Use of formate gradients for improving biomass yield of Pichia pinus growing continuously on methanol

Summary Investigations were made into the improvement of growth yield (Y) of Pichia pinus MH 4 growing continuously on methanol by feeding formate so as to create an increasing concentration gradient (transient state). Under particular formate supply conditions, Y could be increased from 0.37 g·g^-1 on methanol alone to 0.55 and 0.47 g·g^-1 in the presence of formate at dilution rates (D) of 0.045 and 0.075 h^-1, respectively. These differences could be explained as being due to a limiting formate consumption rate of 50–60 nmol·min^-1·g^-1 dry wt., coupled to a net-energy generation independent of D. Any further formate oxidation proceeded without energy gain. Deviations from optimum conditions of biomass increase are discussed in terms of different formate oxidizing systems and uncoupling properties of formate itself. These results are compared to and confirmed by steady-state considerations.Abbreviations a steepness of the formate gradient (g·l^-1·h^-1) - a acceleration of change of formate concentration in the fermenter (g·l^-1·h^-2) - D dilution rate (h^-1) - Ft formate - S₁ and S₂ initial and final formate concentration of the gradient (g·l^-1) - Y growth yield in g·g^-1 methanol     

Kinetics of α-amylase production in a batch and fed-batch culture of Bacillus subtilis with caseinate as nitrogen source and starch as carbon source

Summary Analysis of a large number of experimental data from the cultivation of Bacillus subtilis formed the basis for a kinetic model of the process explaining the effect of composition of the culture medium and of the growth rate on the rate of enzyme production. The resulting rate of formation of -amylase (EC 3.2.1.1) reflects the sum of the rate of enzyme production and the rate of its degradation as affected by the environment. The kinetic dependence confirms the previously described mechanism of regulation of enzyme biosynthesis. The mathematical model of the process served here to determine the optimal conditions for enzyme biosynthesis which were then verified in a fed-batch cultivation. The production of the enzyme in fed-batch culture was found to be twice that found in a batch cultivation.Symbols X biomass concentration, g·l^-1 - t time, h - S ₁ caseinate concentration, g·l^-1 - S ₂ starch concentration, g·l^-1 - P product concentration, U·ml^-1 - r _P specific rate of product formation, U·g^-1·h^-1 - R _P total rate of product formation, U·l^-1·h^-1 - Y yield coefficient - specific growth rate, h^-1     

Growth yields and growth rates of Desulfovibrio vulgaris (Marburg) growing on hydrogen plus sulfate and hydrogen plus thiosulfate as the sole energy sources

Desulfovibrio vulgaris (Marburg) was grown on H₂ plus sulfate and H₂ plus thiosulfate as the sole energy sources and acetate plus CO₂ as the sole carbon sources. Conditions are described under which the bacteria grew exponentially. Specific growth rates () and molar growth yields (Y) at different pH were determined. and Y were found to be strongly dependent on the pH. Highest growth rates and molar growth yields were observed for growth on H₂ plus sulfate at pH 6.5 (=0.15h^-1; Y _{SO 4} ^2- =8.3g·mol^-1) and for growth on H₂ plus thiosulfate at pH 6.8 (=0.21h^-1; Y _{S 2}O ₃ ² =16.9g·mol^-1).The growth yields were found to increase with increasing growth rates: plots of 1/Y versus 1/ were linear. Via extrapolation to infinite growth rates a Y _SO4 ^2- /max of 12.2g·mol^-1 and a YS₂O ₃ ^2- /max of 33.5g·mol^-1 was obtained.The growth yield data are interpred to indicate that dissimilatory sulfate reduction to sulfide is associated with a net synthesis of 1 mol of ATP and that near to 3 mol of ATP are formed during dissimilatory sulfite reduction to sulfide.     

