Development of a new method for testing strength of cells against fluid shear stress

A new method for testing the strength of cells against fluid shear stress by using a long capillary column was proposed. The trajectories of cells in the column were simulated by introducing the Brownian motion model. The Brownian motion was performed by the generation of random numbers. The mean exposure time to shear stress and the mean shear stress acting on the surface of cells were discussed by the result of computer simulation. The mean shear stress acting on the surface of cells flowing in the capillary column was estimated as 4/3-fold of the shear stress at the column wall provided that the ratio of the cell radius to the column radius does not exceed 0.08. The effectiveness of this new method for testing the strength of cells against fluid shear stress was shown.List of Symbols a m radius of cell - c constant - E distribution function - L m length of capillary column - M number of division - N number of division - p probability - Q m³/s flow rate - R m radius of capillary column - r m radial position - t s time - T s exposure time - T _m s mean exposure time - T ₀ s mean residence time - m/s axial velocity - u _m m/s cross-sectional flow velocity - z m axial position - s^–1 shear rate - _w s^–1 shear rate at wall - Pa s viscosity - spherical coordinate - spherical coordinate - Pa shear stress - _m Pa mean shear stress - _w Pa shear stress at wall     

Anchorage-dependent animal cell culture by using a porous microcarrier

CHO-K1 cells were cultured by using a porous microcarrier. The effects of microcarrier concentration and agitation rate on cell growth in porous microcarrier cultures were investigated. The specific growth rate of 0.041 h^–1 in porous microcarrier cultures was independent of both microcarrier concentration and agitation rate. By estimating the total surface area occupied by cells from the maximum cell number, it was found that not all the surface area of the porous microcarrier was utilizable for cell growth.The maximum cell number decreased with increasing the microcarrier concentration and the agitation rate. From this result, it was also found that not all the cells grown on the interior surface of the porous microcarrier were protected against mechanical damage due to agitation. The protection capacity of the porous microcarrier was estimated to be 300 cells/carrier. The direct gas sparging into the culture broth in porous microcarrier cultures improved the cell density without mechanical damage to animal cells.List of Symbols d m microcarrier diameter - d _i m impeller diameter - d _p m mean pore diameter - n _i s^–1 agitation rate - p Pa pressure difference - v m/s velocity of microcarrier - v _p m/s average velocity flowing through cyclinder - Pa · s viscosity of medium - angle measured from stagnant point - Pa average shear stress - Pa shear stress distribution     

Process and molecular data of branched 1,3-β-D-glucans in comparison with Xanthan

Bioreactor cultivations were carried out with Schizophyllum commune and Xanthomonas campestris. Influence of process parameters and downstream processing on molecular data (molecular weight, intrinsic and shear viscosity) of the secreted exopolysaccharide are shown. Glucan formation of S. commune was enhanced by oxygen limitation. Depending on the type of agitator used, a maximum glucan formation rate of 0.12 kg/(m³ · h) was reached. During cultivation molecular weight and intrinsic viscosity went through a broad maximum with maximum data of 1.3 10⁷ g/mol and 15,400 cm³/g, respectively. After substrate consumption glucan degrading enzymes (glucananses) were released by S. commune. For washing out low molecular substances and concentrating cellfree glucan solutions cross-flow filtration technique with hollow fiber cartridges (molecular cut-off 100,000) were used. After this procedure the shear and intrinsic viscosity were decreased. In contrast to Xanthan, shear viscosity of glucan solutions was not affected by a change in pH from 2 to 12. The intrinsic viscosity of aqueous Xanthan and glucan solutions was opposingly altered by adding salt.List of Symbols A number of capillaries - C ^*g/(dm³ · h) formation rate - D ^–1 shear rate - k Pa/sⁿ consistency index - n flow behaviour index - MW g/mol molecular weight - R m radius - t h time - V dm³ volume - Y yield coefficient - mPas shear viscosity - [] cm³/g intrinsic viscosity - Pa shear stress Indices PS polysaccharide - X cell mass - S substrate - m maximum Dedicated to Prof. Dr. Fritz Wagner on his 60th birthday     

