Dichloromethane and trichloroethylene inhibition of methane oxidation by the membrane-associated methane monooxygenase of Methylosinus trichosporium OB3b

Whole-cell assays were used to measure the effect of dichloromethane and trichloroethylene on methane oxidation by Methylosinus trichosporium OB3b synthesizing the membrane-associated or particulate methane monooxygenase (pMMO). For M. trichosporium OB3b grown with 20 μM copper, no inhibition of methane oxidation was observed in the presence of either dichloromethane or trichloroethylene. If 20 mM formate was added to the reaction vials, however, methane oxidation rates increased and inhibition of methane oxidation was observed in the presence of dichloromethane and trichloroethylene. In the presence of formate, dichloromethane acted as a competitive inhibitor, while trichloroethylene acted as a noncompetitive inhibitor. The finding of noncompetitive inhibition by trichloroethylene was further examined by measuring the inhibition constants K _iE and K _iES. These constants suggest that trichloroethylene competes with methane at some sites, although it can bind to others if methane is already bound. Whole-cell oxygen uptake experiments for active and acetylene-treated cells also showed that provision of formate could stimulate both methane and trichloroethylene oxidation and that trichloroethylene did not affect formate dehydrogenase activity. The finding that different chlorinated hydrocarbons caused different inhibition patterns can be explained by either multiple substrate binding sites existing in pMMO or multiple forms of pMMO with different activities. The whole-cell analysis performed here cannot distinguish between these models, and further work should be done on obtaining active preparations of the purified pMMO. Received: 3 November 1998 / Accepted: 1 March 1999     

Gas phase photocatalytic degradation on TIO2 pellets of volatile chlorinated organic compounds from a soil vapor extraction well

The degradation of trichloroethylene (TCE, Cl₂C=CHCl) and tetrachloroethylene (PCE, Cl₂C=CCI₂) in a gas stream from a soil vapor extraction (SVE) well was demonstrated with an annular photocatalytic reactor packed with porous TiO₂ pellets in a field trial at the Savannah River Site in Aiken, SC. The TiO₂ pellets were prepared using a sol‐gel method. The experiments were performed at 55 to 60°C using space times of 10⁸ to 10¹⁰ g ? s ? mol^‐1 for TCE and PCE. Chloroform (CHCl₃) and carbon tetrachloride (CCl₄) were detected as minor products from side reactions. On a molar basis, the amounts CCl₄ and CHCl₃ produced were about 2 and 0.2% of the reactants, respectively.     

Weak Electron–Phonon Coupling and Enhanced Thermoelectric Performance in n-type PbTe–Cu2Se via Dynamic Phase Conversion

This study investigates Ga-doped n-type PbTe thermoelectric materials and the dynamic phase conversion process of the second phases via Cu₂Se alloying. Introducing Cu₂Se enhances its electrical transport properties while reducing its lattice thermal conductivity (κ_lat) via weak electron–phonon coupling. Cu₂Te and CuGa(Te/Se)₂ (tetragonal phase) nanocrystals precipitate during the alloying process, resulting in Te vacancies and interstitial Cu in the PbTe matrix. At room temperature, Te vacancies and interstitial Cu atoms serve as n-type dopants, increasing the carrier concentration and electrical conductivity from ≈1.18 × 10¹⁹ cm⁻³ and ≈1870 S cm⁻¹ to ≈2.26 × 10¹⁹ cm⁻³ and ≈3029 S cm⁻¹, respectively. With increasing temperature, the sample exhibits a dynamic change in Cu₂Te content and the generation of a new phase of CuGa(Te/Se)₂ (cubic phase), strengthening the phonon scattering and obtaining an ultralow κ_lat. Pb_0.975Ga_0.025Te-3%CuSe exhibits a maximum figure of merit of ≈1.63 at 823 K, making it promising for intermediate-temperature device applications.     

