The influence of light on copper‐limited growth of an oceanic diatom,Thalassiosira oceanica (Coscinodiscophyceae)

Thalassiosira oceanica (CCMP 1005) was grown over a range of copper concentrations at saturating and subsaturating irradiance to test the hypothesis that Cu and light were interacting essential resources. Growth was a hyperbolic function of irradiance in Cu‐replete medium (263 fmol Cu′ · L^?1) with maximum rates achieved at 200 μmol photons · m^?2 · s^?1. Lowering the Cu concentration at this irradiance to 30.8 fmol Cu′ · L^?1 decreased cellular Cu quota by 7‐fold and reduced growth rate by 50%. Copper‐deficient cells had significantly slower (P < 0.0001) rates of maximum, relative photosynthetic electron transport (rETR_max) than Cu‐sufficient cells, consistent with the role of Cu in photosynthesis in this diatom. In low‐Cu medium (30.8 fmol Cu′ · L^?1), growth rate was best described as a positive, linear function of irradiance and reached the maximum value measured in Cu‐replete cells when irradiance increased to 400 μmol photons · m^?2 · s^?1. Thus, at high light, low‐Cu concentration was no longer limiting to growth: Cu concentration and light interacted strongly to affect growth rate of T. oceanica (P < 0.0001). Relative ETR_max and Cu quota of cells grown at low Cu also increased at 400 μmol photons · m^?2 · s^?1 to levels measured in Cu‐replete cells. Steady‐state uptake rates of Cu‐deficient and sufficient cells were light‐dependent, suggesting that faster growth of T. oceanica under high light and low Cu was a result of light‐stimulated Cu uptake.     

Wall shear over high degree stenoses pertinent to atherothrombosis

Atherothrombosis can induce acute myocardial infarction and stroke by progressive stenosis of a blood vessel lumen to full occlusion. Since thrombus formation and embolization may be shear-dependent, we quantify the magnitude of shear rates in idealized severely stenotic coronary arteries (≥75% by diameter) using computational fluid dynamics to characterize the shear environment that may exist during atherothrombosis. Maximum shear rates in severe short stenoses were found to exceed 250,000 s^?1 (9500 dynes/cm²) and can reach a peak value of 425,000 s^?1 for a 98% stenosis. These high shear rates exceed typical shear used for in vitro blood flow experiments by an order of magnitude, indicating the need to examine thrombosis at very high shear rates. Pulsatility and stenosis eccentricity were found to have minor effects on the maximum wall shear rates in severe stenoses. In contrast, increases in the stenosis length reduced the maximum shear to 107,000 s^?1 (98% stenosis), while surface roughness could increase focal wall shear rates to a value reaching 610,000 s^?1 (90% stenosis). The “shear histories” of circulating platelets in these stenoses are far below reported activation thresholds. Platelets may be required to form bonds in 5 μs and resist shear forces reaching 8000 pN per platelet. Arterial thrombosis occurs in the face of pathological high shear stress, creating rapid and strong bonds without prior activation of circulating platelets.     

Investigation of human platelet adhesion under low shear conditions in a rotational flow chamber

Even though blood pumps have come into clinical usage, thrombo-embolic complications still pose a major problem, and they have not yet been clarified and quantified. However, it is known that the basis of thrombus formation is platelet adhesion, which is thought to be closely associated with the shear rate. Therefore, our current interest focuses on the effect of shear conditions on platelet adhesion. We have designed and carried out an experimental setup allowing fluorescent microscopy of whole blood within a rotational viscometer under controllable shear conditions. A small area of the bottom plate was coated with type I collagen, which provided a model of the injured vessel as a target for platelet adhesion. Using this setup, the time course of platelet adhesion under several different shear rates, ranging from 127 to 723 s^?1, was studied. Platelet adhesion increased along with shear rates up to 283 s^?1, followed by a gradual decrease when the shear rate exceeded 346 s^?1. The adhesion amounts were statistically significant between 283 and 173 s^?1 (p = 0.02), 173 and 127 s^?1 (p = 0.035), and 283 and 503 s^?1 (p = 0.03), respectively. This result suggests that there is an optimal shear condition around 300 s^?1 for platelet adhesion to type I collagen.     

