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.
Highlights
To thrive in environments with diverse geometrical and physical characteristics, from open spaces to constraining environments, motile bacteria have evolved a multitude of propelling mechanisms [17], with flagellum-driven being the most common [18, 19]
To make progress toward a more general understanding of the motility of individual bacterial cells in confining microenvironments, as well as to assess the extent to which the behavior of bacteria with complex architectures can be assimilated with that of the more predictable monotrichous bacteria, the present work investigated the movement of five species (i.e., Vibrio natriegens, Magnetococcus marinus, Pseudomonas putida, Vibrio fischeri, and Escherichia coli) in microfluidic geometries with various levels of confinement and geometrical complexity
In the absence of pressure and concentration gradients, this approach allowed the study of the interaction between hydrodynamics and the steric interactions of bacteria with the walls, unobscured by other external factors
Summary
To thrive in environments with diverse geometrical and physical characteristics, from open spaces to constraining environments, motile bacteria have evolved a multitude of propelling mechanisms [17], with flagellum-driven being the most common [18, 19]. To make progress toward a more general understanding of the motility of individual bacterial cells in confining microenvironments, as well as to assess the extent to which the behavior of bacteria with complex architectures can be assimilated with that of the more predictable monotrichous bacteria, the present work investigated the movement of five species (i.e., Vibrio natriegens, Magnetococcus marinus, Pseudomonas putida, Vibrio fischeri, and Escherichia coli) in microfluidic geometries with various levels of confinement and geometrical complexity.
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