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Modeling Nisin-Induced Bacterial FluorescenceKey properties of the systemCertain types of bacteria are sensitive to nisin (peptide)High levels of nisin induce cell deathWe can engineer the bacteria to fluoresce (produce GFP) for intermediate levels of nisin1

Nisin sourceModeling Nisin-Induced Bacterial FluorescenceExperimental setupWe can grow a population of nisin sensitive bacteria in a petri dishWe then place a chemical mask (high nisin concenration) on top of the cell layerThe nisin diffuses down to the cells and causes fluorescence2

Modeling Nisin-Induced Bacterial FluorescenceModeling diffusion on a computerDiffusionMolecules are in constant motion, and they move in all directionsThe constant motion tends to eliminate areas of high/low concentration (think about how you can smell someone cooking in a different room gas molecules can diffuse freely throughout your house)Computer ModelWe can model diffusion on a computer by simulating the movement of each moleculeWe model space as a grid of pointsEach molecule can move to an adjacent point at each time step with an equal probabilityWe also incorporate the degradation of molecules by decreasing the total number at each time step

3Modeling Nisin-Induced Bacterial FluorescenceModeling fluorescence on a computerWe model our petri dish and cell layer as a 3-dimensional gridThe top layer of the dish has a high initial nisin concentration in some specific shapeWe then simulate diffusion of the nisin down to the cell layerThe cell layer then fluoresces for a certain amount of nisin reaching the bottom layerIf the nisin concentration is above a certain threshold value, the cells do not fluoresce (because of cell death)If the nisin concentration is below a certain threshold value, the cells are not stimulated to fluoresce4Modeling Nisin-Induced Bacterial Fluorescence5

DiffusionTop View Initial SetupIndicator Layer