Influence of hydrodynamics and nutrients on biofilm structure

Hydrodynamic conditions control two interlinked parameters; mass transfer and drag, and will, therefore, significantly influence many of the processes involved in biofilm development. The goal of this research was to determine the effect of flow velocity and nutrients on biofilm structure. Biofilms were grown in square glass capillary flow cells under laminar and turbulent flows. Biofilms were observed microscopically under flow conditions using image analysis. Mixed species bacterial biofilms were grown with glucose (40 mg/l) as the limiting nutrient. Biofilms grown under laminar conditions were patchy and consisted of roughly circular cell clusters separated by interstitial voids. Biofilms in the turbulent flow cell were also patchy but these biofilms consisted of patches of ripples and elongated 'streamers' which oscillated in the flow. To assess the influence of changing nutrient conditions on biofilm structure the glucose concentration was increased from 40 to 400 mg/l on an established 21 day old biofilm growing in turbulent flow. The cell clusters grew rapidly and the thickness of the biofilm increased from 30 μ to 130 μ within 17 h. The ripples disappeared after 10 hours. After 5 d the glucose concentration was reduced back to 40 mg/l. There was a loss of biomass and patches of ripples were re-established within a further 2 d.     

Investigation of how agitation during precipitation,and subsequent processing affects the particle size distribution and separation of α-lactalbumin enriched whey protein precipitates

In this work, α-lactalbumin (α-la) rich precipitate particles are formed and aged in a batch stirred-tank from a whey protein concentrate (WPC) dispersion. Precipitation of the proteins occurs during a period of acid-addition followed by an ageing period. This study investigates how stirred-tank impeller agitation and subsequent processing, by means of passing precipitate suspensions through a capillary tube or a partially open ball-valve, affect particle size and composition. Precipitate particles are largely unaffected when subjected to laminar capillary tube flow. However, as flow becomes transitional and thereafter turbulent, particle breakage increases, especially for precipitates formed and aged under mild agitation conditions. Precipitates passed through the ball-valve experience even greater particle size reduction as a sharp geometrical transition results in highly turbulent flow. Moreover, particles formed and aged under low shear conditions, though initially larger, are in fact weaker and fragment to a greater extent during turbulent processing through the ball-valve. This has process design implications for separation processes where particle size is important, as shear history can influence particle toughness. Substantial size reduction of particles can best be mitigated by identifying regions of high turbulence or sudden changes in flow geometry, and by redesigning these regions so as to reduce these effects.     

Improvement of the microcirculation in the acute ischemic rat limb during intravenous infusion of drag-reducing polymers

Drag-reducing polymers (DRPs) are blood-soluble macromolecules that can increase blood flow and reduce vascular resistance. The purpose of the present study is to examine the effects of DRPs on microcirculation in rat hind limb during acute femoral artery occlusion. Two groups of 20 male Wistar rats were subjected to either hemodynamic measurement or contrast enhanced ultrasound (CEU) imaging during peripheral ischemia. Both groups were further subdivided into a DRP-treated group or a saline-treated group. Polyethylene oxide (PEO) was chosen as the test DRP, and rats were injected with either 10 ppm PEO solution or saline through the caudal vein at a constant rate of 5 ml/h for 20 min. Abdominal aortic flow, iliac artery pressure, iliac vein pressure, heart rate, carotid artery pressure and central venous pressure (CVP) were monitored, and vascular resistance was calculated by (iliac artery pressure-iliac vein pressure)/abdominal aortic blood flow. Flow perfusion and capillary volume of skeletal muscle were measured by CEU. During PEO infusion, abdominal aortic blood flow increased (p<0.001) and vascular resistance decreased (p<0.001) compared to rats that received saline during peripheral ischemia. There was no significant change in ischemic skeletal capillary volume (A) with DRP treatment (p>0.05), but red blood cell velocity (β) and capillary blood flow (A×β) increased significantly (p<0.05) during PEO infusion. In addition, A, β and A×β all increased (p<0.05) in the contralateral hind limb muscle. In contrast, PEO had no significant influence on heart rate, mean carotid artery blood pressure or CVP. Intravenous infusion of drag reducing polymers may offer a novel hydrodynamic approach for improving microcirculation during acute peripheral ischemia.     

