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Modeling took a large place in the project; it was not only used for the characterization of KillerRed and the Voigt plasmids, it was needed for the control of the bacteria’s population. With our device, we cannot control a population of living cells with a simple closed-loop transfer function. First, this is because optical measurements (OD 600 nm or fluorescence) originate from all cells, whether they are alive or not. This fluorescence intensity gives clues about living cell activity and therefore its temporal evolution permits to find the number of living cells, but there is no simple relation between them. Second, there is a large delay between an action and its effect: there are about one or two hours between the onset of illumination and the deceleration of fluorescence. In those conditions, a simple closed-loop transfer function is predictably unstable, and a model predictive control is needed to stabilize the population of living cells.