Oscillation of delayed luminescence from PS II: recombination of S2Q−B and S3Q−B

Luminescence decaying in the seconds to minutes time scale was studied in spinach chloroplasts and the following results were obtained: (1) After a series of flashes a slow phase which decays in the tens of seconds to minutes time scale was observed to oscillate with a pattern characteristic of S₂Q^?_B and S₃Q^?_B recombination. This phase was lost upon Tris-treatment or upon the addition of DCMU. (2) After every flash a small faster phase of luminescence decaying in the seconds time scale was also present. This phase progressively increased with increasing numbers of flashes but when methyl viologen was present no such progressive increase of this phase occurred. In the presence of DCMU this seconds time scale luminescence was greatly increased. This phase of luminescence is attributed to S₂Q^?_A recombination. (3) Tris-treatment resulted in the appearance of an even faster phase of luminescence which may be due to Z⁺Q^?_B recombination. These results demonstrate a close correlation of the kinetics of luminescence decay with thermoluminescence emission temperature.     

Aerobic Mineralization of Trichloroethylene, Vinyl Chloride, and Aromatic Compounds by Rhodococcus Species

Two Rhodococcus strains which were isolated from a trichloroethylene (TCE)-degrading bacterial mixture and Rhodococcus rhodochrous ATCC 21197 mineralized vinyl chloride (VC) and TCE. Greater than 99.9% of a 1-mg/liter concentration of VC was degraded by cell suspensions. [1,2-¹⁴C]VC was degraded by cell suspensions, with the production of greater than 66% ¹⁴CO₂ and 20% ¹⁴C-aqueous phase products and incorporation of 10% of the ¹⁴C into the biomass. Cultures that utilized propane as a substrate were able to mineralize greater than 28% of [1,2-¹⁴C]TCE to ¹⁴CO₂, with approximately 40% appearing in ¹⁴C-aqueous phase products and another 10% of ¹⁴C incorporated into the biomass. VC degradation was oxygen dependent and occurred at a pH range of 5 to 10 and temperatures of 4 to 35°C. Cell suspensions degraded up to 5 mg of TCE per liter and up to 40 mg of VC per liter. Propane competitively inhibited TCE degradation. Resting cell suspensions also degraded other chlorinated aliphatic hydrocarbons, such as chloroform, 1,1-dichloroethylene, and 1,1,1-trichloroethane. The isolates degraded a mixture of aromatic and chlorinated aliphatic solvents and utilized benzene, toluene, sodium benzoate, naphthalene, biphenyl, and n-alkanes ranging in size from propane to hexadecane as carbon and energy sources. The environmental isolates appeared more catabolically versatile than R. rhodochrous ATCC 21197. The data report that environmental isolates of Rhodococcus species and R. rhodochrous ATCC 21197 have the potential to degrade TCE and VC in addition to a variety of aromatic and chlorinated aliphatic compounds either individually or in mixtures.     

Relations between uptake and utilization of NO−3 in Pisum growing exponentially under nitrogen limitation

The utilization and translocation of nitrogen was investigated in exponentially growing, nitrogen-limited Pisum sativum L. cv. Marma. The plants were given N daily at exponentially increasing, although suboptimal, relative nitrogen addition rates (R_N) calculated to yield a relative increment in N of 0.06 day^?1 and 0.12 day^?1. After 10 days of NO^?₃ additions (26 days after sowing), the relative growth rate more or less equaled R_N. Uptake of NO^?₃ was several-fold higher than the N requirement for the growth rate set by R_N. The daily addition of NO^?₃ was taken up after 7 to 8 h, resulting in a cyclic behaviour in the NO^?₃ utilization. During the phase of net NO^?₃ influx, the filling phase (0 to 8 h), in vitro nitrate reductase activity (NR activity) and intracellular levels of soluble N in the root increased. In the phase of no net influx of NO^?₃ the depletion phase (8 to 24 h), the plants were entirely dependent on stored N. During this phase both in vitro NR activity and intracellular levels of soluble N decreased. Also the calculated actual rate of NO^?₃ reduction was high in the filling phase, while it was close to zero in the depletion phase. The pattern of these fluctuations indicates that the regulation of NO^?₃ utilization involves an interplay between transmembrane fluxes of NO^?₃, the cytosolic NO^?₃ concentration and NR activity. Cyclic fluctuations in N-containing compounds were also found in the xylem. Nitrogen was mainly transported as amino acids. The pattern of NO^?₃ transport in the xylem and the fluctuations in the shoot of in vitro NR activity indicate that a reasoning similar to that for the regulation of NO^?₃ assimilation in the root also applies for the shoot. The results also indicate a substantial supply of amino acids to the xylem through recirculation from the shoot.     

