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Huang C, Clark GG, Zaki FR, Won J, Ning R, Boppart SA, Elbanna AE, Nguyen TH. Effects of phosphate and silicate on stiffness and viscoelasticity of mature biofilms developed with simulated drinking water. BIOFOULING 2023; 39:36-46. [PMID: 36847486 PMCID: PMC10065970 DOI: 10.1080/08927014.2023.2177538] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Revised: 01/19/2023] [Accepted: 02/02/2023] [Indexed: 05/21/2023]
Abstract
Biofilms, a porous matrix of cells aggregated with extracellular polymeric substances under the influence of chemical constituents in the feed water, can develop a viscoelastic response to mechanical stresses. In this study, the roles of phosphate and silicate, common additives in corrosion control and meat processing, on the stiffness, viscoelasticity, porous structure networks, and chemical properties of biofilm were investigated. Three-year biofilms on PVC coupons were grown from sand-filtered groundwater with or without one of the non-nutrient (silicate) or nutrient additives (phosphate or phosphate blends). Compared with non-nutrient additives, the phosphate and phosphate-blend additives led to a biofilm with the lowest stiffness, most viscoelastic, and more porous structure, including more connecting throats with greater equivalent radii. The phosphate-based additives also led to more organic species in the biofilm matrix than the silicate additive did. This work demonstrated that nutrient additives could promote biomass accumulation but also reduce mechanical stability.
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Affiliation(s)
- Conghui Huang
- Department of Civil and Environmental Engineering, University of Illinois at Urbana Champaign, Urbana, IL
| | - Gemma G. Clark
- Department of Civil and Environmental Engineering, University of Illinois at Urbana Champaign, Urbana, IL
| | - Farzana R. Zaki
- Beckman Institute for Advanced Science and Technology, 405 North Mathews Avenue, Urbana, Illinois 61801, USA
| | - Jungeun Won
- Beckman Institute for Advanced Science and Technology, 405 North Mathews Avenue, Urbana, Illinois 61801, USA
- Department of Bioengineering, University of Illinois Urbana Champaign, 1304 West Springfield Avenue, Urbana, Illinois 61801, USA
| | - Runsen Ning
- Department of Civil and Environmental Engineering, University of Illinois at Urbana Champaign, Urbana, IL
| | - Stephen A. Boppart
- Beckman Institute for Advanced Science and Technology, 405 North Mathews Avenue, Urbana, Illinois 61801, USA
- Carle Illinois College of Medicine, University of Illinois at Urbana-Champaign, 506 South Mathews Avenue, Urbana, Illinois 61801, USA
- Department of Bioengineering, University of Illinois Urbana Champaign, 1304 West Springfield Avenue, Urbana, Illinois 61801, USA
- Department of Electrical and Computer Engineering, University of Illinois Urbana Champaign, 306 North Wright Street, Urbana, Illinois 61801, USA
| | - Ahmed E. Elbanna
- Department of Civil and Environmental Engineering, University of Illinois at Urbana Champaign, Urbana, IL
| | - Thanh H. Nguyen
- Department of Civil and Environmental Engineering, University of Illinois at Urbana Champaign, Urbana, IL
- Institute of Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois, 61801, United States
- Carle Illinois College of Medicine, University of Illinois at Urbana-Champaign, 506 South Mathews Avenue, Urbana, Illinois 61801, USA
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2
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Zhang J, Wang W, Wang Y, Qiu C, Mao C, Deng S, Wang J. Effect of Cross‐Linked Structures on Mechanical Properties of Styrene‐Butadiene Rubber via Molecular Dynamics Simulation. MACROMOL THEOR SIMUL 2021. [DOI: 10.1002/mats.202100054] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Jing Zhang
- Institute of Industrial Catalysis State Key Laboratory Breeding Base of Green‐Chemical Synthesis Technology College of Chemical Engineering Zhejiang University of Technology Hangzhou 310014 P. R. China
| | - Wei Wang
- Institute of Industrial Catalysis State Key Laboratory Breeding Base of Green‐Chemical Synthesis Technology College of Chemical Engineering Zhejiang University of Technology Hangzhou 310014 P. R. China
| | - Yinbin Wang
- Institute of Industrial Catalysis State Key Laboratory Breeding Base of Green‐Chemical Synthesis Technology College of Chemical Engineering Zhejiang University of Technology Hangzhou 310014 P. R. China
| | - Chenglong Qiu
- Institute of Industrial Catalysis State Key Laboratory Breeding Base of Green‐Chemical Synthesis Technology College of Chemical Engineering Zhejiang University of Technology Hangzhou 310014 P. R. China
| | - Chengli Mao
- Shanghai Xinli Power Equipment Research Institute Shanghai 201100 P. R. China
| | - Shengwei Deng
- Institute of Industrial Catalysis State Key Laboratory Breeding Base of Green‐Chemical Synthesis Technology College of Chemical Engineering Zhejiang University of Technology Hangzhou 310014 P. R. China
| | - Jian‐guo Wang
- Institute of Industrial Catalysis State Key Laboratory Breeding Base of Green‐Chemical Synthesis Technology College of Chemical Engineering Zhejiang University of Technology Hangzhou 310014 P. R. China
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3
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Jana S, Charlton SGV, Eland LE, Burgess JG, Wipat A, Curtis TP, Chen J. Nonlinear rheological characteristics of single species bacterial biofilms. NPJ Biofilms Microbiomes 2020; 6:19. [PMID: 32286319 PMCID: PMC7156450 DOI: 10.1038/s41522-020-0126-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2019] [Accepted: 03/09/2020] [Indexed: 12/15/2022] Open
Abstract
Bacterial biofilms in natural and artificial environments perform a wide array of beneficial or detrimental functions and exhibit resistance to physical as well as chemical perturbations. In dynamic environments, where periodic or aperiodic flows over surfaces are involved, biofilms can be subjected to large shear forces. The ability to withstand these forces, which is often attributed to the resilience of the extracellular matrix. This attribute of the extracellular matrix is referred to as viscoelasticity and is a result of self-assembly and cross-linking of multiple polymeric components that are secreted by the microbes. We aim to understand the viscoelastic characteristic of biofilms subjected to large shear forces by performing Large Amplitude Oscillatory Shear (LAOS) experiments on four species of bacterial biofilms: Bacillus subtilis, Comamonas denitrificans, Pseudomonas fluorescens and Pseudomonas aeruginosa. We find that nonlinear viscoelastic measures such as intracycle strain stiffening and intracycle shear thickening for each of the tested species, exhibit subtle or distinct differences in the plot of strain amplitude versus frequency (Pipkin diagram). The biofilms also exhibit variability in the onset of nonlinear behaviour and energy dissipation characteristics, which could be a result of heterogeneity of the extracellular matrix constituents of the different biofilms. The results provide insight into the nonlinear rheological behaviour of biofilms as they are subjected to large strains or strain rates; a situation that is commonly encountered in nature, but rarely investigated.
