Pili mediated intercellular forces shape heterogeneous bacterial microcolonies prior to multicellular differentiation

TL;DR

This study reveals that in bacterial microcolonies formed by Neisseria gonorrhoeae, cells exhibit heterogeneous motility behaviors driven by mechanical forces, which may lead to bacterial differentiation and biofilm formation.

Contribution

It demonstrates that mechanical interactions cause differential motility within microcolonies, providing new insights into early bacterial community development.

Findings

Cells near the surface are more motile than those at the center.

Mechanical forces can induce heterogeneity in otherwise identical bacteria.

Heterogeneous behavior may be a precursor to biofilm maturation.

Abstract

Microcolonies are aggregates of a few dozen to a few thousand cells exhibited by many bacteria. The formation of microcolonies is a crucial step towards the formation of more mature bacterial communities known as biofilms, but also marks a significant change in bacterial physiology. Within a microcolony, bacteria forgo a single cell lifestyle for a communal lifestyle hallmarked by high cell density and physical interactions between cells potentially altering their behaviour. It is thus crucial to understand how initially identical single cells start to behave differently while assembling in these tight communities. Here we show that cells in the microcolonies formed by the human pathogen Neisseria gonorrhoeae (Ng) present differential motility behaviors within an hour upon colony formation. Observation of merging microcolonies and tracking of single cells within microcolonies reveal a heterogeneous motility behavior: cells close to the surface of the microcolony exhibit a much higher motility compared to cells towards the center. Numerical simulations of a biophysical model for the microcolonies at the single cell level suggest that the emergence of differential behavior within a multicellular microcolony of otherwise identical cells is of mechanical origin. It could suggest a route toward further bacterial differentiation and ultimately mature biofilms.