Slowdown of the surface diffusion during early stages of bacterial colonization

TL;DR

This study investigates how surface diffusion of cyanobacteria slows down during early colonization stages, linked to extracellular polysaccharide production, and suggests this slowdown may be crucial for biofilm formation.

Contribution

It reveals the time-dependent decrease in diffusion coefficient during bacterial surface colonization and links it to polysaccharide production, providing insights into biofilm development.

Findings

Diffusion coefficient decreases over time during colonization.

Polysaccharide production is essential for the slowdown.

Surface coverage by polysaccharides correlates with diffusion slowdown.

Abstract

We study the surface diffusion of the model cyanobacterium Synechocystis sp. PCC $6803$ during the incipient stages of cell contact with a glass surface in the dilute regime. We observe a twitching motility with alternating immobile "tumble" and mobile "run" periods, resulting in a normal diffusion described by a continuous time random walk with a coefficient of diffusion $D$. Surprisingly, $D$ is found to decrease with time down to a plateau. This is observed only when the cyanobacterial cells are able to produce released extracellular polysaccharides, as shown by a comparative study between the wild-type strain and various polysaccharides-depleted mutants. The analysis of the trajectories taken by the bacterial cells shows that the temporal characteristics of their intermittent motion depend on the instantaneous fraction of visited sites during diffusion. This describes quantitatively the time dependence of $D$, related to the progressive surface coverage by the polysaccharides. The observed slowdown of the surface diffusion may constitute a basic precursor mechanism for microcolony formation and provides clues for controlling biofilm formation.