Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session N05: Biomaterials and BiofilmsFocus Recordings Available
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Sponsoring Units: DBIO DPOLY DSOFT Chair: Sima Setayeshgar, DBIO Room: McCormick Place W-178A |
Wednesday, March 16, 2022 11:30AM - 11:42AM |
N05.00001: Microrheology of Pseudomonas aeruginosa Biofilms Grown in Wound Beds Gordon Christopher, Vernita Gordon, Kendra P Rumbaugh, Minhaz Rahman, Liyun Wang, Derek F Fleming Pseudomonas aeruginosa biofilms cause persistent, deadly infections in wounds due to their resistance to antibiotic treatments and physical removal. The biofilm’s viscoelasticity plays an important role in enabling it to thrive. Understanding the mechanisms causing biofilm viscoelasticity can aid in designing novel treatments. Furthermore, it is necessary to establish how host proteins, such as collagen, in the wound bed affect viscoelasticity. |
Wednesday, March 16, 2022 11:42AM - 11:54AM |
N05.00002: How Surface Fluidity Impacts the Mechanics of Biofilm Adhesion Katherine E Powell, Jessica L Faubel, Robert E Edmiston, Ellen J Park, Jennifer E Curtis Biofilm communities are notoriously difficult to eliminate once they have adhered to a surface. One approach to suppress biofilm adhesion is to vary the physical properties of the interface, such as the hydrophobicity, charge, or roughness. In this study we explore whether tuning the fluidity of a surface prevents bacterial adhesion by minimizing mechanical cues, thereby blocking the transition from the planktonic bacteria state to the biofilm state. To approach this question, we use a tunable, ultra-thick polymer brush comprised of the polymer hyaluronan. Unlike most polymer brushes used in antimicrobial interfaces, the extraordinary thickness and hence softness of these brushes confers them with fluid-like properties. We will present results on the dependence of biofilm formation versus the brush height ranging from 500 nm to 10 μm. We will then introduce crosslinking methods to tune the brush mechanics, and examine how loss of the brush fluidity and increasing stiffness impacts bacteria adhesion. This study should facilitate insight into the role of surface fluidity in preventing biofilm adhesion, and potentially provide a roadmap for the development of a new class of anti-microbial surface coatings. |
Wednesday, March 16, 2022 11:54AM - 12:06PM |
N05.00003: Bayesian estimation of Pseudomonas aeruginosa viscoelastic properties Mohammad Nooranidoost, NG Cogan, M. Yousuff Hussaini Pseudomonas aeruginosa biofilms are relevant for a variety of disease settings including cystic fibrosis infections. Biofilms are initiated by individual bacteria that undergo a phenotypic switch and produce various types of extracellular polymeric substances such as Psl, Pel, and alginate, which are involved in biofilm development. However, the viscoelastic characteristics of such polysaccharides are not fully explored in literature. For this purpose, we developed a mathematical model to study the rheological behavior of components of three biofilms: P. aeruginosa PAO1, isogenic PAO1ΔwspF, and their mucoid variant PAO1mucA22. Our model consists of a combination of springs and dashpots, which represent the elasticity and viscosity of the substances, respectively. Using a Bayesian inference to estimate these viscoelastic properties, we separate the characteristics and share of each polysaccharide in biofilm structure. A Monte Carlo Markov Chain algorithm is used to estimate these properties in the three biofilm variants, which helps us understand the composition of the biofilm at different stages of their development. This understanding may be used for targeted treatments designed to manipulate the biofilm, making it easier to remove. |
Wednesday, March 16, 2022 12:06PM - 12:42PM |
N05.00004: Microgels from food waste as a tool to understand microbe interactions with hierarchical fiber networks Invited Speaker: Symone L Alexander The gut microbiome can drastically influence mortality and disease progression for end stage kidney disease patients. This is largely due to their production of toxic metabolites known as uremic toxins that originate in the intestinal tract and are absorbed into the blood stream. Recent studies demonstrated that switching patients to a high fiber diet composed of structurally complex foods can completely alter the gut microbiome by promoting beneficial communities and binding and removing toxins. However, this proactive action is not well understood. Our work focuses on demystifying the structure-function relationships of indigestible fibrous biomaterials and the effects of structural hierarchy on toxin binding and microbial interactions. We have developed microgel sorbents from cellulose extracted from food waste with the goal of binding and removing uremic toxins from simulated intestinal conditions. We can tune the hierarchical structure of the cellulose using small molecule additives that control gelation during microgel formation. The resistance of the microgels to digestion were investigated by exposing them to an in vitro digestive system and simultaneously tracking changes in structure and mechanics with time. Finally, the microgels are introduced to microbial communities to understand how structure and mechanics influence microbial interactions and toxin absorption. |