The characterization of a viscoelasticity parameter and other rheological properties of various xanthan gum fermentation broths and solutions

Viscoelasticity has important implications in mass transfer and mixing processes. Previous studies regarding to the viscoelastic behaviour of xanthan solutions have been carried out with diluted solutions or they have not covered a wide range of polymer concentrations. In this study, it was shown that the first normal stress difference measured in fermentation broths is highly dependent on shear rate, and this viscoelastic level is modified by the heat treatment to which the broths are subjected as a postfermentative procedure. The viscoelasticity level is different for xanthan solutions prepared with products arising from different sources and for fermentation broths before the heat treatment, if compared with that measured in end-products. In general, the higher the polymer concentration, the higher the viscoelasticity (expressed as first normal stress difference or Weissenberg number). The addition of a biocide, the change in ionic strength and the addition of sucrose to the xanthan solutions, lead to significant changes in the first normal stress difference.List of Symbols A Pa.S^b constant in first normal stress difference power law (N ₁= ) - b constant in first normal stress difference power law (N ₁= ) - c kg m^–3 polymer concentration - K Nsⁿ m^–2 consistency index - N ₁ Pa first normal stress difference - n flow behaviour index - Wi Weissenberg number,N ₁/ - s^–1 shear rate - Pa shear stress - _y Pa Yield stress     

Apparent viscosity for non-Newtonian fermentation media in bioreactors

The apparent viscosity of non-Newtonian fermentation media is examined. The present state of this subject is discussed. The energy dissipation rate concept is used for a new evaluation of the apparent viscosity in bioreactors, i.e. stirred tank and bubble column bioreactors. The proposed definition of the apparent viscosity is compared with the definitions available in the literature.List of Symbols A _d m ² downcomer cross-sectional area - A _r m ² riser cross-sectional area - a m^–1 specific surface area - C constant in eq. (13) - D m column diameter - D _I m impeller diameter - g m s^–2 gravitational acceleration - h J m^–2 s^–1 K^–1 heat transfer coefficient - K Pa s ⁿ consistency index in a power-law model - k constant in eq. (3) - k _L m s ^–1 liquid-phase mass transfer coefficient - N s^–1 impeller speed - n flow index in a power-law model - P W power input - Re Reynolds number ND _I ^/2 /(/) - U _sg m s ^–1 superficial gas velocity - (U _sg ) _r m s^–1 superficial gas velocity based on riser - V-m³ liquid volume - v ₀ m s^–1 friction velocity Greek Symbols s^–1 shear rate - _c s^–1 characteristic shear rate - W kg^–1 energy dissipation rate per unit mass - W kg^–1 characteristic energy dissipation rate per unit mass - Pa s viscosity - _app Pa s apparent viscosity - kg m^–3 density - Pa shear stress     

Changes of cytoplasmic free Ca2+ in the green alga Mougeotia scalaris as monitored with indo-1, and their effect on the velocity of chloroplast movements

