1
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Zinßmeister D, Leibovitch M, Natan E, Turjeman S, Koren O, Travisano M, Vortman Y, Baselga-Cervera B. Detecting life by behavior, the overlooked sensitivity of behavioral assays. Sci Rep 2024; 14:18904. [PMID: 39143360 PMCID: PMC11324786 DOI: 10.1038/s41598-024-69942-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2024] [Accepted: 08/12/2024] [Indexed: 08/16/2024] Open
Abstract
Detecting life has driven research and exploration for centuries, but recent attempts to compile and generate a framework that summarizes life features, aimed to develop strategies for life detection missions beyond planet Earth, have disregarded a key life feature: behavior. Yet, some behaviors such as biomineralization or motility have occasionally been proposed as biosignatures to detect life. Here, we capitalize on a specific taxis' motility behavior, magnetotaxis, to experimentally provide insights in support of behavior as an unambiguous, sensitive biosignature, and magnetic forces as a prescreening option. Using a magnetotactic bacterial species, Magnetospirillum magneticum, we conducted a lab sensitivity experiment comparing PCR with the hanging drop behavioral assay, using a dilution series. The hanging drop behavioral assay visually shows the motility of MTB toward magnetic poles. Our findings reveal that the behavioral assay exhibits higher sensitivity in the detection of M. magneticum when compared to the established PCR protocol. While both methods present similar detection sensitivities at high concentrations, at ≥ 10-7 fold dilutions, the behavioral method proved more sensitive. The behavioral method can detect bacteria even when samples are diluted at 10-9. Comparable results were obtained with environmental samples from the Hula Valley. We propose behavioral cues as valuable biosignatures in the ongoing efforts of life detection in unexplored aquatic habitats on Earth and to stimulate and support discussions about how to detect extant life beyond Earth. Generic and robust behavioral assays can represent a methodological revolution.
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Affiliation(s)
- Daniela Zinßmeister
- Hula Research Center, Department of Animal Sciences, Tel-Hai Academic College, Tel Hai, Israel
| | - Moshe Leibovitch
- Hula Research Center, Department of Biotechnology, Tel-Hai Academic College, Tel Hai, Israel
| | | | - Sondra Turjeman
- Azrieli Faculty of Medicine, Bar-Ilan University, Safed, Israel
| | - Omry Koren
- Azrieli Faculty of Medicine, Bar-Ilan University, Safed, Israel
| | - Michael Travisano
- Department of Ecology, Evolution and Behavior, University of Minnesota, St Paul, MN, USA
- Minnesota Center for Philosophy of Science, University of Minnesota, Minneapolis, MN, USA
- The BioTechnology Institute, University of Minnesota, St Paul, MN, USA
| | - Yoni Vortman
- Hula Research Center, Department of Animal Sciences, Tel-Hai Academic College, Tel Hai, Israel
- MIGAL-Galilee Research Institute, 11016, Kiryat Shmona, Israel
| | - Beatriz Baselga-Cervera
- Department of Ecology, Evolution and Behavior, University of Minnesota, St Paul, MN, USA.
- Minnesota Center for Philosophy of Science, University of Minnesota, Minneapolis, MN, USA.
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2
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Joy R. An evaluation of the xenobotic cognitive project: Towards Stage 1 of xenobotic cognition. ENDEAVOUR 2024; 48:100927. [PMID: 38679490 DOI: 10.1016/j.endeavour.2024.100927] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2023] [Revised: 10/30/2023] [Accepted: 04/22/2024] [Indexed: 05/01/2024]
Abstract
Xenobot, the world's first biological robot, puts numerous philosophical riddles before us. One among them pertains to the cognitive status of these entities. Are these biological robots cognitive? To evaluate the cognitive status of xenobots and to resolve the puzzle of a single mind emerging from smaller sub-units, in this article, I juxtapose the cognitive capacities of xenobots with that of two other minimal models of cognition, i.e., basal cognition and nonliving active matter cognition. Further, the article underlines the essential cognitive capabilities that xenobots need to achieve to enter what I call stage 1 of xenobotic cognition. Stage 1 is characterized by numerous cognitive mechanisms, which are integral for the survival and cognition of basal organisms. Finally, I suggest that developing xenobots that can reach Stage 1 can help us achieve sophistication in the areas of evolution of the human mind, robotics, biology and medicine, and artificial intelligence (AI).
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Affiliation(s)
- Reshma Joy
- Indian Institute of Technology Ropar, India.
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3
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Johnson S, Deme JC, Furlong EJ, Caesar JJE, Chevance FFV, Hughes KT, Lea SM. Structural basis of directional switching by the bacterial flagellum. Nat Microbiol 2024; 9:1282-1292. [PMID: 38459206 DOI: 10.1038/s41564-024-01630-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Accepted: 02/01/2024] [Indexed: 03/10/2024]
Abstract
The bacterial flagellum is a macromolecular protein complex that harvests energy from uni-directional ion flow across the inner membrane to power bacterial swimming via rotation of the flagellar filament. Rotation is bi-directional, with binding of a cytoplasmic chemotactic response regulator controlling reversal, though the structural and mechanistic bases for rotational switching are not well understood. Here we present cryoelectron microscopy structures of intact Salmonella flagellar basal bodies (3.2-5.5 Å), including the cytoplasmic C-ring complexes required for power transmission, in both counter-clockwise and clockwise rotational conformations. These reveal 180° movements of both the N- and C-terminal domains of the FliG protein, which, when combined with a high-resolution cryoelectron microscopy structure of the MotA5B2 stator, show that the stator shifts from the outside to the inside of the C-ring. This enables rotational switching and reveals how uni-directional ion flow across the inner membrane is used to accomplish bi-directional rotation of the flagellum.
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Affiliation(s)
- Steven Johnson
- Center for Structural Biology, CCR, NCI, Frederick, MD, USA.
| | - Justin C Deme
- Center for Structural Biology, CCR, NCI, Frederick, MD, USA
| | - Emily J Furlong
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
- Division of Biomedical Science and Biochemistry, Australian National University, Canberra, Australian Capital Territory, Australia
| | - Joseph J E Caesar
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
- Central Oxford Structural Molecular Imaging Centre, University of Oxford, Oxford, UK
| | | | - Kelly T Hughes
- Department of Biology, University of Utah, Salt Lake City, UT, USA
| | - Susan M Lea
- Center for Structural Biology, CCR, NCI, Frederick, MD, USA.
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4
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Escoubet N, Brette R, Pontani LL, Prevost AM. Interaction of the mechanosensitive microswimmer Paramecium with obstacles. ROYAL SOCIETY OPEN SCIENCE 2023; 10:221645. [PMID: 37234495 PMCID: PMC10206458 DOI: 10.1098/rsos.221645] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Accepted: 04/25/2023] [Indexed: 05/28/2023]
Abstract
In this work, we report investigations of the swimming behaviour of Paramecium tetraurelia, a unicellular microorganism, in micro-engineered pools that are decorated with thousands of cylindrical pillars. Two types of contact interactions are measured, either passive scattering of Paramecium along the obstacle or avoiding reactions (ARs), characterized by an initial backward swimming upon contact, followed by a reorientation before resuming forward motion. We find that ARs are only mechanically triggered approximately 10% of the time. In addition, we observe that only a third of all ARs triggered by contact are instantaneous while two-thirds are delayed by approximately 150 ms. These measurements are consistent with a simple electrophysiological model of mechanotransduction composed of a strong transient current followed by a persistent one upon prolonged contact. This is in apparent contrast with previous electrophysiological measurements where immobilized cells were stimulated with thin probes, which showed instantaneous behavioural responses and no persistent current. Our findings highlight the importance of ecologically relevant approaches to unravel the motility of mechanosensitive microorganisms in complex environments.
