Applied Numerical Mathematics 59 (2009) 487–494 www.elsevier.com/locate/apnum A comparison of the dynamics of the structured cell population in virtual and experimental Proteus mirabilis swarm colonies Bruce P. Ayati 1,2 Department of Mathematics, Southern Methodist University, Dallas, TX 75205, USA Available online 22 March 2008 Abstract We present size distributions of Proteus mirabilis cells obtained from age- and space-structured models and simulations of swarm colonies, and compare them to experimental results from the manuscript of Matsuyama et al. [T. Matsuyama, Y. Takagi, Y. Nakagawa, H. Itoh, J. Wakita, M. Matsushita, Dynamic aspects of the structured cell population in a swarming colony of Proteus mirabilis, J. Bacteriol. 182 (2000) 385–393] that considers the evolution of the cell size structure at fixed points in the colony. Our comparison clarifies the importance of including explicit age structure in models of Proteus mirabilis swarm-colony development, as opposed to reaction–diffusion models that homogenize the system in age. We close with a discussion of our scientific computing methodology and how it enables modelers to move beyond reaction–diffusion models of biological pattern formation and include within their models the distributions of important traits of individuals.  2008 IMACS. Published by Elsevier B.V. All rights reserved. MSC: 35M20; 65M20; 65M60; 92C15; 92C17 Keywords: Proteus mirabilis; Size structure; Age structure; Natural age-grid Galerkin methods 1. Introduction We present size distributions of Proteus mirabilis cells obtained from age- and space-structured models and sim- ulations of swarm colony development similar to those presented in [2], and compare them to experimental results from the manuscript of Matsuyama et al. [8] that considers the evolution of the cell size structure at fixed points in the colony. When placed on an agar surface, Proteus form regularly spaced concentric rings in a bulls-eye pattern, with the total time taken to form a ring remaining invariant under changes in the agar or glucose concentration in the substrate [10,11]. These rings are in fact terraces: regions where differences in biomass result in physically different heights. The edges of the terraces create the visual impression of rings. The formation of a terrace occurs in two phases. The first phase, “swarming”, consists of the outward movement of the colony radius. This is followed by “consolidation”, where the outermost edge of the colony, or “front”, is stationary and the terrace height increases. Although the total E-mail address: ayati@math.uiowa.edu. 1 The author was partially supported by the NSF under award number DMS-0609854. 2 Current address: Department of Mathematics, University of Iowa, Iowa City, IA 55242. 0168-9274/$30.00  2008 IMACS. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.apnum.2008.03.023