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Affiliation(s)
- Saikat Jana
- School of Biomedical Sciences, University of Leeds, Leeds, UK.
- School of Engineering, Newcastle University, Newcastle Upon Tyne, UK.
| | | | - Lucy E Eland
- Interdisciplinary Computing & Complex BioSystems Research Group, School of Computing, Newcastle University, Newcastle upon Tyne, UK
| | - J Grant Burgess
- School of Natural & Environmental Sciences, Newcastle University, Newcastle upon Tyne, UK
| | - Anil Wipat
- Interdisciplinary Computing & Complex BioSystems Research Group, School of Computing, Newcastle University, Newcastle upon Tyne, UK
| | - Thomas P Curtis
- School of Engineering, Newcastle University, Newcastle Upon Tyne, UK
| | - Jinju Chen
- School of Engineering, Newcastle University, Newcastle Upon Tyne, UK.
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4
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Kretschmer M, Lieleg O. Chelate chemistry governs ion-specific stiffening of Bacillus subtilis B-1 and Azotobacter vinelandii biofilms. Biomater Sci 2020; 8:1923-1933. [PMID: 32031543 DOI: 10.1039/c9bm01763a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Unwanted formation of bacterial biofilms can cause problems in both the medical sector and industrial settings. However, removing them from surfaces remains an ongoing challenge since biofilm bacteria efficiently protect themselves from external influences such as mechanical shear forces by embedding themselves into a matrix of extracellular polymeric substances. Here, we discuss microscopic principles, which are responsible for alterations in the viscoelastic properties of biofilms upon contact with metal ions. We suggest that it is a combination of mainly two parameters, that decides if biofilm stiffening occurs or not: the ion size and the detailed configuration of polyanionic macromolecules from the biofilm matrix. Our results provide new insights in the molecular mechanisms that govern the mechanical properties of biofilms. Also, they indicate that hydrogels comprising purified biopolymers can serve as suitable model systems to reproduce certain aspects of biofilm mechanics - provided that the correct biopolymer is chosen.
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Affiliation(s)
- Martin Kretschmer
- Munich School of Bioengineering and Department of Mechanical Engineering, Technical University of Munich, 85748 Garching, Germany.
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5
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Kumar R, Bhowmik S. Quantitative probing of static and dynamic mechanical properties of different bio-filler-reinforced epoxy composite under assorted constraints. Polym Bull (Berl) 2020. [DOI: 10.1007/s00289-020-03156-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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6
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Charlton SGV, White MA, Jana S, Eland LE, Jayathilake PG, Burgess JG, Chen J, Wipat A, Curtis TP. Regulating, Measuring, and Modeling the Viscoelasticity of Bacterial Biofilms. J Bacteriol 2019; 201:e00101-19. [PMID: 31182499 PMCID: PMC6707926 DOI: 10.1128/jb.00101-19] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Biofilms occur in a broad range of environments under heterogeneous physicochemical conditions, such as in bioremediation plants, on surfaces of biomedical implants, and in the lungs of cystic fibrosis patients. In these scenarios, biofilms are subjected to shear forces, but the mechanical integrity of these aggregates often prevents their disruption or dispersal. Biofilms' physical robustness is the result of the multiple biopolymers secreted by constituent microbial cells which are also responsible for numerous biological functions. A better understanding of the role of these biopolymers and their response to dynamic forces is therefore crucial for understanding the interplay between biofilm structure and function. In this paper, we review experimental techniques in rheology, which help quantify the viscoelasticity of biofilms, and modeling approaches from soft matter physics that can assist our understanding of the rheological properties. We describe how these methods could be combined with synthetic biology approaches to control and investigate the effects of secreted polymers on the physical properties of biofilms. We argue that without an integrated approach of the three disciplines, the links between genetics, composition, and interaction of matrix biopolymers and the viscoelastic properties of biofilms will be much harder to uncover.