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Affiliation(s)
- Nicolas Escoubet
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Jean Perrin, 4 place Jussieu, Paris 75005, France
| | - Romain Brette
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, Paris 75012, France
| | - Lea-Laetitia Pontani
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Jean Perrin, 4 place Jussieu, Paris 75005, France
| | - Alexis Michel Prevost
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine, Laboratoire Jean Perrin, 4 place Jussieu, Paris 75005, France
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5
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Elices I, Kulkarni A, Escoubet N, Pontani LL, Prevost AM, Brette R. An electrophysiological and kinematic model of Paramecium, the "swimming neuron". PLoS Comput Biol 2023; 19:e1010899. [PMID: 36758112 PMCID: PMC9946239 DOI: 10.1371/journal.pcbi.1010899] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Revised: 02/22/2023] [Accepted: 01/26/2023] [Indexed: 02/11/2023] Open
Abstract
Paramecium is a large unicellular organism that swims in fresh water using cilia. When stimulated by various means (mechanically, chemically, optically, thermally), it often swims backward then turns and swims forward again in a new direction: this is called the avoiding reaction. This reaction is triggered by a calcium-based action potential. For this reason, several authors have called Paramecium the "swimming neuron". Here we present an empirically constrained model of its action potential based on electrophysiology experiments on live immobilized paramecia, together with simultaneous measurement of ciliary beating using particle image velocimetry. Using these measurements and additional behavioral measurements of free swimming, we extend the electrophysiological model by coupling calcium concentration to kinematic parameters, turning it into a swimming model. In this way, we obtain a model of autonomously behaving Paramecium. Finally, we demonstrate how the modeled organism interacts with an environment, can follow gradients and display collective behavior. This work provides a modeling basis for investigating the physiological basis of autonomous behavior of Paramecium in ecological environments.
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Affiliation(s)
- Irene Elices
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
| | - Anirudh Kulkarni
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
- Department of Bioengineering and Centre for Neurotechnology, Imperial College London, South Kensington Campus, London, United Kingdom
| | - Nicolas Escoubet
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine (IBPS), Laboratoire Jean Perrin (LJP), Paris
| | - Léa-Laetitia Pontani
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine (IBPS), Laboratoire Jean Perrin (LJP), Paris
| | - Alexis Michel Prevost
- Sorbonne Université, CNRS, Institut de Biologie Paris-Seine (IBPS), Laboratoire Jean Perrin (LJP), Paris
| | - Romain Brette
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
- * E-mail:
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6
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Pawluchin A, Galic M. Moving through a changing world: Single cell migration in 2D vs. 3D. Front Cell Dev Biol 2022; 10:1080995. [PMID: 36605722 PMCID: PMC9810339 DOI: 10.3389/fcell.2022.1080995] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Accepted: 12/05/2022] [Indexed: 12/24/2022] Open
Abstract
Migration of single adherent cells is frequently observed in the developing and adult organism and has been the subject of many studies. Yet, while elegant work has elucidated molecular and mechanical cues affecting motion dynamics on a flat surface, it remains less clear how cells migrate in a 3D setting. In this review, we explore the changing parameters encountered by cells navigating through a 3D microenvironment compared to cells crawling on top of a 2D surface, and how these differences alter subcellular structures required for propulsion. We further discuss how such changes at the micro-scale impact motion pattern at the macro-scale.
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Affiliation(s)
- Anna Pawluchin
- Institute of Medical Physics and Biophysics, Medical Faculty, University of Münster, Münster, Germany,Cells in Motion Interfaculty Centre, University of Münster, Münster, Germany,CIM-IMRPS Graduate Program, Münster, Germany
| | - Milos Galic
- Institute of Medical Physics and Biophysics, Medical Faculty, University of Münster, Münster, Germany,Cells in Motion Interfaculty Centre, University of Münster, Münster, Germany,*Correspondence: Milos Galic,
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7
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Liu X, Inda ME, Lai Y, Lu TK, Zhao X. Engineered Living Hydrogels. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022; 34:e2201326. [PMID: 35243704 PMCID: PMC9250645 DOI: 10.1002/adma.202201326] [Citation(s) in RCA: 61] [Impact Index Per Article: 30.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2022] [Revised: 03/01/2022] [Indexed: 05/31/2023]
Abstract
Living biological systems, ranging from single cells to whole organisms, can sense, process information, and actuate in response to changing environmental conditions. Inspired by living biological systems, engineered living cells and nonliving matrices are brought together, which gives rise to the technology of engineered living materials. By designing the functionalities of living cells and the structures of nonliving matrices, engineered living materials can be created to detect variability in the surrounding environment and to adjust their functions accordingly, thereby enabling applications in health monitoring, disease treatment, and environmental remediation. Hydrogels, a class of soft, wet, and biocompatible materials, have been widely used as matrices for engineered living cells, leading to the nascent field of engineered living hydrogels. Here, the interactions between hydrogel matrices and engineered living cells are described, focusing on how hydrogels influence cell behaviors and how cells affect hydrogel properties. The interactions between engineered living hydrogels and their environments, and how these interactions enable versatile applications, are also discussed. Finally, current challenges facing the field of engineered living hydrogels for their applications in clinical and environmental settings are highlighted.
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Affiliation(s)
- Xinyue Liu
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Maria Eugenia Inda
- Synthetic Biology Group, Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Yong Lai
- Synthetic Biology Group, Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Timothy K Lu
- Synthetic Biology Group, Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Xuanhe Zhao
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
- Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
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8
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Colin R, Ni B, Laganenka L, Sourjik V. Multiple functions of flagellar motility and chemotaxis in bacterial physiology. FEMS Microbiol Rev 2021; 45:fuab038. [PMID: 34227665 PMCID: PMC8632791 DOI: 10.1093/femsre/fuab038] [Citation(s) in RCA: 113] [Impact Index Per Article: 37.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Accepted: 07/02/2021] [Indexed: 12/13/2022] Open
Abstract
Most swimming bacteria are capable of following gradients of nutrients, signaling molecules and other environmental factors that affect bacterial physiology. This tactic behavior became one of the most-studied model systems for signal transduction and quantitative biology, and underlying molecular mechanisms are well characterized in Escherichia coli and several other model bacteria. In this review, we focus primarily on less understood aspect of bacterial chemotaxis, namely its physiological relevance for individual bacterial cells and for bacterial populations. As evident from multiple recent studies, even for the same bacterial species flagellar motility and chemotaxis might serve multiple roles, depending on the physiological and environmental conditions. Among these, finding sources of nutrients and more generally locating niches that are optimal for growth appear to be one of the major functions of bacterial chemotaxis, which could explain many chemoeffector preferences as well as flagellar gene regulation. Chemotaxis might also generally enhance efficiency of environmental colonization by motile bacteria, which involves intricate interplay between individual and collective behaviors and trade-offs between growth and motility. Finally, motility and chemotaxis play multiple roles in collective behaviors of bacteria including swarming, biofilm formation and autoaggregation, as well as in their interactions with animal and plant hosts.
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Affiliation(s)
- Remy Colin
- Max Planck Institute for Terrestrial Microbiology & Center for Synthetic Microbiology (SYNMIKRO), Karl-von-Frisch Strasse 16, Marburg D-35043, Germany
| | - Bin Ni
- Max Planck Institute for Terrestrial Microbiology & Center for Synthetic Microbiology (SYNMIKRO), Karl-von-Frisch Strasse 16, Marburg D-35043, Germany
- College of Resources and Environmental Science, National Academy of Agriculture Green Development, China Agricultural University, Yuanmingyuan Xilu No. 2, Beijing 100193, China
| | - Leanid Laganenka
- Institute of Microbiology, D-BIOL, ETH Zürich, Vladimir-Prelog-Weg 4, Zürich 8093, Switzerland
| | - Victor Sourjik
- Max Planck Institute for Terrestrial Microbiology & Center for Synthetic Microbiology (SYNMIKRO), Karl-von-Frisch Strasse 16, Marburg D-35043, Germany
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9
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Evstigneeva SS, Telesheva EM, Mokeev DI, Borisov IV, Petrova LP, Shelud’ko AV. Response of Bacteria to Mechanical Stimuli. Microbiology (Reading) 2021. [DOI: 10.1134/s0026261721050052] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Abstract—
Bacteria adapt rapidly to changes in ambient conditions, constantly inspecting their surroundings by means of their sensor systems. These systems are often thought to respond only to signals of a chemical nature. Yet, bacteria are often affected by mechanical forces, e.g., during transition from planktonic to sessile state. Mechanical stimuli, however, have seldom been considered as the signals bacteria can sense and respond to. Nonetheless, bacteria perceive mechanical stimuli, generate signals, and develop responses. This review analyzes the information on the way bacteria respond to mechanical stimuli and outlines how bacteria convert incoming signals into appropriate responses.
