The Evolution of Bacteria Repeatedly Exposed to Ultraviolet Radiation

by Brennan Holm, Tyler Lefeber, and Alex Davis
Faculty advisor: Dr. Brian Lenzmeier

One way to control microbial contamination on surfaces and food is through the use of ultraviolet (UV) light. We were interested in determining the long term effects of exposing bacteria repeatedly to UV radiation. We studied three different types of bacteria: Escherichia coli, Bacillus cereus, and Staphylococcus epidermidis. We repeatedly exposed these bacteria to levels of ultraviolet light that killed more than 99% of the cells and then cultured and further exposed the cells that had survived the highest doses. We then quantitatively analyzed the UV sensitivity differences between bacteria that had survived 6 rounds of irradiation and control bacteria that had not been irradiated with any UV light. The goal was to see if the mutated bacteria adapted and became resistant genetically to UV light. The results of these tests will allow us to test the bacteria further and see if the mutations allowing the bacteria to grow after exposure to ultraviolet radiation affected the bacteria in any other ways such as sensitivity to antibiotics or metabolism of different food sources.