Minimum Membrane Bending Energies of Fusion Pores

Membranes fuse by forming highly curved intermediates, culminating in structures described as fusion pores. These hourglass-like figures that join two fusing membranes have high bending energies, which can be estimated using continuum elasticity models. Fusion pore bending energies depend strongly on shape, and the present study developed a method for determining the shape that minimizes bending energy. This was first applied to a fusion pore modeled as a single surface and then extended to a more realistic model treating a bilayer as two monolayers. For the two-monolayer model, fusion pores were found to have metastable states with energy minima at particular values of the pore diameter and bilayer separation. Fusion pore energies were relatively insensitive to membrane thickness but highly sensitive to spontaneous curvature and membrane asymmetry. With symmetrical bilayers and monolayer spontaneous curvatures of ?0.1 nm^?1 (a typical value) separated by 6 nm (closest distance determined by repulsive hydration forces), fusion pore formation required 43–65 kT. The pore radius of ~2.25 nm fell within the range estimated from conductance measurements. With bilayer separation >6 nm, fusion pore formation required less energy, suggesting that protein scaffolds can promote fusion by bending membranes toward one another. With nonzero spontaneous monolayer curvature, the shape that minimized the energy change during fusion pore formation differed from the shape that minimized its energy after it formed. Thus, a nascent fusion pore will relax spontaneously to a new shape, consistent with the experimentally observed expansion of nascent fusion pores during viral fusion.     

Numerical 1D PIC-simulations of ion acceleration during laser-plasma interaction: Optimization of a two-component multilayered target structure

Ion beam acceleration is simulated using a one-dimensional 1D2P PIC code. The dependences of the maximum energy and width of the energy spectrum of the generated ion beams on the duration and intensity of laser radiation, as well as on the target parameters (thickness and number of layers, types and densities of atoms), are investigated. The optimal target configuration at which the energy of the accelerated ions is maximum (5–160 MeV for intensities of 5 × 10^{18 −5} × 10²⁰ W/cm²) is found. The optimal target configuration is shown to depend on the intensity and be independent of the laser pulse duration.     

Coupled-Resonator-Induced Fano Resonances for Plasmonic Sensing with Ultra-High Figure of Merits

Fano resonances are numerically predicted in an ultracompact plasmonic structure, comprising a metal-isolator-metal (MIM) waveguide side-coupled with two identical stub resonators. This phenomenon can be well explained by the analytic model and the relative phase analysis based on the scattering matrix theory. In sensing applications, the sensitivity of the proposed structure is about 1.1?×?10³ nm/RIU and its figure of merit is as high as 2?×?10⁵ at λ?=?980 nm, which is due to the sharp asymmetric Fano line-shape with an ultra-low transmittance at this wavelength. This plasmonic structure with such high figure of merits and footprints of only about 0.2 μm² may find important applications in the on-chip nano-sensors.     

Proteomics of the milk fat globule membrane from Camelus dromedarius

Camel milk has been widely characterized with regards to casein and whey proteins. However, in camelids, almost nothing is known about the milk fat globule membrane (MFGM), the membrane surrounding fat globules in milk. The purpose of this study was thus to identify MFGM proteins from Camelus dromedarius milk. Major MFGM proteins (namely, fatty acid synthase, xanthine oxidase, butyrophilin, lactadherin, and adipophilin) already evidenced in cow milk were identified in camel milk using MS. In addition, a 1D‐LC‐MS/MS approach led us to identify 322 functional groups of proteins associated with the camel MFGM. Dromedary MFGM proteins were then classified into functional categories using DAVID (the Database for Annotation, Visualization, and Integrated Discovery) bioinformatics resources. More than 50% of MFGM proteins from camel milk were found to be integral membrane proteins (mostly belonging to the plasma membrane), or proteins associated to the membrane. Enriched GO terms associated with MFGM proteins from camel milk were protein transport (p‐value = 1.73 × 10^?14), translation (p‐value = 1.08 × 10^?11), lipid biosynthetic process (p‐value = 6.72 × 10^?10), hexose metabolic process (p‐value = 1.89 × 10^?04), and actin cytoskeleton organization (p‐value = 2.72 × 10^?04). These findings will help to contribute to a better characterization of camel milk. Identified MFGM proteins from camel milk may also provide new insight into lipid droplet formation in the mammary epithelial cell.     