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10
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Brette R. Integrative Neuroscience of Paramecium, a "Swimming Neuron". eNeuro 2021; 8:ENEURO.0018-21.2021. [PMID: 33952615 PMCID: PMC8208649 DOI: 10.1523/eneuro.0018-21.2021] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Revised: 03/17/2021] [Accepted: 03/18/2021] [Indexed: 11/28/2022] Open
Abstract
Paramecium is a unicellular organism that swims in fresh water by beating thousands of cilia. When it is stimulated (mechanically, chemically, optically, thermally…), it often swims backward then turns and swims forward again. This "avoiding reaction" is triggered by a calcium-based action potential. For this reason, some authors have called Paramecium a "swimming neuron." This review summarizes current knowledge about the physiological basis of behavior of Paramecium.
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Affiliation(s)
- Romain Brette
- Sorbonne Université, Institut National de la Santé et de la Recherche Médicale, Centre National de la Recherche Scientifique, Institut de la Vision, Paris 75012, France
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11
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Rogowski LW, Oxner M, Tang J, Kim MJ. Heterogeneously flagellated microswimmer behavior in viscous fluids. BIOMICROFLUIDICS 2020; 14:024112. [PMID: 32341723 PMCID: PMC7173976 DOI: 10.1063/1.5137743] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2019] [Revised: 05/04/2020] [Accepted: 04/03/2020] [Indexed: 06/01/2023]
Abstract
An analysis of heterogeneously flagellated microswimmers inside viscous fluids is presented. Flagella harvested from Salmonella typhimurium were isolated, repolymerized, and functionalized to have biotin at their ends, allowing for chemical attachment along the surfaces of avidin-coated microparticles. Assembled microswimmers were rotated under incremental magnetic field frequencies, in saline and methylcellulose solutions, to baseline their velocity responses. A mean square displacement analysis revealed that rotating microswimmers exhibited anomalous diffusive behavior at small time scales in each fluid and had increased diffusivity compared with the non-rotating cases. Flagellated microswimmers had decreased diffusivity when compared with non-flagellated microparticles in Brownian conditions. Microswimmers were demonstrated to perform selected trajectories under proportional feedback control with reasonable accuracy. Finally, microswimmer propulsion was shown to be heavily influenced by the handedness of the rotating magnetic fields, with frequency induced reversals of swimming direction observed under clockwise rotation; this effect was determined to be the result of flagellar bundling and unbundling.
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Affiliation(s)
- Louis William Rogowski
- Department of Mechanical Engineering, Southern Methodist University, 3101 Dyer Street, Suite 200, Dallas, Texas 75206, USA
| | - Micah Oxner
- Department of Mechanical Engineering, Southern Methodist University, 3101 Dyer Street, Suite 200, Dallas, Texas 75206, USA
| | - Jiannan Tang
- Department of Mechanical Engineering, Southern Methodist University, 3101 Dyer Street, Suite 200, Dallas, Texas 75206, USA
| | - Min Jun Kim
- Department of Mechanical Engineering, Southern Methodist University, 3101 Dyer Street, Suite 200, Dallas, Texas 75206, USA
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12
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Böddeker TJ, Karpitschka S, Kreis CT, Magdelaine Q, Bäumchen O. Dynamic force measurements on swimming Chlamydomonas cells using micropipette force sensors. J R Soc Interface 2020; 17:20190580. [PMID: 31937233 PMCID: PMC7014799 DOI: 10.1098/rsif.2019.0580] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Accepted: 12/10/2019] [Indexed: 11/12/2022] Open
Abstract
Flagella and cilia are cellular appendages that inherit essential functions of microbial life including sensing and navigating the environment. In order to propel a swimming microorganism they displace the surrounding fluid by means of periodic motions, while precisely timed modulations of their beating patterns enable the cell to steer towards or away from specific locations. Characterizing the dynamic forces, however, is challenging and typically relies on indirect experimental approaches. Here, we present direct in vivo measurements of the dynamic forces of motile Chlamydomonas reinhardtii cells in controlled environments. The experiments are based on partially aspirating a living microorganism at the tip of a micropipette force sensor and optically recording the micropipette's position fluctuations with high temporal and sub-pixel spatial resolution. Spectral signal analysis allows for isolating the cell-generated dynamic forces caused by the periodic motion of the flagella from background noise. We provide an analytic, elasto-hydrodynamic model for the micropipette force sensor and describe how to obtain the micropipette's full frequency response function from a dynamic force calibration. Using this approach, we measure the amplitude of the oscillatory forces during the swimming activity of individual Chlamydomonas reinhardtii cells of 26 ± 5 pN, resulting from the coordinated flagellar beating with a frequency of 49 ± 5 Hz. This dynamic micropipette force sensor technique generalizes the applicability of micropipettes as force sensors from static to dynamic force measurements, yielding a force sensitivity in the piconewton range. In addition to measurements in bulk liquid environment, we study the dynamic forces of the biflagellated microswimmer in the vicinity of a solid/liquid interface. As we gradually decrease the distance of the swimming microbe to the interface, we measure a significantly enhanced force transduction at distances larger than the maximum extent of the beating flagella, highlighting the importance of hydrodynamic interactions for scenarios in which flagellated microorganisms encounter surfaces.
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Affiliation(s)
| | | | | | | | - Oliver Bäumchen
- Max Planck Institute for Dynamics and Self-Organization (MPIDS), Am Faßberg 17, 37077 Göttingen, Germany
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13
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Datta SR, Anderson DJ, Branson K, Perona P, Leifer A. Computational Neuroethology: A Call to Action. Neuron 2019; 104:11-24. [PMID: 31600508 PMCID: PMC6981239 DOI: 10.1016/j.neuron.2019.09.038] [Citation(s) in RCA: 196] [Impact Index Per Article: 39.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2019] [Revised: 09/16/2019] [Accepted: 09/23/2019] [Indexed: 12/11/2022]
Abstract
The brain is worthy of study because it is in charge of behavior. A flurry of recent technical advances in measuring and quantifying naturalistic behaviors provide an important opportunity for advancing brain science. However, the problem of understanding unrestrained behavior in the context of neural recordings and manipulations remains unsolved, and developing approaches to addressing this challenge is critical. Here we discuss considerations in computational neuroethology-the science of quantifying naturalistic behaviors for understanding the brain-and propose strategies to evaluate progress. We point to open questions that require resolution and call upon the broader systems neuroscience community to further develop and leverage measures of naturalistic, unrestrained behavior, which will enable us to more effectively probe the richness and complexity of the brain.
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Affiliation(s)
| | - David J Anderson
- Division of Biology and Biological Engineering 156-29, California Institute of Technology, Pasadena, CA 91125, USA; Howard Hughes Medical Institute, Pasadena, CA, 91125, USA; Tianqiao and Chrissy Chen Institute for Neuroscience, California Institute of Technology, Pasadena, CA 91125, USA
| | - Kristin Branson
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA 20147, USA
| | - Pietro Perona
- Division of Engineering & Applied Sciences 136-93, California Institute of Technology, Pasadena, CA 91125, USA
| | - Andrew Leifer
- Department of Physics, Princeton University, Princeton, NJ 08544, USA; Princeton Neuroscience Institute, Princeton University, Princeton, NJ 08544, USA.
