Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session Q3: BiofilmsBio Fluids: External Interfacial
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Chair: Jesse Belden, Naval Undersea Warfare Center, Newport Room: 403 |
Tuesday, November 21, 2017 12:50PM - 1:03PM |
Q3.00001: The Fluid Dynamics of Nascent Biofilms Nicola Farthing, Ben Snow, Laurence Wilson, Martin Bees Many anti-biofilm approaches target mature biofilms with biochemical or physio-chemical interventions. We investigate the mechanics of interventions at an early stage that aim to inhibit biofilm maturation, focusing on hydrodynamics as cells transition from planktonic to surface-attached.~ Surface-attached~cells generate flow fields that are relatively long-range compared with cells that are~freely-swimming. We look at the effect of these flows on the biofilm formation. In particular, we use digital inline holographic microscopy to determine the three-dimensional flow due to a surface-attached cell and the effect this flow has on both tracers and other cells in the fluid.~ We compare experimental data with two models of cells on boundaries. The first approach utilizes slender body theory and captures many of the features of the experimental field. The second model develops a simple description in terms of singularity solutions of Stokes' flow, which produces qualitatively similar dynamics to both the experiments and more complex model but with significant computational savings. The range of validity of multiple cell arrangements is investigated.~ These two descriptions can be used to investigate the efficacy of actives developed by Unilever on nascent biofilms. [Preview Abstract] |
Tuesday, November 21, 2017 1:03PM - 1:16PM |
Q3.00002: Air bubbles induce a critical continuous stress to prevent marine biofouling accumulation Jesse Belden, Mark Menesses, Natasha Dickenson, James Bird Significant shear stresses are needed to remove established hard fouling organisms from a ship hull. Given that there is a link between the amount of time that fouling accumulates and the stress required to remove it, it is not surprising that more frequent grooming requires less shear stress. One approach to mitigate marine biofouling is to continuously introduce a curtain of air bubbles under a submerged surface; it is believed that this aeration exploits the small stresses induced by rising bubbles to continuously prevent accumulation. Although curtains of rising bubbles have successfully prevented biofouling accumulation, it is unclear if a single stream of bubbles could maintain a clean surface. In this talk, we show that single bubble stream aeration can prevent biofouling accumulation in regions for which the average wall stress exceeds approximately 0.01 Pa. This value is arrived at by comparing observations of biofouling growth and prevention from field studies with laboratory measurements that probe the associated flow fields. We also relate the spatial and temporal characteristics of the flow to the size and frequency of the rising bubbles, which informs the basic operating conditions required for aeration to continuously prevent biofouling accumulation. [Preview Abstract] |
Tuesday, November 21, 2017 1:16PM - 1:29PM |
Q3.00003: Integrating fluid dynamic and biologic effects on staphylococci bacteria biofilms Erica Sherman, Jennifer Endres, Kenneth Bayles, Timothy Wei \textit{Staphylococcus aureus} bacteria are able to form biofilms and distinctive tower structures that facilitate their ability to tolerate treatment and to spread within the human body. The formation of towers, which break off, get carried downstream and serve to initiate biofilms in other parts of the body are of particular interest here. In previous work on biofilm growth and evolution in steady, laminar microchannel flows, it has been established that tower formation occurs around a very limited range of applied shear stresses centered on 0.6 dynes/cm$^{\mathrm{2}}$. Quantifying cell density characteristics as a function of time during biofilm formation reveals indicators of tower development hours before towers actually form and become visible. The next step in this research is to explore biological factors that might explain why this specific shear is so important. Additional studies with mutants, $e.g.$ ica-A, that have been tied to tower formation have been conducted. The shear dependence of these mutants and their correlation to the behavior of wild type \textit{S. aureus} is examined. [Preview Abstract] |
Tuesday, November 21, 2017 1:29PM - 1:42PM |
