Spatial drug heterogeneity changes the bacteria persistence in a deleterious diffusive environment

Diffusion and migration play a significant role in microbial communities—shaping, for example, colonization of new environments or the maintenance of spatial structure. In this work, we study the interplay of migration and spatial heterogeneity in an experimental meta-community of E. faecalis, a Gram-positive opportunistic pathogen. When the community is confined to a single habitat surrounded with deleterious boundaries, we find that population survival depends on a growth-rate dependent trade-off between intra-island migration rate and the physical size of the island—a phenomenon we explore by modulating antibiotic concentration within the island. When the island itself is heterogeneous—comprised of spatially patterned patches that support different levels of growth (e.g. different drug concentrations)—the fate of the population becomes dependent on the specific spatial arrangement of patches, even across populations that are identical at a mean-field level. These results are partially captured by simple analytical expressions which we derive using WKB-like approximations to reaction-diffusion models with explicit spatial dependence. Finally, we discuss our ongoing extensions of this approach to investigate increasingly complex, but tunable, experimental communities that can be quantitatively tracked on both ecological and evolutionary timescales.