Prediction of mechanical damage to animal cells in turbulence

In previous work a model was proposed for estimation of disruption of animal cells in turbulent capillary flows using information about the hydrodynamics, and cell mechanical properties determined by micromanipulation. The model assumed that the capillary flow consists of a laminar sublayer and a homogeneous turbulent region, and within the latter eddies of sizes similar to or smaller than the cells interact with those cells, causing local surface deformations. The proposed mechanism of cell damage was that such deformations result in an increase in membrane tension and surface energy, and that a cell disrupts when its bursting membrane tension and bursting surface energy are exceeded. The surface energy of the cells was estimated from the kinetic energy of appropriate sized eddies. To test the model, cells were disrupted in turbulent flows in capillaries at mean energy dissipation rates ranging from 800 to 2×10⁴ Wkg^–1. The model assumed that the specific lysis rate is almost independent of the number of passes, which was verified by the experimental data. The implication was that despite the damage the cell mechanical properties did not change markedly during multiple recirculations through the capillaries. On average the model underestimated the cell disruption by about 15%. Although the model gave reasonably good predictions, it lacks proper explanation of the independence of the specific lysis rate on the number of passes. In this paper it is shown that this problem can be resolved in principle by consideration of the localisation of the energy dissipation in turbulent capillary flows. The necessity of further modelling of cell-turbulence interactions is demonstrated.     

A Potential Cost of Long Genitalia in Male Guppies: the Effects of Current Speed on Reproductive Behaviour

In the fish family Poeciliidae, male genitalia, the gonopodia, are remarkably diverse across species; however, we still do not have a good understanding of the evolutionary processes promoting this diversity. For one trait, gonopodium length, several studies support a role for sexual conflict in selection for longer gonopodia. However, genital elongation may come at a cost of reduced locomotor abilities (e.g. resulting from greater drag and resistance). In this study, we were interested in the potential role of natural selection on the evolution of gonopodium length in poeciliids. Specifically, we asked whether a greater genital length impedes male reproductive behaviours at higher flow rates in the Trinidadian guppy, Poecilia reticulata. Using a flow chamber, males were placed with females in low‐ and high‐flow regimes and reproductive behaviours were measured. We did not find evidence for a cost of bearing a longer gonopodium at high flow. However, males did alter their mating tactics in response to current flow. We discuss the implications of our findings, in the light of habitat selection, on the forms of selection operating on gonopodium length and the mating interactions between the sexes in poeciliids.     

The influence of biofilms on skin friction drag

The contribution of biofilms to skin friction drag is not clearly defined, and as regulations continue to restrict the use of biocides in antifouling paints, they are likely to form a greater presence on ship hulls. This paper reviews the flow regime around a ship's hull, the basics of boundary layer structure, and the effects of rigid surface roughness on drag. A review of experimental studies of biofilms in turbulent shear flows at laboratory and ship-scale is made. The consensus of these studies shows that biofilms increase skin friction drag. Some measurements carried out in turbulent boundary layer flow using a two-component, laser Doppler velocimeter (LDV) are also presented. These results indicate an increase in skin friction for biofilms that is dependent on composition as well as thickness.     

Skin-friction drag analysis from the forced convection modeling in simplified underwater swimming

This study deals with skin-friction drag analysis in underwater swimming. Although lower than profile drag, skin-friction drag remains significant and is the second and only other contribution to total drag in the case of underwater swimming. The question arises whether varying the thermal gradient between the underwater swimmer and the pool water may modify the surface shear stress distribution and the resulting skin-friction drag acting on a swimmer's body. As far as the authors are aware, such a question has not previously been addressed. Therefore, the purpose of this study was to quantify the effect of this thermal gradient by using the integral formalism applied to the forced convection theory. From a simplified model in a range of pool temperatures (20-30 degrees C) it was demonstrated that, whatever the swimming speeds, a 5.3% reduction in the skin-friction drag would occur with increasing average boundary-layer temperature provided that the flow remained laminar. However, as the majority of the flow is actually turbulent, a turbulent flow analysis leads to the major conclusion that friction drag is a function of underwater speed, leading to a possible 1.5% reduction for fast swimming speeds above 1m/s. Furthermore, simple correlations between the surface shear stress and resulting skin-friction drag are derived in terms of the boundary-layer temperature, which may be readily used in underwater swimming situations.     