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14
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Xu F, Newby JM, Schiller JL, Schroeder HA, Wessler T, Chen A, Forest MG, Lai SK. Modeling Barrier Properties of Intestinal Mucus Reinforced with IgG and Secretory IgA against Motile Bacteria. ACS Infect Dis 2019; 5:1570-1580. [PMID: 31268295 DOI: 10.1021/acsinfecdis.9b00109] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The gastrointestinal (GI) tract is lined with a layer of viscoelastic mucus gel, characterized by a dense network of entangled and cross-linked mucins together with an abundance of antibodies (Ab). Secretory IgA (sIgA), the predominant Ab isotype in the GI tract, is a dimeric molecule with 4 antigen-binding domains capable of inducing efficient clumping of bacteria, or agglutination. IgG, another common Ab at mucosal surfaces, can cross-link individual viruses to the mucin mesh through multiple weak bonds between IgG-Fc and mucins, a process termed muco-trapping. Relative contributions by agglutination versus muco-trapping in blocking permeation of motile bacteria through mucus remain poorly understood. Here, we developed a mathematical model that takes into account physiologically relevant spatial dimensions and time scales, binding and unbinding rates between Ab and bacteria as well as between Ab and mucins, the diffusivities of Ab, and run-tumble motion of active bacteria. Our model predicts both sIgA and IgG can accumulate on the surface of individual bacteria at sufficient quantities and rates to enable trapping individual bacteria in mucins before they penetrate the mucus layer. Furthermore, our model predicts that agglutination only modestly improves the ability for antibodies to block bacteria permeation through mucus. These results suggest that while sIgA is the most potent Ab isotype overall at stopping bacterial penetration, IgG may represent a practical alternative for mucosal prophylaxis and therapy. Our work improves the mechanistic understanding of Ab-enhanced barrier properties of mucus and highlights the ability for muco-trapping Ab to protect against motile pathogens at mucosal surfaces.
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15
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Ouellette MH, Desrochers MJ, Gheta I, Ramos R, Hendricks M. A Gate-and-Switch Model for Head Orientation Behaviors in Caenorhabditis elegans. eNeuro 2018; 5:ENEURO.0121-18.2018. [PMID: 30627635 PMCID: PMC6325537 DOI: 10.1523/eneuro.0121-18.2018] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2018] [Revised: 09/29/2018] [Accepted: 10/04/2018] [Indexed: 11/24/2022] Open
Abstract
The nervous system seamlessly integrates perception and action. This ability is essential for stable representation of and appropriate responses to the external environment. How the sensorimotor integration underlying this ability occurs at the level of individual neurons is of keen interest. In Caenorhabditis elegans, RIA interneurons receive input from sensory pathways and have reciprocal connections with head motor neurons. RIA simultaneously encodes both head orientation and sensory stimuli, which may allow it to integrate these two signals to detect the spatial distribution of stimuli across head sweeps and generate directional head responses. Here, we show that blocking synaptic release from RIA disrupts head orientation behaviors in response to unilaterally presented stimuli. We found that sensory encoding in RIA is gated according to head orientation. This dependence on head orientation is independent of motor encoding in RIA, suggesting a second, posture-dependent pathway upstream of RIA. This gating mechanism may allow RIA to selectively attend to stimuli that are asymmetric across head sweeps. Attractive odor removal during head bends triggers rapid head withdrawal in the opposite direction. Unlike sensory encoding, this directional response is dependent on motor inputs to and synaptic output from RIA. Together, these results suggest that RIA is part of a sensorimotor pathway that is dynamically regulated according to head orientation at two levels: the first is a gate that filters sensory representations in RIA, and the second is a switch that routes RIA synaptic output to dorsal or ventral head motor neurons.
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Affiliation(s)
| | | | - Ioana Gheta
- Department of Biology, McGill University, Montreal, Quebec H3A 1B1, Canada
| | - Ryan Ramos
- Department of Biology, McGill University, Montreal, Quebec H3A 1B1, Canada
| | - Michael Hendricks
- Department of Biology, McGill University, Montreal, Quebec H3A 1B1, Canada
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Neutrophil-inspired propulsion in a combined acoustic and magnetic field. Nat Commun 2017; 8:770. [PMID: 28974671 PMCID: PMC5626690 DOI: 10.1038/s41467-017-00845-5] [Citation(s) in RCA: 117] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Accepted: 07/28/2017] [Indexed: 12/24/2022] Open
Abstract
Systems capable of precise motion in the vasculature can offer exciting possibilities for applications in targeted therapeutics and non-invasive surgery. So far, the majority of the work analysed propulsion in a two-dimensional setting with limited controllability near boundaries. Here we show bio-inspired rolling motion by introducing superparamagnetic particles in magnetic and acoustic fields, inspired by a neutrophil rolling on a wall. The particles self-assemble due to dipole–dipole interaction in the presence of a rotating magnetic field. The aggregate migrates towards the wall of the channel due to the radiation force of an acoustic field. By combining both fields, we achieved a rolling-type motion along the boundaries. The use of both acoustic and magnetic fields has matured in clinical settings. The combination of both fields is capable of overcoming the limitations encountered by single actuation techniques. We believe our method will have far-reaching implications in targeted therapeutics. Devising effective swimming and propulsion strategies in microenvironments is attractive for drug delivery applications. Here Ahmed et al. demonstrate a micropropulsion strategy in which a combination of magnetic and acoustic fields is used to assemble and propel colloidal particles along channel walls.
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Sztuk - Sikorska E, Gradon L. Biofouling reduction for improvement of depth water filtration. Filter production and testing. ACTA ACUST UNITED AC 2016. [DOI: 10.1515/cpe-2016-0026] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
AbstractWater is a strategic material. Recycling is an important component of balancing its use. Deep-bed filtration is an inexpensive purification method and seems to be very effective in spreading water recovery. Good filter designs, such as the fibrous filter, have high separation efficiency, low resistance for the up-flowing fluid and high retention capacity. However, one of the substantial problems of this process is the biofouling of the filter. Biofouling causes clogging and greatly reduces the life of the filter. Therefore, the melt-blown technique was used for the formation of novel antibacterial fibrous filters. Such filters are made of polypropylene composites with zinc oxide and silver nanoparticles on the fiber surface. These components act as inhibitors of bacterial growth in the filter and were tested in laboratory and full scale experiments. Antibacterial/bacteriostatic tests were performed on Petri dishes with E. coli and B. subtilis. Full scale experiments were performed on natural river water, which contained abiotic particles and mutualistic bacteria. The filter performance at industrial scale conditions was measured using a particle counter, a flow cytometer and a confocal microscope. The results of the experiments indicate a significant improvement of the composite filter performance compared to the regular fibrous filter. The differences were mostly due to a reduction in the biofouling effect.
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Rapid, high-throughput tracking of bacterial motility in 3D via phase-contrast holographic video microscopy. Biophys J 2016; 108:1248-56. [PMID: 25762336 PMCID: PMC4375448 DOI: 10.1016/j.bpj.2015.01.018] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Revised: 01/02/2015] [Accepted: 01/08/2015] [Indexed: 12/25/2022] Open
Abstract
Tracking fast-swimming bacteria in three dimensions can be extremely challenging with current optical techniques and a microscopic approach that can rapidly acquire volumetric information is required. Here, we introduce phase-contrast holographic video microscopy as a solution for the simultaneous tracking of multiple fast moving cells in three dimensions. This technique uses interference patterns formed between the scattered and the incident field to infer the three-dimensional (3D) position and size of bacteria. Using this optical approach, motility dynamics of multiple bacteria in three dimensions, such as speed and turn angles, can be obtained within minutes. We demonstrated the feasibility of this method by effectively tracking multiple bacteria species, including Escherichia coli, Agrobacterium tumefaciens, and Pseudomonas aeruginosa. In addition, we combined our fast 3D imaging technique with a microfluidic device to present an example of a drug/chemical assay to study effects on bacterial motility.
