Spatio-selection in Expanding Bacterial Colonies

TL;DR

This paper investigates how spatial segregation occurs in expanding bacterial colonies, revealing that expansion promotes stable sub-populations and coexistence of mutants, with models showing increased segregation likelihood in dynamic colonies.

Contribution

It introduces models demonstrating that colony expansion enhances segregation and coexistence of mutants, advancing understanding of spatial population dynamics in bacterial growth.

Findings

Expansion increases segregation likelihood in colonies.

Stable sub-populations can form with neutral mutations.

Wild-type and mutant populations can coexist during expansion.

Abstract

Segregation of populations is a key question in evolution theory. One important aspect is the relation between spatial organization and the population's composition. Here we study a specific example -- sectors in expanding bacterial colonies. Such sectors are spatially segregated sub-populations of mutants. The sectors can be seen both in disk-shaped colonies and in branching colonies. We study the sectors using two models we have used in the past to study bacterial colonies -- a continuous reaction-diffusion model with non-linear diffusion and a discrete ``Communicating Walkers'' model. We find that in expanding colonies, and especially in branching colonies, segregation processes are more likely than in a spatially static population. One such process is the establishment of stable sub- population having neutral mutation. Another example is the maintenance of wild-type population along side with sub-population of advantageous mutants. Understanding such processes in bacterial colonies is an important subject by itself, as well as a model system for similar processes in other spreading populations.