Factors which influence the sedimentation characteristics of Torulopsis glabrata after growth in a recirculation system

Summary Some environmental affects on cell aggregation described in the literature are briefly summarized. By means of a biomass recirculation culture (Contact system), using the yeast Torulopsis glabrata, the aggregation behavior of cells in static and in dynamic test systems is described. Sedimentation times required to obtain 50 g · l^–1 yeast dry matter in static systems were always higher than in dynamic ones.In addition to, influencing the biomass yield, the specific growth rate of the yeast also affected cell aggregation. The specific growth rate and therefore the aggregation could be regulated by the biomass recirculation rate as well as by the sedimenter volume.Abbreviations f_o Overflow flow rate (l·h^–1) - f_R Recycle flow rate (l·h^–1) - f_t0t Total flow rate through the fermenter (l·h^–1) - g Gram - h Hour - D_R Fermenter dilution rate due to recycle (h^–1) - D_S Fermeter dilution rate due to substrate (h^–1) - D_tot Total fermenter dilution rate (h^–1) - l Liter - Specific growth rate (h^–1) - P_F Fermenter productivity (g·l^–1·h^–1) - P_FS Overall productivity (g·l^–1·h^–1) - R_pM Rates per minute - RS Residual sugar content in the effluent with respect to the substrate concentration (%) - Y Yield of biomass with respect to sugar concentration (%) - Sed 50 Sedimentation time to reach a YDM of 50 g·l^–1 (min) - V Volume (l) - V_F Fermenter volume (l) - V_Sed Sedimenter volume (l) - VVM Volumes per volume and minute - X_F YDM in the fermenter (g·l^–1) - X_F YDM in the recycle (g·l^–1) - X_S Yeast dry matter due to substrate concentration (g·l^–1) - YDM Yeast dry matter (g·l^–1)     

Growth of Thermoanaerobium brockii in batch and continuous culture at supraoptimal temperatures

Summary Thermoanaerobium brockii was grown in batch and continuous culture at supraoptimal temperatures (>65° C). Specific growth rates were lower in batch (_max>1.0 h^-1) than in continuous cultures (_max1.2–1.4 h^-1). Acetone addition to the medium did not increase critical dilution rate significantly. The media used contained significantly less organic material and sulfide than previously reported media; however, yeast extract requirements were shown to be exceptionally high (60% of the glucose concentration used). Organic substrates inhibited growth and product formation in chemostat cultures whereas the slow formation of acetic acid was observed in batch cultures, but also with virtually no growth. The inhibiting concentration was found to be approximately 15 g organic carbon·l^-1. The maintenance requirements of T. brockii were in the same range as expected of aerobic extreme thermophiles (m_s0.5 g·g^-1·h^-1) and could be met only by glucose and not by yeast extract. Maintenance was obviously not independent of specific growth rate. Production of the stereospecific alcohol-aldehyde/ketone oxidore-ductase was strictly growth associated and its formation was not affected by acetone added to medium.     

Development of aldosterone-stimulation of short-circuit current across larval frog skin