In vivo determination of young's modulus for the human cornea

The present paper describes a calculation technique to determine a value of Young's modulus for the cornea when the intraocular pressure, the shape of the cornea and the thickness variation along the cornea are known fromin vivo measurements. Twenty-eight persons were examined in both eyes and a mean value of Young's modulus for the cornea was calculated to 2.45×10⁴±0.57×10⁴ N/m² (S.D.).     

Implications of Using Steady-State Conditions in Estimating Dermal Uptake of Volatile Compounds in Municipal Drinking Water: An Example of THMs

Dermal exposure to volatile compounds (VC) in municipal water while showering is typically estimated using a steady-state condition between VC in water impacting on skin and skin exposed to water. The lag times to achieve steady-state between VC and skin can vary in the range of 7.5–218.3 min, while shower duration is often less than these values. Estimates of dermal exposure to VC using steady-state while showering may misinterpret exposure. This study developed models and estimated exposure to some disinfection byproducts (DBPs) through dermal pathway by considering lag times while showering. Dermal uptakes of VC were compared using different approaches. In the proposed approach, uptakes of trihalomethanes were estimated between 9.55 × 10^?10–1.43 × 10^?8 mg/cm² of skin during the lag times from exposure to water with trihalomethanes of 50 μg/L. These values were higher than the steady-state estimates (1.37 × 10^?10–4.34 × 10^?9 mg/cm²), and lower than the average exposure analysis (4.12 × 10^-8–1.93 × 10^?6 mg/cm²). Using the Drinking Water Surveillance Program data in Ontario, chronic daily intakes of trihalomethanes were estimated to be 9.40 × 10^?7 (1.85 × 10^?7–1.65 × 10^?6), 3.89 × 10^?6 (7.11 × 10^?7–2.33 × 10^?5), and 1.40 × 10^?6 (4.0 × 10^?7–1.77 × 10^?6) mg/kg/day in Toronto, Ottawa, and Hamilton, respectively. The findings can be useful in understanding THMs exposure and risk through dermal pathway.     

Pretreatment with alum or powdered activated carbon reduces bacterial predation-associated irreversible fouling of membranes

This study evaluated the co-application of bacterial predation by Bdellovibrio bacteriovorus and either alum coagulation or powdered activated carbon adsorption to reduce fouling caused by Escherichia coli rich feed solutions in dead-end microfiltration tests. The flux increased when the samples were predated upon or treated with 100 ppm alum or PAC, but co-treatment with alum and predation gave the best flux results. The total membrane resistance caused by the predated sample was reduced six-fold when treated with 100 ppm PAC, from 11.8 to 1.98 × 10¹¹ m^?1, while irreversible fouling (R_p) was 2.7-fold lower. Treatment with 100 ppm alum reduced the total resistance 14.9-fold (11.8 to 0.79 × 10¹¹ m^?1) while the R_p decreased 4.25-fold. SEM imaging confirmed this, with less obvious fouling of the membrane after the combined process. This study illustrates that the combination of bacterial predation and the subsequent removal of debris using coagulation or adsorption mitigates membrane biofouling and improves membrane performance.     

The effect of pressure on the electrical breakdown in the membranes of Valonia utricularis

