Microbial transport and dispersion in heterogeneous flows created by pillar arrays

Abstract

Swimming microbes, such as bacteria and algae, live in diverse habitats including soil, seawater, and the human body. The habitats are characterized by structural boundaries and heterogeneous fluid flows. Although in recent decades much progress has been made in understanding the Brownian ratchet motion of microbes and their hydrodynamic interactions with the wall, the complex interplay between the structural and fluid environment with self-propelling microbial motion still remains elusive. Here, we developed a Langevin model to simulate and investigate the transport and dispersion of microbes in periodic pillar arrays. By tracing the spatiotemporal evolution of microbial trajectories, we show that a no-slip pillar surface induces local fluid shear, which redirects microbial movements. In the vicinity of pillars, looping trajectories and slow motion lead to a transient accumulation and sluggish transport of microbes. Several modes of microscopic motion, including swinging, zigzag, and adhesive motion, were observed. In an asymmetric pillar array, adjacent downstream pillars provide geometric guidance such that the microbial population has a deterministic shift perpendicular to the flow direction. Moreover, the effects of the topology of the pillar array, fluid flow properties, and microbial properties on microbial advection and dispersion in a pillar array were quantitatively analyzed. Our results highlight the importance of surrounding structures and flow on microbial transport and distribution, and these should be carefully considered in the study of microbial processes.