Stochastic assembly produces heterogeneous communities in the Caenorhabditis elegans intestine
(A) Bacterial population dynamics in the worm were modeled using a density-dependent logistic framework, in which worms are colonized at a rate c, bacteria grow and die within the worm at rates b and d, and populations within the worm saturate at a carrying capacity K. All parameters are constant in time and identical for both bacterial strains. (B) A single Gillespie stochastic simulation algorithm (GSSA) run using a low colonization rate (c = 0.1 h-1) is presented to illustrate the different timescales that determine community assembly in this system. In simulations, worms were colonized with a 50/50 mix of identical bacterial strains, shown here as green and red lines. Tgrow is the characteristic timescale of colony growth inside the worm, and Test is the expected time between successful colonization events. (C) Simulations were performed at a range of colonization rates (top panel, c = 10; middle, c = b = 0.6; bottom panel, c = 0.1) to illustrate how the critical ratio Tgrow/Test = c/b controls the transition from bimodal to unimodal community composition. See Methods, S2 and S4 Data for code.