Preparative electrophoresis: on the estimation of maximum temperature

The quantity of proteins processed by an electrophoretic technique is proportional to the cross-sectional area of the gel. For preparative purifications, an increase in the cross-sectional area is desired, but the Joule heating phenomenon restricts such an increase. The governing heat equation is analyzed and simplified with reference to Counteracting Chromatographic Electrophoresis. The application of the method of weighted residuals yields a compact and accurate solution for the maximum temperature rise in the column which is suitable for design calculations. Similar estimations indicate the efficiency of heat dissipation in annular configuration.List of Symbols C _p specific heat capacity, J g^–1 K^–1 - h heat transfer coefficient at the wall, W cm^–2K^–1 - i current density, A cm^–2 - k effective thermal conductivity of the packing, W cm^–1 K^–1 - k _b electrical conductivity of the buffer, mho cm^–1 - k _e effective electrical conductivity of the packing, mho cm^–1 - k _g electrical conductivity of the gel, mho cm^–1 - L length of the packing, cm - N _Pr Prandtl number - N _Re Reynolds number - r radial coordinate, cm - r _i inner radius of annulus, cm - r _o outer radius of annulus, cm - S heat source term, defined by eqn. (6) - T temperature, K - T _c cooling fluid temperature, K - T _i initial temperature, K - T _max highest temperature in the column, K - u superficial buffer velocity, cm s^–1 - V voltage gradient, V cm^–1 - porosity of the packing, dimensionless - buffer density, g cm^–3 - temperature, dimensionless Material presented in this paper has been adapted from the author's dissertation [15] which was accepted (supervisor: Dr. Jean B. Hunter) by the Cornell University Graduate Faculty in partial requirement of a graduate degree. Thoughtful discussions with Professors J. Robert Cooke and Michael L. Shuler regarding the annulus problem and the financial support provided by the Department of Agricultural and Biological Engineering, Cornell University, Ithaca, USA are gratefully appreciated.     

Diffusion of sucrose in xanthan gum solutions

Molecular diffusion of solutes, like sucrose in the xanthan gum fermentation, is important in order to understand the complex behavior of mass transfer mechanisms during the process. This work was focused to determine the diffusion coefficient of sucrose, a carbon source for xanthan production, using similar sucrose and xanthan concentrations to those occurring in a typical fermentation. The diaphragm cell method was used in experimental determinations. The data showed that diffusion coefficient of sucrose significantly decreases when xanthan gum concentration increases. Theoretical and semiempirical models were used to predict sucrose diffusivity in xanthan solutions. Molecular properties and rheological behavior of the system were considered in the modeling. The models tested fitted well the behavior of experimental data and that reported for oxygen in the same system.List of Symbols A constant in eq. (5) - C _pg cm^–3 polymer concentration - D cm² s^–1 diffusivity - D _ABcm² s^–1 diffusivity of A through liquid solvent - D _APcm² s^–1 diffusivity of A in polymer solution - D _AWcm² s^–1 diffusivity of A in water - D _Pcm² s^–1 diffusivity of polymer in liquid solvent - E _D gradient of the activation energy for diffusion - H _P hydratation factor of the polymer in water (g of bound water/g of polymer) - K dyn sⁿ cm^–2 consistency index - K ₁ constant in eq. (5) - K _P overall binding coefficient [g of bound solute/cm³ of solution]/[g of free solute/cm³ of polymer free solution] - n flow behavior index - M _Bg g mol^–1 molucular weight of liquid solvent - M _Pg g mol^–1 molecular weight of the polymer - M _Sg g mol^–1 Molecular weight of polymer solution (= M _BX_B+M_PX_P) - R cm³ atm g mol^–1 K^–1 ideal gas law constant - T K absolute temperature - V _Bcm³ g mol^–1 molar volume of liquid solvent - V _Pcm³ g mol^–1 molar volume of polymer - V _Scm³ g mol^–1 molar volume of polymer solution - X _B solvent molar fraction - X _P polymer molar fraction - polymer blockage shape factor - _P volume fraction of polymer in polymer solution - g cm^–1 s^–1 viscosity - _ag cm^–1 s^–1 apparent viscosity of the polymer solution - _icm³ g^–1 intrinsic viscosity - ₀ g cm^–1 s^–1 solvent viscosity - _Pg cm^–1 s^–1 polymer solution viscosity - _R relative viscosity (= / ₀) - ₌₀ g cm^–1 s^–1 viscosity of polymer solution obtained at zero shear rate - ₀ g cm^–3 water density     