Growth and dry-mass partitioning in tomato as affected by phosphorus nutrition and light

We studied the effects of phosphorus (P) and light on the physiological and morphological components of growth of young tomato plants (Lycopersicon esculentum Mill. cv. Capita). The importance of dry‐mass partitioning and starch accumulation in explaining the effects of P limitation on growth was examined more closely. Plants were grown at a wide range of exponential P supply rates (between 70 and 320 mg g^?1 d^?1) and one free‐access treatment (1 mm ). Two light levels (70 and 300 µmol m^?2 s^?1) were applied. Growth response coefficients (GRCs) were calculated to address the importance of different growth parameters in explaining relative growth rate (RGR). At both light levels, net assimilation rate (NAR) was more important than leaf area ratio (LAR) in explaining the effects of P on growth as indicated by GRCs. At less severe P limitation, LAR became more important and NAR less important. Dry‐mass partitioning to both roots and leaves played a minor role in determining the effects of P limitation on growth as indicated by low GRCs. The increase in starch at mild P limitation showed that the assimilate supply was not limiting. At severe P limitation, the rate of photosynthesis was decreased, as suggested by the decrease in starch accumulation.     

Photoautotrophic potato cells: Transition from heterotrophic to autotrophic growth

Cells of potato (Solanum tuberosum L.) were obtained which were capable of photoautotrophic growth in liquid suspension culture under a photon flux density of 90–110 μmol m^?2 s^?1 PAR and in an atmosphere enriched with 2% CO₂. These photoautotrophic cells contained between 100 to 200 μg Chl (g fresh weight)^?1 and fixed CO₂ at a maximum rate of 16 μmol CO₂ (g fresh weight)^?1h^?1. In order to obtain cells capable of photoautotrophic growth it was necessary to adapt highly chlorophyllous heterotrophic cells (>50 μg Chl (g fresh weight)^?1) for growth in medium with 2.5 g sucrose 1^?1 (photomixotrophic cells). The photomixotropic cells had a Chl content of ca 100 μg Chl (g fresh weight)^?1 and were capable of photosynthetic activity which allowed them to survive after sugars had been depleted from the medium. It was from the photomixotrophic cells that cells capable of photoautotrophic growth were obtained. Heterotrophic cells initially established in liquid medium with 25 g sucrose I^?1 from chlorophyllous callus contained about 50 to 150 μg Chl (g fresh weight)^?1. However, after 5 to 10 passages the Chl content decreased to a maximum of 15 μg Chl (g fresh weight)^?1. These cells could not be adapted to photomixotrophic or photoautotrophic growth. These cells also were not able to regain Chl or initiate high rates of CO₂ fixation during the stationary phase of growth as did photomixotrophic cells or chlorophyllous heterotrophic cells. The loss of Chl exhibited by the cells during adaption to heterotrophic growth could be attributed at least in part to unbalanced growth (when cell division and growth exceeds Chl accumulation). Sucrose appeared to have an inhibitory effect directly on photosynthesis independent of Chl accumulation.     

Platelet Transport Rates and Binding Kinetics at High Shear over a?Thrombus

Thrombus formation over a ruptured atherosclerotic plaque cap can occlude an artery with fatal consequences. We describe a computational model of platelet transport and binding to interpret rate-limiting steps seen in experimental thrombus formation over a collagen-coated stenosis. The model is used to compute shear rates in stenoses with growing boundaries. In the model, moving erythrocytes influence platelet transport based on shear-dependent enhanced diffusivity and a nonuniform platelet distribution. Adhesion is modeled as platelet-platelet binding kinetics. The results indicate that observed thrombus growth rates are limited by platelet transport to the wall for shear rates up to 6000 s⁻¹. Above 7000 s⁻¹, the thrombus growth rate is likely limited by binding kinetics (10⁻⁴ m/s). Thrombus growth computed from these rate-limiting steps match the thrombus location and occlusion times for experimental conditions if a lag time for platelet activation is included. Using fitted parameters, the model is then used to predict thrombus size and shape at a higher Reynolds number flow consistent with coronary artery disease.     

