Continuous production of itaconic acid by Aspergillus terreus immobilized in a porous disk bioreactor

Summary Aspergillus terreus NRRL 1960 was grown on porous disks rotating intermittently in and out of the liquid phase. This immobilized fungal cell bioreactor was used to produce itaconic acid from glucose in a continuous operation. The effect of temperature, pH, disk rotation speed, and feed rate on the itaconic acid concentration and volumetric productivity were studied. The highest itaconic acid concentration and volumetric productivity obtained were 18.2 g/l and 0.73 g/l·h, respectively, under the following conditions: temperature at 36°C, pH 3.0, disk rotation speed at 8 rpm, and feed rate at 60 ml/h. These results are better than those by conventional fermentation or by other immobilized method.Nomenclature F feed rate (l/h) - K _1s saturation constant for immobilized cells (g/l) - K _2s saturation constant for suspended cells (g/l) - M ₁ increased mass of immobilized cells (g) - M ₂ total mass of immobilized cells (g) - P concentration of itaconic acid (g/l) - S substrate concentration in and out of the reactor (g/l) - S ₀ substrate concentration in the feed (g/l) - V liquid volume of the reactor (1) - X concentration of the suspended cells (g/l) - Y ₁ apparent yield of the immobilized cells (g cells/g substrate) - Y ₂ apparent yield of the suspended cells (g cell/g substrate) - Y ₃ apparent yield of itaconic acid (g itaconic acid/g substrate) - m ₁ maintenance and by-products coefficient of the immobilized cells (g substrate/g cell·h) - m ₂ maintenance and by-products coefficient of the suspended cells (g substrate/g cell·h) - µ_1max maximum specific growth rate of the immobilized cells (h^-1) - µ_2max maximum specific growth rate of the suspended cells (h^-1)     

Production of sorbitol and gluconic acid by permeabilized cells of Zymomonas mobilis

Summary Zymomonas mobilis is able to convert glucose and fructose to gluconic acid and sorbitol. The enzyme, glucose-fructose oxidoreductase, catalysing the intermolecular oxidation-reduction of glucose and fructose to gluconolactone and sorbitol, was formed in high amounts [1.4 units (U)·mg^-1] when Z. mobilis was grown in chemostats with glucose as the only carbon source under non-carbon-limiting conditions. The activity of a gluconolactone-hydrolysing lactonase was constant at 0.2 U·mg^-1. Using glucose-grown cells for the conversion of equimolar fructose and glucose mixtures up to 60% (w/v), a maximum product concentration of only 240 g·1^-1 of sorbitol was found. The gluconic acid accumulated was further metabolized to ethanol. After permeabilizing the cells using cationic detergents, maximum sorbitol and gluconic acid concentrations of 295 g·1^-1 each were reached; no ethanol production occurred. In a continuous process with -carrageenan-immobilized and polyethylenimin-hardened, permeabilized cells no significant decrease in the conversion yield was observed after 75 days. The specific production rates for a high yield conversion ( > 98%) in a continuous two-stage process were 0.19 g·g^-1·h^-1 for sorbitol and 0.21 g·g^-1·h^-1 for gluconic acid, respectively. For the sugar conversion of cetyltrimethylammonium bromide-treated -carrageenan-immobilized cells a V _max of 1.7 g·g^-1·h^-1 for sorbitol production and a K _m of 77.2 g·1^-1 were determinedOffprint requests to: B. Rehr     

Ammonium photoproduction by free and immobilized cells of Chlamydomonas reinhardtii

Summary Free-living or immobilized Chlamydomonas reinhardtii cells photoproduce ammonium from nitrite in a medium containing 1 mM of l-methionine-d,l-sulphoximine (MSX). Ammonium is accumulated in the medium to 8 mM final concentration, which inhibits nitrite uptake by the MSX-treated cells and consequently the excretion of ammonium is blocked. However, if ammonium was removed from the medium and nitrite and MSX periodically restored, the photoproduction process could be maintained over 96 h, with a final ammonium concentration of about 18 mM for free-living cells and 28 mM for immobilized ones. The MSX-treated cells showed a photoproduction productivity of 1300 mol NH ₄ ⁺ · mg chlorophyll (Chl)^-1, with an average production rate of 14 mol NH ₄ ⁺ · mg Chl^-1 per hour, for calcium alginate-entrapped cells, while the corresponding data for free-living ones was 650 mol NH ₄ ⁺ · mg Chl^-1 and 6.7 mol NH ₄ ⁺ · mg Chl^-1 per hour, respectively. Immobilized cells showed a significant increase in the nitrite uptake rate, probably due to a change in membrane permeability as a consequence of cell-matrix interactions.     