Exchange of HCO 3 − for monovalent anions across the human erythrocyte membrane

Summary A stopped-flow rapid reaction apparatus was used for measuring changes in extracellular pH (pH _o ) of red cell suspensions under conditions wheredpH _o /dt was determined by the rate of HCO ₃ ^– /X ^– exchange across the membrane (X ^–=Cl^–, Br^–, F^–, I^–, NO ₃ ^– or SCN^–). The rate of the exchange at 37°C decreased forX ^– in the order: Cl^–>Br^–>F^–>I^–>NO ₃ ^– >SCN^–, with rate constants in the ratios 10.860.770.550.520.31. When HCO ₃ ^– is exchanged for Cl^–, Br^–, F^–, NO ₃ ^– or SCN^–, a change in the rate-limiting step of the process takes place at a transition temperature (T _T ) between 16 and 26°C. In I^– medium, however, no transition temperature is detected between 3 and 42°C. AlthoughT _T varies withX ^–, the activation energies both above and belowT _T are similar for Cl^–, Br^–, NO ₃ ^– and F^–. The values of activation energy are considerably higher whenX ^–=I^– or SCN^–. The apparent turnover numbers calculated for HCO ₃ ^– /X ^– exchange (except forX ^–=I^–) at the correspondingT _T ranged from 140 to 460 ions/site ·sec for our experimental conditions. These findings suggest that: (i) HCO ₃ ^– /X ^– exchange for allX ^– studied takes place via the rapid anion exchange pathway; (ii) the rate of HCO ₃ ^– /X ^– exchange is influenced by the specific anions involved in the 11 obligatory exchange; and (iii) the different transition temperatures in the Arrhenius diagrams of the HCO ₃ ^– /X ^– exchange do not seem to be directly related to a critical turnover number, but may be dependent upon the influence ofX ^– on protein-lipid interactions in the red blood cell membrane.     

Passive ionic properties of frog retinal pigment epithelium

Summary The isolated pigment epithelium and choroid of frog was mounted in a chamber so that the apical surfaces of the epithelial cells and the choroid were exposed to separate solutions. The apical membrane of these cells was penetrated with microelectrodes and the mean apical membrane potential was –88 mV. The basal membrane potential was depolarized by the amount of the transepithelial potential (8–20mV). Changes in apical and basal cell membrane voltage were produced by changing ion concentrations on one or both sides of the tissue. Although these voltage changes were altered by shunting and changes in membrane resistance, it was possible to estimate apical and basal cell membrane and shunt resistance, and the relative ionic conductanceT _i of each membrane. For the apical membrane:T _K0.52,T _{HCO 3}=0.39 andT _Na=0.05, and its specific resistance was estimated to be 6000–7000 cm². From the basalT _K=0.90 and its specific resistance was estimated to be 400–1200 cm². From the basal potassium voltage responses the intracellular potassium concentration was estimated at 110mm. The shunt resistance consisted of two pathways: a paracellular one, due to the junctional complexes and another, around the edge of the tissue, due to the imperfect nature of the mechanical seal. In well-sealed tissues, the specific resistance of the shunt was about ten times the apical plus basal membrane specific resistances. This epithelium, therefore, should be considered tight. The shunt pathway did not distinguish between anions (HCO₃ ^–, Cl^–, methylsulfate, isethionate) but did distinguish between Na⁺ and K⁺.     