The fluorescent calcium-sensitive dye 1-[2-amino-5-(6-carboxyindol-2-yl)-phenoxy]-2-(2-amino-5-methylphenoxy)-ethane-N,N,N,N-tetraacetic acid (indo-1) was loaded by a transplasmalemma pH gradient into filamentous cells and protoplasts of Mougeotia scalaris, such that most of the indo-1 fluorescence originated from the cytoplasm. Incubation of M. scalaris filaments in ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid (EGTA)-buffered media (-log [Ca²⁺] (=pCa) 8 versus pCa 3) caused a consistent and significant decrease in the cytoplasmic free [Ca²⁺]. Pulses of the fluorescence excitation light (UV-A 365 nm, 0.7 s) caused an increase in cytoplasmic free [Ca²⁺] in M. scalaris that was nearly independent of the external [Ca²⁺] and of chloroplast dislocation by centrifugation. This calcium flux, highest in UV-A light, compared with blue or red light, probably resulted from a release of Ca²⁺ from intracellular stores. Increased cytoplasmic [Ca²⁺] may affect the velocity of chloroplast rotation since UV-A-light-mediated chloroplast movement was faster than in blue or red light. Consistently, the calcium ionophore A23187 and the calcium-channel agonist Bay-K8644 both increased the velocity of the red-light-mediated chloroplast rotation. Based on these and other observations, a Ca²⁺-induced decrease in cytoplasmic viscosity in Mougeotia is presumed to occur.Abbreviations EGTA ethylene glycol-bis-(-aminoethyl ether)N,N,N,N-tetraacetic acid - indo-1 1-[2-amino-5-(6-carboxyindol-2-yl)-phenoxy]-2-(2-amino-5-methylphenoxy)-ethane-N,N,N,Ntetraacetic acid - pCa log [Ca²⁺] - P_fr far-red-absorbing form of phytochrome - P_r red-absorbing form of phytochrome - x_G geometric mean Dedicated to Professor Wolfgang Haupt on the occasion of his 70th birthdayThis paper is part of the Ph.D. thesis of U. Russ at the Justus-Liebig-Universitat Giessen (FRG). Part of this work has been presented at a meeting on Calcium and intracellular signalling in plants in Plymouth, UK, Dec. 1990We are indebted to Dr. G. Seibold and Dipl. Phys. H. Weintraut for their advice on the technique of microspectrofluorometry and for allowing access to the microspectrophotometric facilities in the Strahlenzentrum der Justus-Liebig-Universität, Giessen, FRG. We thank Mrs. A. Quanz for reliable culture of the algae and evaluation of the videotapes. Bay-K8644 was a generous gift of Bayer AG, Wuppertal, FRG. U. russ was supported by a scholarship according to the Hessisches Graduierten Förderungsgesetz. This work was supported by the Deutsche Forschungsgemeinschaft.     

Purification and characterization of sialidase fromClostridium sordellii G12

Sialidase secreted by the urease-positiveClostridium sordellii strain G12 was isolated from culture medium and purified to apparent homogeneity as estimated by Fast Protein Liquid Chromatography (FPLC) and sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE). For this purpose, ion-exchange chromatography, gel filtration, isoelectric focusing, and FPLC on ion-exchange resin and gel filtration materials were used. The sialidase was purified 159 300-fold from 5 l of culture medium, yielding 9 g of enzyme protein with a specific activity of 480 U/mg. For the denatured (SDS-PAGE) and native (FPLC) sialidase relative molecular masses of 40 000 and 38 500 Da, respectively, were estimated. The substrate specificity, kinetic data, and pH-optimum of the enzyme are similar to those of other bacterial sialidases. The influences of salt or serum proteins on enzyme activity are of interest.Abbreviations MU-Neu5Ac 4-methylumbelliferyl -d-N-acetylneuraminic acid - Ganglioside GD1a IV³NeuAc, ll³NeuAc-GgOse₄Cer - Neu5Ac2en 2-deoxy-2,3-didehydro-N-acetylneuraminic acid     

Oligomerization reactions of deoxyribonucleotides on montmorillonite clay: The effect of mononucleotide structure,phosphate activation and montmorillonite composition on phosphodiester bond formation

2-d-5-GMP and 2-d-5-AMP bind 2 times more strongly to montmorillonite 22A than do 2-d-5-CMP and 5-TMP. The dinucleotide d(pG)₂ forms in 9.2% yield and the cyclic dinucleotide c(dpG)₂ in 5.4% yield in the reaction of 2-d-5-GMP with EDAC in the presence of montmorillonite 22A. The yield of d(pC)₂ (2.0%) is significantly lower but comparable to that obtained from 5-TMP. The yield of dimers which contain the phosphodiester bond decreases as the reaction medium is changed from 0.2 M NaCl to a mixture of 0.2 M NaCl and 0.075 M MgCl₂. A low yield of d(pA)₂ was observed in the condensation reaction of 5-ImdpA on montmorillonite 22A. The cyclic nucleotide (3,5-cdAMP) was obtained in 14% yield from 3-ImdpA. The yield of d(pA)₂ obtained when EDAC is used as the condensing agent increases with increasing iron content of the Na⁺-montmorillonite used as catalyst. Evidence is presented which shows that the acidity of the Na⁺-montmorillonite is a necessary but not sufficient factor for the montmorillonite catalysis of phosphodiester bond formation.     