Relationships between metabolic rate, muscle electromyograms and swim performance of adult chinook salmon

Oxygen consumption rates of adult spring chinook salmon Oncorhynchus tshawytscha increased with swim speed and, depending on temperature and fish mass, ranged from 609 mg O₂ h^?1 at 30 cm s^?1 (c. 0·5 BL s^?1) to 3347 mg O₂ h^?1 at 170 cm s^?1 (c. 2·3 BL s^?1). Corrected for fish mass, these values ranged from 122 to 670 mg O₂ kg^?1 h^?1, and were similar to other Oncorhynchus species. At all temperatures (8, 12·5 and 17° C), maximum oxygen consumption values levelled off and slightly declined with increasing swim speed >170 cm s^?1, and a third‐order polynomial regression model fitted the data best. The upper critical swim speed (U_crit) of fish tested at two laboratories averaged 155 cm s^?1 (2·1 BL s^?1), but U_crit of fish tested at the Pacific Northwest National Laboratory were significantly higher (mean 165 cm s^?1) than those from fish tested at the Columbia River Research Laboratory (mean 140 cm s^?1). Swim trials using fish that had electromyogram (EMG) transmitters implanted in them suggested that at a swim speed of c. 135 cm s^?1, red muscle EMG pulse rates slowed and white muscle EMG pulse rates increased. Although there was significant variation between individual fish, this swim speed was c. 80% of the U_crit for the fish used in the EMG trials (mean U_crit 168·2 cm s^?1). Bioenergetic modelling of the upstream migration of adult chinook salmon should consider incorporating an anaerobic fraction of the energy budget when swim speeds are ≥80% of the U_crit.     

Shear rate dependence of free energy barrier height for phenyl ring rotations in polystyrene based on non-equilibrium molecular dynamics simulations

Polystyrene properties are influenced by ring motions in side groups. The main chain conformation and interaction with the surroundings dominate the ring rotations. It is known that shear flow affects linear chain conformation and molecular distribution. However, shear-induced variations in the ring rotations have yet to be studied. This study presents a shear flow system of polystyrene via non-equilibrium molecular dynamics simulations. The free energy barrier of the phenyl ring rotations was obtained from the distribution of angle χ between the ring and main chain based on the Boltzmann distribution law. The results showed that the barrier height approaches a constant value at a shear rate less than 10¹⁰ s^? 1, but decreases with an increase in shear rate higher than 10^10.5 s^? 1. Furthermore, the radial distribution function and potential energies were compared. Remarkably, the shear flow reduced the bond vibrations of the phenyl rings, but increased the separation between intermolecular particles. Hence, a smaller cavity is necessary for the rings to rotate once but more volume is occupied by the rings. The smaller volume obtained via main chain motions needed to construct the cavity lowers the energy barrier height at shear rate higher than 10^10.5 s^? 1.     

Adhesion study of silicone coatings: the interaction of thickness,modulus and shear rate on adhesion force

Abstract

Interactions between coating thickness, modulus and shear rate on pseudobarnacle adhesion to a platinum-cured silicone coating were studied using a statistical experimental design. A combined design method was used for two mixture components and two process variables. The two mixture components, vinyl end-terminated polydimethylsiloxanes (V21: MW = 6 kg mole^?1 and V35: MW = 4 9.5 kg mole^?1, Gelest Inc.) were mixed at five different levels to vary the modulus. The dry coating thickness was varied from 160 – 740 μm and shear tests were performed at four different shear rates (2, 7, 12, and 22 μm s^?1). The results of the statistical analysis showed that the mixture components were significant factors on shear stress, showing an interaction with the process variable. For the soft silicone coating based on the high molecular weight polydimethylsiloxane (E = 0.08 MPa), shear stress significantly increased as coating thickness decreased, while shear rate slightly impacted shear force especially at 160 μm coating thickness. As the modulus was increased (E = 1.3 MPa), more force was required to detach the pseudobarnacle from the coatings, but thickness and rate dependence on shear stress became less important.     