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Affiliation(s)
- Samuel G V Charlton
- School of Engineering, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Michael A White
- Interdisciplinary Computing & Complex BioSystems Research Group, School of Computing, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Saikat Jana
- School of Engineering, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Lucy E Eland
- Interdisciplinary Computing & Complex BioSystems Research Group, School of Computing, Newcastle University, Newcastle upon Tyne, United Kingdom
| | | | - J Grant Burgess
- School of Natural & Environmental Sciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Jinju Chen
- School of Engineering, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Anil Wipat
- Interdisciplinary Computing & Complex BioSystems Research Group, School of Computing, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Thomas P Curtis
- School of Engineering, Newcastle University, Newcastle upon Tyne, United Kingdom
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7
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Aggarwal S, Gomez-Smith CK, Jeon Y, LaPara TM, Waak MB, Hozalski RM. Effects of Chloramine and Coupon Material on Biofilm Abundance and Community Composition in Bench-Scale Simulated Water Distribution Systems and Comparison with Full-Scale Water Mains. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2018; 52:13077-13088. [PMID: 30351033 DOI: 10.1021/acs.est.8b02607] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The vast majority of bacteria in drinking water distribution systems (DWDSs) reside in biofilms on the interior walls of water mains. Little is known about how water quality conditions affect water-main biofilms because of the inherent limitations in experimenting with drinking water supplies and accessing the water mains for sampling. Bench-scale reactors permit experimentation and ease of biofilm sampling, yet questions remain as to how well biofilms in laboratory reactors represent those on water mains. In this study, the effects of DWDS pipe materials and chloramine residual on biofilms were investigated by cultivating biofilms on cement, polyvinyl chloride, and high density polyethylene coupons in CDC reactors for up to 28 months in the presence of chloraminated or dechlorinated tap water. The bench-scale biofilm microbiomes were then compared with the microbiome on a water main from the full-scale system that supplied the water to the reactors. The presence of a chloramine residual (1.74 ± 0.21 mg/L) suppressed biofilm accumulation and selected for Mycobacterium-like and Sphingopyxis-like operational taxonomic units (OTUs) while the destruction of the chloramine residual resulted in a significant increase in biomass quantity and a shift toward a more diverse community dominated by Nitrospira-like OTUs, which, our results suggest, may be complete ammonia oxidizers (comammox). Coupon material, however, had a relatively minor effect on the abundance and community composition of the biofilm bacteria. Although biofilm communities from the chloraminated water reactor and the water mains shared some dominant populations (namely, Mycobacterium- and Nitrosomonas-like OTUs), the communities were significantly different. This manuscript provides novel insights into the effects of dechlorination and pipe material on biofilm community composition. Furthermore, to our knowledge, it is the first study to compare biofilm in a tap water-fed, bench-scale simulated distribution system to biofilm on water mains from the full-scale system supplying the tap water.
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Affiliation(s)
- Srijan Aggarwal
- Department of Civil and Environmental Engineering , University of Alaska Fairbanks , Fairbanks , Alaska 99775 , United States
| | - C Kimloi Gomez-Smith
- Department of Civil, Environmental, and Geo-Engineering , University of Minnesota , Minneapolis , Minnesota 55455 , United States
| | - Youchul Jeon
- Department of Civil and Environmental Engineering , University of Toledo , Toledo , Ohio 43606-339 , United States
| | - Timothy M LaPara
- Department of Civil, Environmental, and Geo-Engineering , University of Minnesota , Minneapolis , Minnesota 55455 , United States
- BioTechnology Institute , University of Minnesota , St. Paul , Minnesota 55108 , United States
| | - Michael B Waak
- Department of Civil and Environmental Engineering , Norwegian University of Science and Technology , 7491 Trondheim , Norway
| | - Raymond M Hozalski
- Department of Civil, Environmental, and Geo-Engineering , University of Minnesota , Minneapolis , Minnesota 55455 , United States
- BioTechnology Institute , University of Minnesota , St. Paul , Minnesota 55108 , United States
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8
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Joo SH, Aggarwal S. Factors impacting the interactions of engineered nanoparticles with bacterial cells and biofilms: Mechanistic insights and state of knowledge. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2018; 225:62-74. [PMID: 30071367 DOI: 10.1016/j.jenvman.2018.07.084] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2017] [Revised: 03/19/2018] [Accepted: 07/24/2018] [Indexed: 06/08/2023]
Abstract
Since their advent a few decades ago, engineered nanoparticles (ENPs) have been extensively used in consumer products and industrial applications and their use is expected to continue at the rate of thousands of tons per year in the next decade. The widespread use of ENPs poses a potential risk of large scale environmental proliferation of ENPs which can impact and endanger environmental health and safety. Recent studies have shown that microbial biofilms can serve as an important biotic component for partitioning and perhaps storage of ENPs released into aqueous systems. Considering that biofilms can be one of the major sinks for ENPs in the environment, and that the field of biofilms itself is only three to four decades old, there is a recent and growing body of literature investigating the ENP-biofilm interactions. While looking at biofilms, it is imperative to consider the interactions of ENPs with the planktonic microbial cells inhabiting the bulk systems in the vicinity of surface-attached biofilms. In this review article, we attempt to establish the state of current knowledge regarding the interactions of ENPs with bacterial cells and biofilms, identifying key governing factors and interaction mechanisms, as well as prominent knowledge gaps. Since the context of ENP-biofilm interactions can be multifarious-ranging from ecological systems to water and wastewater treatment to dental/medically relevant biofilms- and includes devising novel strategies for biofilm control, we believe this review will serve an interdisciplinary audience. Finally, the article also touches upon the future directions that the research in the ENP-microbial cells/biofilm interactions could take. Continued research in this area is important to not only enhance our scientific knowledge and arsenal for biofilm control, but to also support environmental health while reaping the benefits of the 'nanomaterial revolution'.