Summary The short-circuit current (SCC) across isolated skin from bullfrog larvae in developmental stage XXI was small and insensitive to amiloride. Overnight incubation of this tissue with 10^-6 M aldosterone stimulated the SCC from 1.35±0.55 to 14.55±4.12 A·cm^-2 with 11.18±4.46 A·cm^-2 being blocked by 100 M amiloride. Histologic examination of aldosterone-treated skins revealed a separation of the apical cell layer from the underlying epidermis that was not seen in untreated preparations. The onset of amiloride-sensitive Na⁺ transport thus coincided with the exposure of the apical surface of newly differentiated epithelial cells. Similar results were obtained with skin from stage XXI larvae whose rate of metamorphosis had been stimulated by 10 g·l^-1 thyroxine (T₄) but not with skin from T₄-treated larvae in stages XIX and XX. Fluctuation analysis of the amiloride-sensitive SCC of the above preparations failed to show a consistent Lorentzian component in the power-density spectrum. Fluctuation analysis was possible on skins from larvae whose development had been accelerated by 7–9 days treatment with 10 g·l^-1 triiodothyronine (T₃). Aldosterone treatment of these tissues resulted in a significant increase in Na⁺ channel density.Abbreviations ASCC component of the short-circuit current (A·cm^-2) that is blocked by amiloride - fc frequency (Hz) at which the magnitude of the Lorenzian component of the power spectra is reduced by half - i current (pA) through individual amiloride-sensitive Na⁺ channels - I _Na+ amiloride-sensitive short-circuit current (A·cm^-2) that remains after treatment with a given amiloride concentration - k ₀₁ the rate constant (s^-1·M^-1) for the association of amiloride with Na⁺ channels - k ₁₀ rate constant (s^-1) for the dissociation of amiloride from Na⁺ channels - K _b magnitude of the power spectrum (A²·s·cm^-2) at a frequency of 1 Hz - KSCC short-circuit (A·cm^-2) current with K⁺ as the primary mucosal cation - M density of amiloride-sensitive Na⁺ channels in the apical cell membrane - SCC short-circuit current (A·cm^-2) - S _(f) magnitude of the power spectra (A²·s·cm^-2) at a given frequency - S ₀ the magnitude of the plateau region of the Lorentzian component of the power spectra (A²·s·cm^-2) - T ₃ Triiodothyronine - T ₄ Thyroxine     

Organic reduction of tapioca wastewaters using modified RBC

A modified Rotating Biological Contactor (RBC) was used for the treatability studies of synthetic tapioca wastewaters. The RBC used was a four stage laboratory model and the discs were modified by attaching porous nechlon sheets to enhance biofilm area. Synthetic tapioca wastewaters were prepared with influent concentrations from 927 to 3600 mg/l of COD. Three hydraulic loads were used in the range of 0.03 to 0.09 m³·m^–2·d^–1 and the organic loads used were in the range of 28 to 306 g COD· m^–2·d^–1. The percentage COD removal were in the range from 97.4 to 68. RBC was operated at a rotating speed of 18 rpm which was found to be the optimal rotating speed. Biokinetic coefficients based on Kornegay and Hudson models were obtained using linear analysis. Also, a mathematical model was proposed using regression analysis.List of Symbols A m² total surface area of discs - d m active depth of microbial film onany rotating disc - K _s mg ·l^–1 saturation constant - P mg·m^–2·^–1 area capacity - Q l·d^–1 hydraulic flow rate - q m³·m^–2·d^–1 hydraulic loading rate - S ₀ mg·l^–1 influent substrate concentration - S _e mg·l^–1 effluent substrate concentration - w rpm rotational speed - V m³ volume of the reactor - X _f mg·l^–1 active biomass per unit volume ofattached growth - X _s mg·l^–1 active biomass per unit volume ofsuspended growth - X mg·l^–1 active biomass per unit volume - Y _s yield coefficient for attachedgrowth - Y _A yield coefficient for suspendedgrowth - Y yield coefficient, mass of biomass/mass of substrate removed Greek Symbols hr mean hydraulic detention time - (_max)_A d^–1 maximum specific growth rate forattached growth - (_max)_s d^–1 maximum specific growth rate forsuspended growth - _max d^–1 maximum specific growth rate - d^–1 specific growth rate - _v mg·l^–1·hr^–1 maximum volumetric substrateutilization rate coefficient     