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Analyzing bacterial movements on surfaces. Methods Cell Biol 2015. [PMID: 25640444 DOI: 10.1016/bs.mcb.2014.10.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Bacteria have long been ideal model systems for studying many biological phenomena. But when it comes to motility, we are quite often just figuring out the mechanisms underlying their ability to move in liquid or on surfaces. In the last few decades, research has emphasized the importance for bacteria to be able to adhere to and move on surfaces in order to form complex bacterial communities called biofilms. To better understand the multiple chemical and biophysical mechanisms responsible for the initial interactions of bacteria on surfaces that develop into biofilms, we present here low-cost and easy-to-implement protocols to quantitatively analyze the movement of single bacteria on surfaces by microscopy. These protocols are presented in the case of the human pathogen Neisseria gonorrhoeae that moves on surfaces solely powered by Type IV pili, motility referred to as twitching motility. These methods, however, are applicable for any motile bacteria interacting with surfaces. The precise quantification of motility coupled with genetic tools will enable us to precisely dissect the mechanisms and dynamics of bacterial surface motility which are still poorly understood.
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van Vliet S, Hol FJH, Weenink T, Galajda P, Keymer JE. The effects of chemical interactions and culture history on the colonization of structured habitats by competing bacterial populations. BMC Microbiol 2014; 14:116. [PMID: 24884963 PMCID: PMC4032360 DOI: 10.1186/1471-2180-14-116] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2013] [Accepted: 05/01/2014] [Indexed: 02/01/2023] Open
Abstract
Background Bacterial habitats, such as soil and the gut, are structured at the micrometer scale. Important aspects of microbial life in such spatial ecosystems are migration and colonization. Here we explore the colonization of a structured ecosystem by two neutrally labeled strains of Escherichia coli. Using time-lapse microscopy we studied the colonization of one-dimensional arrays of habitat patches linked by connectors, which were invaded by the two E. coli strains from opposite sides. Results The two strains colonize a habitat from opposite sides by a series of traveling waves followed by an expansion front. When population waves collide, they branch into a continuing traveling wave, a reflected wave and a stationary population. When the two strains invade the landscape from opposite sides, they remain segregated in space and often one population will displace the other from most of the habitat. However, when the strains are co-cultured before entering the habitats, they colonize the habitat together and do not separate spatially. Using physically separated, but diffusionally coupled, habitats we show that colonization waves and expansion fronts interact trough diffusible molecules, and not by direct competition for space. Furthermore, we found that colonization outcome is influenced by a culture’s history, as the culture with the longest doubling time in bulk conditions tends to take over the largest fraction of the habitat. Finally, we observed that population distributions in parallel habitats located on the same device and inoculated with cells from the same overnight culture are significantly more similar to each other than to patterns in identical habitats located on different devices inoculated with cells from different overnight cultures, even tough all cultures were started from the same −80°C frozen stock. Conclusions We found that the colonization of spatially structure habitats by two interacting populations can lead to the formation of complex, but reproducible, spatiotemporal patterns. Furthermore, we showed that chemical interactions between two populations cause them to remain spatially segregated while they compete for habitat space. Finally, we observed that growth properties in bulk conditions correlate with the outcome of habitat colonization. Together, our data show the crucial roles of chemical interactions between populations and a culture’s history in determining the outcome of habitat colonization.
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Affiliation(s)
- Simon van Vliet
- Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, Delft, CJ 2628, The Netherlands.
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21
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Sailapu SK, Chattopadhyay A. Induction of Electromotive Force by an Autonomously Moving Magnetic Bot. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201309029] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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22
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Sailapu SK, Chattopadhyay A. Induction of Electromotive Force by an Autonomously Moving Magnetic Bot. Angew Chem Int Ed Engl 2014; 53:1521-4. [DOI: 10.1002/anie.201309029] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2013] [Indexed: 11/10/2022]
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23
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Baraban L, Harazim SM, Sanchez S, Schmidt OG. Chemotactic Behavior of Catalytic Motors in Microfluidic Channels. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201301460] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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24
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Baraban L, Harazim SM, Sanchez S, Schmidt OG. Chemotactic behavior of catalytic motors in microfluidic channels. Angew Chem Int Ed Engl 2013; 52:5552-6. [PMID: 23616282 DOI: 10.1002/anie.201301460] [Citation(s) in RCA: 121] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Indexed: 01/20/2023]
Affiliation(s)
- Larysa Baraban
- Institute for Integrative Nanosciences, Leibniz Institute for Solid State and Materials Research Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany
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Ping L, Birkenbeil J, Monajembashi S. Swimming behavior of the monotrichous bacterium Pseudomonas fluorescens SBW25. FEMS Microbiol Ecol 2013; 86:36-44. [PMID: 23346905 DOI: 10.1111/1574-6941.12076] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2012] [Revised: 01/20/2013] [Accepted: 01/21/2013] [Indexed: 11/26/2022] Open
Abstract
Motility is an important trait for some bacteria living in nature and the analyses of it can provide important information on bacterial ecology. While the swimming behavior of peritrichous bacteria such as Escherichia coli has been extensively studied, the monotrichous bacteria such as the soil inhabiting and plant growth promoting bacterium Pseudmonas fluorescens is not very well characterized. Unlike E. coli that is propelled by a left-handed flagella bundle, P. fluorescens SBW25 swims several times faster by rotating a right-handed flagellum. Its swimming pattern is the most sophisticated known so far: it swims forward (run) and backward (backup); it can swiftly 'turn' the run directions or 'reorient' at run-backup transitions; it can 'flip' the cell body continuously or 'hover' in the milieu without translocation. The bacteria swam in circles near flat surfaces with reduced velocity and increased turn frequency. The viscous drag load due to wall effect potentially accounts for the circular motion and velocity change, but not the turn frequency. The flagellation and swimming behavior of P. fluorescens SBW25 show some similarity to Caulobacter, a fresh-water inhabitant, while the complex swimming pattern might be an adaptation to the geometrically restricted rhizo- and phyllospheres.
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Affiliation(s)
- Liyan Ping
- Max-Planck-Institute for Chemical Ecology, Jena, Germany
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Zot HG, Hasbun JE, Minh NV. Second-chance signal transduction explains cooperative flagellar switching. PLoS One 2012; 7:e41098. [PMID: 22844429 PMCID: PMC3402542 DOI: 10.1371/journal.pone.0041098] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2011] [Accepted: 06/21/2012] [Indexed: 01/02/2023] Open
Abstract
The reversal of flagellar motion (switching) results from the interaction between a switch complex of the flagellar rotor and a torque-generating stationary unit, or stator (motor unit). To explain the steeply cooperative ligand-induced switching, present models propose allosteric interactions between subunits of the rotor, but do not address the possibility of a reaction that stimulates a bidirectional motor unit to reverse direction of torque. During flagellar motion, the binding of a ligand-bound switch complex at the dwell site could excite a motor unit. The probability that another switch complex of the rotor, moving according to steady-state rotation, will reach the same dwell site before that motor unit returns to ground state will be determined by the independent decay rate of the excited-state motor unit. Here, we derive an analytical expression for the energy coupling between a switch complex and a motor unit of the stator complex of a flagellum, and demonstrate that this model accounts for the cooperative switching response without the need for allosteric interactions. The analytical result can be reproduced by simulation when (1) the motion of the rotor delivers a subsequent ligand-bound switch to the excited motor unit, thereby providing the excited motor unit with a second chance to remain excited, and (2) the outputs from multiple independent motor units are constrained to a single all-or-none event. In this proposed model, a motor unit and switch complex represent the components of a mathematically defined signal transduction mechanism in which energy coupling is driven by steady-state and is regulated by stochastic ligand binding. Mathematical derivation of the model shows the analytical function to be a general form of the Hill equation (Hill AV (1910) The possible effects of the aggregation of the molecules of haemoglobin on its dissociation curves. J Physiol 40: iv-vii).