The interpretation of electrical breakdown in terms of electro-mechanical instabilities, predicts that the breakdown potential should decrease with increasing cell turgor pressure.Experiments were conducted to test this hypothesis on cells of Valonia utricularis over a turgor pressure range of 0.5 · 10⁵–5.0 · 10⁵ N/m². Electrical breakdown was measured using intracellular electrodes and 500 μs current pulses. The pressure was monitored by an intracellular micropipette pressure transducer. The results obtained show a linear decrease in the critical breakdown potential with pressure. The effective compressive modulus of the cell membrane, γ, is calculated from the slope of this line to 69 ± 10 · 10⁵N/m² (average value of seven measurements). This is consistent with the theoretical prediction of the electromechanical model using our previously determined values of the elastic modulus of the membrane.A theoretical analysis is given of the effects of pressure on the breakdown. This includes also considerations of the indirect effect of pressure on the membrane via stretching of the cell wall with a possible coupling of such strains to the cell membrane. The results and analysis presented allow us to conclude on the basis of the experimentally determined breakdown P.D. of 959 mV that the region of membrane where electrical breakdown occurs is a dielectric with one of the following combinations of parameters: (A) a thickness δ = 7–9 nm with a dielectric constant ? = >10, e.g. a hydrated protein spanning the whole membrane. (B) δ = 4–5 nm with ? = 3–8, e.g. a lipoprotein of lipid bilayer dimensions. (C) δ ≈ 2 nm with ? = 2–3, e.g. a half lipid bilayer.If we assume that the breakdown P.D. of the tonoplast and plasmalemma are identical, that is 480 mV, then there is only one reasonable choice for the membrane thickness and the dielectric constant: δ = 2nm, ? = 3–8, e.g. a (lipo-)proteinaceous module facing a half lipid bilayer.     

Phase-transition properties of glycerol-monopalmitate lipid bilayers investigated by molecular dynamics simulation: influence of the system size and force-field parameters

Phase-transition properties of glycerol-1-monopalmitate (GMP) bilayers are investigated using explicit-solvent molecular dynamics (MD) simulations, initiated from structures appropriate for the gel (GL) or liquid crystal (LC) phases, and carried out at different hydration levels and temperatures. Building up on a previous study and based on 600 ns simulations, the influence of the system size and of the force field on the equilibrium thermodynamic and dynamic parameters of the bilayers in the GL and LC phases, as well as on the temperature T_m and properties of the GL ? LC phase transition, are analysed. Qualitatively speaking, the results agree with the available experimental data for the area per lipid in the two phases and for the phase-transition temperatures at the three hydration levels irrespective of the selected model parameters. They also suggest that the total number of hydrogen bonds formed between a lipid headgroup and its environment is essentially constant, amounting to about four in both the LC and the GL phases. Quantitatively speaking, the dependence of T_m on the hydration level is found to be non-systematic across the different combinations of model parameters. This results in part from a sensitivity of the results on the system size and force-field parameters but also from the limited accuracy of the bracketing approach employed here to estimate T_m. Finally, a simple kinetic model is proposed to account for the timescales of the transitions. This model involves enthalpy and entropy increases of about 26 kJ mol^? 1 and 83 J mol^? 1 K^? 1 per lipid, upon going from the GL to the LC phase. The transition state is associated with activation parameters corresponding to 13% and 11%, respectively, of these values along the GL → LC transition, resulting in an activation free energy of about 0.3 kJ mol^? 1 per lipid at T_m.     

Analysis of the binding of phenylalanine to phenylalanyl-tRNA synthetase

Using the complete rate equation for the PP_i-ATP exchange reaction at equilibrium, the dissociation constants of phenylalanine (10^?5m), phenylalanine butyl ester (8 × 10^?5m), benzyl alcohol (6 × 10^?4m), phenylalaninol (2 × 10^?4m), hydrocinnamic acid (3 × 10^?3m) and glycine (>1 m) with the phenylalanyl-tRNA synthetase (Escherichia coli K12) were determined. Taking the model of Koshland (1962) for the estimation of the configurational free energy change due to proximity and orientation, and decomposing the process of binding into several thermodynamic steps, the contribution to binding of the benzyl group, glycine unit, protonated amino group, carboxylate group and joint interactions were estimated. The results are: (1) the standard free energy contributions for binding phenylalanine are benzyl group (?8.2 kcal/mol), glycine unit (?2.5 kcal/mol), protonated amino group (?0.8 kcal/mol) and carboxylate group (1 kcal/mol). (2) The standard free energy change due to the change in the interaction between the protonated amino group and carboxylate group when they are transferred from the aqueous environment to the enzyme environment is ?2.7 kcal/mol. (3) A dissociation constant for glycine of 7.5 m is calculated without the hypothesis that a conformational change occurs in the enzyme when the benzyl unit of phenylalanine binds, permitting an interaction of the enzyme with the protonated amino and/or carboxylate groups.The detection of E·AA² and E·ATP shows that a sequential addition of substrates is not necessary for binding. A comparison of the dissociation constants of E·AA (10^?5m), E·ATP (1.5 × 10^?3m), E·PP (5.5 × 10^?4m), E·I (8 × 10^?5m) and the mixed complexes E·I·ATP (6 × 10^?8m²), E·I·PP (5 × 10^?8m²) and E·AA·PP (7 × 10^?9m²), with phenylalanine butyl ester as the inhibitor, indicates no strong interaction between the binding of ATP or PP_i with the binding of phenylalanine.     