Methods for measuring the properties of the turbulence in bubble flow

Summary A constant temperature hot film anemometer has been used to evaluate mean liquid flow velocity, bubble frequency, turbulence scale and intensity, and the rate of energy dissipation by liquid phase bubble flow.Symbols M mass - L lenght - T time - a gas/liquid interfacial area L² - a=a/V_L specific gas/liquid interfacial area with regard to the volume of the liquid L^–1 - d bubble diameter L - d mean bubble diameter L - d_e dynamic equilibrium (maximum stable) bubble size L - d_p primary bubble diameter L - d_s Sauter bubble diameter L - E specific energy dissipation rate with regard to the volume of the liquid ML^–1T^–3 - E V_L energy dissipation rate ML²T^–3 - E=E/ since =1 g cm^–3, E has the same numerical value as E. Therefore, the symbol E is used everywhere in the present paper for E and called energy dissipation rate (S. s^–2=Stokes. s^–2) L²T^–3 - E_G or _G local relative gas hold up L²T^–3 - f() autocorrelation function [Eq. (10)] L²T^–3 - f(r) cross correlation function [Eq. (11)] L²T^–3 - g acceleration of gravity LT^–2 - k constant LT^–2 - k_L mass transfer coefficient LT^–1 - k_La volumetric mass transfer coefficient with regard to the volume of the liquid T^–1 - N₀ number of crossings of u and T^–1 - n_B bubble frequency T^–1 - r distance between two points 1 and 2 of the cross correlation function L - t time T - u momentaneous liquid velocity LT^–1 - mean liquid velocity LT^–1 - mean square fluctuation velocity L²T^–2 - intensity of turbulence LT^–1 - x position coordinate L - V volume of the bubbling layer in the column L³ - V_L volume of the bubble free layer in the column L³ - V electrical voltage (in Fig. 2) L³ - v velocity scale [Eq. (6)] LT^–1 - We_crit critical Weber number [Eq. (4)] LT^–1 - w_SG superficial gas velocity LT^–1 - w_SL superficial liquid velocity LT^–1 - _G or E_G local relative gas hold up LT^–1 - smallest scale [Eq. (6)] L - time delay in the autocorrelation function [Eq. (10)] T - energy dissipation scale [E. (15)] L - _f: Taylor's vorticity scale [E. (14)] L - kinematic viscosity of the liquid L²T^–1 - density of the liquid ML^–3 - surface tension MT^–2 - dynamic pressure of the turbulence [Eq. (8)] ML^–1T^–2 - p primary (at the aerator) - e equilibrium (far from the aerator)     

Direct ab initio dynamics studies of the hydrogen abstraction reactions of hydrogen atom with n-propyl radical and isopropyl radical

The kinetics of the hydrogen abstraction reactions of hydrogen atom with n-propyl radical and isopropyl radical were studied using the direct ab initio dynamics approach. BHandHLYP/cc-pVDZ method was employed to optimize the geometries of stationary points as well as the points on the minimum energy path (MEP). The energies of all the points for the two reactions were further refined at the QCISD(T)/cc-pVTZ level of theory. No barrier was found at the QCISD(T)/cc-pVTZ//BHandHLYP/cc-pVDZ level of theory for both reactions. The forward and reverse rate constants were evaluated with both canonical variational transition state theory (CVT) and microcanonical variational transition state theory ( VT) in the temperature range of 300–2,500 K. The fitted three-parameter Arrhenius expression of the calculated CVT rate constants at the QCISD(T)/cc-pVTZ//BHandHLYP/cc-pVDZ level of theory are k^CVT (n – C₃H₇)=1.68×10^–14 T^0.84 e^(319.5/T) cm³ molecule^–1 s^–1 and k^CVT (iso-C₃H₇)=4.99×10^–14 T^0.90 e^(159.5/T) cm³ molecule^–1 s^–1 for reactions of n-C₃H₇ + H and iso-C₃H₇ + H, respectively, which are in good agreement with available literature data. The variational effects were analysed.Figure Comparison of the calculated forward rate constants at the QCISD(T)/cc-pVTZ//BHandHLYP/cc-pVDZ level of theory and the available experimental and theoretical data of the reaction vs 1,000/T for the two reactions.     

Biological denitrification of water in a two-chambered immobilized-cell bioreactor

Summary A double-chambered bioreactor based on a composite immobilized-cell gel layer/microporous membrane structure was applied to the continuous denitrification of high-nitrate water. Immobilized denitrifying bacteria (Pseudomonas denitrificans) were provided with separate flows of nitrate and carbon (C) nutrient, with no contamination of the treated water by cell leakage from the gel. Using acetate (7.5 mm) as a C source and a C/N ratio of 3 (mol/mol), specific denitrification rates ranging from 15 to 25 g NO _inf3 ^sup– · h^–1 · – cm^–2 membrane surface (50–85 g NO _inf3 ^sup– · h^–1 · cm^–3 gel) were obtained. The denitrifying activity remained stable for several months. At the flow rate used (10 cm³ · h^–1), the effluents contained noticeable amounts of NO _inf2 ^sup– ions but the treated water remained uncontaminated by the carbon nutrient. Most NO _inf2 ^sup– ions disappeared from the treated water in a second reactor connected in series. When fed with an unchlorinated sludge supernatant as C nutrient, immobilized bacteria performed efficient denitrification of water for only 3 weeks. Diffusion experiments showed that acetate ions diffused much less rapidly than NO _inf3 ^sup– or NO _inf2 ^sup– ions through the composite structure. Further developments of the system are considered.     

