Collective behavior of confined growing bacterial monolayers

Langeslay, Blake

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https://hdl.handle.net/2142/127163 Copy

Description

Title

Collective behavior of confined growing bacterial monolayers

Author(s)

Langeslay, Blake

Issue Date

2024-10-24

Director of Research (if dissertation) or Advisor (if thesis)

Juarez, Gabriel

Doctoral Committee Chair(s)

Dahmen, Karen

Committee Member(s)

• Hilgenfeldt, Sascha
• Kim, Sangjin

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• active matter
• active nematics
• biophysics
• soft matter
• simulation
• collective behavior

Abstract

Active matter and the collective behavior it produces are a critical part of understanding biological systems at scales ranging from flocks of many organisms to sub-cellular processes. Monolayers of growing rod-shaped bacteria, important for their roles in disease and fouling and their general ubiquity, fall into the active nematic class of collective behavior. The structure and motion of these monolayers can be profoundly changed by their confinement geometry. However, understanding of the mechanical sources of these changes are limited, and some important confinement geometries such as curved surfaces are unexplored. We first apply hard-rod molecular dynamics simulations to describe the behavior of monolayers confined to lie on curved surfaces. Monolayers growing to cover the surface of a sphere organize into highly aligned microdomains separated by discontinuous grain boundaries. Microdomain size increases with higher cell aspect ratios but decreases with higher surface curvatures, demonstrating that curvature inhibits cell alignment. Alignment in sphere-confined monolayers affects internal stress distributions, with low-order (misaligned) cells at the boundaries between microdomains experiencing up to 40% more compressive stress than the average. A flat, channel-like confinement geometry can generate similar near-perfect alignment to the interior of a microdomain on a system-wide scale. This results in a laminar state with cells oriented parallel to the channel in discrete rows. Circular obstacles fixed within the channel can disrupt the laminar state (with the size of the disrupted region increasing with obstacle radius). These effects are dependent on particle-scale interactions, specifically the competition between cell anchoring parallel to the surface and alignment to the bulk laminar state. The same competing alignment effects allow larger arc-shaped obstacles to produce and pin +1/2 charge nematic topological defects, while smaller arcs produce less well-defined disorder in their interior. Based on the importance of particle-scale mechanics in channel-confined laminar states, a general model of confinement-induced alignment in growing hard-rod monolayers was developed. Previously, different confinement geometries produced different alignment behaviors that could not be unified under a single model. The strain element model presented here, based on equating the net deformation of the growing monolayer due to flow with the average cell-level deformation due to growth and rotation, correctly predicts the direction of preferential alignment in all three previously studied confinement geometries (unconfined flat growth, channel-confined growth, and inward growth). Additionally, in cases where there is no negative component of the strain rate, the model quantitatively predicts the orientational order within the monolayer. The strain-element model is further tested in the case of a monolayer expanding on a spherical surface from a single initial cell. It correctly predicts that there is no preferential alignment near the initial cell location, and that with increasing distance cells become increasingly aligned radially with respect to the initial cell. Quantitative predictions of order are also correct in the top half of the sphere after correcting for compressibility of the monolayer, but fail in the lower half as there is a negative component of strain rate. This model allows for the development of improved simulation and prediction of cell monolayer behavior in complex environments. Future research directions expanding on this work include investigation of multi-cell rearrangement events in the context of the avalanche universality class, effects of curved surface confinement on genetic mixing within monolayers, and interfacial deformations sourced from the growth of adsorbed bacteria.

Graduation Semester

2024-12

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/127163

Copyright and License Information

Copyright 2024 Blake Langeslay

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