Bioaccessibility-Based Risk Assessment of PAHs in Soils from Sites of Different Anthropogenic Activities in Lagos,Nigeria Using the Fed Organic Estimation Human Simulation Test Method

The aim of this study was to carry out a bioaccessibility-based risk assessment of polycyclic aromatic hydrocarbons (PAHs) in soils from sites of different anthropogenic activities in Lagos, Nigeria. Using an in vitro gastrointestinal model—Fed Organic Estimation Human Simulation Test method (FOREShT), the concentration of bioaccessible 16 priority US Environmental Protection Agency (USEPA) PAHs in soils were determined. Total concentration of 16 priority USEPA PAHs was also determined. The concentration range was 702–253,922 ng g^?1 and 92–760 ng g^?1 for total and bioaccessible PAHs, respectively. For persons involved with activities at these sites no health risks were observed, based on bioaccessibility values of PAHs. Mean daily intake of PAHs from these soils were below the oral mean daily intake threshold for PAHs in food. Also, overall estimated theoretical cancer risk (2.5 × 10^?09, 6.5 × 10^?07, 5.5 × 10^?10, 2.7 × 10^?09, 6.5 × 10^?10, 9.5 × 10^?10, 2.0 × 10^?09, and 4.1 × 10^?07 for the eight sites based on their bioaccessible concentration) for exposure to PAHs in surface soils were below the health guidelines for extreme (1 × 10^?04) and normal (1 × 10^?06) exposures.     

PURIFICATION AND CHARACTERIZATION OF PHOSPHODIESTERASE I FROM Walterinnesia aegyptia VENOM

A phosphodiesterase I (EC 3.1.4.1; PDE-I) was purified from Walterinnesia aegyptia venom by preparative native polyacrylamide gel electrophoresis (PAGE). A single protein band was observed in analytical native PAGE and sodium dodecyl sulfate (SDS)-PAGE. PDE-I was a single-chain glycoprotein with an estimated molecular mass of 158 kD (SDS-PAGE). The enzyme was free of 5′-nucleotidase and alkaline phosphatase activities. The optimum pH and temperature were 9.0 and 60°C, respectively. The energy of activation (Ea) was 96.4, the V_max and K_m were 1.14 µM/min/mg and 1.9 × 10^?3 M, respectively, and the K_cat and K_sp were 7 s^?1 and 60 M ^?1 min^?1 respectively. Cysteine was a noncompetitive inhibitor, with K_i = 6.2 × 10^?3 M and an IC₅₀ of 2.6 mM, whereas adenosine diphosphate was a competitive inhibitor, with K_i = 0.8 × 10^?3 M and an IC₅₀ of 8.3 mM. Glutathione, o-phenanthroline, zinc, and ethylenediamine tetraacetic acid (EDTA) inhibited PDE-I activity whereas Mg²⁺ slightly potentiated the activity. PDE-I hydrolyzed thymidine-5′-monophosphate p-nitrophenyl ester most readily, whereas cyclic 3′-5′-AMP was least susceptible to hydrolysis. PDE-I was not lethal to mice at a dose of 4.0 mg/kg, ip, but had an anticoagulant effect on human plasma. These findings indicate that W. aegyptia PDE-I shares various characteristics with this enzyme from other snake venoms.     