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Affiliation(s)
- Sung Hee Joo
- Department of Civil, Architectural, and Environmental Engineering, University of Miami, 1251 Memorial Dr. McArthur Engineering Building, Coral Gables, FL 33146-0630, USA.
| | - Srijan Aggarwal
- Department of Civil and Environmental Engineering, University of Alaska Fairbanks, 1760 Tanana Loop, Duckering Building, Fairbanks, AK 99775, USA
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9
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WANG XIAOLING, ZHAO KAI, ZHAO HUI. FINITE ELEMENT SIMULATION OF BIOFILM VISCOELASTIC BEHAVIOR UNDER VARIOUS LOADINGS. J MECH MED BIOL 2018. [DOI: 10.1142/s0219519418500562] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Experiments showed that biofilms exhibit viscoelasticity under both displacement and stress loadings, irrespective of pellicles at liquid–air interface or biofilms at solid–liquid interface. However, the general theoretical models are lacking inuniformly and quantitatively describing biofilms’ viscoelastic behavior under various loading conditions. We use the linear viscoelastic theory — Generalized Maxwell model to describe the viscoelastic mechanical properties of biofilms, and study the responses of biofilms under different loadings, including various strain/stress loading rates and cyclic loadings, by finite element method. The results can capture the typical viscoelastic characteristics of biofilms, such as creep, hysteresis, energy dissipation and loading rate-dependent behavior. Our work provides a simple viscoelastic model not only for bacterial biofilms but also for other biological materials.
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Affiliation(s)
- XIAOLING WANG
- School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, P. R. China
- School of Engineering and Applied Sciences, Harvard University, 02138 Cambridge MA, USA
| | - KAI ZHAO
- School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, P. R. China
| | - HUI ZHAO
- Beijing Advanced Innovation Center for Imaging Technology, Capital Normal University, No. 105, North Road of West 3rd Ring Road, Haidian District, Beijing 100048, China
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10
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Thomen P, Robert J, Monmeyran A, Bitbol AF, Douarche C, Henry N. Bacterial biofilm under flow: First a physical struggle to stay, then a matter of breathing. PLoS One 2017; 12:e0175197. [PMID: 28403171 PMCID: PMC5389662 DOI: 10.1371/journal.pone.0175197] [Citation(s) in RCA: 70] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Accepted: 03/22/2017] [Indexed: 02/02/2023] Open
Abstract
Bacterial communities attached to surfaces under fluid flow represent a widespread lifestyle of the microbial world. Through shear stress generation and molecular transport regulation, hydrodynamics conveys effects that are very different by nature but strongly coupled. To decipher the influence of these levers on bacterial biofilms immersed in moving fluids, we quantitatively and simultaneously investigated physicochemical and biological properties of the biofilm. We designed a millifluidic setup allowing to control hydrodynamic conditions and to monitor biofilm development in real time using microscope imaging. We also conducted a transcriptomic analysis to detect a potential physiological response to hydrodynamics. We discovered that a threshold value of shear stress determined biofilm settlement, with sub-piconewton forces sufficient to prevent biofilm initiation. As a consequence, distinct hydrodynamic conditions, which set spatial distribution of shear stress, promoted distinct colonization patterns with consequences on the growth mode. However, no direct impact of mechanical forces on biofilm growth rate was observed. Consistently, no mechanosensing gene emerged from our differential transcriptomic analysis comparing distinct hydrodynamic conditions. Instead, we found that hydrodynamic molecular transport crucially impacts biofilm growth by controlling oxygen availability. Our results shed light on biofilm response to hydrodynamics and open new avenues to achieve informed design of fluidic setups for investigating, engineering or fighting adherent communities.
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Affiliation(s)
- Philippe Thomen
- Sorbonne Universités, UPMC Univ Paris 06 & CNRS, UMR 8237, Laboratoire Jean Perrin, Paris, France
| | - Jérôme Robert
- Sorbonne Universités, UPMC Univ Paris 06 & CNRS, UMR 8237, Laboratoire Jean Perrin, Paris, France
| | - Amaury Monmeyran
- Sorbonne Universités, UPMC Univ Paris 06 & CNRS, UMR 8237, Laboratoire Jean Perrin, Paris, France
| | - Anne-Florence Bitbol
- Sorbonne Universités, UPMC Univ Paris 06 & CNRS, UMR 8237, Laboratoire Jean Perrin, Paris, France
| | - Carine Douarche
- Université Paris Sud, UMR 8502, Laboratoire de Physique des Solides, Orsay, France
| | - Nelly Henry
- Sorbonne Universités, UPMC Univ Paris 06 & CNRS, UMR 8237, Laboratoire Jean Perrin, Paris, France
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11
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Barai P, Kumar A, Mukherjee PP. Modeling of Mesoscale Variability in Biofilm Shear Behavior. PLoS One 2016; 11:e0165593. [PMID: 27806068 PMCID: PMC5091762 DOI: 10.1371/journal.pone.0165593] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Accepted: 10/16/2016] [Indexed: 12/24/2022] Open
Abstract
Formation of bacterial colonies as biofilm on the surface/interface of various objects has the potential to impact not only human health and disease but also energy and environmental considerations. Biofilms can be regarded as soft materials, and comprehension of their shear response to external forces is a key element to the fundamental understanding. A mesoscale model has been presented in this article based on digitization of a biofilm microstructure. Its response under externally applied shear load is analyzed. Strain stiffening type behavior is readily observed under high strain loads due to the unfolding of chains within soft polymeric substrate. Sustained shear loading of the biofilm network results in strain localization along the diagonal direction. Rupture of the soft polymeric matrix can potentially reduce the intercellular interaction between the bacterial cells. Evolution of stiffness within the biofilm network under shear reveals two regimes: a) initial increase in stiffness due to strain stiffening of polymer matrix, and b) eventual reduction in stiffness because of tear in polymeric substrate.