Rapid kinetic study of the passive permeability of a Ca2+-ATPase rich fraction of the sarcoplasmic reticulum

Summary A method was developed for the study of divalent cation transport events on the time scale of 20 msec or longer. Passive Ca²⁺ equilibration across the membranes of the Ca²⁺-ATPase rich fraction of sarcoplasmic reticulum (SR) was studied. The method makes use of the divalent cation sensitivity of the surface binding of the fluorescent probe 1-anilino-8-naphthalenesulfonate (ANS^–). Binding to the inside and outside surfaces is distinguished in fluorescent stopped-flow experiments. The surface binding reactions of the probe are faster than the time resolution of the instrument (ca. 3 msec), while binding reactions requiring transport across the membrane could be resolved. In Ca²⁺ influx experiments, the time course of fluorescent enhancement was monitored following a Ca²⁺ jump. The kinetics of Ca²⁺ efflux were studied by pre-equilibrating Ca²⁺ across the membrane, removing the external Ca²⁺ with an EGTA jump, and observing the time course of the fluorescence decrease. Rapid transport of ANS^– (coupled to K⁺) was ensured by the addition of valinomycin. Two processes of Ca²⁺ influx were observed: (i) a rapid process with small fluorescent amplitudes and at _1/2 of 40–60 msec and (ii) a slow process with a large amplitude and at _1/2 of 70–100 sec. The rates and extents of the two phases were quantitated in terms of the rates and extents of change in the Ca²⁺ concentration in the SR lumen. The slow phase accounted for a larger change, in the internal free Ca²⁺ concentration than did the first phase. For the influx of 10 mM Ca²⁺, the rapid phase raises the internal Ca²⁺ concentration to ca. 1 mM within its apparentt _1/2 of 20 msec. The slow phase brings about an increase of the internal Ca²⁺ concentration to 4 mM within its apparentt _1/2 of 90 sec. The two phases have average rates of increase of internal free Ca²⁺ concentration, [Ca] _i /sec of ca. 50 mM/sec and ca. 0.02 mM/sec, respectively. The Ca²⁺ influx rates increased with increasing KCl concentration and with increasing external Ca²⁺ concentration.Two phases of Ca²⁺ efflux were observed. The amplitudes and rates were analyzed and the fast phase was shown to account for more Ca²⁺ movement than the slow phase. The rate of the fast phase was greatly increased by increasing the K⁺ concentration. The rate of the slow phase efflux decreased with increasing Ca²⁺ concentration in the external medium. The concentration for half-maximal inhibition was 4 M, a value close to the dissociation constant of the high affinity site on the Ca²⁺-ATPase.The above constitutes a body of circumstantial evidence that the passive Ca²⁺ permeability observed is mediated by the Ca²⁺-ATPase, acting as a Ca²⁺ for 2 K⁺ exchanger. The fast phases are explained as a partial turnover of the pump in the steady state. The slow rate is explained by a preference of the ion binding translocator site of the carrier for an outward orientation.The ANS^– technique was applied to the monovalent cation permeability of the Ca²⁺-ATPase rich SR and the results of other studies were corroborated and extended. The interaction of valinomycin with intrinsic permeability mechanisms of the SR was considered.     

