Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session GG09: V: Multicellular Phenomena IFocus
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Sponsoring Units: DBIO Chair: Trung Phan, Yale University Room: Virtual Room 9 |
Monday, March 20, 2023 12:30PM - 12:42PM |
GG09.00001: Visualizing self-generated gradients of chemoattractants by bacteria Trung V Phan, Henry H Mattingly, Jonathan Marvin, Lam Vo, Loren Loogan, Thierry Emonet Chemotactic bacteria such as E. coli can bias their motility in response to local concentrations of chemicals, which are also influenced by the bacteria themselves. Here, we repurpose a fluorescent sensor for the attractant aspartate, developed in the neuroscience community, to visualize self-generated gradients during collective bacterial migration. Our preliminary results are consistent with a Patlak-Keller-Segel-type model of collective migration. However, they also suggest that the presence of multiple attractants, like oxygen, can generate complex, geometry-dependent spatial arrangements of chemotaxis phenotypes. |
Monday, March 20, 2023 12:42PM - 12:54PM |
GG09.00002: What shapes bacterial biofilms? A Physics perspective. Eleonora Secchi Biofilms are aggregates of microorganisms in which cells are embedded in a self-secreted matrix of extracellular polymeric substances (EPS) and are adherent to each other and/or to a surface. The composition of the matrix can vary greatly depending on the microorganisms present and the environmental conditions. However, its functions are universal: the matrix forms the scaffold of the biofilm structure, is responsible for adhesion and cohesion, keeps the cells close, thus favoring interactions, and protects the microbial community from chemical and mechanical insults. Despite its importance, the matrix remains the least understood component of biofilms. |
Monday, March 20, 2023 12:54PM - 1:06PM |
GG09.00003: The role of viscoelasticity of gel-like biofilms on mechanical clearance by immune cells Marilyn J Wells, Vernita Gordon, Isabella C Chavez, Hailey A Currie Biofilms are communities of bacteria which produce a matrix of extracellular polymeric substances (EPS), providing chemical and mechanical protection against antibiotic treatment and phagocytic clearance by immune cells such as neutrophils. Pseudomonas aeruginosa, an opportunistic human pathogen, produces four major EPS components: polymers pel, psl, and alginate, and extracellular DNA (eDNA). Bacterial strains that overproduce alginate, a negatively charged polysaccharide, can interact with divalent cations such as Ca2+ to form a gel-like biofilm structure. Extracellular DNA, also negatively charged, may interact separately with calcium ions to form distinct regions with unique properties within a biofilm. Here we investigate the individual and combined effects of eDNA and alginate on biofilm structure, the impact of polymer-specific enzymes as mechanically compromising agents, and the role of viscoelasticity of calcium-gelled biofilms in the success of mechanical clearance by neutrophils. |
Monday, March 20, 2023 1:06PM - 1:18PM |
GG09.00004: Jump-start and push-start: How signal crosstalk can drive the activation of quorum sensing pathways Joseph Sanders, Hoda Akl, Stephen J Hagen, BingKan Xue Many bacterial species are able to coordinate population-wide phenotypic responses through the exchange of diffusible chemical signals, a behavior known as quorum sensing. A quorum sensing bacterium may employ multiple types of chemical signals and detect them using pathways that are intertwined and crosstalk with each other. While there are many hypotheses for the benefits of using multiple signals, the prevalence of crosstalk and its functional significance are much less understood. Here we explore the effect of intracellular signal crosstalk on quorum sensing using a simple model. Our model captures key aspects of typical quorum sensing pathways, including positive feedback, signal crosstalk at the receptor and promoter levels, and upstream/downstream positioning of different pathways. We find that a variety of behaviors can be tuned by modifying crosstalk and feedback strengths. These include both activation and inhibition of an output by a non-cognate signal, broadening of dynamic range of the outputs, and the ability of the upstream or downstream branches to activate each other. Our findings suggest that signal crosstalk between quorum sensing pathways is not as much a detriment to the flow of information as it is a mechanism that enhances the functional range of the entire regulatory system. The general formulation of crosstalk as synergizing with feedback is readily applicable to a variety of quorum sensing pathways that regulate important phenotypes in microbial communities. |
Monday, March 20, 2023 1:18PM - 1:30PM |
GG09.00005: Computational modelling to predict how extracellular polymeric substances production on biofilm mechanics and detachment Jinju Chen, yuqing xia, Jayathilake Pahala Gedara, Bowen Li, Paolo Zuliani, David Deehan, Jennifer Longyear, Paul Stoodley A wide range of microorganisms produce extracellular polymeric substances (EPS) that are fundamental for microbial life. EPS provides many functions, such as adhesion to surfaces and cohesion to maintain the mechanical stability of the biofilm system. However, it remains elusive how the extracellular polymeric substances production on biofilm mechanics and detachment. It is difficult to quantify EPS by microscopy or chemistry analysis due to the complexity of the chemistry, as well as extraction and purification techniques. Although EPS is complex, the computational modelling could be simplified to represent its physical function rather than the polymer components, hence, to gain better understanding of the contribution of EPS production to biofilm mechanical properties. |
Monday, March 20, 2023 1:30PM - 1:42PM |
GG09.00006: Orientational dynamics of bacterial active fluids Kaiwei Wang The dynamics of bacterial active matter have caught wide attention due to their rich phenomenon in non-equilibrium physics as well as their biological importance. While theoretical models such as polar fluid model describe certain dynamics of bacterial active fluid well, an essential, yet not fully investigated problem is how single cell orientation, the direction of active energy input, distributes and interacts with flow in dense bacterial collective motion, typically induced by viscoelasticity. We build a variable-step multichannel imaging setup for the observation of fluorescent cell body, stained flagellar and phase contrast. We analyze orientation statistics such as polar order and nematic order in bacterial turbulence and channel flow. Our results reveal the intrinsic relation between cell orientation and collective flow and give insights on the viability of potential models. |
Monday, March 20, 2023 1:42PM - 1:54PM Author not Attending |
GG09.00007: Comparison between phase-field model and coarse-grained model for characterizing cell-resolved morphological and mechanical properties in a multicellular system Guoye Guan Embryonic development is a precise and complex process involving the cell morphology and mechanics interacting in space and time. The difficulty in quantitatively acquiring cellular morphological and mechanical information in vivo makes mathematical modeling a challenging problem and impedes model validation. Recently, the three-dimensional time-lapse live imaging and delineated developmental programs in the roundworm Caenorhabditis elegans provide an excellent platform for establishing quantitative models. In this paper, we study two popular computational models for multicellular systems, i.e., the phase-field model and the coarse-grained model, and compare their performance in characterizing the cell morphologies, cell adhesion, and cell stiffness in a real C. elegans embryo. We show that both models can capture cell-cell contact areas and heterogeneous cell adhesion, but only the phase-field model succeeds in inferring the heterogeneous cell stiffness by fitting cell shapes or cell-cell interface curvatures. Moreover, we demonstrate that the phase-field model converges to the coarse-grained model when increasing cell surface tension to dominance, obtaining a distance-dependent isotropic intercellular force. |
Monday, March 20, 2023 1:54PM - 2:30PM |
GG09.00008: Wenying Shou, UCL, wenying.shou@gmail.com Invited Speaker: Wenying Shou
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