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Affiliation(s)
- Pallab Barai
- Department of Mechanical Engineering, Texas A&M University, College Station, Texas, United States of America
| | - Aloke Kumar
- Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, Canada
- * E-mail: (PPM); (AK)
| | - Partha P. Mukherjee
- Department of Mechanical Engineering, Texas A&M University, College Station, Texas, United States of America
- * E-mail: (PPM); (AK)
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12
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Kundukad B, Seviour T, Liang Y, Rice SA, Kjelleberg S, Doyle PS. Mechanical properties of the superficial biofilm layer determine the architecture of biofilms. SOFT MATTER 2016; 12:5718-26. [PMID: 27273453 DOI: 10.1039/c6sm00687f] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Cells in biofilms sense and interact with their environment through the extracellular matrix. The physicochemical properties of the matrix, particularly at the biofilm-environment interface, determine how cells respond to changing conditions. In this study we describe the application of atomic force microscopy and confocal imaging to probe in situ the mechanical properties of these interfacial regions and to elucidate how key matrix components can contribute to the physical sensing by the cells. We describe how the Young's modulus of microcolonies differs according to the size and morphology of microcolonies, as well as the flow rate. The Young's modulus increased as a function of microcolony diameter, which was correlated with the production of the polysaccharide Psl at later stages of maturation for hemispherical or mushroom shaped microcolonies. The Young's modulus of the periphery of the biofilm colony was however independent of the hydrodynamic shear. The morphology of the microcolonies also influenced interfacial or peripheral stiffness. Microcolonies with a diffuse morphology had a lower Young's modulus than isolated, circular ones and this phenomenon was due to a deficiency of Psl. In this way, changes in the specific polysaccharide components imbue the biofilm with distinct physical properties that may modulate the way in which bacteria perceive or respond to their environment. Further, the physical properties of the polysaccharides are closely linked to the specific architectures formed by the developing biofilm.
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Affiliation(s)
- Binu Kundukad
- BioSystems and Micromechanics (BioSym) IRG, Singapore MIT Alliance for Research and Technology (SMART), Singapore
| | - Thomas Seviour
- Singapore Centre on Environmental Life Sciences Engineering, Nanyang Technological University, Singapore
| | - Yang Liang
- Singapore Centre on Environmental Life Sciences Engineering, Nanyang Technological University, Singapore and School of Biological Sciences, Nanyang Technological University, Singapore
| | - Scott A Rice
- Singapore Centre on Environmental Life Sciences Engineering, Nanyang Technological University, Singapore and School of Biological Sciences, Nanyang Technological University, Singapore and Centre for Marine Bio-Innovation and School of Biotechnology and Biomolecular Science, University of New South Wales, Sydney, NSW, Australia
| | - Staffan Kjelleberg
- Singapore Centre on Environmental Life Sciences Engineering, Nanyang Technological University, Singapore and School of Biological Sciences, Nanyang Technological University, Singapore and Centre for Marine Bio-Innovation and School of Biotechnology and Biomolecular Science, University of New South Wales, Sydney, NSW, Australia
| | - Patrick S Doyle
- BioSystems and Micromechanics (BioSym) IRG, Singapore MIT Alliance for Research and Technology (SMART), Singapore and Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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13
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Hollenbeck EC, Douarche C, Allain JM, Roger P, Regeard C, Cegelski L, Fuller GG, Raspaud E. Mechanical Behavior of a Bacillus subtilis Pellicle. J Phys Chem B 2016; 120:6080-8. [PMID: 27046510 DOI: 10.1021/acs.jpcb.6b02074] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Bacterial biofilms consist of a complex network of biopolymers embedded with microorganisms, and together these components form a physically robust structure that enables bacteria to grow in a protected environment. This structure can help unwanted biofilms persist in situations ranging from chronic infection to the biofouling of industrial equipment, but under certain circumstances it can allow the biofilm to disperse and colonize new niches. Mechanical properties are therefore a key aspect of biofilm life. In light of the recently discovered growth-induced compressive stress present within a biofilm, we studied the mechanical behavior of Bacillus subtilis pellicles, or biofilms at the air-liquid interface, and tracked simultaneously the force response and macroscopic structural changes during elongational deformations. We observed that pellicles behaved viscoelastically in response to small deformations, such that the growth-induced compressive stress was still present, and viscoplastically at large deformations, when the pellicles were under tension. In addition, by using particle imaging velocimetry we found that the pellicle deformations were nonaffine, indicating heterogeneous mechanical properties with the pellicle being more pliable near attachment surfaces. Overall, our results indicate that we must consider not only the viscoelastic but also the viscoplastic and mechanically heterogeneous nature of these structures to understand biofilm dispersal and removal.
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Affiliation(s)
- Emily C Hollenbeck
- Department of Chemical Engineering, Stanford University , Stanford, California 94305, United States
| | - Carine Douarche
- Laboratoire de Physique des Solides, CNRS, Université Paris-Sud, Université Paris-Saclay , Orsay, France
| | - Jean-Marc Allain
- Laboratoire de Mécanique des Solides, École Polytechnique, CNRS, Université Paris-Saclay , Palaiseau, France
| | - Philippe Roger
- Institut de Chimie Moléculaire et des Matériaux d'Orsay (ICMMO), CNRS, Université Paris-Sud, Université Paris-Saclay , Orsay, France
| | - Christophe Regeard
- Institut de Biologie Intégrative de la Cellule (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay , Gif sur Yvette, France
| | - Lynette Cegelski
- Department of Chemistry, Stanford University , Stanford, California 94305, United States
| | - Gerald G Fuller
- Department of Chemical Engineering, Stanford University , Stanford, California 94305, United States
| | - Eric Raspaud
- Laboratoire de Physique des Solides, CNRS, Université Paris-Sud, Université Paris-Saclay , Orsay, France
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Biomechanical Analysis of Infectious Biofilms. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 915:99-114. [PMID: 27193540 DOI: 10.1007/978-3-319-32189-9_8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The removal of infectious biofilms from tissues or implanted devices and their transmission through fluid transport systems depends in part of the mechanical properties of their polymeric matrix. Linking the various physical and chemical microscopic interactions to macroscopic deformation and failure modes promises to unveil design principles for novel therapeutic strategies targeting biofilm eradication, and provide a predictive capability to accelerate the development of devices, water lines, etc, that minimise microbial dispersal. Here, our current understanding of biofilm mechanics is appraised from the perspective of biophysics , with an emphasis on constitutive modelling that has been highly successful in soft matter. Fitting rheometric data to viscoelastic models has quantified linear and nonlinear stress relaxation mechanisms, how they vary between species and environments, and how candidate chemical treatments alter the mechanical response. The rich interplay between growth, mechanics and hydrodynamics is just becoming amenable to computational modelling and promises to provide unprecedented characterisation of infectious biofilms in their native state.