NITRATE REDUCTASE ACTIVITY OF AMPHIDINIUM CARTERI AND CACHONINA NIEI (DINOPHYCEAE) IN BATCH CULTURE: DIEL PERIODICITY AND EFFECTS OF LIGHT INTENSITY AND AMMONIA1,2

The activity of extracted NADH-NO₃^? reductase was measured in the marine dinoflagellates Amphidinium carteri Hulburt and Cachonina niei Loeblich. Its activity showed a diel periodicity and was ca. twice as great at midday as at midnight. The enzyme activity was unstable, with an in vitro half-life of 2–3 h. Values of enzyme activity were low or undetectable during lag phase but paralleled the instantaneous growth rate value during log phase. Nitrate reductase activity was not found in the stationary phase of growth, but additions of NO₃^? resulted in enzyme activity after 24h. When A. carteri was exposed to a series of light intensities for several weeks, the division rate and enzyme activity increased with increasing light intensity up to saturating intensities. In 6 h exposures, enzyme activity decreased with decreasing light intensities below light intensities saturating division rate. Additions of NH₄⁺ (0.5–50 μm) to A. carteri cultures decreased the amount of extractable enzyme. The in vitro activity was not inhibited by similar NH⁺₄ concentrations.     

Stimulation of albumin synthesis in mouse hepatoma cells by Bt2cAMP: cell cycle specificity

Addition of 1 mm dibutyryl cyclic AMP (Bt₂cAMP) to cultures of mouse hepatoma cells, Hepa, specifically stimulates the synthesis of serum proteins including albumin. This stimulation is accompanied by an inhibition of cell proliferation. We have investigated these phenomena in synchronous cultures of Hepa. Proliferation of Hepa was arrested by isoleucine starvation. Synchronous growth was initiated by addition of complete growth medium or complete growth medium supplemented with 1 mm Bt₂cAMP. S phase and mitosis were estimated by determinations of [³H]thymidine incorporation and by cell numbers. The rate of albumin synthesis relative to total protein synthesis was measured by pulse labeling cultures for 30 min with [³H]leucine and comparing amounts of immunoprecipitable label with trichloroacetic acid-precipitable label. Treatment of synchronous cultures with Bt₂cAMP did not alter the duration of S phase or the onset of mitosis. The relative rate of albumin synthesis in Bt₂cAMP-treated culture began increasing after mitosis. The timing of the Bt₂cAMP stimulation of albumin synthesis was further investigated by adding Bt₂cAMP to cultures of Hepa at various times after the initiation of synchronous growth. The relative rate of albumin synthesis was then measured at a fixed postmitotic time. An increased relative rate of albumin synthesis was observed only in cultures exposed to Bt₂cAMP before or during S phase. Thus the postmitotic increase in the synthesis of albumin requires the presence of Bt₂cAMP during S phase.     

INTRACELLULAR AND EXTRACELLULAR AMINO ACID POOLS OF THE MARINE DIATOM PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE) GROWN ON UNENRICHED SEAWATER IN HIGH-CELL-DENSITY DIALYSIS CULTURE1