Gas holdup and mass transfer characteristics of carboxymethyl cellulose solutions in a bubble column with a radial gas sparger

The gas phase holdup and mass transfer characteristics of carboxymethyl cellulose (CMC) solutions in a bubble column having a radial gas sparger have been determined and a new flow regime map has been proposed. The gas holdup increases with gas velocity in the bubbly flow regime, decreases in the churn-turbulent flow regime, and increases again in the slug flow regime. The volumetric mass transfer coefficient (k _La) significantly decreases with increasing liquid viscosity. The gas holdup and k _La values in the present bubble column of CMC solutions are found to be much higher than those in bubble columns or external-loop airlift columns with a plate-type sparger. The obtained gas phase holdup ( _g) and k _La data have been correlated with pertinent dimensionless groups in both the bubbly and the churn-turbulent flow regimes.List of Symbols a m^–1 specific gas-liquid interfacial area per total volume - A _d m² cross-sectional area of downcomer - A _r m² cross-sectional area of riser - d _b m individual bubble diameter - d _vs m Sauter mean bubble diameter - D _c m column diameter - D _L m²/s oxygen diffusivity in the liquid - Fr Froude number, U _g/(g D_c)^1/2 - g m/s² gravitational acceleration - G _a Galileo number, gD _c ^{3 2}/² _app - H _a m aerated liquid height - H _c m unaerated liquid height - K Pa · sⁿ fluid consistency index - k _L a s^–1 volumetric mass transfer coefficient - n flow behavior index - N _i number of bubbles having diameter d _bi - Sc Schmidt number, _app/( D _L) - Sh Sherwood number, k _L a D _c ² /D_L - U _sg m/s superficial gas velocity - U _gr m/s superficial riser gas velocity - V _a m³ aerated liquid volume - V _c m³ unaerated liquid volume - N/m surface tension of the liquid phase - _g gas holdup - _app Pa · s effective viscosity of non-Newtonian liquid - kg/m³ liquid density - ý s^–1 shear rate - Pa shear stress     

Study of the liquid circulation velocity in external-loop airlift bioreactors

Liquid circulation velocity was studied in externalloop air-lift bioreactors of laboratory and pilot scale, respectively for different gas input rates, downcomer-to-riser cross-sectional area ratio, A _D/A_R and liquid phase apparent viscosities.It was found that, up to a gas superficial velocity in the riser v _SGR 0.04 m/s the dependency of v _SLR on v _SGR is in the following form: v _SLR = a v _SGR ^b , with the exponent b being 0.40. Over this value of v _SGR, only a small increase in liquid superficial velocity, v _SLR is produced by an increase in v _SGR. A _D/A_R ratio affects the liquid superficial velocity due to the resistance in flow and overall friction.For non-Newtonian viscous liquids, the circulation liquid velocity in the riser section of the pilot external-loop airlift bioreactor is shown to be dependent mainly on the downcomer-to-riser cross-sectional area ratio, A _D/A_R, the effective (apparent) liquid viscosity, _eff and the superficial gas velocity, v _SGR.The equation proposed by Popovic and Robinson [11] was fitted well, with an error of ± 20%.List of Symbols A _D m² downcomer cross-sectional area - A _Rm² riser cross-sectional area - a = coefficient in Eq. (7) - b = exponent in Eq. (7) - c _s m^–1 Coefficient in Eq. (3) - D _D m downcomer diameter - D _R m riser diameter - g m²/s gravitational acceleration - H _D m dispersion height - H _L m ungassed liquid height - K Pa s ⁿ consistency index - K _B = friction factor at the bioreactor bottom - K _F = friction factor - K _T = friction factor at the bioreactor top - V _L m³ liquid volume in the bioreactor - V _D m³ liquid volume in downcomer - V _R m³ liquid volume in riser - v _LDm/s downcomer linear liquid velocity - v _LR m/s riser linear liquid velocity - v _SGR m/s riser superficial liquid velocity - v _SLR m/s riser superficial liquid velocity - s^–1 shear rate - _GD = downcomer gas holdup - _GR = riser gas holdup - _eff Pa s effective (apparent) viscosity - Pa shear stress The authors wish to thank Mrs. Rodica Roman for the help in experimental data collection and to Dr. Stefanluca for the financial support.     