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15
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Interfacial separation of a mature biofilm from a glass surface - A combined experimental and cohesive zone modelling approach. J Mech Behav Biomed Mater 2015; 54:205-18. [PMID: 26474034 DOI: 10.1016/j.jmbbm.2015.09.013] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Revised: 09/11/2015] [Accepted: 09/13/2015] [Indexed: 11/20/2022]
Abstract
A good understanding of the mechanical stability of biofilms is essential for biofouling management, particularly when mechanical forces are used. Previous biofilm studies lack a damage-based theoretical model to describe the biofilm separation from a surface. The purpose of the current study was to investigate the interfacial separation of a mature biofilm from a rigid glass substrate using a combined experimental and numerical modelling approach. In the current work, the biofilm-glass interfacial separation process was investigated under tensile and shear stresses at the macroscale level, known as modes I and II failure mechanisms respectively. The numerical simulations were performed using a Finite Volume (FV)-based simulation package (OpenFOAM®) to predict the separation initiation using the cohesive zone model (CZM). Atomic force microscopy (AFM)-based retraction curve was used to obtain the separation properties between the biofilm and glass colloid at microscale level, where the CZM parameters were estimated using the Johnson-Kendall-Roberts (JKR) model. In this study CZM is introduced as a reliable method for the investigation of interfacial separation between a biofilm and rigid substrate, in which a high local stress at the interface edge acts as an ultimate stress at the crack tip.This study demonstrated that the total interfacial failure energy measured at the macroscale, was significantly higher than the pure interfacial separation energy obtained by AFM at the microscale, indicating a highly ductile deformation behaviour within the bulk biofilm matrix. The results of this study can significantly contribute to the understanding of biofilm detachments.
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16
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Grumbein S, Opitz M, Lieleg O. Selected metal ions protect Bacillus subtilis biofilms from erosion. Metallomics 2015; 6:1441-50. [PMID: 24770836 DOI: 10.1039/c4mt00049h] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Many problems caused by bacterial biofilms can be traced back to their high resilience towards chemical perturbations and their extraordinary sturdiness towards mechanical forces. However, the molecular mechanisms that link the mechanical properties of a biofilm with the ability of bacteria to survive in different chemical environments remain enigmatic. Here, we study the erosion stability of Bacillus subtilis (B. subtilis) biofilms in the presence of different chemical environments. We find that these biofilms can utilize the absorption of certain metal ions such as Cu(2+), Zn(2+), Fe(2+), Fe(3+) and Al(3+) into the biofilm matrix to avoid erosion by shear forces. Interestingly, many of these metal ions are toxic for planktonic B. subtilis bacteria. However, their toxic activity is suppressed when the ions are absorbed into the biofilm matrix. Our experiments clearly demonstrate that the biofilm matrix has to fulfill a dual function, i.e. regulating both the mechanical properties of the biofilm and providing a selective barrier towards toxic chemicals.
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Affiliation(s)
- S Grumbein
- Zentralinstitut für Medizintechnik, Technische Universität München, 85748 Garching, Germany.
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17
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Pavlovsky L, Sturtevant RA, Younger JG, Solomon MJ. Effects of temperature on the morphological, polymeric, and mechanical properties of Staphylococcus epidermidis bacterial biofilms. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:2036-42. [PMID: 25602470 PMCID: PMC5563478 DOI: 10.1021/la5044156] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Changes in temperature were found to affect the morphology, cell viability, and mechanical properties of Staphylococcus epidermidis bacterial biofilms. S. epidermidis biofilms are commonly associated with hospital-acquired medical device infections. We observed the effect of heat treatment on three physical properties of the biofilms: the bacterial cell morphology and viability, the polymeric properties of the extracellular polymeric substance (EPS), and the rheological properties of the bulk biofilm. After application of a 1 h heat treatment at 45 °C, cell reproduction had ceased, and at 60 °C, cell viability was significantly reduced. Size exclusion chromatography was used to fractionate the extracellular polymeric substance (EPS) based on size. Chemical analysis of each fraction showed that the relative concentrations of the polysaccharide, protein, and DNA components of the EPS were unchanged by the heat treatment at 45 and 60 °C. The results suggest that the EPS molecular constituents are not significantly degraded by the temperature treatment. However, some aggregation on the scale of 100 nm was found by dynamic light scattering at 60 °C. Finally, relative to control biofilms maintained at 37 °C, we observed an order of magnitude reduction in the biofilm yield stress after 60 °C temperature treatment. No such difference was found for treatment at 45 °C. From these results, we conclude that the yield stress of bacterial biofilms is temperature-sensitive and that this sensitivity is correlated with cell viability. The observed significant decrease in yield stress with temperature suggests a means to weaken the mechanical integrity of S. epidermidis biofilms with applications in areas such as the treatment of biofilm-infected medical devices.
