Lubricating Bacteria Model for Branching growth of Bacterial Colonies

TL;DR

This paper introduces a new bacterial colony growth model incorporating lubricant excretion and nonlinear diffusion, explaining branching patterns through simulations and comparison with experiments.

Contribution

It presents an advanced reaction-diffusion model including lubricant dynamics, chemotaxis, and food interaction to better replicate bacterial colony branching patterns.

Findings

Branching patterns depend on lubricant diffusion and emission rates.

Inclusion of chemotaxis improves pattern accuracy.

Model aligns well with experimental colony structures.

Abstract

Various bacterial strains (e.g. strains belonging to the genera Bacillus, Paenibacillus, Serratia and Salmonella) exhibit colonial branching patterns during growth on poor semi-solid substrates. These patterns reflect the bacterial cooperative self-organization. Central part of the cooperation is the collective formation of lubricant on top of the agar which enables the bacteria to swim. Hence it provides the colony means to advance towards the food. One method of modeling the colonial development is via coupled reaction-diffusion equations which describe the time evolution of the bacterial density and the concentrations of the relevant chemical fields. This idea has been pursued by a number of groups. Here we present an additional model which specifically includes an evolution equation for the lubricant excreted by the bacteria. We show that when the diffusion of the fluid is governed by nonlinear diffusion coefficient branching patterns evolves. We study the effect of the rates of emission and decomposition of the lubricant fluid on the observed patterns. The results are compared with experimental observations. We also include fields of chemotactic agents and food chemotaxis and conclude that these features are needed in order to explain the observations.