Description
Transport of microorganisms is an integral part of many natural and industrial processes, such as energy storage, bacterial infections, and soil remediation. With almost half of the living microorganisms living in porous media, the interplay between bacterial motility, and flow-induced transport identifies the niche selection and colonization. To do so, cells need to explore the widest space possible to increase their chance of finding a suitable condition. This is while, increasing the cell density will increase the chance to occupy a space. For survival, environmental cells need to find a balance between dispersion and densification.
Previous researches have shown the densification of cells in 2D porous media. However, the environmental habitat of bacteria is a 3D space, which recently has been shown that has a chaotic dispersal behavior. This would raise the question on how does chaotic advection (i) smears the densification pattern and (ii) dictates the lateral dispersal of cells?
Here, we explore experimentally the various regimes over which chaotic advection and cell motility control both the fine structure of densification and the large-scale transport of swimming cells in porous media flows. To do this we use a versatile 2.5D micromodel which combines the precise control of the microstructure allowed by standard lithography techniques while emulating the hydrological hallmarks of 3D porous media flows. Surprisingly, we find that densification and dispersion can coexist—cells maintain local aggregation even as chaotic advection drives maximal lateral spreading. These findings provide new insights for predicting microbial colonization in subsurface flows and optimizing bacterial transport in bioremediation and bioreactor design.