Ion transport across leech integument

The dorsal skin of the leech Hirudo medicinalis was used for electrophysiological measurements performed in Ussing chambers. The leech skin is a tight epithelium (transepithelial resistance = 10.5±0.5 k· cm^-2) with an initial short-circuit current of 29.0±2.9 A·cm^-2. Removal of Na⁺ from the apical bath medium reduced short-circuit current about 55%. Ouabain (50mol·l^-1) added to the basolateral solution, depressed the short-circuit current completely. The Na⁺ current saturated at a concentration of 90 mmol Na⁺·l^-1 in the apical solution (K _M=11.2±1.8 mmol·l^-1). Amiloride (100 mol·l^-1) on the apical side inhibited ca. 40% of the Na⁺ current and indicated the presence of Na⁺ channels. The dependence of Na⁺ current on the amiloride concentration followed Michaclis-Menten kinetics (K _i=2.9±0.4 mol·l^-1). The amiloride analogue benzamil had a higher affinity to the Na⁺ channel (K _i=0.7±0.2 mol·l^-1). Thus, Na⁺ channels in leech integument are less sensitive to amiloride than channels known from vertebrate epithelia. With 20 mmol Na⁺·l^-1 in the mucosal solution the tissue showed an optimum amiloride-inhibitable current, and the amiloride-sensitive current under this condition was 86.8±2.3% of total short-circuit current. Higher Na⁺ concentrations lead to a decrease in amiloride-blockade short-circuit current. Sitmulation of the tissue with cyclic adenosine monophosphate (100 mol·l^-1) and isobutylmethylxanthine (1 mmol·l^-1) nearly doubled short-circuit current and increased amiloride-sensitive Na⁺ currents by 50%. By current fluctuation analysis we estimated single Na⁺ channel current (2.7±0.9 pA) and Na⁺ channel density (3.6±0.6 channels·m^-2) under control conditions. After cyclic adenosine monophosphate stimulation Na⁺ channel density increased to 5.4±1.1 channels·m^-2, whereas single Na⁺ channel current showed no significant change (1.9±0.2 pA). These data present a detailed investigation of an invertebrate epithelial Na⁺ channel, and show the similarities and differences to vertebrate Na⁺ channels. Whereas the channel properties are different from the classical vertebrate Na⁺ channel, the regulation by cyclic adenosine monophosphate seems similar. Stimulation of Na⁺ uptake by cyclic adenosine monophosphate is mediated by an increasing number of Na⁺ channels.Abbreviations slope of the background noise component - ADH antidiuretic hormone - cAMP cyclic adenosine monophosphate - f frequency - f _c coner frequency of the Lorentzian noise component - Hepes N-hydroxyethylpiperazine-N-ethanesulphonic acid - BMX isobutyl-methylxanthine - i _Na single Na⁺ channel current - I _Na max, maximal inhibitable Na⁺ current - I _SC short circuit current - K _i half maximal blocker concentration - K _M Michaelis constandard error of the mean - S _(f) power density of the Lorentzian noise component - S ₀ plateau value of the Lorentzian noise component - TMA tetramethylammonium - Trizma TRIS-hydroxymethyl-amino-methane - V _max maximal reaction velocity - V _T transepithelial potential - K half maximal blocker concentration     

Studies on the variables and kinetics of SCP production from nopal fruit juice

Summary Submerged batch cultivation under controlled environmental conditions of pH 3.8, temperature 30°C, and K_La200 h^–1 (above 180 mMO₂ l ^–1 h^–1 oxygen supply rate) produced a maximum (12.0 g·l ^–1) SCP (Candida utilis) yield on the deseeded nopal fruit juice medium containing C/N ratio of 7.0 (initial sugar concentration 25 g·l ^–1) with a yield coefficient of 0.52 g cells/g sugar. In continuous cultivation, 19.9 g·l ^–1 cell mass could be obtained at a dilution rate (D) of 0.36 h^–1 under identical environmental conditions, showing a productivity of 7.2 g·l ^–1·h^–1. This corresponded to a gain of 9.0 in productivity in continuous culture over batch culture. Starting with steady state values of state variables, cell mass (C_X–19.9 g·l ^–1), limiting nutrient concentration (C_ln–2.5 g·l ^–1) and sugar concentration (C_S–1.5 g·l ^–1) at control variable conditions of pH 3.8, 30°C, and K_La 200 h^–1 keeping D=0.36 h^–1 as reference, transient response studies by step changes of these control variables also showed that this pH, temperature and K_La conditions are most suitable for SCP cultivation on nopal fruit juice. Kinetic equations obtained from experimental data were analysed and kinetic parameters determined graphically. Results of SCP production from nopal fruit juice are described.Nomenclature C_ln concentration of ammonium sulfate (g·l ^–1) - C_S concentration of total sugar (g·l ^–1) - C_X cell concentration (g·l ^–1) - D dilution rate (h^–1) - K_ln Monod's constant (g·l ^–1) - m maintenance coefficient (g ammonium sulfate cell^–1 h^–1) - m_(S) maintenance coefficient (g sugar g cell^–1 h^–1) - t time, h - Y yield coefficient (g cells/g ammonium sulfate) - Y_m maximum of Y - Y_S yield coefficient based on sugar consumed (g cells · g sugar^–1) - Y_S(m) maximum value of Y_S - ^µm maximum specific growth rate constant (h^–1)     

