Trapping and Assembly of Living Colloids at Water/Water Interfaces

TL;DR

This study demonstrates the assembly and trapping of living bacteria and inert colloids at water-water interfaces formed by phase separation, revealing potential for structuring living colloids and studying microbial interactions.

Contribution

It introduces a novel water-water phase separation system that can trap and organize living bacteria and colloids at interfaces, enabling new studies of microbial spatial organization.

Findings

Living bacteria attach to water-water interfaces via capillarity.

Inert colloids are also trapped at the interfaces.

Structures coarsen and degrade over time, showing dynamic behavior.

Abstract

We study the assembly of colloids in a two phase water-water system that provides an environment that can sustain bacteria, providing a new structure with rich potential to confine and structure living colloids. The water-water system, formed via phase separation of a casein and xanthan mixture, forms a 3-D structure of coexisting casein-rich and xanthan-rich phases. Fluorescent labelling and confocal microscopy reveal the attachment of these living colloids, including Escherichia coli and Pseudomonas aeruginosa, at the interface between the two phases. Inert colloids also become trapped at the interfaces, suggesting that the observed attachment can be attributed to capillarity. Over time, these structures coarsen and eventually degrade, illustrating the dynamic nature of these systems. This system lays the foundation for future studies of the interplay of physicochemical properties of the fluid interfaces and bulk phases and microbial responses they provoke to induce complex spatial organization, to study species which occupy distinct niches, and to optimize efficient microbial cross-feeding or protection from competitors.