Investigation of the structure of two-phase flow model-media in bubble-column bioreactors

Summary By applying photographic, electrical conductivity, and electrooptical methods, the transverse variation of bubble size and velocity, the local gas hold up, and the local specific gas/liquid interfacial area were estimated in a bench scale bubble-column bioreactor containing model cultivation media. The liquid velocity profile, the transverse turbulence intensity variations, and the turbulence energy dissipation scale were also measured by a hot film turbulence probe and constant temperature anemometer technique.A significant relationship was found between the two-phase flow fluid dynamical state and the transverse variation of the various properties.Symbols M mass - L length - T time - a gas/liquid interfacial area L² - specific gas/liquid interfacial area with regard to the bubbling layer volume L^–1 - D transverse coordinate (measured from the wall of the column) L - d bubble diameter L - d mean bubble diameter L - d_e dynamic equilibrium (maximum stable) bubble diameter L - d_p primary bubble diameter L - d_s Sauter bubble diameter L - E specific energy dissipation rate with regard to the volume of the liquid ML^–1T^–3 - EV_L energy dissipation rate ML²T^–3 - , since =1 g/cm³, E has the same numerical value as E. Therefore, the symbol E is used everywhere in the present paper for E for simplicity and called energy dissipation rate (S.s^–2=Stokes.s^–2) L²T^–3 - E_G or local relative gas holdup - f (r) cross correlation function - g acceleration of gravity LT^–2 - h longitudinal distance from the aerator L - relative turbulence intensity - N_O number of u and crossings T^–1 - n_B bubble frequency T^–1 - r distance between two points 1 and 2 of the cross correlation function L - t time - u instantaneous liquid velocity LT^–1 - mean liquid velocity LT^–1 - mean square fluctuation velocity L²T^–2 - turbulence intensity LT^–1 - w_SG superficial gas velocity LT^–1 - w_SL superficial liquid velocity LT^–1 - or E_G local relative gas holdup LT^–1 - energy dissipation scale L - kinematic liquid viscosity L²T^–1 - liquid density M L^–3 - surface tension M T^–2 - dynamic turbulence pressure M L^–1T^–2 Indices p primary (at the aerator) - e equilibrium (far from the aerator)     

Use of 4-Thiouridine and 4-Thiothymidine in Studies on Pyrimidine Nucleoside Phosphorylases

The new substrates 4-thiouridine and 4-thiothymidine were proposed for spectrophotometric measurement of the activity of uridine (UP) and thymidine (TP) phosphorylases. At pH 7.5, 4-thiouridine has an absorbance maximum at 330 nm, and the difference in extinction coefficient () between 4-thiouridine and 4-thiouracil is 3000 ^–1cm^–1. 4-Thiouridine proved to be a good substrate for UP: the Michaelis ( ) and catalytic (k _cat) constants were estimated respectively at 130 M and 49 s^–1 at 25°C. Even a greater (5000 M^–1cm^–1 at 336 nm) was observed for the 4-thiothymidine/4-thiothymine pair.     

Simulation of a multicolumn recirculated packed bed reactor (MRPBR) for penicillin acylase

Enzyme reactors for the industrial hydrolysis of penicillin are analyzed in terms of biocatalyst stability to pH. A multicolumn system with packed beds placed in parallel and operating under recirculating conditions is proposed as an adequate reactor for this process. The system is studied both experimentally and with the aid of a simulation program.List of Symbols A transversal area (cm²) - C _A ammonia concentration in the reaction mixture (M) - C ₁ concentration of KH₂PO₄ in buffer (M) - C ₂ concentration of K₂HPO₄ in buffer (M) - d _p biocatalyst diameter (cm) - E enzyme or biocatalyst concentration (gcat l^–1) - K _APA APA non competitive inhibition constant (M) - K _IS excess substrate inhibition constant (M) - Km constant Michaelis-Menten (M) - K _PAA PAA competitive inhibition constant (M) - Q recirculation flow rate (cm³ min^–1) - Q _T recirculation flow rate per column (cm³ min^–1) - Re Reynolds number - S _E substrate concentration entering the neutralization tank (M) - S ₀ initial substrate concentration (M) - S _T substrate concentration in neutralization tank (M) - t time (min) - v _i initial reactor rate (mol min^–1 gcat^–1) - V _s superficial velocity (cm seg^–1) - V _T volume of neutralization tank (cm³) - X _E substrate conversion entering tank - X _T substrate conversion in neutralization tank - X conversion - Z reactor length (cm) - z axial position in reactor (cm) - z ^* non-dimensional axial position in reactor - biocatalyst's density (gcat cm^–3) - p pressure drop in the packed-bed reactor     

