Reduced adhesion between cells and substrate confers selective advantage in bacterial colonies

TL;DR

This study demonstrates that reduced cell-surface adhesion in E. coli leads to faster colony expansion on agar, conferring a competitive advantage during spatial growth, independent of growth rate in liquid media.

Contribution

It reveals that mechanical interactions like adhesion influence bacterial colony expansion and fitness, highlighting a novel factor in microbial evolution.

Findings

Shaved strain expands faster on agar than wild type.

Reduced adhesion confers a selective advantage in spatial competition.

Growth rates in liquid media are similar for both strains.

Abstract

Microbial colonies cultured on agar Petri dishes have become a model system to study biological evolution in populations expanding in space. Processes such as clonal segregation and gene surfing have been shown to be affected by interactions between microbial cells and their environment. In this work we investigate the role of mechanical interactions such as cell-surface adhesion. We compare two strains of the bacterium E. coli: a wild-type strain and a "shaved" strain that adheres less to agar. We show that the shaved strain has a selective advantage over the wild type: although both strains grow with the same rate in liquid media, the shaved strain produces colonies that expand faster on agar. This allows the shaved strain outgrow the wild type when both strains compete for space. We hypothesise that, in contrast to a more common scenario in which selective advantage results from increased growth rate, the higher fitness of the shaved strain is caused by reduced adhesion and friction with the agar surface.