The consumption of inorganic macronutrients (NO₃^?+ NO₂^?, NH₄⁺, and PO₄^?3) and the composition of intra- and extracellular dissolved free amino acid pools (IDFAA and EDFAA, respectively) were determined in continuous-reservoir batch dialysis cultures of the marine diatom Phaeodactylum tricornutum Bohlin maintained on unenriched natural seawater as a growth medium. Nutrient diffusion (Nd), which equals the nutrient uptake of the culture, increased with the cell density and the age of the culture. A concentration of 6.77 × 10⁷ cells · mL^?1 was obtained in stationary phase, which coincided with the NO₃^?+ NO₂^? diffusion limit (Nd_max) of the dialysis apparatus. The Nd_max for NH₄⁺ occurred much earlier, at the end of exponential growth, whereas Nd_max for PO₄^?3 was not attained during the growth cycle of the culture, even in early stationary phase. A significant depletion (77%) of the IDFAA pool during exponential phase was followed by a reestablishment–to approximately 60% of the initial level–of internal pools during linear and stationary growth phases. This recovery occurred during the illuminated portion of the photoperiod (12:12 h LD) and involved principally the amino acids GLN, GLU, β-GLU, and ASN. The recovery of GLN and ASN levels was particularly significant, because the intracellular concentrations of these amino acids were higher at the end of the growth cycle than before. The EDFAA pool was generally dominated by the amino acids SER and GLY+THR; however, during active growth, ORN and LYS often constituted an important fraction. The EDFAA concentration increased until linear growth phase was reached, during which a higher concentration of total free amino acids was attained in darkness than under illumination. The EDFAA component diminished afterward, and in stationary phase this fraction returned to concentrations equivalent to those observed at the beginning of the growth cycle. The variations in EDFAA concentrations were expressed by a pronounced decrease in the cellular excretion of amino acids with increasing cell density. These cellular responses of Phaeodactylum tricornutum in dense culture, specifically the regulation of amino acid excretion and intracellular pool size, may affect the N-conversion coefficient (Y_N). Consequently, by prolonging the linear phase of growth and reducing the concentration of autoinhibitory metabolites by diffusion, a markedly enhanced final cell density can be achieved in cultures grown on natural unenriched seawater.     

Pitfalls in the measurement of membrane potential in yeast cells using tetraphenylphosphonium

The uptake of the lipophilic cation tetraphenylphosphonium (Ph₄P⁺) by Saccharomyces cerevisiae was measured using yeast grown on glucose and harvested either at the logarithmic or at the stationary phase of growth. When yeast was collected at the stationary phase, Ph₄P⁺ uptake proceeded steadily during several hours until an equilibrium was reached. When yeast was collected in the logarithmic phase of growth, a biphasic uptake was observed. The second phase of uptake began when the glucose of the incubation medium had been exhausted. From experiments in the presence of cycloheximide or chloramphenicol it is concluded that the second phase of Ph₄P⁺ uptake is dependent on the synthesis of some protein(s) repressed by glucose but unrelated with the existence of functional mitochondria. The addition of compounds which collapse the membrane potential provokes an efflux from the yeast cells of the Ph₄P⁺ accumulated both during the first phase and the second phase of uptake. It is concluded that accumulation of Ph₄P⁺ in yeast cells is a complex process and that Ph₄P⁺ cannot be used to give a quantitative measure of the yeast plasma membrane potential.     

Kinetics on Demand Is a Simple Mathematical Solution that Fits Recorded Caffeine-Induced Luminal SR Ca2+ Changes in Smooth Muscle Cells

The process of Ca²⁺ release from sarcoplasmic reticulum (SR) comprises 4 phases in smooth muscle cells. Phase 1 is characterized by a large increase of the intracellular Ca²⁺ concentration ([Ca²⁺]_i) with a minimal reduction of the free luminal SR [Ca²⁺] ([Ca²⁺]_FSR). Importantly, active SR Ca²⁺ ATPases (SERCA pumps) are necessary for phase 1 to occur. This situation cannot be explained by the standard kinetics that involves a fixed amount of luminal Ca²⁺ binding sites. A new mathematical model was developed that assumes an increasing SR Ca²⁺ buffering capacity in response to an increase of the luminal SR [Ca²⁺] that is called Kinetics-on-Demand (KonD) model. This approach can explain both phase 1 and the refractory period associated with a recovered [Ca²⁺]_FSR. Additionally, our data suggest that active SERCA pumps are a requisite for KonD to be functional; otherwise luminal SR Ca²⁺ binding proteins switch to standard kinetics. The importance of KonD Ca²⁺ binding properties is twofold: a more efficient Ca²⁺ release process and that [Ca²⁺]_FSR and Ca²⁺-bound to SR proteins ([Ca²⁺]_BSR) can be regulated separately allowing for Ca²⁺ release to occur (provided by Ca²⁺-bound to luminal Ca²⁺ binding proteins) without an initial reduction of the [Ca²⁺]_FSR.     