Fermentation ofCandida utilis for uricase production

Summary Conditions for the production of microbial uricase byCandida utilis were studied. For the selected strain, hypoxanthine proved to be the most effective inducer of uricase formation. The highest values of biomass as well as uricase activity in the mechanically agitated fermentor were obtained under the following conditions: 50 h, rotation impeller speed 7 s^–1, air flow rate 1.25×10^–5 m³s^–1, concentration of inducer 0.1%.List of symbols b width of baffle, m - c length of baffle, m - D diameter of cylindrical fermentor, m - d diameter of impeller, m - d ₁ diameter of impeller disc, m - Fr _m impeller Froud number - g gravitional acceleration, ms^–2 - H height of batch surface above bottom, m - H ₂ height of impeller disc above bottom, m - h height of impeller blade, m - Kp _g flow rate number - L length of impeller blade, m - N rotational speed of impeller, s^–1 - Re _m impeller Reynolds number - T time, h - V volume of batch, m³ - V _g air (gas) flow rate, m³s^–1 - x mass fraction of the dry matter of cells - x ₀ initial value of the mass fraction of the dry matter of cells - _r volume fraction of the dry matter of cells - <eta<₁ viscosity of pure liquid, Pa s - viscosity of batch (suspension of microbial suspension), Pa s - density of batch, kg m^–3     

Rheological measurements of three Actinomycete in submerged cultures

Fermentation experiments were performed to obtain time-dependent data on broth rheology for three filamentous microorganisms, Streptomyces rimosus, Actinomadura roseorufa and Saccharopolyspora erythraea, cultivated under standard conditions in a mechanically stirred bioreactor. Rheological data were successfully analysed using Mitschka's technique and flow curves of the cultures described by the power law model in the range of shear rate between 5 and 100 s^–1. Consistency coefficients of the cultures were found to vary continuously with fermentation time while flow behaviour index fell sharply within the first few hours of cultivation and then remained practically unchanged till the end of fermentation. The pH of the biomass was found to have a strong influence on both consistency coefficient and flow behaviour index.List of Symbols k n Mitschka shear rate constant - K consistency coefficient (Pa s ⁿ ) - n flow behaviour index (–) - N spindle speed (rps) - T torque on spindle (Nm) - gg _A average shear rate (s^–1)     

A novel device for the assessment of shear effects on suspended microbial cultures

Summary A novel device has been designed for the evaluation of the effects of shear on microorganisms. The device consists of a combination of a coaxial cylinder plus cone and plate viscometers and enables cultures of both eukaryotic and prokaryotic microorganisms to be grown under fully defined and controlled fluid dynamic characteristics for serveral generations. In the preliminary tests performed a change in cell length was observed in Escherichia coli, and with Penicillium chrysogenum the septal length, hyphal diameter, and branching frequency all changes as shear was increased.Symbols L Height of liquid (m) - r Radius of cone/bob (m) - r _m Arithmetic mean of R and r (m) - R Radius of cup (m) - T Torque (Nm) - Shear rate (s^-1) - ₀ Angle of cone (rad) - Shear stress (Nm^-2) - Annular velocity (rad s^-1)     

Lectin-histochemical analysis of glycans in ovine and bovine near-term placental binucleate cells