Protein production from whey usingPenicillium cyclopium; growth parameters and cellular composition

Summary The growth parameters ofPenicillium cyclopium have been evaluated in a continuous culture system for the production of fungal protein from whey. Dilution rates varied from 0.05 to 0.20 h^–1 under constant conditions of temperature (28°C) and pH (3.5). The saturation coefficients in the Monod equation were 0.74 g l^–1 for lactose and 0.14 mg l^–1 for oxygen, respectively. For a wide range of dilution rates, the yield was 0.68 g g^–1 biomass per lactose and the maintenance coefficient 0.005 g g^–1 h^–1 lactose per biomass, respectively. The maximum biomass productivity achieved was 2 g l^–1 h^–1 biomass at dilution rates of 0.16–0.17 h^–1 with a lactose concentration of 20 g l^–1 in the feed. The crude protein and total nucleic acid contents increased with a dilution rate, crude protein content varied from 43% to 54% and total nucleic acids from 6 to 9% in the range of dilution rates from 0.05 to 0.2 h^–1, while the Lowry protein content was almost constant at approximately 37.5% of dry matter.Nomenclature (mg l^–1) C_o initial concentration of dissolved oxygen - (h^–1) D dilution rate - (mg l^–1) K₀₂ saturation coefficient for oxygen - (g l^–1) K_s saturation coefficient for substrate - (g g^–1 h^–1) lactose per biomass) m maintenance energy coefficient - (mM g^–1 h^–1O₂ per biomass) Q₀₂ specific oxygen uptake rate - (g l^–1) S residual substrate concentration at steady state - (g l^–1) S_o initial substrate concentration in feed - (min) t_1/2 time when C_o is equal to C_o/2 - (g l^–1) X biomass concentration - (g l^–1) X biomass concentration at steady state - (g g^–1 biomass per lactose) Y_G yield coefficient for cell growth - (g g^–1 biomass per lactose) Y_x/s overall yield coefficient - (h^–1) specific growth rate     

Enhanced production of scopolin bySolanum aviculare cells immobilised within Ca-alginate gel beads

Summary Different matrices, obtained by varying calcium (0.1 to 1.5M) and alginate (1 to 1.5%) concentrations, were used to study the influence of immobilisation parameters on the behaviour ofS. aviculare. A significant modulation of cell growth, cell release, and scopolin production and excretion has been observed. Physiological and morphological characteristics ofSolanum aviculare cells immobilised within Ca-alginate beads were notably different from those of suspended cells. ImmobilisedS. aviculare have accumulated scopolin (up to 120 g·g^–1 FWB) within beads and excreted it into the culture medium (up to 8 g·g^–1 FWB). Contrary to suspended cells which have accumulated only traces of this metabolite within intracellular compartments (1 g·g^–1 FWB), no scopolin has been found into the culture medium.Abbreviations ANA -Naphthaleneacetic acid - HPLC high performance liquid chromatography - FWB fresh weight biomass - LS medium Linsmaier and Skoog medium - MS mass spectroscopy - NMR nuclear magnetic resonance - r² coefficient of determination - s standard deviation     

Lactic acid production by batch fermentation of whey permeate: A mathematical model