Direct alcoholic fermentation of starchy biomass using amylolytic yeast strains in batch and immobilized cell systems

Summary Direct alcoholic fermentation of dextrin or soluble starch with selected amylolytic yeasts was studied in both batch and immobilized cell systems. In batch fermentations, Saccharomyces diastaticus was capable of fermenting high dextrin concentrations much more efficiently than Schwanniomyces castellii. From 200 g·l^–1 of dextrin S. diastaticus produced 77 g·l^–1 of ethanol (75% conversion efficiency). The conversion efficiency decreased to 59% but a higher final ethanol concentration of 120 g·l^–1 was obtained with a medium containing 400 g·l^–1 of dextrin. With a mixed culture of S. diastaticus and Schw. castellii 136 g·l^–1 of ethanol was produced from 400 g·l^–1 of dextrin (67% conversion efficiency). S. diastaticus cells attached well to polyurethane foam cubes and a S. diastaticus immobilized cell reactor produced 69 g·l^–1 of ethanol from 200 g·l^–1 of dextrin, corresponding to an ethanol productivity of 7.6g·l^–1·h^–1. The effluent from a two-stage immobilized cell reactor with S. diastaticus and Endomycopsis fibuligera contained 70 g·l^–1 and 80 g·l^–1 of ethanol using initial dextrin concentrations of 200 and 250 g·l^–1 respectively. The corresponding values for ethanol productivity were 12.7 and 9.6 g·l^–1·h^–1. The productivity of the immobilized cell systems was higher than for the batch systems, but much lower than for glucose fermentation.     

Continuous ethanol production by Zymomonas mobilis in a fluidized bed reactor. Part I. Kinetic studies of immobilization in macroporous glass beads

A model has been developed to calculate the ethanol production in a well-mixed fluidized bed reactor. This model takes into account diffusion and the reaction inside porous glass beads and the activity of suspended cells in the fluidized bed reactor. The associated model parameters have been determined from the literature and by kinetic studies with Zymomonas mobilis in a continuous stirred tank reactor. The model permits good predictions of steady-state data in a fluidized bed reactor at residence times longer than 1–1.5 h. The immobilization of Z. mobilis in a fluidized bed reactor results in high ethanol space-time yields of more than 50 g·^–1·h^–1 at a glucose conversion of 80% (glucose in substrate: 120 gl^–1). At 99% conversion a space-time yield of 30 g·^–1·^–1 can be achieved when two fluidized bed reactors operate as cascade.     

Nitrite uptake by Chlamydomonas reinhardtii cells immobilized in calcium alginate

When an initial cell loading of about 30–40 µg chlorophyll (Chl)·g^–1 gel and alginate suspension of 3% (w/v) were used for immobilization of Chlamydomonas reinhardtii, the resulting cell beads showed optimum nitrite uptake rate, at 30° C and pH 7.5, of 14 µmol NO _inf2 ^sup– ·mg^–1 Chl·h^–1, the photosynthetic and respiratory activities being about 120 µmol O₂ produced·mg^–1 Chl·h^–1, and 40 µmol O₂ consumed ·mg^–1 Chl·h^–1, respectively. The nitrite uptake activity required CO₂ in the culture and persisted after 8 days of cells immobilization, or in the presence of 0.2 mm ammonium in the medium. Our data indicate that alginate-entrapped C, reinhardtii cells may provide a stable and functional system for removing nitrogenous contaminants from waste-waters.Correspondence to: C. Vílchez     

