Modeling Nisin -Induced Bacterial Fluorescence

1. Modeling Nisin-Induced Bacterial Fluorescence • Key properties of the system • Certain types of bacteria are sensitive to nisin (peptide) • High levels of nisin induce cell death • We can engineer the bacteria to fluoresce (produce GFP) for intermediate levels of nisin Nisin source

2. Modeling Nisin-Induced Bacterial Fluorescence • Experimental setup • We can grow a population of nisinsensitive bacteria in a petri dish • We then place a chemical mask (high nisinconcenration) on top of the cell layer • The nisin diffuses down to the cells and causes fluorescence

3. Modeling Nisin-Induced Bacterial Fluorescence • Modeling diffusion on a computer • Diffusion • Molecules are in constant motion, and they move in all directions • The 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 Model • We can model diffusion on a computer by simulating the movement of each molecule • We model space as a grid of points • Each molecule can move to an adjacent point at each time step with an equal probability • We also incorporate the degradation of molecules by decreasing the total number at each time step

4. Modeling Nisin-Induced Bacterial Fluorescence • Modeling fluorescence on a computer • We model our petri dish and cell layer as a 3-dimensional grid • The top layer of the dish has a high initial nisin concentration in some specific shape • We then simulate diffusion of the nisin down to the cell layer • The cell layer then fluoresces for a certain amount of nisin reaching the bottom layer • If 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 fluoresce

5. Modeling Nisin-Induced Bacterial Fluorescence Diffusion Top View – Initial Setup Indicator Layer