolating our organism of interest but it could be improved.  It failed to take into account the extreme resistance of spores to UV radiation.  We were able to grow spores from swabs of the surfaces inside the UV hood and some of the plates exposed for long durations showed signs of airborne contamination.  Ideally, we would have used Cobalt-60, a γ-ray source, to eliminate spores as well as susceptible vegetative cells.  In the absence of a suitable γ-ray source, we could modify our original enrichment method to reduce the numbers of spores.  Most of the original protocol remains the same.  The changes are to the step when the samples are irradiated.  D. radiodurans recovers from radiation exposure after a few hours so the new protocol would be:

    1.  Expose plates closer to the UV light to decrease the exposure time and reduce contamination.

    2.  Let cells recover for 4 hours.

    3.  Radiate again to kill spores that germinate.

    This cycle can be repeated multiple times.  It also the cultured broth to incubate until there are more D. radiodurans cells to plate while still eliminating susceptible organisms to prevent confluent growth.  

Our experience shows the importance of detailed research and knowing all of the traits about the target organism.  Also, it is not a good idea to pick an organism that takes a week to form colonies.