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Affiliation(s)
- Henry G Zot
- Department of Biology, University of West Georgia, Carrollton, Georgia, United States of America.
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Jin T. GPCR-controlled chemotaxis in Dictyostelium discoideum. WILEY INTERDISCIPLINARY REVIEWS-SYSTEMS BIOLOGY AND MEDICINE 2011; 3:717-27. [PMID: 21381217 DOI: 10.1002/wsbm.143] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Dictyostelium discoideum has been chosen as the key model organism for the study of eukaryotic chemotaxis. Studies in this lower eukaryotic organism have allowed us to discover eukaryotic chemotaxis behavior and to gradually understand the mechanism of chemotaxis. Investigations in this simple organism often guide the direction of chemotaxis studies in areas such as forming concepts, discovering molecular components, revealing pathways and networks. The cooperation between experimental approaches and computational modeling has helped us to comprehend the signaling network as a system. To further reveal the relationships among the molecular mechanisms of individual signaling steps, a continuous interplay between model development and refinement and experimental testing and verification will be useful. This article focuses on a chemoattractant G-protein-coupled receptor (GPCR)/G-protein gradient sensing machinery, which is monitored by PIP(3) responses and investigated by the interplay between live cell imaging experiments and computational modeling. We believe that such an approach will lead to a much better understanding of GPCR-controlled chemotaxis of all eukaryotic cells.
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Affiliation(s)
- Tian Jin
- Chemotaxis Signal Section, Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, NIH, Twinbrook Facility, Rockville, MD, USA.
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Moraud EM, Martinez D. Effectiveness and robustness of robot infotaxis for searching in dilute conditions. Front Neurorobot 2010; 4:1. [PMID: 20407611 PMCID: PMC2856589 DOI: 10.3389/fnbot.2010.00001] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2009] [Accepted: 02/08/2010] [Indexed: 11/20/2022] Open
Abstract
Tracking scents and locating odor sources is a major challenge in robotics. The odor plume is not a continuous cloud but consists of intermittent odor patches dispersed by the wind. Far from the source, the probability of encountering one of these patches vanishes. In such dilute conditions, a good strategy is to first ‘explore’ the environment and gather information, then ‘exploit’ current knowledge and direct toward the estimated source location. Infotactic navigation has been recently proposed to strike the balance between exploration and exploitation. Infotaxis was tested in simulation and produced trajectories similar to those observed in the flight of moths attracted by a sexual pheromone. In this paper, we assess the performance of infotaxis in dilute conditions by combining robotic experiments and simulations. Our results indicate that infotaxis is both effective (seven detections on average were sufficient to reach the source) and robust (the source is found in presence of inaccurate modeling by the searcher). The biomimetic characteristic of infotaxis is also preserved when searching with a robot in a real environment.
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Affiliation(s)
- Eduardo Martin Moraud
- CORTEX Research Team, Laboratoire Lorrain de Recherche en Informatique et ses Applications Nancy, France
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29
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Ping L. The asymmetric flagellar distribution and motility of Escherichia coli. J Mol Biol 2010; 397:906-16. [PMID: 20156455 DOI: 10.1016/j.jmb.2010.02.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2009] [Revised: 02/03/2010] [Accepted: 02/08/2010] [Indexed: 10/19/2022]
Abstract
Rod-shaped bacteria such as Escherichia coli divide by binary fission. They inherit an old pole from the parent cell. The new pole is recently derived from the septum. Because the chemoreceptor accumulates linearly with time on the cell pole, the old pole carries more receptors than does the new pole. Here, further evidence is provided that the old pole appears more frequently at the rear when bacteria swim. This phenomenon had been observed, yet not extensively explored in the literature. The biased swimming orientation is the consequence of the asymmetric distribution of flagella over the cell surface. On about 75% of cells, there are more flagella on the old-pole half of the cell than on the new-pole half, regardless of growth conditions. Most flagella are lateral, and few were found on the cell pole per se. The asymmetric flagellar distribution makes cells more efficient in chemotaxis. Both swimming orientation and receptor localization are components of chemotaxis, by which bacteria follow environmental stimuli. If unipolarly flagellated cells, such as the swarmer cells of Caulobacter crescentus, are regarded as 100% polar with respect to chemotaxis, E. coli is about 75%. The difference is quantitative. The peritrichous flagellation might enhance the motility and chemotaxis in the viscous environment of enteric bacteria.
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Affiliation(s)
- Liyan Ping
- Department of Bioorganic Chemistry, Max Planck Institute for Chemical Ecology, Hans-Knoell-Strasse 8, 07745 Jena, Germany.
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30
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A 3D Motile Rod-Shaped Monotrichous Bacterial Model. Bull Math Biol 2009; 71:1228-63. [DOI: 10.1007/s11538-009-9400-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2008] [Accepted: 01/15/2009] [Indexed: 10/21/2022]
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31
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Copeland MF, Weibel DB. Bacterial Swarming: A Model System for Studying Dynamic Self-assembly. SOFT MATTER 2009; 5:1174-1187. [PMID: 23926448 PMCID: PMC3733279 DOI: 10.1039/b812146j] [Citation(s) in RCA: 150] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Bacterial swarming is an example of dynamic self-assembly in microbiology in which the collective interaction of a population of bacterial cells leads to emergent behavior. Swarming occurs when cells interact with surfaces, reprogram their physiology and behavior, and adapt to changes in their environment by coordinating their growth and motility with other cells in the colony. This review summarizes the salient biological and biophysical features of this system and describes our current understanding of swarming motility. We have organized this review into four sections: 1) The biophysics and mechanisms of bacterial motility in fluids and its relevance to swarming. 2) The role of cell/molecule, cell/surface, and cell/cell interactions during swarming. 3) The changes in physiology and behavior that accompany swarming motility. 4) A concluding discussion of several interesting, unanswered questions that is particularly relevant to soft matter scientists.
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Affiliation(s)
- Matthew F. Copeland
- Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI, U.S.A
| | - Douglas B. Weibel
- Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI, U.S.A
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Potdar AA, Lu J, Jeon J, Weaver AM, Cummings PT. Bimodal analysis of mammary epithelial cell migration in two dimensions. Ann Biomed Eng 2008; 37:230-45. [PMID: 18982450 DOI: 10.1007/s10439-008-9592-y] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2008] [Accepted: 10/23/2008] [Indexed: 01/19/2023]
Abstract
Cell migration paths of mammary epithelial cells (expressing different versions of the promigratory tyrosine kinase receptor Her2/Neu) were analyzed within a bimodal framework that is a generalization of the run-and-tumble description applicable to bacterial migration. The mammalian cell trajectories were segregated into two types of alternating modes, namely, the "directional mode" (mode I, the more persistent mode, analogous to the bacterial run phase) and the "re-orientation mode" (mode II, the less persistent mode, analogous to the bacterial tumble phase). Higher resolution (more pixel information, relative to cell size) and smaller sampling intervals (time between images) were found to give a better estimate of the deduced single cell dynamics (such as directional-mode time and turn angle distribution) of the various cell types from the bimodal analysis. The bimodal analysis tool permits the deduction of short-time dynamics of cell motion such as the turn angle distributions and turn frequencies during the course of cell migration compared to standard methods of cell migration analysis. We find that the 2-h mammalian cell tracking data do not fall into the diffusive regime implying that the often-used random motility expressions for mammalian cell motion (based on assuming diffusive motion) are invalid over the time steps (fraction of minute) typically used in modeling mammalian cell migration.
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Affiliation(s)
- Alka A Potdar
- Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN 37235-1604, USA
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Loi D, Mossa S, Cugliandolo LF. Effective temperature of active matter. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 77:051111. [PMID: 18643030 DOI: 10.1103/physreve.77.051111] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2007] [Revised: 03/04/2008] [Indexed: 05/26/2023]
Abstract
We follow the dynamics of an ensemble of interacting self-propelled motorized particles in contact with an equilibrated thermal bath. We find that the fluctuation-dissipation relation allows for the definition of an effective temperature that is compatible with the results obtained using a tracer particle as a thermometer. The effective temperature takes a value which is higher than the temperature of the bath, and it is continuously controlled by the motor intensity.