Fluxes of carbohydrate metabolism in ripening bananas

The major fluxes of carbohydrate metabolism were estimated during starch breakdown by ripening bananas (Musa cavendishii Lamb ex Paxton). Hands of bananas, untreated with ethylene, were allowed to ripen in the dark at 21° C. Production of CO₂ and the contents of starch, sucrose, glucose and fructose of intact fruit were determined for a period of 10 d that included the climacteric. The detailed distribution of label was determined after supplying the following to cores of pulp from climacteric fruit: [U-¹⁴C]-, [1-¹⁴C]-, [3,4-¹⁴C]-and [6-¹⁴C]glucose, [U-¹⁴C]glycerol, ¹⁴CO₂. The data obtained were used to estimate the following fluxes, values given as mol hexose · (g FW)^–1 · h^–1 in parenthesis: starch to hexose monophosphates (5.9) and vice versa (0.4); hexose monophosphates to sucrose (7.7); sucrose to hexose (4.7); hexose to hexose monophosphate (3.8); glycolysis (0.5–1.6); triose phosphate to hexose monophosphates (0.14); oxidative pentose-phosphate pathway (0.48); CO₂ fixation in the dark (0.005). These estimates are related to our understanding of carbohydrate metabolism during ripening.We both thank Mr Richard Trethewey for his constructive criticism: S.A.H. thanks the Managers of the Broodbank Fund for a fellowship.     

Intraparticle mass-transfer resistance and apparent time stability of immobilized yeast alcohol dehydrogenase

The stability and, consequently, the lifetime of immobilized enzymes (IME) are important factors in practical applications of IME, especially so far as design and operation of the enzyme reactors are concerned. In this paper a model is presented which describes the effect of intraparticle diffusion on time stability behaviour of IME, and which has been verified experimentally by the two-substrate enzymic reaction. As a model reaction the ethanol oxidation catalysed by immobilized yeast alcohol dehydrogenase was chosen. The reaction was performed in the batch-recycle reactor at 303 K and pH-value 8.9, under the conditions of high ethanol concentration and low coenzyme (NAD⁺) concentration, so that NAD⁺ was the limiting substrate. The values of the apparent and intrinsic deactivation constant as well as the apparent relative lifetime of the enzyme were calculated.The results show that the diffusional resistance influences the time stability of the IME catalyst and that IME appears to be more stabilized under the larger diffusion resistance.List of Symbols C _A, C_B, C_E mol · m^–3 concentration of coenzyme NAD⁺, ethanol and enzyme, respectively - C _p mol · m³ concentration of reaction product NADH - d _p mm particle diameter - D _eff m² · s^–1 effective volume diffusivity of NAD⁺ within porous matrix - k _d s^–1 intrinsic deactivation constant - K _A, K_A, K_B mol · m^–3 kinetic constant defined by Eq. (1) - K _A ^x mol · m^–3 kinetic constant defined by Eq. (5) - r _A mol · m^–3 · s^–1 intrinsic reaction rate - R m particle radius - R _v mol · m^–3 · s^–1 observed reaction rate per unit volume of immobilized enzyme - t _E s enzyme deactivation time - t _r s reaction time - V mol · m^–3 · s^–1 maximum reaction rate in Eq. (1) - V ^x mol · m^–3 · s^–1 parameter defined by Eq. (4) - V _f m³ total volume of fluid in reactor - w _s kg mass of immobilized enzyme bed - factor defined by Eqs. (19) and (20) - kg · m^–3 density of immobilized enzyme bed - unstableness factor - effectiveness factor - Thiele modulus - relative half-lifetime of immobilized enzyme Index o values obtained with fresh immobilized enzyme     

Glycolate photoproduction by free and alginate-entrapped cells of Chlamydomonas reinhardtii

Summary Chlamydomonas reinhardtii cells provide an effective system for glycolate photoproduction, operative during 30 h when they are growing under low CO₂, in the presence of 1 mM aminooxyacetate and 50 M acetazolamide. Glycolate excretion by the cells can proceed for about 4 days if every other 12 h a high CO₂ level is restored in the culture in the absence of inhibitors. The immobilized system in alginate beads has about a twofold higher glycolate photoproduction rate (23 mol·mg chlorophyll (Chl)^–1·h^–1) than free-living cells (12 mol · mg Chl^–1 · h^–1). Offprint requests to: C. Vílchez     

Comparative study of the enzymatic synthesis of l-valine by purified enzymes,crude extract,intact or permeabilized cells from Bacillus megaterium