Physical characterisations of a single-stage Kühni-type aqueous two-phase extraction column

The main parameters which influence the behaviour of phase separation in a single-stage Kühni-type aqueous two-phase extraction column containing polyethylene (PEG) and di-potassium hydrogen phosphate were characterised. Two aqueous two-phase system (ATPS) composed of 12% (w/w) PEG 1450 and 12% (w/w) di-potassium hydrogen phosphate (designated as 12/12) and 12% (w/w) PEG 1450 and 11% (w/w) di-potassium hydrogen phosphate (designated as 12/11) were chosen in this study. The hold-up ɛ_D increased with increasing impeller speeds and mobile phase flow rates. Phase separation for the 12/11 system was slower than that for the 12/12 system, which resulted in higher dispersed phase hold-up values for the 12/11 system. For 12/12 system, mass transfer of plasmid DNA (pDNA) from the dispersed mobile phase to the stationary phase increased rapidly with increasing impeller speeds of 130, 160 and 200 rpm which was reflected in the decreased values for C_T/C_To. The degree of back-mixing quantified by the axial dispersion coefficient D_ax was estimated to be 2.7 × 10⁻⁶ m² s⁻¹.     

Cell kinetic studies on the JB-1 ascites tumour of the mouse

Abstract. The FLM method, modified by double labelling with [³H]- and [¹⁴C]-thymidine, has been applied to the 4-day old JB-1 ascites tumour of the mouse. It results in well separated waves of purely [³H]- and purely [¹⁴C]-labelled mitoses, which show a remarkable asymmetry with long tails to the right. The following values for the mean transit times of the cells have been derived from this FLM curve, for a tumour age of 4–6 days: T_C= 32.5 hr, T_S= 16.7 hr, T_G1= 3.7 hr, T_G1= 11.0 hr and T_M= 1.1 hr. A further evaluation of the FLM curve, however, is difficult, due to the non-stationary growth of the tumour. A number of other experimental findings (growth curve, decrease of the labelling and mitotic index with increasing tumour age, two single-labelled FLM curves starting 4 and 6 days after tumour inoculation) indicate that the cell cycle time increases during the experimental period of the double-labelled FLM curve (about 2 days). A lengthening of the cycle time should result in an increasing enlargement of the areas under the waves of the modified FLM curve. However, such an increase in area has not been found; the areas are constant. All the results of the present cell kinetic studies would be consistent if it were postulated that the cell cycle time lengthens with increasing tumour age up to about 4 days after inoculation, then remains relatively constant at between 4 and 6 days and thereafter increases again. Short-term double labelling experiments suggest that this is actually the case. Under the assumption of nearly constant phase durations during the 5th and 6th day of tumour growth further conclusions can be drawn from the modified FLM curve. In particular, it follows that the transit times of the cells through successive cycle phases are uncorrelated and the variances of the transit times through a cycle phase are proportional to the duration of this phase.     

Methane and Trichloroethylene Degradation by Methylosinus trichosporium OB3b Expressing Particulate Methane Monooxygenase