Effects of growth temperature on maximal specific growth rate,yield, maintenance,and death rate in glucose-limited continuous culture of the thermophilic Bacillus caldotenax

Summary The influence of temperature on the growth of the theromophilic Bacillus caldotenax was investigated using chemostat techniques and a chemically defined minimal medium. All determined growth constants, that is maximal specific growth rate, yield and maintenance, were temperature dependent. It was striking that the very large maintenance requirement was about 10 times higher than for mesophilic cells under equivalent conditions. A death rate, which was very substantial at optimal and supraoptimal growth temperatures, was estimated by comparing the maintenance for substrate and oxygen. There was no indication for a thermoadaptation as postulated by Haberstich and Zuber (1974).Symbols D Dilution rate (h^–1) - D_c=_max Critical dilution rate (h^–1) - E Temperature characteristic (J mol^–1) - k Organism constant - k_d Death rate coefficient (h^–1) - k_m Maintenance substrate coefficient estimated from M_O (h^–1) - M_O Maintenance respiration, mmol O₂ per g dry biomass and h (mmol g^–1h^–1) - M_O Maintenance respiration, taking k_d into account - m_S Maintenance substrate coefficient, g glucose per g dry biomass and h (h^–1) - OD Optical density at 546 nm - QO₂ Specific O₂-uptake rate (mmol g^–1h^–1) - Q _O2 ^V Specific O₂-uptake rate for viable portion of biomass (mmol g^–1 h^–1) - Q_S Specific glucose uptake rate (h^–1) - Q _S ^V Specific glucose uptake rate for viable portion of biomass (h^–1) - R Gas constant 8.28 J mol^–1K^–1 - S Substrate concentration in reactor (g l^–1) - S_O Influent substrate concentration (g l^–1) - T_max Maximal growth temperature (°C) - T_min Minimal growth temperature (°C) - X Dry biomass (g l^–1) - X_tOt=X Dry biomass containing dead and viable cells - X_v Viable portion of biomass - Y _O ^m Potential yield for O₂ corrected for maintenance respiration (g mol^–1) - Y _S ^m Potential yield for substrate corrected for maintenance requirement, g biomass per g glucose (–) - Specific growth rate (h^–1) - _max Maximal specific growth rate (h^–1)     

Growth simulation ofHansenula polymorpha

Summary Using the model presented in part I, the measured time and spacial variations of process variables were simulated with satisfactory accuracy. Especially the experimentally found minima of the longitudinal dissolved oxygen concentration profiles in the substrate limiting growth range, which are caused by the transition from oxygen transfer limited to substrate limited growth along the tower, can be simulated with great accuracy.Symbols L length - M mass - T time - K temperature - M_M mole mass - a Specific gas/liquid interfacial area with regard to the liquid volume in the tower (L^–1) - DS_R Substrate feed rate (ML^–3T^–1) - K_O Saturation constant of Monod kinetics with regard to oxygen (ML^–3) - K_S Saturation constant of Monod kinetics with regard to the substrate (ML^–3) - K_ST Constant - K_L Mass transfer coefficient (LT^–1) - k_La Volumetric mass transfer coefficient (T^–1) - k_La^E Volumetric mass transfer coefficient at the entrance (T^–1) - k_La Volumetric mass transfer coefficient at large distances from the entrance (T^–1) - k_La ₀ Volumetric mass transfer coefficient in the absence of substrate (ethanol) (T^–1) - L_R Gas-liquid layer height in the tower (L) - L_R Height of the loop (L) - - O_B Dissolved oxygen concentration in the loop liquid (ML^–3) - O_F Dissolved oxygen concentration in the tower liquid (ML^–3) - O _F ^* Saturation value of O_F (ML^–3) - OTR Oxygen transfer rate (ML^–3T^–1) - P Pressure - Oxygen transfer rate (ML^–3T) - S_B Substrate concentration in the loop liquid (ML^–3) - S_D Substrate concentration at which k_La=2 k_La ₀ (ML^–3) - S_F Substrate concentration in the tower liquid (ML^–3) - T Absolute temperature - t Time (T) - u_Go Superficial gas velocity in the tower - V_R Reactor volume (L³) - V_G Volumetric gas flow rate in the tower (L³T^–1) - V_B Volumetric liquid flow rate in the loop (L³T^–1) - V_F Volumetric liquid flow rate in the tower (L³T^–3) - V_u Liquid recycling rate (L³T^–1) - X_B Biomass concentration in the loop liquid (ML^–3) - X_F Biomass concentration in the tower liquid (ML^–3) - x Longitudinal coordinate in the tower (L) - x^* Longitudinal coordinate in the loop (L) - x_OG O₂ mole fraction in the gas phase - Y_X/O Yield coefficient of biomass with regard to oxygen - Y_X/S Yield coefficient of biomass with regard to substrate - z=x/L_R Dimensionless longitudinal coordinate in the tower - z^*=x^*/L_B Dimensionless longitudinal coordinate in the loop - Constant (L_R is the distance from the aerator on which k_L a is space dependent) - Liquid recirculation ratio - _G Mean relative gas holdup in the tower - _exp Experimentally determined (T^–1) - _max Maximum specific growth rate (T^–1) - _F Liquid density (ML^–3) - A At the exit - E At the inlet     

