Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session M39: Bio: Bacterial Accumulation and Growth |
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Chair: Michele Guala, University of Minnesota Room: Portland Ballroom 256 |
Tuesday, November 22, 2016 8:00AM - 8:13AM |
M39.00001: Understanding Abiotic Triggers For Cyanobacteria Blooms in Lakes Using a Long Term In-situ Monitoring Research Station Anne Wilkinson, Miki Hondzo, Christine Salomon, Shahram Missaghi, Michele Guala Harmful Algal Blooms (HAB) are ubiquitous ecological and public health hazards. HAB are made up of potentially toxic freshwater cyanobacteria. The occurrences of toxic HAB are unpredictable and highly spatially/temporary variable in freshwater ecosystems. To study the abiotic triggers for toxic HAB, a research station has been deployed in a eutrophic lake from June-October 2016. This station provides hourly water quality profiles and meteorological (every 5 minutes) monitoring with real time access. Water quality monitoring is performed by an autonomously traversed sonde that provides chemical, physical and biological measurements; including phycocyanin, a light-absorbing pigment distinct to cyanobacteria. The research station is a sentinel for HAB accumulation, prompting focused HAB analysis, including: phytoplankton and toxin composition/concentration, and turbulent kinetic energy dissipation rates. We will discuss how mixing conditions, temperature stratification, light intensity, surface wind magnitude and energy dissipation mediate a)HAB formation/composition b)toxicity and c)cyanobacteria stratification.The results will help illuminate abiotic processes that trigger HAB accumulation/toxicity, which can direct timely toxic HAB prediction and prevention efforts. [Preview Abstract] |
Tuesday, November 22, 2016 8:13AM - 8:26AM |
M39.00002: Clustering of floating particles in stratified turbulence Guido Boffetta, Filippo De Lillo, Stefano Musacchio, Alessandro Sozza We study the dynamics of small floating particles transported by stratified turbulence in presence of a mean linear density profile as a simple model for the confinement and the accumulation of plankton in the ocean. By means of extensive direct numerical simulations we investigate the statistical distribution of floaters as a function of the two dimensionless parameters of the problem. We find that vertical confinement of particles is mainly ruled by the degree of stratification, with a weak dependency on the particle properties. Conversely, small scale fractal clustering, typical of non-neutral particles in turbulence, depends on the particle relaxation time and is only weakly dependent on the flow stratification. The implications of our findings for the formation of thin phytoplankton layers are discussed. [Preview Abstract] |
Tuesday, November 22, 2016 8:26AM - 8:39AM |
M39.00003: Bacterial finite-size effects for population expansion under flow Federico Toschi, Francesca Tesser, Jos C.H. Zeegers, Herman J.H. Clercx, Luc Brunsveld For organisms living in a liquid ecosystem, flow and flow gradients have a dual role as they transport nutrient while, at the same time, dispersing the individuals. In absence of flow and under homogeneous conditions, the growth of a population towards an empty region is usually described by a reaction-diffusion equation. The effect of fluid flow is not yet well understood and the interplay between transport of individuals and growth opens a wide scenario of possible behaviors. In this work, we study experimentally the dynamics of non-motile E. coli bacteria colonies spreading inside rectangular channels, in PDMS microfluidic devices. By use of a fluorescent microscope we analyze the dynamics of the population density subjected to different co- and counter-flow conditions and shear rates. A simple model incorporating growth, dispersion and drift of finite size beads is able to explain the experimental findings. This indicates that models based on the Fisher-Kolmogorov-Petrovsky-Piscounov equation (FKPP) may have to be supplemented with bacterial finite-size effects in order to be able to accurately reproduce experimental results for population spatial growth. [Preview Abstract] |
Tuesday, November 22, 2016 8:39AM - 8:52AM |
M39.00004: Dynamics of water uptake in spreading bacterial colonies C. Nadir Kaplan, L. Mahadevan Bacteria can colonize a moist, nutrient-rich surface by secreting osmolytes to recruit water from the underlying substrate. We consider the outermost region of an expanding \textit{Escherichia coli} biofilm, where the rim width is set by the cell growth rate and the colony expansion speed. Based on the hypothesis that sliding due to the mechanical contact between cells governs their speed, we model the interplay between the flow of cells and the water uptake via osmolyte production. This allows us to determine the front expansion speed and the non-uniform biofilm thickness, in agreement with experiments. [Preview Abstract] |
Tuesday, November 22, 2016 8:52AM - 9:05AM |
M39.00005: ABSTRACT WITHDRAWN |
Tuesday, November 22, 2016 9:05AM - 9:18AM |
