Bistability in dynamics of worm-microbe interactions

Microbial community composition across nominally identical hosts is highly variable. Sources of this variation are not well understood. To explore the variability, we let the roundworm C. elegans be colonized with single bacterial species from its native gut microbiome. We then observed the temporal dynamics of the bacterial population in many individual hosts. We observe a bistable distributions of population sizes across individual hosts. Our analysis of the temporal evolution of these distributions after perturbations suggests that demographic noise and stationary host heterogeneity alone cannot account for the observed variation. To account for this bistability, we suggest that the bacterial growth rate in the hosts should have multiple stable fixed points or alternatively the host has stochastic state switching.