Determining possible thrombus sites in an extracorporeal device,using computational fluid dynamics-derived relative residence time

The prediction of conditions that may result in thrombus formation is a useful application of computational fluid dynamics. A number of techniques exist, based on the consideration of wall shear stress and regions of low blood flow; however, no clear guideline exists for the best practice of their use. In this paper, the sensitivity of each parameter and the specific mechanical forces are explained, before the optimal indicator of thrombosis risk is outlined. An extracorporeal access device cavity provides a suitable geometry to test the methodology. The recommended method for thrombus prediction considers areas with a calculated residence time (RT) and shear strain rate (SSR) thresholds, here set to RT>1 and SSR < 10 s^? 1. Evidence of thrombosis was found for physiological waveforms with an absence of reverse flow, which is expected to ‘wash out’ the cavity. The predicted thrombosis sites compare well with evidence collected from explanted devices.     

Effects from shear stress on morphology and growth of early stages of Norway spruce somatic embryos

The shear stress effect on directional expansion of pro embryogenic masses (PEMs) and suspensor cell development of somatic embryos of Norway spruce (Picea abies) at the proliferation stage was studied by a direct and quantitative image analysis system. The experimental system allowed for detailed observations of the effect of hydrodynamic shear stress in rotating and deforming liquid cultures of proliferating Norway spruce somatic embryos. Briefly, somatic embryos at an early development stage comprised only of clusters of meristematic cells without suspensor cells were fixed on an alginate film. The alginate film was affixed on the bottom of a flow cell and the somatic embryos were subjected to laminar flow through the chamber of the flow cell. Magnified images of the cell clusters were collected every 24 h. The image data was processed based on a normalized cross‐correlation method, capable of measuring morphological and size features of individual cell clusters in both temporal and spatial domains. No suspensor cells developed in the cell clusters under shear stress of 140 s^?1 for the duration of the experiments. Cell clusters in the control cultured in stationary liquid conditions developed suspensor cells after 5–9 days in culture. Furthermore, the radial growth of meristematic cell clusters was inhibited by shear rates of 86 and 140 s^?1, corresponding to shear stress of 0.086 and 0.14 N/m², compared to growth under stationary conditions. The shear rate showed a significant negative correlation to growth rate. Control group showed no preference for direction during growth under static conditions. Biotechnol. Bioeng. 2010; 105: 588–599. © 2009 Wiley Periodicals, Inc.     

GROWTH,PHOTOSYNTHESIS AND MAINTENANCE METABOLIC COST IN THE DIATOM PHAEODACTYLUM TRICORNUTUM AT VERY LOW LIGHT LEVELS 1

The compensation point for growth of Phaeodactylum tricornutum Bohlin is less than 1 μmol. m^?2s^?1. Growth at low PFDs (<3.5 μmol. m^?2.s^?1) does not appear to reduce the maximum quantum efficiency of photosynthesis (ø_m) or to greatly inhibit the potential for light-saturated, carbon-specific photosynthesis (P_m^c). The value for ø_m in P. tricornutum is 0.10–0.12 mol O₂-mol photon^?1, independent of acclimation PFD between 0.75 and 200 μmol.m^?2.s^?1 in nutrient-sufficient cultures. P_m^c in cells of P. tricornutum acclimated to PFDs <3.5 μmol m^?2?s^?1 is approximately 50% of the highest value obtained in nutrient-sufficient cultures acclimated to growth-rate-saturating PFDs. In addition, growth at low PFDs does not severely restrict the ability of cells to respond to an increase in light level. Cultures acclimated to growth at lees than 1% of the light-saturated growth rate respond rapidly to a shift-up in PFD after a short initial lag period and achieve exponential growth rates of 1.0 d^?1 (65% of the light- and nutrient-saturated maximum growth rate) at both 40 and 200 μmol.m^?2.s^?1     