Q3.00004: Electrochemical determination of the onset of bacterial surface adhesion Akhenaton-Andrew Jones, Cullen Buie Microbial biofouling causes economic loss through corrosion and drag losses on ship hulls, and in oil and food distribution. Microorganisms interacting with surfaces under these open channel flows contend with high shear rates and active transport to the surface. The metallic surfaces they interact with carry charge at various potentials that are little addressed in literature. In this study we demonstrate that the Levich curve, chronoamperometry, and cyclic voltammetry in a rotating disk electrode are ideal for studying adhesion of microbes to metallic surfaces. We study the adhesion of \textit{Escherichia coli}, \textit{Bacillus subtilis}, and $1\,\mu \textrm{m}$ silica microspheres over a 0.15 -- ${37.33}{\,\,\textrm{dynes}\cdot \textrm{cm}^{-2}}$ or shear rates of 14.73 -- ${3727.28}{\,\,\textrm{s}^{-1}}$ range. Our results agree with literature on red blood cells in rotating disk electrodes, deposition rates from optical systems, and show that we can quantify changes in active electrode area by bacteria adhesion and protein secretion. These methods measure changes in area instead of mass, are more accurate than fluorescence microscopy, and apply to a larger range of problems than on-chip flow devices. [Preview Abstract] |
Tuesday, November 21, 2017 1:42PM - 1:55PM |
Q3.00005: Characterization of Mechanical Properties of Microbial Biofilms Elizabeth Callison, James Gose, Marc Perlin, Steven Ceccio The physical properties of microbial biofilms grown subject to shear flows determine the form and mechanical characteristics of the biofilm structure, and consequently, the turbulent interactions over and through the biofilm. These biofilms -- sometimes referred to as slime -- are comprised of microbial cells and extracellular polymeric substance (EPS) matrices that surround the multicellular communities. Some of the EPSs take the form of streamers that tend to oscillate in flows, causing increased turbulent mixing and drag. As the presence of EPS governs the compliance and overall stability of the filamentous streamers, investigation of the mechanical properties of biofilms may also inform efforts to understand hydrodynamic performance of fouled systems. In this study, a mixture of four diatom genera was grown under turbulent shear flow on test panels. The mechanical properties and hydrodynamic performance of the biofilm were investigated using rheology and turbulent flow studies in the Skin-Friction Flow Facility at the University of Michigan. The diatoms in the mixture of algae were identified, and the elastic and viscous moduli were determined from small-amplitude oscillations, while a creep test was used to evaluate the biofilm compliance. [Preview Abstract] |
Tuesday, November 21, 2017 1:55PM - 2:08PM |
Q3.00006: Measurements of drag and flow over biofilm Joel Hartenberger, James W. Gose, Marc Perlin, Steven L. Ceccio Microbial `slime' biofilms detrimentally affect the performance of every day systems from medical devices to large ocean-going vessels. In flow applications, the presence of biofilm typically results in a drag increase and may alter the turbulence in the adjacent boundary layer. Recent studies emphasize the severity of the drag penalty associated with soft biofouling and suggest potential mechanisms underlying the increase; yet, fundamental questions remain---such as the role played by compliance and the contribution of form drag to the overall resistance experienced by a fouled system. Experiments conducted on live biofilm and 3D printed rigid replicas in the Skin-Friction Flow Facility at the University of Michigan seek to examine these factors. The hydrodynamic performance of the biofilms grown on test panels was evaluated through pressure drop measurements as well as conventional and microscale PIV. High-resolution, 3D rigid replicas of select cases were generated via additive manufacturing using surface profiles obtained from a laser scanning system. Drag and flow measurements will be presented along with details of the growth process and the surface profile characterization method. [Preview Abstract] |
Tuesday, November 21, 2017 2:08PM - 2:21PM |
Q3.00007: ABSTRACT WITHDRAWN |
Tuesday, November 21, 2017 2:21PM - 2:34PM |
Q3.00008: Continuous Microfluidics (Ecology-on-a-Chip) Experiments for Long Term Observation of Bacteria at Liquid-Liquid Interfaces Michael Miranda, Andrew White, Maryam Jalali, Jian Sheng A microfluidic bioassay incorporating a peristaltic pump and chemostat capable of continuously culturing a bacterial suspension through a microchannel for an extended period of time relevant to ecological processes is presented. A single crude oil droplet is dispensed on-chip and subsequently pinned to the top and bottom surfaces of the microchannel to establish a vertical curved oil-water interface to observe bacteria without boundary interference. The accumulation of extracellular polymeric substances (EPS), microbial film formation, and aggregation is provided by DIC microscopy with an EMCCD camera at an interval of 30 sec. Cell-interface interactions such as cell translational and angular motilities as well as encountering, attachment, detachment to the interface are obtained by a high speed camera at 1000 fps with a sampling interval of 10 min. Experiments on \textit{Pseudomonas} sp. (P62) and isolated EPS suspensions from \textit{Sagitulla Stelleta} and \textit{Roseobacter} show rapid formation of bacterial aggregates including EPS streamers stretching tens of drop diameters long. These results provide crucial insights into environmentally relevant processes such as the initiation of marine oil snow, an alternative mode of biodegradation to conventional bioconsumption. [Preview Abstract] |