Total bacterial number concentration in free tropospheric air above the Alps

Over a period from June to October 2010, we carried out four short campaigns on the northern alpine ridge (High Altitude Research Station Jungfraujoch, 3,450 m above sea level) to determine bacterial number concentrations by collecting aerosol with liquid impingers, followed by filtration, fluorescent staining and counting with a microscope. Impinger liquid was also subjected to drop freeze tests to determine the number of ice nucleators. Parallel measurements of ²²²Rn enabled us to distinguish air masses with no, or little, recent land surface contact (free troposphere, ²²²Rn ≤ 0.50 Bq m^?3) from air masses influenced by recent contact with land surface (²²²Rn > 0.50 Bq m^?3). In free tropospheric air, concentration of total bacteria was on average 3.4 × 10⁴ cells m^?3 (SD = 0.8 × 10⁴ cells m^?3). When wind conditions preceding sampling were calm, or when the station was in clouds during sampling, there was no detectable difference in bacterial number concentrations between free tropospheric air and air influenced by recent land surface contact. One campaign was preceded by a storm. Here, recent land surface contact had enriched the air in bacterial cells (up to 7.5 × 10⁴ cells m^?3). Very few of these bacteria may act as ice nucleators in clouds. The median ratio of ice nucleators to the number of bacterial cells in our study was 1.0 × 10^?5. We conclude that injection of bacterial cells into the free troposphere is an intermittent process. Conditions controlling the release of bacteria into near surface air are probably more of a limiting factor than vertical transport and mixing of near surface air into the free troposphere.     

Bacillus thuringiensis CrylAa δ-Endotoxin Affects the K+/Amino Acid Symport in Bombyx mori Larval Midgut

The mechanical properties of brush border membrane vesicles, BBMV, from rabbit kidney proximal tubule cells, were studied by measuring the initial and final equilibrium volumes of vesicles subjected to different osmotic shocks, using cellobiose as the impermeant solute in the preparation buffer. An elevated intracellular hydrostatic pressure was inferred from osmotic balance requirements in dilute solutions. For vesicles prepared in 18 and 85 mosm solutions, these pressures are close to 17 mosm (290 mm Hg). The corresponding membrane surface tension is 6.0 × 10⁻⁵ N cm⁻¹ while the membrane surface area is expanded by at least 2.2%. When these vesicles are exposed to very dilute solutions the internal hydrostatic pressure rises to an estimated 84 mosm (1444 mm Hg) just prior to lysis. The corresponding maximal surface tension (pre-lysis) is 18.7 × 10⁻⁵ N cm⁻¹, and the maximal expansion of membrane area is 6.8%. The calculated area compressibility elastic modulus was 2.8 × 10⁻³ N cm⁻¹. Received: 8 August 1996/Revised: 4 March 1997     

Immobilization of <Emphasis Type="BoldItalic">Irpex lacteus</Emphasis> to liquid-core alginate beads and their application to degradation of pollutants

White rot fungi (WRF) are applicable to biodegradation of recalcitrant pollutants. However, excessive biomass growth typical for WRF cultivation can hinder their large scale applications. Therefore, immobilization of Irpex lacteus to liquid-core alginate beads restricting excessive mycelium growth and simultaneously keeping high degradation rate of pollutants was tested. Effective diffusivities of dyes to the beads varied from (2.98 ± 0.69) × 10^?10 to (10.27 ± 2.60) × 10^?10 m²/s. Remazol Brilliant Blue R (RBBR), Reactive Orange 16 (RO16), and Naphthol Blue Black (NBB) were used as model dyes. The immobilized fungus decolorized model dyes when applied both in microwell plates and in fluidized bed reactors. Using the microwell plates, the apparent reaction rate constants ranged from (2.06 ± 0.11) × 10^?2 to (11.06 ± 0.27) × 10^?2 1/h, depending on the dye used and its initial concentration. High initial concentrations negatively affected the dye decolorization rate. No fungal growth outside the beads was observed in fluidized bed reactors and thus no operational problems linked to an excessive biomass growth occurred. When RBBR was decolorized in subsequent batches in the fluidized bed reactor, the apparent reaction rate constant increased from (11.63 ± 0.35) × 10^?2 to (29.26 ± 7.19) × 10^?2 1/h.     