Whole-cell assays of methane and trichloroethylene (TCE) consumption have been performed on Methylosinus trichosporium OB3b expressing particulate methane monooxygenase (pMMO). From these assays it is apparent that varying the growth concentration of copper causes a change in the kinetics of methane and TCE degradation. For M. trichosporium OB3b, increasing the copper growth concentration from 2.5 to 20 μM caused the maximal degradation rate of methane (V_max) to decrease from 300 to 82 nmol of methane/min/mg of protein. The methane concentration at half the maximal degradation rate (K_s) also decreased from 62 to 8.3 μM. The pseudo-first-order rate constant for methane, V_max/K_s, doubled from 4.9 × 10⁻³ to 9.9 × 10⁻³ liters/min/mg of protein, however, as the growth concentration of copper increased from 2.5 to 20 μM. TCE degradation by M. trichosporium OB3b was also examined with varying copper and formate concentrations. M. trichosporium OB3b grown with 2.5 μM copper was unable to degrade TCE in both the absence and presence of an exogenous source of reducing equivalents in the form of formate. Cells grown with 20 μM copper, however, were able to degrade TCE regardless of whether formate was provided. Without formate the V_max for TCE was 2.5 nmol/min/mg of protein, while providing formate increased the V_max to 4.1 nmol/min/mg of protein. The affinity for TCE also increased with increasing copper, as seen by a change in K_s from 36 to 7.9 μM. V_max/K_s for TCE degradation by pMMO also increased from 6.9 × 10⁻⁵ to 5.2 × 10⁻⁴ liters/min/mg of protein with the addition of formate. From these whole-cell studies it is apparent that the amount of copper available is critical in determining the oxidation of substrates in methanotrophs that are expressing only pMMO.     

The effects of hydration and divalent cations on lamellar-nonlamellar phase transitions in membranes and total lipid extracts from Acholeplasma laidlawii A-EF22 – a 2H NMR study

Acholeplasma laidlawii strain A-EF22 was grown in a medium supplemented with 75 μm α-deuterated palmitic acid (16:0-d ₂) and 75 μm α-deuterated oleic acid (18:1c-d ₂), or with 150 μm 18:1c-d ₂. The fatty acids were incorporated into the membrane lipids and ²H NMR spectra were recorded from intact membranes, total lipid extracts, and the combined glucolipid and neutral lipid fractions of a total lipid extract. The lipids in intact membranes form a bilayer structure up to at least 70 °C. The same result was obtained with membranes digested with pronase, which removes a large fraction of the membrane proteins. A reversed hexagonal liquid crystalline (H_II) phase was formed below 70 °C by the total lipid extracts hydrated with 20 and 30% (w/w) water; in the presence of 40% (w/w) water only one of the extracts formed an H_II phase below 70 °C. The H_II phase was formed at higher temperatures with an increasing water content. However, only a lamellar liquid crystalline (L _α ) phase was formed up to 70 °C by the total lipid extracts when the water concentrations were 50% (w/w) or higher. The temperature (T _LH) for the L _α to H_II phase transition in the combined glucolipid and neutral lipid fractions was only 2–3 °C lower than for the total lipids, and the phospholipids thus have a very modest influence on the T _LH value. Physiologically relevant concentrations of Ca²⁺ and Mg²⁺ ions did not affect the phase equilibria of total lipid extracts significantly. It is concluded from comparison with published data that the membrane lipids of the cell wall-less bacterium A. laidlawii have a smaller tendency to form reversed nonlamellar phases than the membrane lipids of three bacterial species surrounded by a cell wall. Received: 10 March 1997 / Accepted: 4 July 1997     

COPPER TOXICITY TO SKELETONEMA COSTATUM (BACILLARIOPHYCEAE)1,2

Copper toxicity to Skeletonema costatum (Grev.) Cleve has been studied in batch cultures of chemically defined culture media. The alga is relatively insensitive to cupric ion activity, demonstrating no effect on growth up to (Cu²⁺) = 10^?8.5 M. Cultures inoculated from stationary phase stocks exhibit a prolongation of the lag phase with increasing copper concentrations near and above the point of precipitation of the copper. The toxicity of copper is a function of the silicic acid concentration in the medium. This effect is observed in a range of Si(OH)₄ concentrations (10^?5 M to 10^?4 M) above known values for the saturation of silicon uptake kinetics, thus suggesting an influence of copper on silicate metabolism.     