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Affiliation(s)
- Leonid Pavlovsky
- Department of Chemical Engineering and ‡Department of Emergency Medicine, University of Michigan , Ann Arbor, Michigan 48109, United States
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18
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Karimi A, Karig D, Kumar A, Ardekani AM. Interplay of physical mechanisms and biofilm processes: review of microfluidic methods. LAB ON A CHIP 2015; 15:23-42. [PMID: 25385289 PMCID: PMC4261921 DOI: 10.1039/c4lc01095g] [Citation(s) in RCA: 85] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Bacteria in natural and artificial environments often reside in self-organized, integrated communities known as biofilms. Biofilms are highly structured entities consisting of bacterial cells embedded in a matrix of self-produced extracellular polymeric substances (EPS). The EPS matrix acts like a biological 'glue' enabling microbes to adhere to and colonize a wide range of surfaces. Once integrated into biofilms, bacterial cells can withstand various forms of stress such as antibiotics, hydrodynamic shear and other environmental challenges. Because of this, biofilms of pathogenic bacteria can be a significant health hazard often leading to recurrent infections. Biofilms can also lead to clogging and material degradation; on the other hand they are an integral part of various environmental processes such as carbon sequestration and nitrogen cycles. There are several determinants of biofilm morphology and dynamics, including the genotypic and phenotypic states of constituent cells and various environmental conditions. Here, we present an overview of the role of relevant physical processes in biofilm formation, including propulsion mechanisms, hydrodynamic effects, and transport of quorum sensing signals. We also provide a survey of microfluidic techniques utilized to unravel the associated physical mechanisms. Further, we discuss the future research areas for exploring new ways to extend the scope of the microfluidic approach in biofilm studies.
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Affiliation(s)
- A. Karimi
- Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA 02115
- Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556, USA
| | - D. Karig
- Research and Exploratory Development Department, Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723
| | - A. Kumar
- Department of Mechanical Engineering, University of Alberta, Edmonton, Canada AB T6G 2G8
| | - A. M. Ardekani
- School of Mechanical Engineering, Purdue University, West Lafayette, IN 47907
- Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556, USA
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19
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Safari A, Tukovic Z, Walter M, Casey E, Ivankovic A. Mechanical properties of a mature biofilm from a wastewater system: from microscale to macroscale level. BIOFOULING 2015; 31:651-64. [PMID: 26371590 DOI: 10.1080/08927014.2015.1075981] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
A fundamental understanding of biofilm mechanical stability is critical in order to describe detachment and develop biofouling control strategies. It is thus important to characterise the elastic deformation and flow behaviour of the biofilm under different modes of applied force. In this study, the mechanical properties of a mature wastewater biofilm were investigated with methods including macroscale compression and microscale indentation using atomic force microscopy (AFM). The mature biofilm was found to be mechanically isotropic at the macroscale level as its mechanical properties did not depend on the scales and modes of loading. However, the biofilm showed a tendency for mechanical inhomogeneity at the microscale level as indentation progressed deeper into the matrix. Moreover, it was observed that the adhesion force had a significant influence on the elastic properties of the biofilm at the surface, subjected to microscale tensile loading. These results are expected to inform a damage-based model for biofilm detachment.
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Affiliation(s)
- Ashkan Safari
- a School of Electrical, Electronic and Mechanical Engineering , University College Dublin (UCD) , Dublin , Ireland
| | - Zeljko Tukovic
- b Faculty of Mechanical Engineering and Naval Architecture , University of Zagreb , Zagreb , Croatia
| | - Maik Walter
- c School of Chemical and Bioprocess Engineering , University College Dublin (UCD) , Dublin , Ireland
| | - Eoin Casey
- c School of Chemical and Bioprocess Engineering , University College Dublin (UCD) , Dublin , Ireland
| | - Alojz Ivankovic
- a School of Electrical, Electronic and Mechanical Engineering , University College Dublin (UCD) , Dublin , Ireland
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Levering V, Wang Q, Shivapooja P, Zhao X, López GP. Soft robotic concepts in catheter design: an on-demand fouling-release urinary catheter. Adv Healthc Mater 2014; 3:1588-96. [PMID: 24668920 DOI: 10.1002/adhm.201400035] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Revised: 02/24/2014] [Indexed: 01/12/2023]
Abstract
Infectious biofilms are problematic in many healthcare-related devices and are especially challenging and ubiquitous in urinary catheters. This report presents an on-demand fouling-release methodology to mechanically disrupt and remove biofilms, and proposes this method for the active removal of infectious biofilms from the previously inaccessible main drainage lumen of urinary catheters. Mature Proteus mirabilis crystalline biofilms detach from silicone elastomer substrates upon application of strain to the substrate, and increasing the strain rate increases biofilm detachment. The study presents a quantitative relationship between applied strain rate and biofilm debonding through an analysis of biofilm segment length and the driving force for debonding. Based on this mechanism, hydraulic and pneumatic elastomer actuation is used to achieve surface strain selectively within the lumen of prototypes of sections of a fouling-release urinary catheter. Proof-of-concept prototypes of sections of active, fouling-release catheters are constructed using techniques typical to soft robotics including 3D printing and replica molding, and those prototypes demonstrate release of mature P. mirabilis crystalline biofilms (e.g., ≈90%) from strained surfaces. These results provide a basis for the development of a new urinary catheter technology in which infectious biofilms are effectively managed through new methods that are entirely complementary to existing approaches.