Summary A detailed study on the reductive amination of -ketoisovalerate to l-valine by l-valine dehydrogenase using glucose dehydrogenase as an NADH regeneration enzyme was performed. The presence of both enzyme activities in Bacillus megaterium ATCC 39 118 permitted a direct and systematic comparison of the performances (initial l-valine production rate, productivity, molar conversion yield) of different types of conversion systems: purified enzymes or crude extract and whole cells, intact or permeabilized. A maximal l-valine productivity of 8 mmol·l^–1 · h^–1 was obtained using purified enzymes which constituted the most efficient system with a maximal rate of 0.87 mol · ml^–1 · min^–1 and a molar conversion yield of 0.91. Permeabilized cells were also an attractive system because of their easy preparation and of the good performances attained.Offprint requests to: F. Monot     

Analysis of oxygen evolution during photosynthetic induction and in multiple-turnover flashes in sunflower leaves

Exchange of CO₂ and O₂ and chlorophyll fluorescence were measured in the presence of 360 1 · 1^–1 CO₂ in nitrogen in Helianthus annuss L. leaves which had been preconditioned in the dark or at a photon flux density (PFD) of 24 mol · m^–2 · s^–1 either in 21 or 0% O₂. An initial light-dependent O₂ outburst of 6 mol · m^–2 was measured after aerobic dark incubation. It was attributed to the reduction of electron carriers, predominantly plastoquinone. The maximum initial rate of O₂ evolution at PFD 8000 mol · m^–2 · s^–1 was 170 mol · m^–2 · s^–2 or about four times the steady CO₂-and light-saturated rate of photosynthesis. Fluorescence measurements showed that the rate was still acceptor-limited. Fast O₂ evolution ceased after electron carriers were reduced in the dark-adapted leaf, but continued for a short time at the lower rate of 62 mol · m^–2 · s^–1 in the light-adapted leaf. The data are interpreted to show that enzymes involved in 3-phosphoglycerate reduction are dark-inhibited, but were fully active in low light. In a dark-adapted leaf, respiratory CO₂ evolution continued under nitrogen; it was partially inhibited by illumination. Prolonged exposure of a leaf to anaerobic conditions caused reducing equivalents to accumulate. This was shown by a slowly increasing chlorophyll fluorescence yield which indicated the reduction of the PSII acceptor Q_A in the dark. When the leaf was illuminated, no O₂ evolution was detected from short light pulses, although transient O₂ production was appreciable during longer light pulses. This indicates that an electron donor (pool size about 2–3 e/PSII reaction center) became reduced in the dark and the first photons were used to oxidise this donor instead of water.Abbreviations Chl chlorophyll - CRC carbon reduction cycle - GAPDH NADP-glyceraldehyde-phosphate dehydrogenase - PFD photon flux density - PGA 3-phosphoglycerate - RuBP ribulose bisphosphate - TCA tricarboxylic acid cycle To whom correspondence should be addressedThis work received support by the Estonian Academy of Sciences, the Gottfried-Wilhelm-Leibniz Program of the Deutsche For-schungsgemeinschaft and the Sonderforschungsbereich 251 of the University of Würzburg.     

Biological conversion of rifamycin B by live Humicola sp. cells immobilized in a dual hollow fiber bioreactor

The biological transformation from rifamycin B to rifamycin S was carried out with the live whole cells of Humicola sp., ATCC 20620, immobilized in a dual hollow fiber bioreactor (DHFBR). Humicola sp., inoculated in the DHFBR, proliferated successfully to a high density cell mass within the space between an outer silicone tubing and three inner polypropylene hollow fiber membranes. In order to control the cell growth a nitrogen deficient medium was fed. Conversion of rifamycin B continued for more than 30 d, whereas that of immobilized rifamycin B oxidase lasted only for 3 d in comparable conditions.In the DHFBR the volumetric productivity of rifamycin S was 0.65–1.03 mmol/(dm³ · h) with 60% conversion, while that in the rotating packed disk reactor was 0.27 mmol/(dm³ · h) with 40% conversion at a residence time of 0.5–1.5 h.     

