Patterns of bacterial motility in microfluidics-confining environments

Abstract

Understanding the motility behavior of bacteria in confining microenvironments, in which they search for available physical space and move in response to stimuli, is important for environmental, food industry, and biomedical applications. We studied the motility of five bacterial species with various sizes and flagellar architectures (Vibrio natriegens, Magnetococcus marinus, Pseudomonas putida, Vibrio fischeri, and Escherichia coli) in microfluidic environments presenting various levels of confinement and geometrical complexity, in the absence of external flow and concentration gradients. When the confinement is moderate, such as in quasi-open spaces with only one limiting wall, and in wide channels, the motility behavior of bacteria with complex flagellar architectures approximately follows the hydrodynamics-based predictions developed for simple monotrichous bacteria. Specifically, V. natriegens and V. fischeri moved parallel to the wall and P. putida and E. coli presented a stable movement parallel to the wall but with incidental wall escape events, while M. marinus exhibited frequent flipping between wall accumulator and wall escaper regimes. Conversely, in tighter confining environments, the motility is governed by the steric interactions between bacteria and the surrounding walls. In mesoscale regions, where the impacts of hydrodynamics and steric interactions overlap, these mechanisms can either push bacteria in the same directions in linear channels, leading to smooth bacterial movement, or they could be oppositional (e.g., in mesoscale-sized meandered channels), leading to chaotic movement and subsequent bacterial trapping. The study provides a methodological template for the design of microfluidic devices for single-cell genomic screening, bacterial entrapment for diagnostics, or biocomputation.

Active transport in complex environments

“…As a result, a growing number of studies describe active particles using run-and-tumble dynamics, and results obtained with bacteria may be applicable to other systems as well. Furthermore, the use of different bacterial species and genetic mutants enables the study of cells of diverse other motility behaviors, shapes, sizes, and surface chemistries, which provides a means to explore a broad range of microswimmer properties 4,6,11,[35][36][37][38][39] . Thus, studies of bacterial transport in complex environments can provide useful fundamental insights into the dynamics of active matter more broadly.…”

“…Furthermore, we note that many bacteria self-propel through other mechanisms, such as by swarming or pulling themselves on surfaces 39 -which potentially enables them to sense mechanical cues on surfaces 42 and thereby respond to a broader range of stimuli. Investigating these other forms of active transport in complex environments is another important area of current research 35 . Finally, motivated by rapid progress in the synthesis of colloidal microswimmers capable of recapitulating many of the features of bacteria 43 , we also integrate references to studies of synthetic microswimmers throughout this section where relevant.…”

Reliable cell retention of mammalian suspension cells in microfluidic cultivation chambers

“…Therefore, design and dimension of supply channel, cultivation chamber, and the chamber's entrance always represents a tradeoff between optimal nutrient supply and sufficient cell retention. Especially for the long-term cultivation of slow growing cells 11 as well as the microfluidic cultivation of motile cells 12 , a reliable cell retention concept is a fundamental requirement to prevent permanent cell loss, which otherwise compromises qualitative and quantitative cell studies.…”

Transitioning to confined spaces impacts bacterial swimming and escape response

“…Physical confinement is one important factor that bacteria commonly face during motility, and confinement effects can profoundly alter their trajectory and migration patterns (17); nevertheless, this factor is explicitly excluded from open-space swimming measurements. Even under moderate levels of confinement, swimming microorganisms have been observed to accumulate near a solid surface, produce circular trajectories, and scatter from obstacles (15,18). Recent work revealed that even between bacteria with similar flagellar organizations, there are large variations in swimming tendencies, especially with regards to surface association and confined movement (18).…”

“…Even under moderate levels of confinement, swimming microorganisms have been observed to accumulate near a solid surface, produce circular trajectories, and scatter from obstacles (15,18). Recent work revealed that even between bacteria with similar flagellar organizations, there are large variations in swimming tendencies, especially with regards to surface association and confined movement (18). The drastic changes in the behavior of confined bacteria as well as the underlying physical mechanisms are not well understood, and highlight that open space swimming characterizations will often not accurately generalize to swimming in other physical conditions.…”