Wednesday, March 16, 2022 12:42PM - 12:54PM |
N05.00005: Live imaging reveals connections between aggregation and competition among a pair of gut bacterial species Deepika Sundarraman, Jarrod Smith, Jade Kast, Karen Guillemin, Raghuveer Parthasarathy The gut microbiome contains hundreds of interacting species that shape host health and development. Despite their significance, the driving forces of community composition remain poorly understood. We focus on the role of physical factors such as spatial structure on inter-species competition, examining a pair of bacterial species native to the zebrafish gut, namely Aeromonas (AE) and Enterobacter (EN), that both form dense aggregates with similar spatial distributions in the intestine. If co-inoculated, EN faces stiff competition that can be tuned in its favor by allowing it to colonize first. A mutant of AE (AE-MB4), revealed by live imaging to consist mostly of planktonic cells rather than aggregates, has a different spatial distribution than the wild type. Despite the reduction in spatial overlap, EN fares even worse in competition with AE-MB4, even when EN is established first. Strikingly, AE-MB4 induces rapid fragmentation of EN aggregates into planktonic individuals with a low growth rate. In the presence of other commensal bacterial species, we observe a dampening of the strong competition, a rescue of the abundance and spatial distribution of EN and aggregation of AE-MB4, suggesting multi-species communities promote co-existence in the larval zebrafish gut. |
Wednesday, March 16, 2022 12:54PM - 1:06PM |
N05.00006: Role of surface interactions in bacterial biofilms Aawaz R Pokhrel, Gabi Steinbach, Siu Lung Ng, Peter Yunker Bacteria often live in surface attached and densely packed communities called biofilms. As they grow, biofilms experience various internal and external forces. For example, the expanding edge of a biofilm experiences friction as it slides across a surface. Within biofilms, mechanical stresses from reproduction push cells apart while intercellular adhesion pulls cells together. These forces are unavoidable; yet it remains unclear how they impact biofilm morphology and the rate of colony expansion, especially for relatively small colonies, which are common in nature, that have not formed wrinkly or rugose morphologies. Here, we use interferometry to look at the three-dimensional surface morphology of biofilms and investigate the effect of different surface friction and adhesive forces. We show that biofilms look and act similar to sessile drops, and, accordingly, that the growth and morphology of surface attached biofilms depends on the balance between these different forces in a manner reminiscent of the Young equation. Finally, we demonstrate the importance of surface-tension-like adhesive forces when separate colonies merge. |
Wednesday, March 16, 2022 1:06PM - 1:18PM |
N05.00007: Rheology of the Environment Regulates Bacterial Growth Anna M Hancock, Sujit Datta Many bacterial communities inhabit complex environments such as soils and biopolymer gels secreted by a host or the bacteria themselves. In these settings, the cellular surroundings frequently have limited nutrient availability, are subjected to flow and mixing, and are rheologically complex. Within the human body alone, the rheological properties of a microbe's environment can change drastically depending on location in the body and host physiology. Here, by probing bacterial growth in hydrogel matrices with defined structural and rheological properties, we demonstrate that the rheology of the environment modulates flow-induced transport of essential nutrients—thereby regulating cellular physiology. Our work thus reveals a new mechanism, beyond mechanosensing, by which mechanics modulates microbial behavior. |
Wednesday, March 16, 2022 1:18PM - 1:30PM |
N05.00008: Self-organized canals enable long range directed material transport in a biofilm Shiqi LIU, Ye Li, Yingdan Zhang, Zi Jing SENG, Haoran Xu, Liang Yang, Yilin Wu Long-range material transport is essential to maintain the physiological functions of multicellular organisms such as animals and plants. Here, we discover that a large-scale and temporally evolving channel system spontaneously develops in the bacterial colony. Fluid flows in the channels support the high-speed (up to 400 micron/s) transport of cells and outer-membrane vesicles, presumably driven by interfacial tension mediated by cell-secreted biosurfactants. Our findings present a unique form of the long-range directed material transport mechanism, advancing the understanding of multicellular microbial systems and suggesting a new principle to design patterns and functions of synthetic microbial communities. |
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