Limnology of Crater Lakes in Los Tuxtlas,Mexico

Investigations on the abundance, biomass and position of heterotrophic flagellates (HF) in the benthic microbial food web of a melt water stream on King George Island, Antarctic Peninsula, were undertaken during the Antarctic summer from 23rd December 1997 until 13th March 1998. Abundance and biomass of potential HF resources (picophotoautotrophic and non-photoautotrophic bacteria) as well as potential predators on HF (ciliates and meiofauna) were also investigated. HF abundance ranged from approximately 9 × 10³ to 81 × 10³ cells cm^–3, values which fall into the same range as those found in lower latitudes. Numerically important benthic HF were euglenids, kinetoplastids, thaumatomastigids and especially chrysomonads. Most species identified have been shown to have a worldwide distribution. Abundance of the benthic ciliates ranged from 27 to 950 cells cm^–3. Mean bacterial abundance was 1.9 × 10⁷ and 5.2 × 10⁸ cells cm^–3 for picophotoautotrophic and non-photoautotrophic benthos, respectively. The well-developed microbial community was able to support the large number of nematods, gastotrichs, tardigrads and rotifers with abundances reaching more than 1000 individuals cm^–3. The largest portion of heterotrophic biomass was formed by the meiofauna with a mean of 63 g C cm^–3, followed by that of the heterotrophic bacteria with 4.80 g C cm^–3. Picophotoautotrophic bacteria contributed a mean of 1.37 g C cm^–3. HF and ciliates mean biomass was 0.61 and 1.99 g C cm^–3, respectively, with the HF biomass comprising between <10 and 70% of the total protozoan biomass. The data obtained in this study identify the melt water stream as a hot-spot of heterotrophic microbial and meiofaunal activity during the austral summer. The HF in the melt water stream formed a diverse group in terms of taxa and potential feeding types. Chrysomonads, kinetoplastids, euglenids and thaumatomastigida were the most abundant taxa. A classification into feeding types identified an average of 34% of the total HF as bacterivorous while all others were able to utilise other, larger organisms as resources. Potential trophic interactions between HF and bacteria and higher trophic levels are discussed.     

Strain selection,medium development and scale-up of toyocamycin production by streptomyces chrestomyceticus

The batch productivity (Q _TM) of the production of the nucleoside antibiotic toyocamycin (TM) by Streptomyces chrestomyceticus was increased ten-fold by selection of a UV generated mutant, optimization of pH, increasing incubation temperature from 28 °C to 36 °C, and addition of soy oil. Initial high oxygen transfer rates stimulated Q _TM maxima two-fold. Antibiotic production by the mutant strain, U190, however, appeared more shear sensitive than the parent culture FCRF 341 with maximum antibiotic titer being inversely related to impellor tip velocity, T _v . For this reason, scale-up could not be done at constant P/V or constant volumetric oxygen transfer. Instead, programming of impeller speed was evaluated in order to maintain optimal impeller tip velocity during scale-up. It was found that a low constant T _v maintained in scale-up in geometrically similar vessels was most beneficial for duplication of optimal antibiotic productivity, Q _TM. Pilot fermentations (120 dm³ scale) were used to determine coefficients of Q _TM variation from oxygen uptake rate (OUR) and total CO₂ evolution data for monitoring of Q _TM variation during scale-up to the 12,000 dm³ scale. This technique allowed for on-line prediction of antibiotic titer and Q _TM from fermentor exhaust gas data.List of Symbols A scale constant - B shape constant - C location of maximum constant - D m impeller diameter (m) - H m liquid height (m) - OTR MmolO₂·(dm³)^–1min^–1 oxygen transfer rate - OUR MmolO₂·(dm³)^–1min^–1 oxygen uptake rate - PCV cm³ packed cell volume - P/V watts/dm³ volumetric power consumption - Q 1 · min^–1 corrected to standard conditions of temperature, pressure aeration rate - Q _TM g/(cm³ · h) or kg/(m³ · h) antibiotic productivity - T m tank diameter - T _mix s mixing time - T _v cm · s^–1 impeller tip velocity - TM g/cm³ Toyocamycin concentration - TNP Tricyclic nucleoside phosphate     