Variations in the microbial community of biofilms under different near-wall hydraulic shear stresses in agricultural irrigation systems

Abstract

The hydraulic characteristics along agricultural irrigation pipelines directly affect the local near-wall hydraulic shear stress and biofilm accumulation. However, the variations in the microbial community during the process remain unknown. Based on the Couette-Taylor reactor, a device was developed to accurately control the hydraulic shear stress. The results indicated that the near-wall hydraulic shear stresses showed quadratic correlations with microbial contents (represented by phospholipid fatty acids r?>?0.77, p?<?0.05), and the maximum values were obtained under the shear stresses of 0.20-0.35?Pa. For two types of treated wastewater, the mutual operational taxonomic units among different shear stress treatments showed good consistency (>185). Their corresponding response in the microbial community was represented by the quantitative correlations between the near-wall hydraulic shear stresses and the polymorphism indices (r?>?0.82, p?<?0.05). Among the microorganisms, Firmicutes at the phylum level were significantly affected by the shear stress and significantly influenced the biofilm accumulation process.     

When is stream invertebrate drift catastrophic? The role of hydraulics and sediment transport in initiating drift during flood events

1. The term ‘catastrophic drift’ is used to describe the large‐scale displacement of invertebrates that occurs during periods of increased river discharge. However, the physical processes that lead to animals entering the water column at such times remain poorly understood. Specifically, the hypothesis that the movement of bed sediments during floods triggers a large increase in drift has lacked a rigorous field test. 2. Using a portable flume, the hydraulic conditions and rates of bedload transport associated with small, frequent floods were created in situ within a reach of a gravel bed river. Experiments focussed on the patches of fine sediment which are the dominant source of bed material transported during small floods. The flume produced near bed velocities of up to 2 m s^?1 over the patches, increasing shear stress, initiating sediment transport and causing invertebrates to enter the drift. 3. The total number of individuals lost from the bed, as well as the taxonomic composition of the drift, were influenced strongly by shear stress and bedload. The rate of loss from the bed was low at shear stresses <9 dynes cm^?2 (0–4 individuals min^?1 from the 0.5 m² flume bed area). Once shear stress exceeded 9 dynes cm^?2, the threshold that resulted in consistent bedload transport from the patches, the rate of loss of animals increased to a maximum of 56 individuals min^?1. When bedload transport rates were at their highest, the taxonomic composition of the drift was more similar to the benthos than it was to the drift observed when bed material was stable. 4. Absolute rates of bedload transport created by the manipulations were extremely low (<7 g m^?1 s^?1) and typical of those measured during small, frequent floods. Events of this magnitude do not break up the armour layer across the reach as a whole and so exposed patches of fine sediment are the principal source of bedload material. Consequently, discharge events not considered as disturbances in geomorphic terms may initiate frequent episodes of so‐called ‘catastrophic drift’ from patches of stream bed.     

