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Philipps-Universität Marburg
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Abstract
Bacteria are often found in heterogeneous communities organized through physical interaction
with their surrounding environment. Although external physical constraints like shear
flow commonly occur in nature and have been shown to influence the swimming behavior of
active particles, their impact on phenotypically heterogeneous communities remains largely unexplored. Here we investigate the effects of external shear flow - a ubiquitous environmental constraint
- on the spatial organization of heterogeneous communities. We employ bacterial binary mixtures
as a minimal model system, with one component motile and the other non-motile. We
observe that the mixture actively segregates under flow, with the non-motile fraction accumulating
on the “left” side of the channel (i.e. opposite to the vorticity direction) at low shear
rates. Combining experiments and quantitative modeling, we elucidate the purely physical
mechanism responsible for this segregation, which depends on motile cell density and flow rate.
Motile cells drift rheotactically in the vorticity direction along the channel surfaces, generating
a backflow through their slight inward tilt, which produces asymmetric dipolar flows. This
backflow, combined with sedimentation that breaks the symmetry of the system and prevents
non-motile cells from simply following fluid streamlines, leads to lateral accumulation opposite
to the motile cell drift.
Since this segregation emerges over a range of biologically relevant cell densities and shear,
we also investigated the ecological impact of this mechanism. Importantly, we show that this
process is conserved across different bacterial species and can lead to asymmetric formation of
mixed biofilms composed of both motile and non-motile cells.
In summary, these findings underscore the significance of physical interactions, particularly
shear-induced hydrodynamic effects, in shaping the spatial organization and ecological dynamics
of bacterial communities.
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Dates
Created: 2025Issued: 2025-06-04Updated: 2025-06-04
Faculty
Fachbereich Physik
Language
eng
Data types
DoctoralThesis
DDC-Numbers
530
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Di Dio, Giacomo: Active segregation in binary mixtures under flow. : Philipps-Universität Marburg 2025-06-04. DOI: https://doi.org/10.17192/z2025.0119.