158— Optimization and Development of the Luria-Delbrück Experiment for Geneseo Genetics Labs

The classic genetics experiment by Salvador Luria and Max Delbruck showed that mutations are present prior to selection rather than arising in response to selective pressures. In this experiment, we used Escherichia coli as our model organism and the antibiotics streptomycin and rifampicin to show students in a laboratory setting how this hypothesis can be applied. Specifically, we optimized antibiotic concentrations and the amount of bacterial cells to use in order for the activity to run smoothly and consistently in a student laboratory. We found that the ideal conditions are 1000 cells/ml and 25 micrograms/ml of streptomycin. These concentrations showed a larger variance in the individual cultures while the batch culture had a small variance supporting the Luria-Delbruck conclusions. Going further, we completed a variation of the Luria-Delbruck experiment using antibiotic discs. This modification has the potential to show the data in a more hands-on way for the students. In addition, we took samples of the resistant colonies to send for sequencing, and we will test for the presence of common mutations that confer streptomycin resistance.