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Affiliation(s)
- Davide Loi
- European Synchrotron Radiation Facility, Boîte Postale 220, F-38043 Grenoble, France
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Shibata T, Ueda M. Noise generation, amplification and propagation in chemotactic signaling systems of living cells. Biosystems 2008; 93:126-32. [PMID: 18501501 DOI: 10.1016/j.biosystems.2008.04.003] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Revised: 04/11/2008] [Accepted: 04/15/2008] [Indexed: 12/29/2022]
Abstract
Theoretical considerations of stochastic signal transduction in living cells have revealed the gain-fluctuation relation, which provides a theoretical framework to describe quantitatively how noise is generated, amplified and propagated along a signaling cascade in living cells. We chose the chemotactic signaling of bacteria and eukaryotic cells as a typical example of noisy signal transduction and applied the gain-fluctuation relation to these signaling systems in order to analyze the effects of noise on signal transduction. Comparing our theoretical analysis with the experimental results of chemotaxis in bacteria Escherichia coli and eukaryote Dictyostelium discoideum revealed that noise in signal transduction systems limits the cells' chemotactic ability and contributes to their behavioral variability. Based on the kinetic properties of signaling molecules in living cells, the gain-fluctuation relation can quantitatively explain stochastic cellular behaviors.
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Affiliation(s)
- Tatsuo Shibata
- Department of Mathematical and Life Sciences, University of Hiroshima, Higashi-Hiroshima, Hiroshima 739-8526, Japan
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Mitchell JG, Kogure K. Bacterial motility: links to the environment and a driving force for microbial physics. FEMS Microbiol Ecol 2006; 55:3-16. [PMID: 16420610 DOI: 10.1111/j.1574-6941.2005.00003.x] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Bacterial motility was recognized 300 years ago. Throughout this history, research into motility has led to advances in microbiology and physics. Thirty years ago, this union helped to make run and tumble chemotaxis the paradigm for bacterial movement. This review highlights how this paradigm has expanded and changed, and emphasizes the following points. The absolute magnitude of swimming speed is ecologically important because it helps determine vulnerability to Brownian motion, sensitivity to gradients, the type of receptors used and the cost of moving, with some bacteria moving at 1 mm s(-1). High costs for high speeds are offset by the benefit of resource translocation across submillimetre redox and other environmental gradients. Much of environmental chemotaxis appears adapted to respond to gradients of micrometres, rather than migrations of centimetres. In such gradients, control of ion pumps is particularly important. Motility, at least in the ocean, is highly intermittent and the speed is variable within a run. Subtleties in flagellar physics provide a variety of reorientation mechanisms. Finally, while careful physical analysis has contributed to our current understanding of bacterial movement, tactic bacteria are increasingly widely used as experimental and theoretical model systems in physics.
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Affiliation(s)
- James G Mitchell
- Marine Microbiology, Ocean Research Institute, University of Tokyo, Tokyo, Japan.
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Josef K, Saranak J, Foster KW. An electro-optic monitor of the behavior ofChlamydomonas reinhardtii cilia. ACTA ACUST UNITED AC 2005; 61:83-96. [PMID: 15838839 DOI: 10.1002/cm.20064] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The unicellular green alga Chlamydomonas reinhardtii steers through water with a pair of cilia (eukaryotic flagella). Long-term observation of the beating of its cilia with controlled stimulation is improving our understanding of how a cell responds to sensory inputs. Here we describe how to record ciliary motion continuously for long periods. We also report experiments on the network of intracellular signaling that connects the environment inputs with response outputs. Local spatial changes in ciliary response on the time scale of the underlying biochemical dynamics are observed. Near-infrared light monitors the cells held by a micropipette. This condition is tolerated well for hours, not interfering with ciliary beating or sensory transduction. A computer integrates the light stimulation of the eye of Chlamydomonas with the ciliary motion making possible long-term correlations. Measures of ciliary responses include the beating frequency, stroke velocity, and stroke duration of each cilium, and the relative phase of the cis and trans cilia. The stationarity and dependence of the system on light intensity was investigated. About 150,000,000 total beat cycles and up to 8 h on one cell have been recorded. Each beat cycle is resolved so that each asynchronous beat is detected. Responses extend only a few hundred milliseconds, but there is a persistence of momentary changes that last much longer. Interestingly, we see a response that is linear with absolute light intensity as well as different kinds of response that are clearly nonlinear, implying two signaling pathways from the cell body to the cilia.
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Affiliation(s)
- Keith Josef
- Physics Department, Syracuse University, Syracuse, New York 13244-1130, USA
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Park S, Wolanin PM, Yuzbashyan EA, Lin H, Darnton NC, Stock JB, Silberzan P, Austin R. Influence of topology on bacterial social interaction. Proc Natl Acad Sci U S A 2003; 100:13910-5. [PMID: 14623970 PMCID: PMC283520 DOI: 10.1073/pnas.1935975100] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The environmental topology of complex structures is used by Escherichia coli to create traveling waves of high cell density, a prelude to quorum sensing. When cells are grown to a moderate density within a confining microenvironment, these traveling waves of cell density allow the cells to find and collapse into confining topologies, which are unstable to population fluctuations above a critical threshold. This was first observed in mazes designed to mimic complex environments, then more clearly in a simpler geometry consisting of a large open area surrounding a square (250 x 250 microm) with a narrow opening of 10-30 microm. Our results thus show that under nutrient-deprived conditions bacteria search out each other in a collective manner and that the bacteria can dynamically confine themselves to highly enclosed spaces.
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Affiliation(s)
- Sungsu Park
- Department of Physics, Princeton University, Princeton, NJ 08544, USA
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Lee HY, Kardar M. Macroscopic equations for pattern formation in mixtures of microtubules and molecular motors. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2001; 64:056113. [PMID: 11736020 DOI: 10.1103/physreve.64.056113] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2001] [Indexed: 05/23/2023]
Abstract
Inspired by patterns observed in mixtures of microtubules and molecular motors, we propose continuum equations for the evolution of motor density and microtubule orientation. The chief ingredients are the transport of motors along tubules, and the alignment of tubules in the process. The macroscopic equations lead to aster and vortex patterns in qualitative agreement with experiments. While the early stages of evolution of tubules are similar to coarsening of spins following a quench, the rearrangement of motors leads to arrested coarsening at low densities. Even in one dimension, the equations exhibit a variety of interesting behaviors, such as symmetry breaking, moving fronts, and motor localization.
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Affiliation(s)
- H Y Lee
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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Brockie PJ, Mellem JE, Hills T, Madsen DM, Maricq AV. The C. elegans glutamate receptor subunit NMR-1 is required for slow NMDA-activated currents that regulate reversal frequency during locomotion. Neuron 2001; 31:617-30. [PMID: 11545720 DOI: 10.1016/s0896-6273(01)00394-4] [Citation(s) in RCA: 158] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The N-methyl-D-aspartate (NMDA) subtype of glutamate receptor is important for synaptic plasticity and nervous system development and function. We have used genetic and electrophysiological methods to demonstrate that NMR-1, a Caenorhabditis elegans NMDA-type ionotropic glutamate receptor subunit, plays a role in the control of movement and foraging behavior. nmr-1 mutants show a lower probability of switching from forward to backward movement and a reduced ability to navigate a complex environment. Electrical recordings from the interneuron AVA show that NMDA-dependent currents are selectively disrupted in nmr-1 mutants. We also show that a slowly desensitizing variant of a non-NMDA receptor can rescue the nmr-1 mutant phenotype. We propose that NMDA receptors in C. elegans provide long-lived currents that modulate the frequency of movement reversals during foraging behavior.