Drag production mechanisms of filamentous biofilms

Abstract

Biofilms were grown on smooth acrylic surfaces for nominal incubation times of three, five, and ten weeks in a flow loop at the University of Michigan. The biofilm covered surfaces were exposed to the turbulent flow in a high-aspect ratio, fully developed channel flow facility at height-based Reynolds numbers from Re_H ≈ 5,000 to 30,000. Measurements of the pressure drop along each fouled upper surface revealed that the friction drag increased from approximately 10% to 400%. The wide range in drag penalty was linked to variations in flow speed, the average thickness of the biofilms, and the level of film coverage over each surface through scaling parameters and empirical correlations. Rigid replicas of select biofilms were produced from time-averaged laser scans collected while the biofilm was subjected to flow. These rigid biofilm replicas experienced roughly half the drag increase of their compliant counterparts with the increase in friction spanning roughly 50% to 200%.     

The distribution and prevalence of sponges in relation to environmental gradients within a temperate sea lough: vertical cliff surfaces

Abstract. The prevalence and distribution of sponges was surveyed on vertical cliff surfaces at Lough Hyne Marine Nature Reserve, Co. Cork, Ireland. The number of sponge species was recorded at 6-metre depth intervals at four sites within Lough Hyne, and at one site on the adjacent Atlantic coastline to examine differences in abundance and zonation patterns. Sites ranged from an exposed turbulent regime to sheltered, sedimented environments. Individual species showed different distributions and prevalence between sites and with increasing depth. Greatest differences were observed between the most- and least-disturbed sites. Distinct sponge zonation patterns were evident at all sites sampled. Twenty-five species were considered dominant at all five sites with the remaining 48 species considered rare. Only four of the 25 most-dominant species occurred at the site experiencing the most turbulent flow conditions, whereas 12 species were found at the site of unidirectional fast flow. At sites of moderate to slight water movement and high sedimentation, between 18 and 24 of the most dominant species were present. Encrusting forms constituted high proportions of sponge communities at all five sites sampled (although consisting of different species). At sites of turbulent and unidirectional fast flow massive forms also dominated whereas at the least turbulent sites, where sedimentation was high, arborescent sponges were abundant. Few species showed exclusive distribution to a single depth and site, but there was some degree of correlation between species distributions and abiotic factors such as sedimentation rate and flow regimes. Sponge distributions and densities are discussed with respect to the suitability of species' morphologies to particular environments, intra-specific and inter-specific competition and physiological adaptations that enable them to survive in different habitats.     

Rotating cylindrical filters used in perfusion cultures: CFD simulations and experiments

The particle and fluid dynamics in a rotating cylindrical filtration (RCF) system used for animal cell retention in perfusion processes was studied. A validated CFD model was used and the results gave numerical evidence of phenomena that had been earlier claimed, but not proven for this kind of application under turbulent and high mesh permeability conditions, such as bidirectional radial exchange flow (EF) through the filter mesh and particle (cells) lateral migration. Taylor vortices were shown to cause EF 10‐100 times higher than perfusion flow, indicating that EF is the main drag source, at least in early stages of RCF operation. Particle lateral migration caused a cell concentration reduction (CCR) near the filter surface of approximately 10%, contributing significantly to cell separation in RCF systems and giving evidence that the mesh sieving effect is not the sole phenomenon underlying cell retention in RCF systems. Filter rotation rate was shown to significantly affect both EF and CCR. A higher separation efficiency (measured experimentally at 2,000‐L bioreactor scale) and an enhanced CCR (predicted by the numerical simulations) were found for the same rotation rate range, indicating that there is an optimal operational space with practical consequences on RCF performance. Experimental data of a large‐scale perfusion run employing the simulated RCF showed high cell viabilities for over 100 days, which is probably related to the fact that the computed shear stress level in the system was shown to be relatively low (below 20 Pa under all tested conditions). © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1093–1102, 2014     