Chorionic binucleate cells (BNC) occur in several ruminants including cow, deer, goat and sheep. They migrate through the chorionic tight junction to fuse with uterine epithelial cells and discharge their granules into maternal connective tissue. We have compared the BNC of near-term, resin-embedded, ovine and bovine placentae using 15 biotinylated lectins and an avidinperoxidase revealing system. There was pronounced conservation of saccharides between the two species. Several sub-types of N-glycan were present, with highly branched structures being abundant, as shown by Galanthus nivalis, Pisum sativum and Phaseolus vulgaris (leuko) agglutinins. Among the non-reducing terminal saccharides conserved were GalNAc1,3(Fuc1,2)-Gal1,4GlcNAc1-, GalNAc1,6Gal1-, Gal1,4GlcNAc-and Gal1,3GalNAc1- shown by Dolichos biflorus, Wisteria floribunda, Erythrina cristagalli, and Maclura pomifera agglutinins, respectively. Arachis hypogaea and Glycine max agglutinins tended to bind to bovine BNC at different stages of maturity, while fucosyl residues detectable by Tetragonolobus purpureus and Ulex europaeus-1 agglutinins were not observed in either species. The only major difference related to sialyl residues, with 2,3-linked sialic acid being present in bovine (Maackia amurensis, Limax flavus) and 2,6 sialic acid being present in ovine (Sambucus nigra agglutinin) cells. This conservation of glycan may be related to glycosylation of peptide hormones in the granules, and may thus be important in the targeting of these hormones to their receptors.     

Phenotypic expression of Vogesella indigofera upon exposure to hexavalent chromium,Cr6+

A eubacterium producing a blue pigment was isolated from a drinking water filter, and subsequently identified as Vogesella indigofera. This bacterium was further investigated for its morphological and biochemical characteristics after exposure to hexavalent chromium, Cr⁶⁺. The threshold Cr⁶⁺ concentration inhibiting the pigment production by V. indigofera was 200–300 g ml^–1 in liquid cultures of nutrient broth and 100–150 g ml^–1 on nutrient agar plates. The Cr⁶⁺ concentration preventing V. indigofera growth was 300–400 g ml^–1 in liquid cultures, but greater than 150 g ml^–1 on agar plates. Moreover, rugose colonies without the blue pigmentation were observed on agar plates amended with 150 (g Cr⁶⁺) ml^–1. The biochemical utilization profiles of the colonies without pigmentation did not differ from the original pigment-producing ones, indicating phenotypic plasticity of this bacterium. The difference of phenotypic expression of V. indigofera under various Cr⁶⁺ concentrations might have potential application as a pollution bioindicator for heavy metals.     

The effects of 2,2′-bipyridine and other metal chelators on the conversion of 1-aminocyclopropane-1-carboxylic acid to ethylene in rice

Effects of metal chelators, 2,2-bipyridine, 8-hydroxyquinoline and 1,10-phenenthroline, on the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene in detached leaves of light-grown rice (Oryza sativa) seedlings and detached shoots of etiolated rice seedlings were investigated. Metal chelators strongly inhibited the in vivo ACC oxidase activity in detached leaves and detached etiolated shoots. This inhibition could be partially recovered by Fe²⁺. Our results support the notion that Fe²⁺ is an essential cofactor for the conversion of ACC to ethylene in vivo.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - BP 2,2-bypyridine - HQ 8-hydroxylquinoline - MJ methyl jasmonate - PA 1,10-phenanthroline - Put putrescine     

Mixing time in a down-flow jet loop bioreactor

Mixing time was determined in a down-flow jet loop bioreactor with Newtonian and non-Newtonian fluids. It was observed that the mixing time decreased with an increase in linear liquid velocity, superficial gas velocity, draft tube to column diameter ratio, nozzle diameter and shear thinning of media. The optimum draft tube to column diameter ratio was found to be about 0.44. Correlations were presented for prediction of mixing time.List of Symbols A m² cross sectional area of the column - C kmol/m³ local tracer concentration - A _D m² flow area,A _D =/4 (D _Z ² -D _TO ² ) - D m column diameter - D _E m draft tube diameter - D _TO m outside diameter of the air tube - D _TFL m equivalent flow diameter,D _TFL =(D _Z ² -D _TO ² )^0.5 - D _z m nozzle diameter - g m/s² gravitational acceleration - h % inhomogeneity - H m height of the column - H _B m distance between the lower edge of the draft tube and the impact plate - H _T m distance between the upper edge of the draft tube and the liquid nozzle - K Pa.sⁿ consistency index in power-law model - L _E m length of the draft tube - n flow index in the power-law model - Re _j jet Reynolds number,Re _j =(D _TFL×w₁×_L)/ _eff - t _M s mixing time - t _sg m/s superficial gas velocity based onA - W _l m/s linear liquid velocity based onD _D Greek Letters N/m² shear stress - s shear rate - kg/m³ density of liquid - N/m surface tension of the liquid - Pa.sⁿ viscosity of liquid Indices X concentration at infinite time maximum value of tracer concentration - eff effective - L Liquid - obs observed - pred Predicted     