TEMPERATURE AND IRRADIANCE EFFECTS ON GROWTH OF PITHOPHORA OEDOGONIA (CHLOROPHYCEAE) AND SPIROGYRA SP. (CHAROPHYCEAE)1

Growth responses of Pithophora oedogonia (Mont.) Wittr. and Spirogyra sp. to nine combinations of temperature (15°, 25°, and 35°C) and photon flux rate (50, 100, and 500 μmol·m^?2·s^?1) were determined using a three-factorial design. Maximum growth rates were measured at 35°C and 500 pmol·m^?2·s^?1 for P. oedogonia (0.247 d^?1) and 25°C and 500 μmol·m^?2·s^?1 for Spirogyra sp. (0.224 d^?1). Growth rates of P. oedogonia were strongly inhibited at 15°C (average decrease= 89%of maximum rate), indicating that this species is warm stenothermal. Growth rates of Spirogyra sp. were only moderately inhibited at 15° and 35°C (average decrease = 36 and 30%, respectively), suggesting that this species is eurythermal over the temperature range employed. Photon flux rate had a greater influence on growth of Spirogyra sp. (31% reduction at 50 pmol·m^?2·s^?1 and 25°C) than it did on growth of P. oedogonia (16% reduction at 50 μmol·m^?2·s^?1 and 35°C). Spirogyra sp. also exhibited much greater adjustments to its content of chlorophyll a (0.22–3.34 μg·mg fwt^?1) than did P. oedogonia (1.35–3.08 μg·mg fwt^?1). The chlorophyll a content of Spirogyra sp. increased in response to both reductions in photon flux rate and high temperatures (35°C). Observed species differences are discussed with respect to in situ patterns of seasonal abundance in Surrey Lake, Indiana, the effect of algal mat anatomy on the internal light environment, and the process of acclimation to changes in temperature and irradiance conditions.     

Causes of shear sensitivity of the toxic dinoflagellate Protoceratium reticulatum

Dinoflagellates have proven extremely difficult to culture because they are inhibited by low‐level shear forces. Specific growth rate of the toxic dinoflagellate Protoceratium reticulatum was greatly decreased compared with static control culture by intermittent exposure to a turbulent hydrodynamic environment with a bulk average shear rate that was as low as 0.3 s^?1. Hydrodynamic forces appeared to induce the production of reactive oxygen species (ROS) within the cells and this caused peroxidation of cellular lipids and ultimately cell damage. Exposure to damaging levels of shear rate correlated with the elevated level of lipoperoxides in the cells, but ROS levels measured directly by flow cytometry did not correlate with shear induced cell damage. This was apparently because the measured level of ROS could not distinguish between the ROS that are normally generated by photosynthesis and the additional ROS produced as a consequence of hydrodynamic shear forces. Continuously subjecting the cells to a bulk average shear rate value of about 0.3 s^?1 for 24‐h caused an elevation in the levels of chlorophyll a, peridinin and dinoxanthin, as the cells apparently attempted to counter the damaging effects of shear fields by producing pigments that are potential antioxidants. In static culture, limitation of carbon dioxide produced a small but measureable increase in ROS. The addition of ascorbic acid (0.1 mM) to the culture medium resulted in a significant protective effect on lipid peroxidation, allowing cells to grow under damaging levels of shear rates. This confirmed the use of antioxidant additives as an efficient strategy to counter the damaging effects of turbulence in photobioreactors where shear sensitive dinoflagellates are cultivated. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Design of a rotating disk reactor to assess the colonization of biofilms by free-living amoebae under high shear rates

The present study was aimed at designing and optimizing a rotating disk reactor simulating high hydrodynamic shear rates (γ), which are representative of cooling circuits. The characteristics of the hydrodynamic conditions in the reactor and the complex approach used to engineer it are described. A 60 l tank was filled with freshwater containing free-living amoebae (FLA) and bacteria. Adhesion of the bacteria and formation of a biofilm on the stainless steel coupons were observed. FLA were able to establish in these biofilms under γ as high as 85,000 s^?1. Several physical mechanisms (convection, diffusion, sedimentation) could explain the accumulation of amoeboid cells on surfaces, but further research is required to fully understand and model the fine mechanisms governing such transport under γ similar to those encountered in the industrial environment. This technological advance may enable research into these topics.     