A Systematic Approach to Solvent Selection Based on Cohesive Energy Densities in a Molecular Bulk Heterojunction System

The solubilities of 3,6‐bis(5‐(benzofuran‐2‐yl)thiophen‐2‐yl)‐2,5‐bis(2‐ethylhexyl)pyrrolo[3,4‐c]pyrrole‐1,4‐dione ( DPP(TBFu)₂ ) and [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester ( PC₇₁BM ) in a series of solvents are measured, and this data is used to calculate the Hansen solubility parameters of the two materials. The dispersion, polar, and H‐bonding parameters of DPP(TBFu)₂ and PC₇₁BM were found to be (19.3, 4.8, 6.3) and (20.2, 5.4, 4.5) MPa^1/2, respectively, with an error of ± 0.8 MPa^1/2. Based on the solubility properties of the two materials, three new solvents (thiophene, trichloroethylene and carbon disulfide) were utilized for the DPP(TBFu)₂ : PC₇₁BM system which, after device optimization, led to power conversion efficiencies up to 4.3%.     

Enhanced Chlorella vulgaris Buitenzorg growth by photon flux density alteration in serial photobioreactors

Microalgae perform oxygenic photosynthesis and are capable of taking up a large amount of CO₂, using an inducible CO₂ concentrating mechanism (CCM), and fixing CO₂ into higher compounds. These characteristics make the microalgae potentially useful for removal and utilization of CO₂ emitted from industrial plants and, generally, the usage of photosynthetic microorganisms has increased and significantly improved as a solution for CO₂ emissions. In this light and based on previous research using Anabaena cylindrica IAM M1 and Spirulina platensis IAM M 135, enhancement was sought for CO₂ fixation and biomass production by Chlorella vulgaris Buitenzorg by increasing the photon flux density concurrent with increases in culture biomass during the cellular growth phase and was compared to cultures of Chlorella grown at optimal constant illumination, with all cultures grown using Bennick basal medium, 29°C, and a flow of 1.0 atm. 10% CO₂ enriched air delivered to three in serial photobioreactors of 0.200 dm³ capacity each. The results showed that increasing illumination during culture increased biomass production of Chlorella by ∼60% as well as increased CO₂ fixation ability by ∼7.0%. It was also demonstrated that the non-competitive inhibition of [HCO₃ ⁻] as a carbon source significantly affected the cultivation in both the increasing and constant photon flux density regimes.     

Thermodynamic and structural properties of phosphatidylserine bilayer membranes in the presence of lithium ions and protons

The binding of lithium ions to phosphatidylserine has been studied by differential scanning calorimetry for dialkyl and diacyl lipid forms and by X-ray diffraction for dihexadecylphosphatidylserine (DHPS). On first mixing DHPS with LiCl solutions an ordered L_β (L_c) phase is formed with a bilayer repeat distance of 5.55 nm and one strong wide-angle, chain-chain reflection at 0.405 nm (26°C), corresponding to bilayers of little, (mono)hydrated lipid with chains approximately perpendicular to the membrane surface. On heating, this phase transforms to an inverted hexagonal phase (H₁₁, H_α) with a repeat distance of 3.75 nm, at a chain-melting transition temperature of approximately 90°C (DHPS). Cooling, after equilibration of the DHPS⁻·Li⁺ sample in the fluid phase, creates a new low-temperature phase (L_c') which has a repeat distance of 4.0 nm, corresponding to strongly tilted chains (ϕ=42°). The L_c phase also transforms on heating to the H_α phase, but at a considerably lower chain-melting temperature of approx. 70°C (DHPS). The calorimetric behavior as a function of Li⁺ concentration is qualitatively very similar for the different dialkyl- and diacylphosphatidylserines studied, and is analogous to the results obtained on pH titration. After an initial small increase in transition temperature, that is caused by coulombic ion binding and concomitant surface charge neutralization, a much larger increase in the chain-melting transition temperature occurs, caused by dehydration of the lipid, as a consequence of a further stereospecific ion binding. This suggests that Li⁺ and H⁺ have similar binding sites on the PS headgroup.