Summary The batch fermentation of whey permeate to lactic acid was improved by supplementing the broth with enzyme-hydrolyzed whey protein. A mathematical model based on laboratory results predicts to a 99% confidence limit the kinetics of this fermentation. Cell growth, acid production and protein and sugar use rates are defined in quantifiable terms related to the state of cell metabolism. The model shows that the constants of the Leudeking-Piret model are not true constants, but must vary with the medium composition, and especially the peptide average molecular weight. The kinetic mechanism on which the model is based also is presented.Nomenclature K _i lactic acid inhibition constant (g/l) - K _pr protein saturation constant during cell growth (g/l) - K _pr protein saturation constant during maintenance (g/l) - K _s lactose saturation constant (g/l) - [LA] lactic acid concentration (g/l) - [PR] protein concentration (g/l) - [S] lactose concentration (g/l) - t time (h) - [X] cell mass concentration (g/l) - , fermentation constants of Leudeking and Piret - specific growth rate (l/h) - Y _{g, LA/S} acid yield during cell growth (g acid/g sugar) - Y _{m, LA/S} acid yield during maintenance (g acid/g sugar) - Y _x/pr yield (g cells/g protein) - specific sugar use rate during cell growth (g sugar/h·g cell) - specific sugar use rate during maintenance (g sugar/h·cell)     

Isolation and physiological study of an amylolytic strain of Lactobacillus plantarum

Summary An amylolytic lactic acid bacterium identified as Lactobacillus plantarum was isolated from cassava roots (Manihot esculenta var. Ngansa) during reting. The amylolytic enzyme synthesized was an extracellular -amylase with an optimum pH of 5.0 and an optimum temperature of 55° C. Cultured on starch, the strain displayed a growth rate of 0.43 h^–1, a biomass yield of 0.19 g·g^–1 and a lactate yield of 0.81 g·g^–1. The growth kinetics were similar on starch and glucose. Sufficient enzyme was synthesized and starch hydrolysis was not a limiting factor for growth. Biosynthesis of the enzyme was observed when the glucose concentration was less than 6.7 g·l^–1 and reached up to 4 IU·ml^–1 at the end of the fermentation. Offprint requests to: M. Raimbault     

Quinidine-sensitive K+ channels in the basolateral membrane of embryonic coprodeum epithelium: regulation by aldosterone and thyroxine

Basolateral K⁺ channels and their regulation during aldosterone- and thyroxine-stimulated Na⁺ transport were studied in the lower intestinal epithelium (coprodeum) of embryonic chicken in vitro. Isolated tissues of the coprodeum were mounted in Ussing chambers and investigated under voltage-clamped conditions. Simultaneous stimulation with aldosterone (1 mol·l^-1) and thyroxine (1 mol·l^-1) raised short-circuit current after a 1- to 2-h latent period. Maximal values were reached after 6–7 h of hormonal treatment, at which time transepithelial Na⁺ absorption was more than tripled (77±11 A·cm^-2) compared to control (24±8 A·cm^-2). K⁺ currents across the basolateral membrane with the pore-forming antibiotic amphotericin B and application of a mucosal-to-serosal K⁺ gradient. This K⁺ current could be dose dependently depressed by the K⁺ channel blocker quinidine. Fluctuation analysis of the short-circuit current revealed a spontaneous and a blocker-induced Lorentzian noise component in the power density spectra. The Lorentzian corner frequencies increased linearly with the applied blocker concentration. This enabled the calculation of single K⁺ channel current and K⁺ channel density. Single K⁺ channel current was not affected by stimulation, whereas the number of quinidine-sensitive K⁺ channels in the basolateral membrane increased from 11 to 26·10⁶·cm^-2 in parallel to the hormonal stimulation transepithelial Na⁺ transport. This suggests that the basolateral membrane is a physiological target during synergistic aldosterone and thyroxine regulation of transepithelial Na⁺ transport for maintaining intracellular K⁺ homeostasis.Abbreviations f frequency - f _c Lorentzian corner frequency - g _K single K⁺ channel conductance - HEPES N-2-hydroxyethylpiperazin-N'-2-ethansulfonic acid - i _K single K⁺ channel current - I_Ampho amphotericin B induced K⁺ current - I _sc short-circuit current - I _K quinidine blockable K⁺ current - I _max maximally blocked current by quinidine - IC ₅₀ half-maximal blocker concentration - k _on, k _off on- and off-rate coefficients of reversible single channel block by quinidine - M _K number of conducting K⁺ channels - [Q] quinidine concentration - R _t transepithelial resistance - S spectral density - S _o Lorentzian plateau - TBM cells toad urinary bladder cell line Present address: University of California at Berkeley, Dept. of Molecular and Cell Biology Berkeley, CA 94720, USA     

