Sabina Altus, Department of Applied Mathematics, Â鶹¹ÙÍø Multi-Structured Population Dynamics in Cyanobacteria Cyanobacteria are photosynthetic microorganisms with promising applications in renewable energy and agriculture as they are able to convert light energy into more stable forms of chemical energy, such as biomass, as well as kinetic energy. This process occurs within microcompartments, called carboxysomes, which are passed discretely, and persist through many cell cycles before they ultimately disintegrate. Carboxysome productivity is a key factor driving cell growth, and is thought to decrease over time. To investigate this claim, we have developed a multi-structured model for the evolution of a cyanobacteria population. The model is formulated as a partial differential equation wherein demographic parameters describing birth, death, and growth processes are all age-, size-, and carboxysome-age-dependent. Model equations are analyzed along with their associated linear operator and the strongly-continuous semigroup it is shown to generate. Comparisons between experimental data, and the predicted age- and size-distribution of cells will be discussed along with implications for selecting appropriate models for carboxysome degradation.