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Multiscale reorganisation of colloidal aggregation by percolating bacterial networks
Summary
Scientists found that even "non-swimming" bacteria can act like scaffolding, causing tiny particles (colloids) to clump together into branching networks—and in turn, those particles help reinforce the bacterial structure. This matters because similar clumping could happen with microplastics in water or soil, meaning bacteria might influence how microplastic pollution spreads, sinks, or gets trapped in the environment—which could ultimately affect our exposure to these particles through water and food.
Self-assembly in colloidal suspensions emerges from the interplay of local ordering and constraints imposed by the surrounding medium. While motile bacteria are known to alter colloidal dynamics, the influence of non-motile species remains largely unexplored. Here, we study suspensions of colloids and non-motile Comamonas denitrificans sedimenting near the wall and forming percolating networks. Using multiscale structural descriptors, we show that bacteria enhance colloidal aggregation into branch-like clusters. In turn, colloids reinforce bacterial networks by extending their elastic backbone. The analysis of mid-range ordering reveals that, unlike purely colloidal suspensions where ordering propagates across 3-4 neighbour shells, bacterial scaffolds suppress this propagation beyond the first shell. These findings highlight how non-motile bacteria reshape colloidal self-assembly across scales, while providing a quantitative framework for studying complex particle-network interactions. This approach opens pathways to understanding analogous processes in natural systems, including those involving microplastic contaminants.