Computational fluid dynamics of flow regime and hydrodynamic forces generated by a gliding North Atlantic right whale (Eubalaena glacialis)

Accurate estimates of drag on marine animals are required to investigate the locomotive cost, propulsive efficiency, and the impacts of entanglement if the animal is carrying fishing gear. In this study, we performed computational fluid dynamics analysis of a 10 m (length over all) right whale to obtain baseline measurements of drag on the animal. Swimming speeds covering known right whale speed range (0.125 m/s to 8 m/s) were tested. We found a weak dependence between drag coefficient and Reynolds number. At a swimming speed of 2 m/s, we analyzed the boundary layer thicknesses, the flow regimes, and drag components. We found the thickest boundary layer at the lateral sides of the peduncle, whereas the boundary layer thickness over the outer part of the flukes was less than 1.7 cm. Laminar flow occurred over the anterior ~0.6 LoA and turbulent flow from ~0.8 LoA to the fluke notch. On the surfaces of the flukes outside of the body wake region, flow was laminar. Our most significant finding is that the drag coefficient (0.0071–0.0059) of a right whale for swimming speeds ranging from 0.25 m/s to 2 m/s is approximately twice that of many previous estimates for cetaceans.     

The application of shear and extensional viscosity measurements to assess the potential of hylan in viscosupplementation

The shear and extensional viscosity characteristics have been compared for hyaluronan and two samples of a cross-linked derivative, hylan, of different molecular weights. While shear thinning behavior was observed for all systems in shear flow, strain thickening was observed in extensional flow for the relatively dilute systems. However, there was a progressive transition to shear thinning behavior as the polymer concentration was increased. It is evident from the results that the shear flow techniques alone provide an incomplete picture of the rheological properties of these materials and that extensional flow characteristics are potentially dominant. For example, at relatively high deformation rates of 500 s¹ and above, our results show that the extensional viscosities of aqueous solutions of the various polymers are at least two orders of magnitude greater than their corresponding shear flow viscosities. The incremental differences in viscosity with concentration increased with increasing molecular mass of the polymers and were greater in exensional flow than shear flow. These results demonstrate that the dynamic network structure formed by the higher molecular mass hylans offer potentially better physical and mechanical properties for viscosupplementation of diseased osteoarthritis joints compared with the parent hyaluronan.     

Pulsed Doppler ultrasound system for the measurement of velocity distributions and flow disturbances in arterial prostheses

For the investigation of flow through prosthetic arteries a pulsed Doppler ultrasound system has been characterized. Preliminary in vitro experiments using this system are described; they verify its suitability for making velocity profile and flow disturbance measurements. The output from a frequency tracker is compared with spectral analysis of Doppler signals for both laminar and turbulent flow regimes and the root mean square fluctuations on the tracker output signal are used to identify transition from laminar to turbulent flow. In addition, the turbulent itensity of poststenotic flow is quantified at several axial locations and for different rates of flow. Finally, we present velocity profile measurements which were obtained using a deconvolution technique to account for the finite size of the sample volume.     