Modelling of temperature effects on batch microbial transglutaminase fermentation with Streptoverticillium mobaraense

Batch transglutaminase (MTG) fermentations by Streptovertivillium mobaraense WSH-Z2 at various temperatures ranging from 25 to 35 °C were studied. Dry cell weight and MTG activity could reach their maximal values of 25.1 g/l and 2.94 U/ml, respectively at 30 °C. One typical equation was used to describe the relationship between specific growth rate and culture temperature by comparing several typical equations. Different lag time was observed under various culture temperature. The low lag time was observed under high culture temperature. X = –a ₀(T – T ₀)² + X ₁ + a ₁ (1 – exp(a ₂ (T – T ₁))) and U = –a ₀ (T – T ₀ )² + U ₀ + a ₁ (1 – exp(a ₂ (T – T ₁ ))) could be used to describe the relationship between temperature and the maximal dry cell weight as well as the maximal MTG activity at each temperature.     

Comparative photosynthesis,growth and transpiration of two species of Atriplex

Summary Throughout a period of 23 days, during which the photosynthesis, growth and transpiration of two species of Atriplex were compared, A. spongiosa, a C₄ species (first products of photosynthesis = 4-C dicarboxylic acids), maintained net rates of leaf photosynthesis as high as, or higher than, those of A. hastata, a C₃ species (photosynthesis exhibiting the Calvin-type characteristics).However, as the experiment progressed, the proportion of photosynthate which was used to produce new leaf material declined progressively in A. spongiosa, so that total plant growth rate, initially more than twice as high as in A. hastata, declined to only 0.8 of the A. hastata value. This result demonstrated clearly that more efficient photosynthesis is only one factor, and in this case a relatively minor factor, in total growth rate.Transpiration rates were consistently lower in A. spongiosa than in A. hastata and the ratio declined slightly during the experiment. In consequence, water-use efficiency, both on a single-leaf and whole-plant basis, was much greater in the C₄ species.Levels of mesophyll resistance (r _m ) were consistently lower in A. spongiosa and increased from about 0.4–0.6 to 1.2–1.5 s cm^–1 during the experiment. In A. hastata there was more variability in r _m levels but little overall trend towards a higher r _m , initial and final values being of the order of 2.5–2.6 and 2.6–2.9 s cm^–1, respectively. Levels of stomatal resistance (r _l ) were higher in A. spongiosa (about 1.0–1.2 s cm^–1) than in A. hastata (about 0.7–0.8 s cm^–1) at the beginning of the experiment and increased to 2.0–2.6 s cm^–1, whereas they remained relatively constant in A. hastata.The combination of relatively low r _m levels and relatively high r _l levels provide the explanation for the substantially greater water use efficiency in A. spongiosa. The progressive changes in these levels and in the pattern of leaf area development in A. spongiosa provide an elegant example of adaptation to arid conditions by this species.     

Effect of dilution rate on the release of pertussis toxin and lipopolysaccharide ofBordetella pertussis

Summary The kinetics ofBordetella pertussis growth was studied in a glutamate-limited continuous culture. Growth kinetics corresponded to Monod's model. The saturation constant and maximum specific growth rate were estimated as well as the energetic parameters, theoretical yield of cells and maintenance coefficient. Release of pertussis toxin (PT) and lipopolysaccharide (LPS) were growth-associated. In addition, they showed a linear relationship between them. Growth rate affected neither outer membrane proteins nor the cell-bound LPS pattern.Nomenclature X cell concentration (g L^–1) - specific growth rate (h^–1) - _m maximum specific growth rate (h^–1) - D dilution rate (h^–1) - S concentration of growth rate-limiting nutrient (glutamate) (mmol L^–1 or g L^–1) - Ks substrate saturation constant (mol L^–1) - m_s maintenance coefficient (g g^–1 h^–1) - Y_x/s theoretical yield of cells from glutamate (g g^–1) - Y_x/s yield of cells from glutamate (g g^–1) - Y_PT/s yield of soluble PT from glutamate (mg g^–1) - Y_KDO/s yield of cell-free KDO from glutamate (g g^–1) - Y_PT/x specific yield of soluble PT (mg g^–1) - Y_KDO/x specific yield of cell-free KDO (g g^–1) - q_PT specific soluble PT production rate (mg g^–1 h^–1) - q_KDO specific cell-free KDO production rate (g g^–1 h^–1)     