Biological tertiary treatment of urban wastewaters with chitosan-immobilizedPhormidium

Summary Chitosan:Phormidium aggregates (chitosan: algae=1:2, dry weight basis) were used as a biological tertiary treatment to remove the nitrogen (NH ₄ ⁺ , NO ₂ ^- , NO ₃ ^- ) and phosphorus (PO ₄ ^3- ) from a secondary effluent. In a batch system, 71 and 92% of P–PO ₄ ^3- were removed after 6 and 24 h, respectively. The orthophosphate removal rate was identical for all three concentrations of algae-chitosan tested (3.3, 4.6, 5.9 g d. wt.·l^-1), and was 90 g±2 g P–PO ₄ ^3- ·l^-1·h^-1, for a 90% removal. Under control conditions (chitosan flakes only added to the effluent) 73 and 78% of PO ₄ ^3- were removed after 6 and 24 h respectively. A 95% removal of inorganic nitrogen (NH ₄ ⁺ , NO ₂ ^- , NO ₃ ^- ) was attained after 4–6 h withPhormidium immobilized on chitosan flakes, as compared to 30% with chitosan flakes alone (5 g d. wt.·l^-1). The system gave a similar performance when operated semi-continuously over 5 days at a daily retention time of 1.0. In the presence of chitosan-immobilized algae, medium P–PO ₄ ^3- levels were reduced by 87.3%±6.4% after 24 h (61.1 g±7.0 g P·l^-1·h^-1). The reduction of inorganic nitrogen in the medium was 98% after 24 h (370 g±50 g N·l^-1·h^-1). In the presence of chitosan alone, some 60% orthophosphate removal was recorded, whereas no reduction of nitrogen was observed. Disappearance of orthophosphate was attributed to its co-precipitation with calcium released from the chitosan by abrasion. The presence of the algae protected the chitosan from abrasion andPhormidium directly assimilated the orthophosphate and inorganic nitrogen, thus reducing their levels in the effluent.     

Presence of an X AG − carrier in frog (Rana esculenta) red blood cells

Evidence is presented that the high levels of internal l-glutamic and l-aspartic acid in frog Rana esculenta red blood cells are due to the existence of a specific carrier for acidic amino acids of high affinity K _m = 3 m and low capacity (V_max) 0.4 mol l-Glu · Kg^–1 dry cell mass · 10 min^–1. It is Na+ dependent and the incorporation of l-glutamic acid can be inhibited by l and d-aspartate and l-cysteic acid, while d-glutamic does not inhibit. Moreover, this glutamic uptake shows a bell-shaped dependence on the external pH. All these properties show that this carrier belongs to the system X _AG ^– family. Besides the incorporation through this system, l-glutamic acid is also taken up through the ASC system, although, under physiological conditions, this transport is far less important, since it has relatively low affinity K _m 39 m but high capacity (V _max) 1.8 mol l-Glu · Kg^–1 dry cell mass · 10 min^–1.     

