Bacterial proliferation pattern formation

TL;DR

This study investigates bacterial pattern formation in controlled environments, revealing how spatial and temporal patterns can be modulated and modeled, providing insights into cellular responses to chemical heterogeneity.

Contribution

It introduces a quantitative experimental approach and a theoretical model to understand bacterial band formation and its modulation by genetic and environmental factors.

Findings

Precise timing and positioning of bacterial bands can be measured.

Different bands show distinct gene expression profiles.

Pattern formation can be modulated independently by environmental and genetic factors.

Abstract

Bacteria can form a great variety of spatially heterogeneous cell density patterns, ranging from simple concentric rings to dynamical spiral waves appearing in growing colonies. These pattern formation phenomena are important as they reflect how cellular processes such as metabolism operate in heterogeneous chemical environments. In the laboratory, they can be studied in simplified set-ups, where spatial gradients of oxygen and nutrients are externally imposed, and cells are immobilized in a gel matrix. An intriguing example, observed in such set-ups over 80 years ago, is the sequential formation of narrow bands of high cell density, taking place even for a clonal population. However, key aspects of the dynamics of band formation remained obscure. Using time-lapse imaging of replicate transparent columns in simplified growth media, we first quantify the precision of the positioning and timing of band formation. We also show that the appearance and position of different bands can be modulated independently. This "modularity" is suggested by the observation that different bands differ in their gene expression, and it is reproduced by a theoretical model based on the existence of internal metabolic states and the induction of a pH gradient. Finally, we can also modify the observed pattern formation by introducing genetic modifications that impair selected metabolic pathways. In our opinion, the possibility of precise measurements and controls, together with the simplicity and richness of the "proliferation pattern formation" phenomenon, can make it a model system to study the response of cellular processes to heterogeneous environments.