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


Wolfram Poenisch, Khaled Alzurqa, Kelly Eckenrode, Hadi Nasrollahi, Christoph A. Weber, Vasily Zaburdaev, and Nicolas Biais. Submitted. “Pili mediated intercellular forces shape heterogeneous bacterial microcolonies prior to multicellular differentiation”.


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 leading to differentiation. 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 of detail suggest that mechanical forces exerted by the bacterial cells are sufficient to generate the observed heterogeneous motility. Further corroborating this idea, bacteria lacking the ability to exert forces on their surroundings segregate on the outside of microcolonies as predicted by the model. This emergence of differential behavior within a multicellular microcolony of otherwise identical cells is thus mainly of mechanical origin and is likely the first step toward further bacterial differentiation and ultimately mature biofilms.