Kinetics of Water Transport in Eel Intestinal Vesicles

Brush border membrane vesicles, BBMV, from eel intestinal cells or kidney proximal tubule cells were prepared in a low osmolarity cellobiose buffer. The osmotic water permeability coefficient P _f for eel vesicles was not affected by pCMBS and was measured at 1.6 × 10⁻³ cm sec⁻¹ at 23°C, a value lower than 3.6 × 10⁻³ cm sec⁻¹ exhibited by the kidney vesicles and similar to published values for lipid bilayers. An activation energy E _a of 14.7 Kcal mol⁻¹ for water transport was obtained for eel intestine, contrasting with 4.8 Kcal mol⁻¹ determined for rabbit kidney proximal tubule vesicles using the same method of analysis. The high value of E _a , as well as the low P _f for the eel intestine is compatible with the absence of water channels in these membrane vesicles and is consistent with the view that water permeates by dissolution and diffusion in the membrane. Further, the initial transient observed in the osmotic response of kidney vesicles, which is presumed to reflect the inhibition of water channels by membrane stress, could not be observed in the eel intestinal vesicles. The P _f dependence on the tonicity of the osmotic shock, described for kidney vesicles and related to the dissipation of pressure and stress at low tonicity shocks, was not seen with eel vesicles. These results indicate that the membranes from two volume transporter epithelia have different mechanisms of water permeation. Presumably the functional water channels observed in kidney vesicles are not present in eel intestine vesicles. The elastic modulus of the membrane was estimated by analysis of swelling kinetics of eel vesicles following hypotonic shock. The value obtained, 0.79 × 10⁻³ N cm⁻¹, compares favorably with the corresponding value, 0.87 × 10⁻³ N cm⁻¹, estimated from measurements at osmotic equilibrium. Received: 28 January 1999/Revised: 15 June 1999     

Physiological responses of CHO cells to repetitive hydrodynamic stress

A majority of the previous investigations on the hydrodynamic sensitivity of mammalian cells have focused on lethal effects as determined by cell death or lysis. In this study, we investigated the effect of hydrodynamic stress on CHO cells in a fed‐batch process using a previously reported system which subjects cells to repetitive, high levels of hydrodynamic stress, quantified by energy dissipation rate (EDR). The results indicated that cell growth and monoclonal antibody production of the test cells were very resistant to the hydrodynamic stress. Compared to the control, no significant variation was observed at the highest EDR tested, 6.4 × 10⁶ W/m³. Most product quality attributes were not affected by intense hydrodynamic stress either. The only significant impact was on glycosylation. A shift of glycosylation pattern was observed at EDR levels at or higher than 6.0 × 10⁴ W/m³, which is two orders of magnitude lower than the EDR where physical cell damage, as measured by lactate dehydrogenase release, was observed. While not as extensively investigated, a second monoclonal antibody produced in a different CHO clone exhibited the same glycosylation change at an intensive EDR, 2.9 × 10⁵ W/m³. Conversely, a low EDR of 0.9 × 10² W/m³ had no effect on the glycosylation pattern. As 6.0 × 10⁴ W/m³, the lowest EDR that triggers the glycosylation shift, is about one order of magnitude higher than the estimated, maximum EDR in typically operated, large‐scale stirred tank bioreactors, further studies in a lower EDR range of 1 × 10³–6.0 × 10⁴ W/m³ are needed to assess the glycosylation shift effect under typical large‐scale bioreactor operation conditions. Follow‐up studies in stirred tanks are also needed to confirm the glycosylation shift effect and to validate the repetitive hydrodynamic stress model. Biotechnol. Bioeng. 2009;103: 1103–1117. © 2009 Wiley Periodicals, Inc.     