Impact of acute temperature transition on enzyme activity levels,oxygen consumption,and exogenous fuel utilization in sea raven (Hemitripterus americanus) hearts

Summary The impact of an acute temperature transition between 5 °C and 15 °C on energy metabolism and performance of sea raven (Hemitripterus americanus) heart was assessed. Maximal in vitro activity of hexokinase was 1.2 and 3.7 mol · min^-1 · g^-1 at 5 °C and 15 °C, respectively. Carnitine palmitoyl transferase and carnitine palmitoleoyl transferase activities were 0.07 mol · min^-1 · g^-1 at 15 °C and declined substantially at 5 °C. Oxygen consumption and power output of perfused isolated hearts offered glucose alone as a metabolic fuel decreased significantly between 15 °C and 5 °C. When palmitoleate was included in the perfusion medium, oxygen consumption and power development remained constant between 15 °C and 5 °C, suggesting that glucose alone was not an adequate metabolic fuel at low temperature. However, maximal in vitro activity of HK implied that the catalytic potential at this locus was quite capable of meeting demands of carbon flow, while the maximal in vitro activity of the carnitine acyl CoA transferases implied that fatty acid metabolism should be greatly compromised at low temperatures. In an effort to resolve the contradiction, hearts were perfused with medium containing ¹⁴C-glucose or ¹⁴C-palmitate. Rates of ¹⁴CO₂ production from labelled metabolic fuels could account for only about 2% of the oxygen consumption rates. Most of the label from ¹⁴C-glucose was incorporated into the glycogen and lipid fractions and label from ¹⁴C-palmitate was incorporated into the lipid fraction. The net incorporation rates of label into intracellular pools were temperature insensitive over the range 5–15 °C. The incorporation of exogenous glucose into the lipid fraction suggests that activity of the entire glycolytic pathway was maintained over the temperature range. Thus, the relatively low rate of oxygen consumption of hearts perfused with glucose alone as an exogenous substrate cannot be attributed to a limitation of glucose catabolism. The alternative explanation is that the presence of fatty acids induces an increase in oxygen consumption, especially at 5 °C. It is speculated that this is due to alterations in Ca²⁺ balance.Abbreviations ATPase adenosine triphosphatase - BSA bovine serum albumin - CoA coenzyme A - C palmitoyl T carnitine palmitoyl transferase - CS citrate synthase - HK hexokinase - MO oxygen consumption - PFK phosphofructokinase - PO ₂ oxygen partial pressure     

Continuous ethanol production by Zymomonas mobilis in a fluidized bed reactor. Part II: Process development for the fermentation of hydrolysed B-starch without sterilization

A continuous fluidized bed reactor operation system has been developed for ethanol production by Zymomonas mobilis using hydrolysed B-starch without sterilization. The operation system consists of two phases. In the first phase macroporous glass carriers in a totally mixed fluidized bed reactor were filled up totally with a monoculture of Z. mobilis by fast computer-controlled colonization, so that in the subsequent production phase no contaminants, especially lactic-acid bacteria, could penetrate into the carrier beads. In the production phase the high concentration of immobilized Z. mobilis cells in the fluidized bed reactor permits unsterile fermentation of hydrolysed B-starch to ethanol at short residence times. This results in wash-out conditions for contaminants from the substrate. Long-term experimental studies (more than 120 days) of unsterile fermentation of hydrolysed B-starch in the laboratory fluidized bed reactor (2.2 l) demonstrated stable operation up to residence times of 5 h. A semi-technical fluidized bed reactor plant (cascade of two fluidized bed reactors, each 55 l) was operated stably at a mean residence time of 4.25 h. Glucose conversion of 99% of the unsterile hydrolysed B-starch was achieved at 120 g glucose/l^–1 in the substrate, resulting in an ethanol concentration of 50 g·l^–1 and an ethanol space-time yield of 13 g·l^–1·h^–1. This is a factor of three compared to ethanol fermentation of hydrolysed B-starch with Z. mobilis in a continuous stirred tank reactor, which can only be operated stably under sterile conditions. Correspondence to: D. Weuster-Botz     

Production of glutamine by micro-gel bead-immobilized Corynebacterium glutamicum 9703-T cells in a stirred tank reactor