Tuesday, November 21, 2017 2:34PM - 2:47PM |
Q3.00009: A Route to Marine Oil Snow: Bacteria Produce Extracellular Polymeric Streamers on Oil Micro-Droplets with Significant Impacts on Drag Andrew White, Maryam Jalali, Michael Miranda, Matthew Amaro, Jian Sheng After the Deepwater Horizon oil spill in 2010 a substantial fraction of oil settled to the seafloor. This contradicts popular belief that dispersed oil merely undergoes bioconsumption and dissolution following a spill; results suggest these only account for up to 50\% of the droplet’s volume. A possible mechanism for sedimentation is Marine Oil Snow (MOS): mucus-rich aggregates of plankton, extracellular polymeric substances (EPS), oil and other debris. However, MOS formation, particularly in real marine environments, are poorly understood. For instance, our previous results suggested plankton encounter rates on a rising oil drop would be too low and microbial residence times too short to form substantial aggregates. In this work we use a microfluidic bioassay (Ecology-on-a-Chip) to simulate a crude oil drop rising in a bacteria suspension by pinning the drop in a microchannel with a continuously flowing bacteria culture. Microbial EPS streamers form on an oil-water interface within 30 min. High speed microscopy provides snapshots of the evolving flow including increased drag due to streamers and recovery when streamers detach. The streamer induced drag and consequential reduction in rising velocity establish a missing link for MOS as a key pathway for the fate of spilled oil. [Preview Abstract] |
Tuesday, November 21, 2017 2:47PM - 3:00PM |
Q3.00010: Bacteria interface interactions in \textit{Ecology-on-a-Chip} by holographic microscopy and interferometry Jian Sheng, Andrew White, Maryam Jalali To improve our remediation of oil spills into marine system, one must understand the fate of oil under complex physical, chemical and biological environments. It is found that various processes such as wind, wave, turbulence and currents break oil into suspensions of droplets, in which states consumption by microbial further degrade the oil. Our prior studies show that marine bacteria do not adopt biofilm life style at oil-water interface in comparison to those near a solid substrate. On the contrary, Extracellular Polymer Substance of oily microbial aggregates is easily formed around an oil droplet. This highlights complexities of cell oil interactions at a liquid-liquid interface. To investigate these mechanisms at oil water interface quantitative, we have developed a micro-bioassay consisting of continuous microfluidics with a substrate printed with oil droplet array, namely Ecology-on-a-Chip, and an integrated digital holographic microscopy (DHM) and interferometer (DHI). The oil-water interface can be maintained over days (\textgreater 10 days), suitable for conducting long-term observations. 3D movements of bacteria are tracked by DHM, while the interface morphology are measured by DHI at 10nm. The system is applied to \textit{Pseudomonas} sp. (PS62) near crude-water interface and \textit{Escherichia coli} (AW405) at hexadecane-water interface subject to low surface tension. The 3D motility, attachment, detachment and dispersion of cells as well as motility induced interface change are discussed. [Preview Abstract] |
Tuesday, November 21, 2017 3:00PM - 3:13PM |
Q3.00011: Dissolution and degradation of crude oil droplets by different bacterial species and consortia by microcosm microfluidics Maryam Jalali, Jian Sheng Bacteria are involved in cleanup and degradation of crude oil in polluted marine and soil environments. A number of bacterial species have been identified for consuming petroleum hydrocarbons with diverse metabolic capabilities. We conducted laboratory experiments to investigate bacterial consumption by monitoring the volume change to oil droplets as well as effects of oil droplet size on this process. To conduct our study, we developed a micro-bioassay containing an enclosed chamber with bottom substrate printed with stationary oil microdroplets and a digital holographic interferometer (DHI). The morphology of microdroplets was monitored in real time over 100 hours and instantaneous flow field was also measured by digital holographic microscope. The substrates with printed oil droplets were further evaluated with atomic force microscopy (AFM) at the end of each experiment. Three different bacteria species,\textit{ Pseudomonas} \textit{sp,} \textit{Alcanivorax borkumensis}, and \textit{Marinobacter hydrocarbonoclasticus}, as well as six bacterial consortia were used in this study. The results show that droplets smaller than 20\textmu m in diameter are not subject to bacterial degradation and the volume of droplet did not change beyond dissolution. Substantial species-specific behaviors have been observed in isolates. The experiments of consortia and various flow shears on biodegradation and dissolution are ongoing and will be reported. [Preview Abstract] |
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