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Affiliation(s)
- Vrad Levering
- Research Triangle MRSEC; Duke University; Durham NC 27708 USA
- Department of Biomedical Engineering; Duke University; Durham NC 27708 USA
| | - Qiming Wang
- Research Triangle MRSEC; Duke University; Durham NC 27708 USA
- Department of Mechanical Engineering and Materials Science; Duke University; Durham NC 27708 USA
| | | | - Xuanhe Zhao
- Department of Biomedical Engineering; Duke University; Durham NC 27708 USA
- Department of Mechanical Engineering and Materials Science; Duke University; Durham NC 27708 USA
| | - Gabriel P. López
- Research Triangle MRSEC; Duke University; Durham NC 27708 USA
- Department of Biomedical Engineering; Duke University; Durham NC 27708 USA
- Department of Mechanical Engineering and Materials Science; Duke University; Durham NC 27708 USA
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21
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Galy O, Zrelli K, Latour-Lambert P, Kirwan L, Henry N. Remote magnetic actuation of micrometric probes for in situ 3D mapping of bacterial biofilm physical properties. J Vis Exp 2014. [PMID: 24837001 DOI: 10.3791/50857] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Bacterial adhesion and growth on interfaces lead to the formation of three-dimensional heterogeneous structures so-called biofilms. The cells dwelling in these structures are held together by physical interactions mediated by a network of extracellular polymeric substances. Bacterial biofilms impact many human activities and the understanding of their properties is crucial for a better control of their development - maintenance or eradication - depending on their adverse or beneficial outcome. This paper describes a novel methodology aiming to measure in situ the local physical properties of the biofilm that had been, until now, examined only from a macroscopic and homogeneous material perspective. The experiment described here involves introducing magnetic particles into a growing biofilm to seed local probes that can be remotely actuated without disturbing the structural properties of the biofilm. Dedicated magnetic tweezers were developed to exert a defined force on each particle embedded in the biofilm. The setup is mounted on the stage of a microscope to enable the recording of time-lapse images of the particle-pulling period. The particle trajectories are then extracted from the pulling sequence and the local viscoelastic parameters are derived from each particle displacement curve, thereby providing the 3D-spatial distribution of the parameters. Gaining insights into the biofilm mechanical profile is essential from an engineer's point of view for biofilm control purposes but also from a fundamental perspective to clarify the relationship between the architectural properties and the specific biology of these structures.
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Affiliation(s)
- Olivier Galy
- Physicochime Curie, CNRS UMR 168, Institut Curie, Sorbonne Universités, UPMC
| | - Kais Zrelli
- Physicochime Curie, CNRS UMR 168, Institut Curie, Sorbonne Universités, UPMC
| | | | - Lyndsey Kirwan
- Laboratoire Jean Perrin, CNRS UMR 8237, Sorbonne Universités, UPMC
| | - Nelly Henry
- Physicochime Curie, CNRS UMR 168, Institut Curie, Sorbonne Universités, UPMC; Laboratoire Jean Perrin, CNRS UMR 8237, Sorbonne Universités, UPMC;
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22
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Pavlovsky L, Younger JG, Solomon MJ. In situ rheology of Staphylococcus epidermidis bacterial biofilms. SOFT MATTER 2013; 9:122-131. [PMID: 25544855 PMCID: PMC4276346 DOI: 10.1039/c2sm27005f] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
We developed a method to grow Staphylococcus epidermidis bacterial biofilms and characterize their rheological properties in situ in a continuously fed bioreactor incorporated into a parallel plate rheometer. The temperature and shear rates of growth modeled bloodstream conditions, a common site of S. epidermidis infection. We measured the linear elastic (G') and viscous moduli (G″) of the material using small-amplitude oscillatory rheology and the yield stress using non-linear creep rheology. We found that the elastic and viscous moduli of the S. epidermidis biofilm were 11 ± 3 Pa and 1.9 ± 0.5 Pa at a frequency of 1 Hz (6.283 rad per s) and that the yield stress was approximately 20 Pa. We modeled the linear creep response of the biofilm using a Jeffreys model and found that S. epidermidis has a characteristic relaxation time of approximately 750 seconds and a linear creep viscosity of 3000 Pa s. The effects on the linear viscoelastic moduli of environmental stressors, such as NaCl concentration and extremes of temperature, were also studied. We found a non-monotonic relationship between moduli and NaCl concentrations, with the stiffest material properties found at human physiological concentrations (135 mM). Temperature dependent rheology showed hysteresis in the moduli when heated and cooled between 5 °C and 60 °C. Through these experiments, we demonstrated that biofilms are rheologically complex materials that can be characterized by a combination of low modulus (~10 Pa), long relaxation time (~103 seconds), and a finite yield stress (20 Pa). This suggests that biofilms should be viewed as soft viscoelastic solids whose properties are determined in part by local environmental conditions. The in situ growth method introduced here can be adapted to a wide range of biofilm systems and applied over a broad spectrum of rheological and environmental conditions because the technique minimizes the risk of irreversible, non-linear deformation of the microbial specimen before analysis.
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Affiliation(s)
- Leonid Pavlovsky
- Department of Chemical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA. Fax: +1 734 763 0459; Tel: +1 734 764 3119
| | - John G. Younger
- Department of Emergency Medicine, University of Michigan, Ann Arbor, MI, 48109, USA. Tel: +1 734 647 7564
- Biointerfaces Institute, University of Michigan, Ann Arbor, MI, 48109, USA
- Michigan Center for Integrative Research in Critical Care, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Michael J. Solomon
- Department of Chemical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA. Fax: +1 734 763 0459; Tel: +1 734 764 3119
- Biointerfaces Institute, University of Michigan, Ann Arbor, MI, 48109, USA
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