Drag and reconfiguration of freshwater macrophytes

SUMMARY 1. Submerged freshwater macrophytes face large hydrodynamic forces in flowing waters in streams and on wave‐swept lake shores and require morphological adaptations to reduce the drag and the physical damage. This experiment studied five species of freshwater macrophytes and strap‐formed plastic leaves to test the predictions that: (i) increasing flexibility leads to greater reconfiguration and lower drag coefficients, (ii) flexible plants experience a steeper decline of drag coefficients with increasing water velocity than unflexible plants and (iii) plants mounted vertically on a horizontal substratum bend over in fast flow attaining a shielded position of low drag. 2. The results confirmed all three predictions. In fast flow, plants mounted upright on a horizontal platform gradually approached a position aligned with the flow, depending on their flexibility. In the range 8–50 cm s^?1 the deflection followed an interspecific negative linear relationship between log (tangent Φ) and velocity, where Φ represents the shoot angle normal to the horizontal level. Above 50 cm s^?1, further deflection was reduced perhaps by a combination of the elasticity and packing of shoots and the increasing lift generated by fast flow. 3. Drag coefficients of plants ranged between 0.01 and 0.1, typical of moderately to very streamlined objects. Drag coefficients declined log‐log linearly at increasing velocity, following negative slopes between ?0.67 and ?1.24 (median: ?1.0) because of reconfiguration and formation of a shielding canopy. Drag coefficients declined much less (median: ?0.55) for plants floating freely in the streaming water and which were capable of changing their shape but unable to form a shielding canopy. Drag coefficients declined even less for relatively unflexible plastic leaves (?0.30 to ?0.40), and they remained constant for stiff, bluff objects. 4. The experiments suggest that flow resistance of flexible, submerged macrophytes in natural streams may increase in direct proportion to water velocity because they form a shielding submerged canopy, and high water stages at peak flow may result in greater proportions of the water passing unimpeded above the canopy. In contrast, stiff amphibious and emergent reed plants should experience an increase of flow resistance with at least the square of velocity as reconfiguration is small and former aerial plant surfaces come into contact with the streaming water at higher water stages. Field experiments to test these predictions are urgently needed.     

Adaptations to increasing hydraulic stress: morphology, hydrodynamics and fitness of two higher aquatic plant species

Sessile organisms often exhibit morphological changes in response to permanent exposure to mechanical stimulation (wind or water movements). The adaptive value of these morphological changes (hydrodynamic performance and consequences on fitness) has not been studied extensively, particularly for higher plants submitted to flow stress. The aim was to determine the adaptive value of morphological patterns observed within two higher aquatic plant species, Berula erecta and Mentha aquatica, growing along a natural flow stress gradient. The hydrodynamic ability of each ramet was investigated through quantitative variables (drag coefficient and E-value). Fitness-related traits based on vegetative growth and clonal multiplication were assessed for each individual. For both species, the drag coefficient and the E-value were explained only to a limited extent by the morphological traits used. B. erecta exhibited a reduction in size and low overall plant drag at higher flow velocities, despite high drag values relative to leaf area, due to a low flexibility. The plants maintained their fitness, at least in part, through biomass reallocation: one tall ramet at low velocity, but shorter individuals with many interconnected stolons when flow velocity increased. For M. aquatica, morphological differences along the velocity gradient did not lead to greater hydrodynamic performance. Plant size increased with increasing velocities, suggesting the indirect effects of current favouring growth in high velocities. The fitness-related traits did not demonstrate lower plant fitness for high velocities. Different developmental constraints linked to plant morphology and trade-offs between major plant functions probably lead to different plant responses to flow stress.     

Fish skin bacteria: Production of friction-reducing polymers

The supernatant fluids of cultures of four bacterial strains isolated from the skin of barracuda contained extracellular polymer concentrations of 0.2–0.5 mg/ml and reduced factional drag by 2.5–22% in a turbulent flow rheometer. The production and properties of one of the drag-reducing polymers, referred to as PS-6, were studied further. Polymer PS-6 was produced by strain NS-31 in minimal salts medium supplemented with ethanol or glucose. The polymer began to accumulate in the culture medium during exponential phase and continued to be produced during stationary phase. It reduced drag by 55% at a concentration of 0.75 mg/ ml. Acid-base titration of the deproteinized polymer PS-6A gave two inflection points: pK₁=3.26 (2.4 eq/mg) and pK₂=9.66 (0.8 eq/mg).¹³C-NMR spectroscopy of PS-6A resolved 25 peaks, including three methyl groups, three carbonyl groups, and four signals in the anomeric region (99–103 ppm), indicating the presence of four different monosaccharides. Strong acid hydrolysis of PS-6A yielded an amino acid, pyruvate, and four reducing sugars: a hexosamine, a uronic acid, and two hexoses which migrated on TLC similarly to glucose and galactose. The possible role of bacteria in production of drag-reducing mucus is discussed.     