Turbidimetric Method for Quantitative Determination of Triton X-100 with Silicotungstic Acid

The formation of Triton X-100–silicotungstic acid complex was studied. Quantitative turbidimetric determination of the detergent based on this process was suggested. This method allows us to determine the complex formation at any wavelength in the range from 350 (₃₅₀ =15600 cm^–1 M^–1) to 600 nm (₆₀₀ = 9090 cm^–1 M^–1). The calibration curve for Triton X-100 recorded at 350 nm is linear in the concentration range of 0 to 30 g/ml. A sigmoid calibration curve was observed at longer wavelengths. A linear fragment of the calibration curve recorded at 600 nm was found at a concentration of Triton X-100 of about 5 g/ml. The complex nature of calibration curves can be explained by the heterogeneity of the complex dispersion.     

Ulva rigida (Ulvales,Chlorophyta) tank culture as biofilters for dissolved inorganic nitrogen from fishpond effluents

Ulva rigida was cultivated in 7501 tanks at different densities with direct and continuous inflow (at 2, 4, 8 and 12 volumes d^–1) of the effluents from a commercial marine fishpond (40 metric tonnes, Tm, of Sparus aurata, water exchange rate of 16 m³ Tm^–1) in order to assess the maximum and optimum dissolved inorganic nitrogen (DIN) uptake rate and the annual stability of the Ulva tank biofiltering system. Maximum yields (40 g DW m^–2 d^–1) were obtained at a density of 2.5 g FW 1^–1 and at a DIN inflow rate of 1.7 g DIN m^–2 d^–1. Maximum DIN uptake rates were obtained during summer (2.2 g DIN M^–2 d^–1), and minimum in winter (1.1 g DIN m^–2 d^–1) with a yearly average DIN uptake rate of 1.77 g DIN m^–2 d^–1 At yearly average DIN removal efficiency (2.0 g DIN m^–2 d^–1, if winter period is excluded), 153 m² of Ulva tank surface would be needed to recover 100% of the DIN produced by 1 Tm of fish.Abbreviations DIN= dissolved inorganic nitrogen (NH _inf4 ^sup+ + NO _inf3 ^sup– + NO _inf2 ^sup– ); - FW= fresh weight; - DW= dry weight; - PFD= photon flux density; - V= DIN uptake rate     

Function and regulation of the avian caecal bulb: influence of dietary NaCl and aldosterone on water and electrolyte fluxes in the hen (Gallus domesticus) perfused in vivo

Summary The function of the caecal bulb, and its adaptation to chronic high- or low-Na⁺ intake, was investigated by in vivo perfusion of anaesthetised birds. Effects of acute aldosterone injection (125 g·kg^–1 body mass) were also measured.Evidence was found for primary active net absorption of Na⁺, inducing parallel Na-linked absorption of water and Cl^– and secretion of K⁺. Around 20–35% of total Cl^– absorption and K⁺ secretion were independent of Na⁺ fluxes, and these components appear to be driven by passive processes with apparent conductances of 6.3×10^–3 (G _Cl) and 1.1×10^–3 (G _K) S·cm^–2.Acetate (40mM) stimulated Na⁺ fluxes (8.5–9.9 Eq·cm^–2·h^–1) and Na-linked water fluxes (27–44 l·cm^–2·h^–1). Increased coupling ratios (2.9–4.6 l·Eq^–1) and other data indicate that these effects may be due to increased osmotic permeabilities of barriers involved in the Na-linked water transfer pathway.Low-Na⁺ maintenance enhanced EPD (49–69 mV, serosa positive) and all net fluxes:J _Na (6.8–11.6);J _K (–3.2––4.3);J _Cl (4.3–5.6 Eq·cm serosal area^–2·h^–1);J _v (28–43 l·cm^–2·h^–1) (mucosal-serosal fluxes positive).Acute aldosterone enhancedJ _Na (10.8–14.0 Eq·cm^–2·h^–1) and EPD (54–66 mV) by 3 h after injection, but had no effect on the Na-linked components ofJ _K orJ _Cl.Abbreviations ECPD, EPD Electrochemical or electrical potential difference - G _Cl ,G _K ionic conductances (Cl^–, K⁺) - J _v ,J _ion net volume or ion flux rate, mucosa-serosa positive;P _d (Cl) diffusive permeability coefficient (of Cl^–) - SEDM standard error of difference between means