The mutation simulation is a simplified version of bacterial mutagenesis experiments. These procedures often involve a number of dilutions in order to calculate data such as viable cell counts and killing curves.
This virtual lab's focus is on analyzing UV light as a mutation inducer. In the simulation, students choose the UV irradiation time and then count the colonies formed on both a control plate and an antibiotic plate.
The UV intensity is not specified; time is the only available independent variable. In addition, this virtual lab is simplified in that the species of bacteria and the type of antibiotic are not specified. The available worksheet (also available as a Google doc) does not specify these factors either, although teachers could certainly develop a version that would take additional details and analysis into account.
The focus on mutation rather than bacteria analysis skills is why this simulation is included under the Evolution section, rather than creating a separate Microbiology section. Having said that, the simulation could be an opportunity to introduce some details of molecular genetics, including base structure, DNA repair functions, and the molecular specifics of UV induced mutation.
UV light is expected to induce mutations, most of which will kill the bacteria. As UV irradiation time increases, the number of surviving bacteria will decrease because UV light causes mutations to DNA. An outcome of UV damage is the fusion of two pyrimidine bases (T or C) to form a pyrimidine dimer. The cell will attempt to repair the damage, but these repairs will not always be successful. Many of the resulting mutations will be fatal or prevent the cells from reproducing. Some mutations will be survivable and may lead to new traits, depending on what gene is mutated.
Different antibiotics affect bacteria in different ways. As such, mutations to a specific gene can lead to resistance to a specific antibiotic. For example, the antibiotic Rifampicin prevents transcription (RNA production) by attaching to bacterial RNA polymerase (the enzyme that makes RNA). A cell that can't make RNA can't make proteins, which will result in the death of the cell. The rpo B gene codes for the part of RNA polymerase that rifampicin binds to. A mutation to the rpo B gene prevents rifampicin from binding and results in rifampicin resistance.
This virtual lab uses a plate with an unspecified antibiotic to select for mutants that are resistant to this antibiotic. While the overall survival rate decreases as UV exposure time increases, the remaining bacteria are more likely to have a mutation resulting in resistance. At a certain point, however, the mutation rate will increase to such a point that survival is unlikely.
As with all the activities available on Biology Simulations, there are random components in calculating the results of the simulation, so while the trends will be the same, each student who performs the virtual lab will get individual results.