Oxygen diffusion from capillary layers with concurrent flow

Oxygen transport from capillary layers with concurrent flow is considered for symmetric and asymmetric distributions of oxygen concentration between the layers. The analysis is based on the solution previously obtained by the author [1]. Solutions for the symmetric case are shown to be very close to the corresponding solutions of the Krogh cylinder model. Asymmetry in oxygen distribution is introduced systematically by considering different velocities of blood in the alternate capillary layers, different inlet capillary oxygen tensions, and different capillary hematocrits. It is shown that increase of the degree of asymmetry leads to diminution of the mean oxygen tension.     

Sampling effort and species richness assessment: a case study on Brazilian spiders

The knowledge on the geographical distribution of species is essential for building biogeographical and macroecological hypotheses. However, information on this regard is not distributed uniformly in space and usually come from biased sampling. The aim of this study is to quantify the influence of spatial distribution of sampling effort on the assessment of spider species richness in Brazil. We used a database of spider distribution records in Brazil, based on the taxonomic and biodiversity survey literature. The results show that the Atlantic Forest was better sampled and had the highest spider species richness among the Brazilian biomes. The Amazon, though having large collecting gaps and high concentration of records around major cities and rivers, showed the second highest number of species. The Pampa had a large number of records, but these are concentrated near a major city in the transition zone with the Atlantic Forest. The Cerrado, Caatinga and Pantanal had shown to be poorly sampled and, consequently, were among the lesser known biomes regarding the spider fauna. A linear regression analysis showed that the spider species richness in Brazil is strongly correlated to the number of records. However, we have identified areas potentially richest in species, which strongly deviate from the predicted by our analyses. Our results show that it is possible to access the spatial variation in species richness, as long as the variation in sampling effort is taken into account.     

The distribution and prevalence of sponges in relation to environmental gradients within a temperate sea lough: inclined cliff surfaces

Abstract. Sponge communities on inclined cliff surfaces (40°) at Lough Hyne Marine Nature Reserve, Co. Cork, Ireland were sampled at five sites (four inside the lough and one on the adjacent Atlantic coast). Each site varied in sedimentation rate and flow regime. Sites ranged from turbulent (with negligible sedimentation) to very low flow (< 3 cm⁻¹) and highly sedimented regimes. Sponge species showed variation between sites and depth. The greatest difference in sponge communities was observed between the most turbulent and most sedimented sites. The distinct zonation patterns, present at all sites, were most pronounced at the highly sedimented sites. Encrusting forms constituted a high proportion of the sponges at all sites. However encrusting species found at the turbulent site were different to those at the sedimented sites. Arborescent species were common, mainly at the sedimented sites within Lough Hyne. Distributions of sponge species are considered with respect to morphological adaptation, competition and physiological adaptation. The distributions of sponge species on inclined surfaces are also compared with those on vertical cliff faces.     

Drag forces on common plant species in temperate streams: consequences of morphology, velocity and biomass

Swift flow in streams may physically influence the morphology and distribution of plants. I quantified drag as a function of velocity, biomass and their interaction on the trailing canopy of seven European stream species in an experimental flume and evaluated its importance for species distribution. Drag increased at a power of 1.3–1.9 with velocity and 0.59–0.77 with biomass in 75% of the measurements. Velocity and biomass interacted because higher velocity causes reconfiguration and greater internal shelter to unimpeded flow and higher biomass enhances shelter among neighbouring shoots. Increase of drag with velocity did not differ systematically among inherently streamlined or non-streamlined species while increase of drag with biomass was smallest among non-streamlined shoots which provide greater mutual shelter. At low shoot density, inherently streamlined species usually experienced the lowest drag conducive to colonisation and growth in swift flow. At high shoot density, no systematic differences in drag existed between the two morphologies. No clear relationship existed between drag forces, morphology and field distribution of species as a function of current velocity probably because a variety of environmental conditions and plant traits influences distribution. Drag on the trailing canopy usually increased 15- to 35-fold for a 100-fold increase of biomass suggesting that an even distribution of plants at low density across the stream bed offers greater resistance to downstream flow than an uneven distribution with the same biomass confined to dense patches surrounded by open flow channels. Thus, management strategies to ensure a patchy plants distribution should be suitable for combining agricultural drainage and ecological stream quality. Handling editor: S. M. Thomaz