Cell recovery by continuous flotation

Summary Cell recovery by means of continuous flotation of the Hansenula polymorpha cultivation medium without additives was investigated as a function of the cultivation conditions as well as of the flotation equipment construction and flotation operational parameters. The cell enrichment and separation is improved at high liquid residence times, high aeration rates, small bubble sizes, increasing height of the aerated column, and diameter of the foam column. Increasing cell age and cultivation with nitrogen limitation reduce the cell separation.Symbols C_P cell mass concentration in medium g·l^–1 - C_R cell mass concentration in residue g·l^–1 - C_S cell mass concentration in foam liquid g·l^–1 - V equilibrium foam volume cm³ - V gas flow rate through the aerated liquid column cm³·s^–1 - V_F feed rate to the flotation column ml/min - ¹ V _S/V foaminess s - mean liquid residence time in the column s     

Mediation of serotonin-induced hyperventilation via 5-HT3-receptor in European eel Anguilla anguilla

The effects of serotonin (5-hydroxytryptamine) on ventilation were investigated by continuous measurements of intrabuccal pressure in unrestrained eel. Intravenous administration of 5-hydroxytryptamine (30 g·kg^-1) caused a large increase in ventilatory frequency (+100%) and amplitude (+140%). The 5-hydroxytryptamine-induced hyperventilation was blocked by the 5-HT₃-receptor antagonists metoclopramide (1.0 mg·kg^-1) or MDL72222 (1.0 mg·kg^-1), and was insensitive to the 5-HT_1/2-receptor antagonist methysergide (3.0 mg·kg^-1) and to the 5-HT₄-receptor antagonist DAU 6285 CL (3.0 mg·kg^-1). The hyperventilatory response to 5-hydroxytryptamine could be mimicked by the 5-HT₃ receptor agonist 1-phenylbiguanide (300 g·kg^-1). These results strongly implicate the 5-HT₃-receptor as the mediator of the 5-hydroxytryptamine-induced hyperventilation in eel.Abbreviations a.u. arbitrary units - 5-HT 5-hydroxytryptamine - SEM standard error of mean - VA ventilatory amplitude - VF ventilatory frequency - RBI 1-phenylbiguanide     

Penicillin recovery from aqueous solutions by continuous foam flotation

Summary Penicillin G recovery is investigated in a continuous flotation column in the presence of different collectors which form a complex with penicillin. The performance of the penicillin recovery was investigated as a function of the mole ratio () of collector-to-penicillin and the aliphatic chain length of the collector. At =1 and low penicillin concentrations (e.g., 20 mg·1^-1), high foam liquid concentrations (680 mg·l^-1), low residue concentrations (12 mg·l^-1) and high penicillin separation (56) can be attained. At =4 the separation increases to 150, and 95% of the penicillin can be recovered.Symbols C_p penicillin concentration in feed (mg·l^-1) - C_R penicillin concentration in outlet liquid (mg·l^-1) - C_S penicillin concentration in foam liquid (mg·l^-1) - C_S/C_P penicillin enrichment (-) - C_S/C_R penicillin separation (-) - % Pen in S penicillin yield in foam liquid (%) - VV}_S foam liquid volume flow (ml·min^-1) - VV}_P feed (ml·min^-1) - VV_{N 2} nitrogen flow rate (ml·s^-1) - temperature     

Influence of cultivation and induction conditions on β-lactamase production in Acinetobacter calcoaceticus

Summary The formation and localization of the -lactamase of Acinetobacter calcoaceticus CCM 5593 is strongly affected by cultivation and induction conditions. Optimal parameters for enzyme yield are cultivation on minimal salts medium with acetate (10 g·1^–1) as carbon source and addition of yeast extract (5–10 g·l^–1), induction by cefotaxime (50g·ml^–1) immediately after inoculation and growth for 24 h at 25° C. The strain forms a basal level of -lactamase constitutively [70 units (U)·g^–1]. Nearly all of this was found to be cell-bound. However, -lactamase activity additionally produced after induction (up to 500 U·g^–1 wet bacteria) was located in the culture medium (up to 96%). This unusual localization is a special feature of A. calcoaceticus and is not attributed to cell lysis. Offprint requests to: P. Borneleit