M39.00006: Bacterial accumulation in viscosity gradients Nicolas Waisbord, Jeffrey Guasto Cell motility is greatly modified by fluid rheology. In particular, the physical environments in which cells function, are often characterized by gradients of viscous biopolymers, such as mucus and extracellular matrix, which impact processes ranging from reproduction to digestion to biofilm formation. To understand how spatial heterogeneity of fluid rheology affects the motility and transport of swimming cells, we use hydrogel microfluidic devices to generate viscosity gradients in a simple, polymeric, Newtonian fluid. Using video microscopy, we characterize the random walk motility patterns of model bacteria (\textit{Bacillus subtilis}), showing that both wild-type (`run-and-tumble') cells and smooth-swimming mutants accumulate in the viscous region of the fluid. Through statistical analysis of individual cell trajectories and body kinematics in both homogeneous and heterogeneous viscous environments, we discriminate passive, physical effects from active sensing processes to explain the observed cell accumulation at the ensemble level. [Preview Abstract] |
Tuesday, November 22, 2016 9:18AM - 9:31AM |
M39.00007: Investigation of cyanobacteria in a controlled hyperbolic straining flow Farzan Akbaridoust, Jimmy Philip, Ivan Marusic Here we report a systematic study on the effect of straining flow on cyanobacteria, which are a cause of significant water contamination issues worldwide. We focus on the species Anaebena Circinalis. A micro-cross channel equipped with two online computer-controlled on-chip membrane valves was designed and fabricated using standard soft-lithography. The device produces a hyperbolic straining flow on a micron-scaled region similar to G. I. Taylor's four-roll mill at larger scale. It was used to investigate the behaviour of a single filament of cynobacteria in a crowded medium under an increasing uniform strain rate flow. The velocity field and the resulting uniform strain-rate was measured in the absence of bacteria filaments using micro-PIV. A large number of single filaments of bacteria were trapped and exposed to stain-rates over $2$ to $15$ s\textsuperscript{-1}. Previous studies have reported anecdotal evidence of suspected mechanical damage to Anaebena Circinalis for strain rates considerably lower than the maximum values studied here. In our case, no mechanical damage was observed. [Preview Abstract] |
Tuesday, November 22, 2016 9:31AM - 9:44AM |
M39.00008: Measurements of fluid transport by controllable vertical migrations of plankton Isabel A. Houghton, John O. Dabiri Diel vertical migration of zooplankton has been proposed to be a significant contributor to local and possibly large-scale fluid transport in the ocean. However, studies of this problem to date have been limited to order-of-magnitude estimates based on first principles and a small number of field observations. In this work, we leverage the phototactic behavior of zooplankton to stimulate controllable vertical migrations in the laboratory and to study the associated fluid transport and mixing. Building upon a previous prototype system, a laser guidance system induces vertical swimming of brine shrimp (Artemia salina) in a 2.1 meter tall, density-stratified water tank. The animal swimming speed and spacing during the controlled vertical migration is characterized with video analysis. A schlieren imaging system is utilized to visualize density perturbations to a stable stratification for quantification of fluid displacement length scales and restratification timescales. These experiments can add to our understanding of the dynamics of active particles in stratified flows. [Preview Abstract] |
Tuesday, November 22, 2016 9:44AM - 9:57AM |
M39.00009: Fluid dynamics of two-dimensional pollination in Ruppia maritima Naga Musunuri, Daniel Bunker, Susan Pell, Fischer Pell, Pushpendra Singh The aim of this work is to understand the physics underlying the mechanisms of two-dimensional aquatic pollen dispersal, known as hydrophily. We observed two mechanisms by which the pollen released from male inflorescences of \textit{Ruppia maritima} is adsorbed on a water surface: (i) inflorescences rise above the surface and after they mature their pollen mass falls onto the surface as clumps and disperses on the surface; (ii) inflorescences remain below the surface and produce air bubbles which carry their pollen mass to the surface where it disperses. In both cases dispersed pollen masses combined under the action of capillary forces to form pollen rafts. This increases the probability of pollination since the capillary force on a pollen raft towards a stigma is much larger than on a single pollen grain. The presence of a trace amount of surfactant can disrupt the pollination process so that the pollen is not transported or captured on the water surface. [Preview Abstract] |
Tuesday, November 22, 2016 9:57AM - 10:10AM |
M39.00010: Stochastic cycle selection in active flow networks Francis Woodhouse, Aden Forrow, Joanna Fawcett, Jorn Dunkel Active biological flow networks pervade nature and span a wide range of scales, from arterial blood vessels and bronchial mucus transport in humans to bacterial flow through porous media or plasmodial shuttle streaming in slime molds. Despite their ubiquity, little is known about the self-organization principles that govern flow statistics in such non-equilibrium networks. By connecting concepts from lattice field theory, graph theory and transition rate theory, we show how topology controls dynamics in a generic model for actively driven flow on a network. Through theoretical and numerical analysis we identify symmetry-based rules to classify and predict the selection statistics of complex flow cycles from the network topology. Our conceptual framework is applicable to a broad class of biological and non-biological far-from-equilibrium networks, including actively controlled information flows, and establishes a new correspondence between active flow networks and generalized ice-type models. [Preview Abstract] |
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