Fig. 1: Model overview and basic evolutionary dynamics.
From: Bacterial motility can govern the dynamics of antibiotic resistance evolution
a Model description. In the staircase model, bacterial cells (blue and red dots) have a specified position x (of increasing antibiotic concentration) and a genotype g (of increasing resistance). The population adapts to a stable spatial antibiotic gradient as cells migrate, mutate, die and divide at specified stochastic rates. Antibiotics prevent cell division of susceptible genotypes g < x (shaded region under the staircase). b Adaptation process. Bacterial adaptation in the staircase model can be conceptualised as a series of random jumps between locally stable resistance states R that happen at an adaptation rate aR. At a given time, R denotes the genotype of highest resistance in the population, as well as the highest spatial compartment where this genotype can divide. Genotypes g ≤ R are defined as wild-type (blue dots) and genotype g = R + 1 as mutant (red dots). Importantly, in the overlap region x = R + 1, mutant cells can divide but wild-type cells cannot. c Snapshots of the population evolving antibiotic resistance for different motility rates, ν = 0.01/h (low motility) and 1/h (high motility). Shades of grey represent density of cells, where black represents highest density. The adaptive dynamics of bacteria with low (top) and high (bottom) motility is qualitatively different. d Population profiles and fitness along the antibiotic gradient. Different motility regimes affect the distribution of wild-type bacteria along the gradient (blue area), which shapes the fitness of resistant mutants (red bars). Parameters: L = 8, K = 105, r = 1/h, δ = 0.1/h, μb = 10−4/h, μf = 10−7/h.