Potassium Channels in Eremosphaera viridis: Modulation of Channel Opening,Conductance and Inhibition*

I/V relationships were performed by the voltage clamp technique in the sphaerical green alga Eremosphaera viridis de Bary. We focused on the course of the transient potential (TP) found in light-off experiments when specific potassium channels open. I/V measurements done during this period show a N-shaped curve. The shape depended on external potassium. TPs could be released by light-off and by addition of barium, strontium, or α-naphthyl phosphate. We calculated the number of specific potassium channels to be between 1750 and 34 825 channels per cell. Barium (1 mol × m^?3) and tetraethylammonium (10 mol × m^?3) inhibited TPs. I/V relationships demonstrated, when N-shaped, that potassium channels start to close at voltages more negative than ?195 mV (0.1 mol × m^?3 K⁺), ?160 mV (1 mol × m^?3 K⁺) and ?148 mV (10 mol × m^?3 K⁺). In the region of ?300 mV conditions similar to those at rest are reached. External sodium suppressed the development of N-shaped I/V relationships and reduced the membrane conductance during a TP between 8 % and 29 %. This indicates an influence of external sodium on potassium channels.     

pH effects on growth and lipid accumulation of the biofuel microalgae Nannochloropsis salina and invading organisms

Biofuels derived from non-crop sources, such as microalgae, offer their own advantages and limitations. Despite high growth rates and lipid accumulation, microalgae cultivation still requires more energy than it produces. Furthermore, invading organisms can lower efficiency of algae production. Simple environmental changes might be able to increase algae productivity while minimizing undesired organisms like competitive algae or predatory algae grazers. Microalgae are susceptible to pH changes. In many production systems, pH is kept below 8 by CO₂ addition. Here, we uncouple the effects of pH and CO₂ input, by using chemical pH buffers and investigate how pH influences Nannochloropsis salina growth and lipid accumulation as well as invading organisms. We used a wide range of pH levels (5, 6, 7, 8, 9, and 10). N. salina showed highest growth rates at pH 8 and 9 (0.19?±?0.008 and 0.19?±?0.011, respectively; mean ± SD). Maximum cell densities in these treatments were reached around 21 days into the experiment (95.6?×?10⁶?±?9?×?10⁶ cells mL^?1 for pH 8 and 92.8?×?10⁶?±?24?×?10⁶ cells mL^?1 for pH 9). Lipid accumulation of unbuffered controls were 21.8?±?5.8 % fatty acid methyl esters content by mass, and we were unable to trigger additional significant lipid accumulation by manipulating pH levels at the beginning of stationary phase. Ciliates (grazing predators) occurred in significant higher densities at pH 6 (56.9?±?39.6?×?10⁴ organisms mL^?1) than higher pH treatments (0.1–6.8?×?10⁴ organisms mL^?1). Furthermore, the addition of buffers themselves seemed to negatively impact diatoms (algal competitors). They were more abundant in an unbuffered control (12.7?±?5.1?×?10⁴ organisms mL^?1) than any of the pH treatments (3.6–4.7?×?10⁴ organisms mL^?1). In general, pH values of 8 to 9 might be most conducive to increasing algae production and minimizing invading organisms. CO₂ addition seems more valuable to algae as an inorganic carbon source and not as an essential mechanism to reduce pH.     

Contribution of aqueous interphases to the permeability barrier of lipid bilayers for non-electrolytes

Equilibrium dialysis experiments are used to measure excluded volumes for the non-electrolyte permeant [U-¹⁴C] erythritol in lipid bilayer systems. The data indicate amounts of water associated with the lipid membranes which correspond with amounts calculated from calorimetric measurements.The membrane systems can be described as composite elements consisting of the lipid bilayers and adjacent water layers on both sides. The finding that the permeant is excluded indicates that the water layers contribute to the permeability barrier.The mean thickness of the water layers is about 6 Å for planar bilayers in multilayered liposomes and 10 Å for curved bilayers in sonicated vesicles. Next to the difference in thickness of the water layers differences in interfacial adsorption between the two systems are apparent.