Characterization of planktonic and biofilm cells from two filamentous cyanobacteria using a shotgun proteomic approach

Abstract

Cyanobacteria promote marine biofouling with significant impacts. A qualitative proteomic analysis, by LC-MS/MS, of planktonic and biofilm cells from two cyanobacteria was performed. Biofilms were formed on glass and perspex at two relevant hydrodynamic conditions for marine environments (average shear rates of 4?s^?1 and 40?s^?1). For both strains and surfaces, biofilm development was higher at 4?s^?1. Biofilm development of Nodosilinea sp. LEGE 06145 was substantially higher than Nodosilinea sp. LEGE 06119, but no significant differences were found between surfaces. Overall, 377 and 301 different proteins were identified for Nodosilinea sp. LEGE 06145 and Nodosilinea sp. LEGE 06119. Differences in protein composition were more noticeable in biofilms formed under different hydrodynamic conditions than in those formed on different surfaces. Ribosomal and photosynthetic proteins were identified in most conditions. The characterization performed gives new insights into how shear rate and surface affect the planktonic to biofilm transition, from a structural and proteomics perspective.     

Interaction between migration behaviour and estuarine mortality in cultivated Atlantic salmon Salmo salar smolts

Migration behaviour and estuarine mortality of cultivated Atlantic salmon Salmo salar smolts in a 16 km long estuary were studied using two methods: (1) acoustic telemetry and (2) group tagging in combination with trap nets. Progression rates of surviving individuals through the estuary were relatively slow using both methods [0·38 L_T (total length) s^?1 v. 0·25 L_T s^?1]. In 2012, the progression rate was slow from the river to the estuary (0·55 L_T s^?1) and the first part of the estuary (0·31 L_T s^?1), but increased thereafter (1·45–2·21 L_T s^?1). In 2013, the progression rate was fast from the river to the estuary (4·31 L_T s^?1) but was slower thereafter (0·18–0·91 L_T s^?1). Survival to the fjord was higher in 2012 (47%) compared to 2013 (6%). Fast moving individuals were more likely to migrate successfully through the estuary compared to slower moving individuals. Adult recapture of coded‐wire‐tagged S. salar was generally low (0·00–0·04%). Mortality hot spots were related to topographically distinct areas such as the river outlet (in 2012) or the sill separating the estuary and the fjord (in 2013). At the sill, an aggregation of cod Gadus morhua predating on cultivated smolts was identified. The results indicate that slow progression rates through the estuary decreases the likelihood of smolts being detected outside the estuary. The highly stochastic and site‐specific mortality patterns observed in this study highlight the complexity in extrapolating mortality patterns of single release groups to the entire smolt run of wild S. salar.     

Response of a concentrated monoclonal antibody formulation to high shear

There is concern that shear could cause protein unfolding or aggregation during commercial biopharmaceutical production. In this work we exposed two concentrated immunoglobulin‐G1 (IgG1) monoclonal antibody (mAb, at >100 mg/mL) formulations to shear rates between 20,000 and 250,000 s^?1 for between 5 min and 30 ms using a parallel‐plate and capillary rheometer, respectively. The maximum shear and force exposures were far in excess of those expected during normal processing operations (20,000 s^?1 and 0.06 pN, respectively). We used multiple characterization techniques to determine if there was any detectable aggregation. We found that shear alone did not cause aggregation, but that prolonged exposure to shear in the stainless steel parallel‐plate rheometer caused a very minor reversible aggregation (<0.3%). Additionally, shear did not alter aggregate populations in formulations containing 17% preformed heat‐induced aggregates of a mAb. We calculate that the forces applied to a protein by production shear exposures (<0.06 pN) are small when compared with the 140 pN force expected at the air–water interface or the 20–150 pN forces required to mechanically unfold proteins described in the atomic force microscope (AFM) literature. Therefore, we suggest that in many cases, air‐bubble entrainment, adsorption to solid surfaces (with possible shear synergy), contamination by particulates, or pump cavitation stresses could be much more important causes of aggregation than shear exposure during production. Biotechnol. Bioeng. 2009;103: 936–943. © 2009 Wiley Periodicals, Inc.