The effect of flow on swimming bacteria controls the initial colonization of curved surfaces

The colonization of surfaces by bacteria is a widespread phenomenon with consequences on environmental processes and human health. While much is known about the molecular mechanisms of surface colonization, the influence of the physical environment remains poorly understood. Here we show that the colonization of non-planar surfaces by motile bacteria is largely controlled by flow. Using microfluidic experiments with Pseudomonas aeruginosa and Escherichia coli, we demonstrate that the velocity gradients created by a curved surface drive preferential attachment to specific regions of the collecting surface, namely the leeward side of cylinders and immediately downstream of apexes on corrugated surfaces, in stark contrast to where nonmotile cells attach. Attachment location and rate depend on the local hydrodynamics and, as revealed by a mathematical model benchmarked on the observations, on cell morphology and swimming traits. These results highlight the importance of flow on the magnitude and location of bacterial colonization of surfaces

The effect of flow on swimming bacteria controls the initial colonization of curved surfaces

The colonization of surfaces by bacteria is a widespread phenomenon with consequences on environmental processes and human health. While much is known about the molecular mechanisms of surface colonization, the influence of the physical environment remains poorly understood. Here we show that the colonization of non-planar surfaces by motile bacteria is largely controlled by flow. Using microfluidic experiments with Pseudomonas aeruginosa and Escherichia coli, we demonstrate that the velocity gradients created by a curved surface drive preferential attachment to specific regions of the collecting surface, namely the leeward side of cylinders and immediately downstream of apexes on corrugated surfaces, in stark contrast to where nonmotile cells attach. Attachment location and rate depend on the local hydrodynamics and, as revealed by a mathematical model benchmarked on the observations, on cell morphology and swimming traits. These results highlight the importance of flow on the magnitude and location of bacterial colonization of surfaces.Fil: Secchi, Eleonora. Eidgenössische Technische Hochschule Zurich. Institute of Environmental Engineering; SuizaFil: Vitale, Alessandra. Universitat Zurich; SuizaFil: Miño, Gastón Leonardo. Universidad Nacional de Entre Ríos. Facultad de Ingeniería. Laboratorio de Microscopía Aplicada a Estudios Moleculares y Celulares; Argentina. Universidad Nacional de Entre Ríos. Instituto de Investigación y Desarrollo en Bioingeniería y Bioinformática - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigación y Desarrollo en Bioingeniería y Bioinformática; ArgentinaFil: Kantsler, Vasily. University of Warwick; Reino UnidoFil: Eberl, Leo. Universitat Zurich; SuizaFil: Rusconi, Roberto. Humanitas University. Department of Biomedical Sciences; Italia. Humanitas Clinical and Research Center; ItaliaFil: Stocker, Roman. Eidgenössische Technische Hochschule Zurich. Institute of Environmental Engineering; Suiz

E coli Accumulation behind an Obstacle

This paper describes our findings regarding the accumulation of motile bacte-ria at the rear of a confined obstacle and the physical description of the me-chanisms at play. We found that the modification of flow due to the presence of the obstacle produces vorticity that favor the diffusion of bacteria towards the downstream stagnation point. By testing different flow rates, we deter-mined the range in which bacteria accumulate. More interestingly, we observe that hydrodynamic interaction between the bacteria and the top and bottom surface of the microfluidic chip maintain the bacteria in the region where the flow velocity is lower than their own velocity. In the case of non-motile bacte-ria, this effect is not observed because bacteria follow the streamlines as pas-sive tracers do.Fil: Miño, Gastón Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Entre Ríos. Universidad Nacional de Entre Ríos. Centro de Investigaciones y Transferencia de Entre Ríos; ArgentinaFil: Baabour, Magali Denise. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física. Grupo de Medios Porosos; ArgentinaFil: Chertcoff, Ricardo Héctor. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física. Grupo de Medios Porosos; ArgentinaFil: Gutkind, Gabriel Osvaldo. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; ArgentinaFil: Clément, Eric. Centre National de la Recherche Scientifique; FranciaFil: Auradou, Harold. Universite de Paris Xi. Laboratoire Automatiques et Systeme Thermiques; FranciaFil: Ippolito, Irene Paula. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física. Grupo de Medios Porosos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Enhanced diffusion due to active swimmers at a solid surface

We consider two systems of active swimmers moving close to a solid surface, one being a living population of wild-type \textit{E. coli} and the other being an assembly of self-propelled Au-Pt rods. In both situations, we have identified two different types of motion at the surface and evaluated the fraction of the population that displayed ballistic trajectories (active swimmers) with respect to those showing random-like behavior. We studied the effect of this complex swimming activity on the diffusivity of passive tracers also present at the surface. We found that the tracer diffusivity is enhanced with respect to standard Brownian motion and increases linearly with the activity of the fluid, defined as the product of the fraction of active swimmers and their mean velocity. This result can be understood in terms of series of elementary encounters between the active swimmers and the tracers.Comment: 4 pages, 2 figures in color, Physical Review Letters (in production

Dispositivo para el estudio de adhesión bacteriana en prótesis metálicas: Formación de biopelículas en contacto con superficies metálicas