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Affiliation(s)
- P J Brockie
- Department of Biology, University of Utah, Salt Lake City 84112, USA
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41
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The Chemistry of Movement. Biochemistry 2001. [DOI: 10.1016/b978-012492543-4/50022-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Richter ML, Hein R, Huchzermeyer B. Important subunit interactions in the chloroplast ATP synthase. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1458:326-42. [PMID: 10838048 DOI: 10.1016/s0005-2728(00)00084-0] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
General structural features of the chloroplast ATP synthase are summarized highlighting differences between the chloroplast enzyme and other ATP synthases. Much of the review is focused on the important interactions between the epsilon and gamma subunits of the chloroplast coupling factor 1 (CF(1)) which are involved in regulating the ATP hydrolytic activity of the enzyme and also in transferring energy from the membrane segment, chloroplast coupling factor 0 (CF(0)), to the catalytic sites on CF(1). A simple model is presented which summarizes properties of three known states of activation of the membrane-bound form of CF(1). The three states can be explained in terms of three different bound conformational states of the epsilon subunit. One of the three states, the fully active state, is only found in the membrane-bound form of CF(1). The lack of this state in the isolated form of CF(1), together with the confirmed presence of permanent asymmetry among the alpha, beta and gamma subunits of isolated CF(1), indicate that ATP hydrolysis by isolated CF(1) may involve only two of the three potential catalytic sites on the enzyme. Thus isolated CF(1) may be different from other F(1) enzymes in that it only operates on 'two cylinders' whereby the gamma subunit does not rotate through a full 360 degrees during the catalytic cycle. On the membrane in the presence of a light-induced proton gradient the enzyme assumes a conformation which may involve all three catalytic sites and a full 360 degrees rotation of gamma during catalysis.
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Affiliation(s)
- M L Richter
- Department of Molecular Biosciences, The University of Kansas, Lawrence 66045, USA
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Abstract
The capacity to predict future events permits a creature to detect, model, and manipulate the causal structure of its interactions with its environment. Behavioral experiments suggest that learning is driven by changes in the expectations about future salient events such as rewards and punishments. Physiological work has recently complemented these studies by identifying dopaminergic neurons in the primate whose fluctuating output apparently signals changes or errors in the predictions of future salient and rewarding events. Taken together, these findings can be understood through quantitative theories of adaptive optimizing control.
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Affiliation(s)
- W Schultz
- Institute of Physiology, University of Fribourg, CH-1700 Fribourg, Switzerland.
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Pedersen PL. Frontiers in ATP synthase research: understanding the relationship between subunit movements and ATP synthesis. J Bioenerg Biomembr 1996; 28:389-95. [PMID: 8951084 DOI: 10.1007/bf02113979] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
How biological systems make ATP has intrigued many scientists for well over half the 20th century, and because of the importance and complexity of the problem it seems likely to continue to be a source of fascination to both senior and younger investigators well into the 21st century. Scientific battles fought to unravel the vast secrets by which ATP synthases work have been fierce, and great victories have been short-lived, tempered with the realization that more structures are needed, additional subunits remain to be conquered, and that during ATP synthesis, not one, but several subunits may undergo either significant conformational changes, repositioning, or perhaps even physical "rotation" similar to bacterial flagella (1,2). In this introductory article, the author briefly summarizes our current knowledge about the complex substructure of ATP synthases, what we have learned from X-ray crystallography of the F1 unit, and current evidence for subunit movements.
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Affiliation(s)
- P L Pedersen
- Department of Biological Chemistry, Johns Hopkins University, School of Medicine, Baltimore, Maryland 21205-2185, USA
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Ben-Jacob E, Shochet O, Tenenbaum A, Cohen I, Czirók A, Vicsek T. Response of bacterial colonies to imposed anisotropy. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 53:1835-1843. [PMID: 9964446 DOI: 10.1103/physreve.53.1835] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Ben-Jacob E, Cohen I, Shochet O, Tenenbaum A, Czirók A, Vicsek T. Cooperative formation of chiral patterns during growth of bacterial colonies. PHYSICAL REVIEW LETTERS 1995; 75:2899-2902. [PMID: 10059433 DOI: 10.1103/physrevlett.75.2899] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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47
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Nogueiral FS, de Barros HGPL. Study of the motion of magnetotactic bacteria. EUROPEAN BIOPHYSICS JOURNAL: EBJ 1995. [DOI: 10.1007/bf00216826] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Nealson KH, Moser DP, Saffarini DA. Anaerobic electron acceptor chemotaxis in Shewanella putrefaciens. Appl Environ Microbiol 1995; 61:1551-4. [PMID: 11536689 PMCID: PMC167410 DOI: 10.1128/aem.61.4.1551-1554.1995] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Shewanella putrefaciens MR-1 can grow either aerobically or anaerobically at the expense of many different electron acceptors and is often found in abundance at redox interfaces in nature. Such redox interfaces are often characterized by very strong gradients of electron acceptors resulting from rapid microbial metabolism. The coincidence of S. putrefaciens abundance with environmental gradients prompted an examination of the ability of MR-1 to sense and respond to electron acceptor gradients in the laboratory. In these experiments, taxis to the majority of the electron acceptors that S. putrefaciens utilizes for anaerobic growth was seen. All anaerobic electron acceptor taxis was eliminated by the presence of oxygen, nitrate, nitrite, elemental sulfur, or dimethyl sulfoxide, even though taxis to the latter was very weak and nitrate and nitrite respiration was normal in the presence of dimethyl sulfoxide. Studies with respiratory mutants of MR-1 revealed that several electron acceptors that could not be used for anaerobic growth nevertheless elicited normal anaerobic taxis. Mutant M56, which was unable to respire nitrite, showed normal taxis to nitrite, as well as the inhibition of taxis to other electron acceptors by nitrite. These results indicate that electron acceptor taxis in S. putrefaciens does not conform to the paradigm established for Escherichia coli and several other bacteria. Carbon chemo-taxis was also unusual in this organism: of all carbon compounds tested, the only positive response observed was to formate under anaerobic conditions.
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Affiliation(s)
- K H Nealson
- Center for Great Lakes Studies, University of Wisconsin-Milwaukee 53204, USA
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Hillesdon AJ, Pedley TJ, Kessler JO. The development of concentration gradients in a suspension of chemotactic bacteria. Bull Math Biol 1995; 57:299-344. [PMID: 7703922 DOI: 10.1007/bf02460620] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
When a suspension of bacterial cells of the species Bacillus subtilis is placed in a chamber with its upper surface open to the atmosphere complex bioconvection patterns are observed. These arise because the cells: (1) are denser than water; and (2) usually swim upwards, so that the density of an initially uniform suspension becomes greater at the top than the bottom. When the vertical density gradient becomes large enough, an overturning instability occurs which ultimately evolves into the observed patterns. The reason that the cells swim upwards is that they are aerotactic, i.e., they swim up gradients of oxygen, and they consume oxygen. These properties are incorporated in conservation equations for the cell (N) and oxygen (C) concentrations, and these are solved in the pre-instability phase of development when N and C depend only on the vertical coordinate and time. Numerical results are obtained for both shallow- and deep-layer chambers, which are intrinsically different and require different mathematical and numerical treatments. It is found that, for both shallow and deep chambers, a thin boundary layer, densely packed with cells, forms near the surface. Beneath this layer the suspension becomes severely depleted of cells. Furthermore, in the deep chamber cases, a discontinuity in the cell concentration arises between this cell-depleted region and a cell-rich region further below, where no significant oxygen concentration gradients develop before the oxygen is fully consumed. The results obtained from the model are in good qualitative agreement with the experimental observations.
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Affiliation(s)
- A J Hillesdon
- Department of Applied Mathematical Studies, University of Leeds, U.K
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Nealson K, Saffarini D, Moser D, Smith MJ. A spectrophotometric method for monitoring tactic responses of bacteria under anaerobic conditions. J Microbiol Methods 1994. [DOI: 10.1016/0167-7012(94)90005-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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