Radial and spiral stream formation in Proteus mirabilis

TL;DR

This study investigates the complex radial and spiral streaming patterns of Proteus mirabilis colonies, combining new experiments with a hybrid chemotactic model to explain the underlying motility and pattern formation mechanisms.

Contribution

The paper introduces a hybrid cell-based model incorporating chemotaxis and swimming bias to explain radial and spiral stream formation in Proteus mirabilis colonies.

Findings

Swimmer cells stream inward, forming complex patterns including radial and spiral streams.

Chemotactic response to self-produced chemicals explains radial stream formation.

Incorporating swimming bias predicts the chirality of spiral streams.

Abstract

The enteric bacterium Proteus mirabilis, which is a pathogen that forms biofilms in vivo, can swarm over hard surfaces and form concentric ring patterns in colonies. Colony formation involves two distinct cell types: swarmer cells that dominate near the surface and the leading edge, and swimmer cells that prefer a less viscous medium, but the mechanisms underlying pattern formation are not understood. New experimental investigations reported here show that swimmer cells in the center of the colony stream inward toward the inoculation site and in the process form many complex patterns, including radial and spiral streams, in addition to concentric rings. These new observations suggest that swimmers are motile and that indirect interactions between them are essential in the pattern formation. To explain these observations we develop a hybrid cell-based model that incorporates a chemotactic response of swimmers to a chemical they produce. The model predicts that formation of radial streams can be explained as the modulation of the local attractant concentration by the cells, and that the chirality of the spiral streams can be predicted by incorporating a swimming bias of the cells near the surface of the substrate. The spatial patterns generated from the model are in qualitative agreement with the experimental observations.