Requirements for in vitro propagation of seven nitrogen-fixing Alnus species

Studies on the in vitro propagation of Alnus crispa, A. glutinosa, A. incana, A. japonica, A. rubra, A. sinuata and A. viridis indicated interspecific as well as intraspecific variations in their requirements for in vitro culture. The WPM and Blaydes media supported, respectively, growth of A. glutinosa and A. crispa but not that of both species, while the MS medium induced equal or significantly better growth than WPM and Blaydes media for both species. The optimum type and concentration of sugar to be used in the multiplication medium varied with species. Only A. glutinosa showed good growth on sucrose while glucose was optimum for all other species but at different concentrations. All species rooted in 3 weeks on half-strength MS medium including 1 M IBA. All clones of A. glutinosa and A. rubra rooted 100%, whereas easy-to-root and difficult-to-root clones were observed in the other species. In the rooting medium, glucose promoted rooting of the difficult-to-root clones better than sucrose. Survival following transfer to an artificial substrate was 100% for all species. Nodulation tests using pure cultures of two Frankia strains showed 100% nodulation on all Alnus clones.     

Initiation and proliferation of carrot callus using a combination of antibiotics

Calli were initiated from carrot (Daucus carota L. subsp. sativus Hoffm.) root expiants and grown on media supplemented with a combination of carbenicillin at 0.3 mg/ml and vancomycin at 0.1 mg/ml in the absence of plant hormones or hormone analogs. The growth rate was about half of that obtained with a combination of -naphthaleneacetic acid and N⁶-benzyladenine at 1 mg/l each. Carbenicillin in the combination with vancomycin could be replaced by penicillin G; other penicillins tested in this combination, however, caused only limited growth. The calli produced can be grown on media supplemented with -naphthaleneacetic acid and N⁶-benzyladenine, but not on media without the antibiotics and the plant growth substances. Calli obtained using the plant growth substances can also be subcultured on media supplemented with only the antibiotics.Abbreviations BA N⁶-benzyladenine - MS Murashige and koog - -NAA -naphthaleneacetic acid     

Enhancement of protein precipitate strength and density by low-frequency conditioning

The use of a continuous, low-frequency conditioning process to alter the structure of protein precipitate aggregates is examined. An increase in the density of aggregates is correlated with the levels of fluid acceleration and hence hydrodynamic stress to which the aggregates are exposed during conditioning. A combination of low-frequency conditioning followed by shear break-up (as in the feed zone to a high-speed disk-stack centrifuge) is shown to result in a precipitate suspension of increased particle size at the fine end of the distribution, and having a greater sedimentation velocity. The resistance of large aggregates to shear disruption is increased by low-frequency conditioning.List of Symbols CR conditioning ratio - CRS conditioning ratio after shearing - d m amplitude of displacement - D m particle size - D _c m critical size for centrifuge recovery - f s^–1 frequency of vibration - G s^–1 mean velocity gradient - Q m³/s volumetric throughput - SR shear ratio - t s ageing time Greek Symbols s^–1 mass-average shear rate - K sedimentation shape factor - _a kg/m³ aggregate density - _f kg/m³ fluid density - _s kg/m³ solids density - kg/m³ aggregate-suspension density difference - Ns/m² kinematic viscosity - amplitude of pulse ratio (ref. 23, 9) - s mean residence time - _s solids volume fraction