La adhesión bacteriana sobre superficies de los materiales puede conducir al desarrollo de biopelículas responsables de infecciones en pacientes. Una detallada comprensión de los mecanismos involucrados en la adhesión bacteriana puede facilitar el desarrollo de superficies “antibacterianas”. En los últimos años el avance por generar nuevos materiales y estrategias que combatan las infecciones enimplante está creciendo. El proyecto intenta aplicar técnicas microfluídicas, microscópicas y de procesamiento de imagen para investigar los procesos de interacción entre bacterias y superficies. Los primeros pasos para consolidar este tipo de líneas innovadores en FIUNER requirieron desarrollar protocolos para observar distintos procesos biológicos a microescala usando diferentes técnicas microscópicas y adaptando el desarrollo de dispositivos microfluídicos a la infraestructura disponible. El desarrollo del proyecto permitió estudiar otros problemas que involucran sistemas microbiológicos, y gracias a enfoque biofísico se pudieron determinar y caracterizar el transporte y dinámicas involucradas en este tipo particular de suspensiones activas. Durante el proyecto se estudió el desarrollo de biopelículas en sustratos semisólidos y sólidos, se determinó la movilidad de diferentes cepas bacterianas y células eucariotas y también se propusieron soluciones mediante el modelado de este tipo de sistemas. ARK/CAICYT: http://id.caicyt.gov.ar/ark:/s22504559/whabk5o5

A two-sphere model for bacteria swimming near solid surfaces

We present a simple model for bacteria like \emph{Escherichia coli} swimming near solid surfaces. It consists of two spheres of different radii connected by a dragless rod. The effect of the flagella is taken into account by imposing a force on the tail sphere and opposite torques exerted by the rod over the spheres. The hydrodynamic forces and torques on the spheres are computed by considering separately the interaction of a single sphere with the surface and with the flow produced by the other sphere. Numerically, we solve the linear system which contains the geometrical constraints and the force-free and torque-free conditions. The dynamics of this swimmer near a solid boundary is very rich, showing three different behaviors depending on the initial conditions: (1) swimming in circles in contact with the wall, (2) swimming in circles at a finite distance from the wall, and (3) swimming away from it. Furthermore, the order of magnitude of the radius of curvature for the circular motion is in the range $8-50\,\mu$m, close to values observed experimentally.Comment: 10 pages, 4 figure

Colloid Transport in Porous Media: A Review of Classical Mechanisms and Emerging Topics

To celebrate the tenth anniversary of InterPore, we present an interdisciplinary review of colloid transport through porous media. This review aims to explore both classical colloid transport and topics that fall outside that purview and thus offer transformative insights into the physics governing transport behavior. First, we discuss the unique colloid characteristics relative to molecules and larger particles. Then, the classical advection?dispersion?filtration models (both conceptual and mathematical) of colloid transport are introduced as well as anomalous transport behaviors. Next, the forces of interaction between colloids and porous media surfaces are discussed. Fourth, applications that are interested in maximizing the transport of colloids through porous media are considered. Then the concept of motile, active biocolloids is introduced, and finally, colloid swarming as a newly recognized mode of transport is summarized.Fil: Molnar, Ian L.. York University; CanadáFil: Pensini, Erica. School Of Engineering; CanadáFil: Asad, Md Abdullah. York University; CanadáFil: Mitchell, Chven A.. Department Of Physics And Astronomy; Estados UnidosFil: Nitsche, Ludwig C.. College Of Engineering; Estados UnidosFil: Pyrak-Nolte, Laura J.. Department Of Physics And Astronomy; Estados UnidosFil: Miño, Gastón Leonardo. Universidad Nacional de Entre Ríos. Instituto de Investigación y Desarrollo en Bioingeniería y Bioinformática - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigación y Desarrollo en Bioingeniería y Bioinformática; ArgentinaFil: Krol, Magdalena M.. York University; Canad

Comparison of metacognitive knowledge about the reading of Biology texts between students of the City of Buenos Aires

En este trabajo se caracteriza y compara el conocimiento metacognitivo procedimental sobre lectura de textos de biología, en estudiantes de primer año de una escuela estatal de nivel medio de la Ciudad de Buenos Aires y estudiantes avanzados de la Licenciatura en Ciencias Biológicas de la Universidad de Buenos Aires (UBA). A partir de un enfoque cualitativo interpretativo, se realizaron entrevistas semi-estructuradas a los estudiantes, y sus relatos fueron analizados a partir de cuatro dimensiones: procesos de planificación de la lectura, procesos de monitoreo de la lectura, procesos de evaluación de la lectura y procesos de remediación de la incomprensión sobre lo leído. A partir del análisis de los resultados se concluye que los estudiantes universitarios avanzados de la Licenciatura en Ciencias Biológicas (UBA) consideran la aplicación de estrategias de carácter más autónomo para aprender a partir de la lectura y que tienen una concepción diferente a los estudiantes de primer año de la escuela de nivel medio estudiada, respecto de lo que significa aprender a través de un texto.In this work, we characterize and compare the procedural metacognitive knowledge about reading biology texts in students attending first year in a state middle school of the City of Buenos Aires and advanced students of the Bachelor in Biological Sciences of the University of Buenos Aires (UBA). Using a qualitative interpretative approach, semi-structured interviews were conducted with the students, and their stories were analysed from four dimensions: reading planning processes, reading monitoring processes, reading evaluation processes and processes for remediation of misunderstanding about what was read. From the analysis of the results, it is concluded that advanced students of the Bachelor in Biological Sciences (UBA) consider the application of more autonomous strategies for learning from reading and that they have a different conception than first year students attending the studied state middle school, with respect to what it means to learn through text.Fil: Miño, Mariela Haydée. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Formación e Investigación en Enseñanza de las Ciencias; ArgentinaFil: Toia, Sol N.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Formación e Investigación en Enseñanza de las Ciencias; ArgentinaFil: Pérez, Gastón Mariano. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Formación e Investigación en Enseñanza de las Ciencias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria; ArgentinaFil: Gutierrrez, Tatiana N.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Formación e Investigación en Enseñanza de las Ciencias; ArgentinaFil: Gonzalez Galli, Leonardo Martin. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Formación e Investigación en Enseñanza de las Ciencias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria; ArgentinaFil: Meinardi, Elsa Noemi. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Formación e Investigación en Enseñanza de las Ciencias; Argentin