The effectiveness of using micro-gel bead-immobilized cells for aerobic processes was investigated. Glutamine production by Corynebacterium glutamicum, 9703-T, cells was used as an example. The cells were immobilized in Sr-alginate micro-gel beads 500 m in diameter and used for fermentation processes in a stirred tank reactor with a modified impeller at 400 min^–1. Continuous production of glutamine was carried out for more than 220 h in this reactor and no gel breakage was observed. As a result of the high oxygen transfer capacity of this system, the glutamine yield from glucose was more than three times higher, while the organic acid accumulation was more than 24 times lower than those obtained with 3.0 mm-gel bead-immobilized cells in an airlift fermentor under similar experimental conditions. During the continuous fermentations there was evolution and proliferation of non-glutamine producing strains which led to a gradual decrease in the productivity of the systems. Although a modified production medium which suppresses cell growth during the production phase was effective in maintaining the productivity, the stability of the whole system was shortened due to high cell deactivation rate in such a medium.List of Symbols C kg/m³ glutamine concentration - C _A mol/m ³ local oxygen concentration inside the gel beads - C _AS mol/m ³ oxygen concentration at the surface of the gel beads - De m²/h effective diffusion coefficient of oxygen in the gel bead - DO mol/m³ dissolved oxygen concentration - F dm³/h medium flow rate - K h^–1 glutamine decomposition rate constant - Km mol/m³ Michaelis Menten constant - QO _2max mol/(kg · h) maximum specific respiration rate - R m radius of the gel beads - r m radial distance - t h time - V _C dm ³ volume of the gel beads - V _L dm ³ liquid volume in the reactor - Vm mol/(m³ · h) maximum respiration rate - X kg/m³ cell concentration - x r/R - y C _A /C_AS - h^–1 cell deactivation rate constant - Thiele modulus defined by R(Vm/De Km) ^1/2 - C _AS /Km - _C kg/(m³-gel · h) specific glutamine formation rate - _c dm³-gel/dm³ V _C /V _L      

Anaerobic degradation of acetone by Desulfococcus biacutus spec. nov.

From anaerobic digestor sludge of a waste water treatment plant, a gram-negative, strictly anaerobic sulfate-reducing bacterium was isolated with acetone as sole organic substrate. The bacterium was characterized as a new species, Desulfococcus biacutus. The strain grew with acetone with doubling times of 72 h to 120 h; the growth yield was 12.0 (±2.1) g · [mol acetone]^-1. Acetone was oxidized completely, and no isopropanol was formed. In labelling studies with ¹⁴CO₂, cell lipids (including approx. 50% PHB) of acetone-grown cells became labelled 7 times as high as those of 3-hydroxy-buyrate-grown cells. Enzyme studies indicated that acetone was degraded via acetoacetyl-CoA, and that acetone was channeled into the intermediary metabolism after condensation with carbon dioxide to a C₄-compound, possibly free acetoacetate. Acetoacetyl-CoA is cleaved by a thiolase reaction to acetyl-CoA which is completely oxidized through the carbon monoxide dehydrogenase pathway. Strain KMRActS was deposited with the Deutsche Sammlung von Mikroorganismen, Braunschweig, under the number DSM 5651.     

Enhanced Microbial Removal of H2S Using Chlorobium in an Optical-Fiber Bioreactor

The removal rate of H₂S in a scratched optical fiber bioreactor using Chlorobium thiosulfatophilum was 0.87 µmol H₂S oxidized·l/min·mg protein, which was 6.7 times that in an external illuminating reactor. Available light intensity with scratched fibers in the bioreactor was 41 µmol/m²·s about 5 times as much as that with unscratched ones.     

Estimation of the energetic biomass yield and efficiency of oxidative phosphorylation in cell-recycle cultures of Schizosaccharomyces pombe

The energetics of growth of the fission yeast Schizosaccharomyces pombe was studied in continuous high-cell concentration cultures using a cell-recycle fermentor. Under non-O₂-limited conditions, steady-states were obtained at various specific growth rates (partial cell-recycle) with purely oxidative (glucose limitation) or respiro-fermentative (glucose excess) metabolic behaviour. The stoichiometry of biomass synthesis was established from the elemental composition of the cells and measurements of all the specific metabolic rates, i.e. consumption of glucose and O₂ and production of CO₂, ethanol and other products. The theoretical yield factor for biomass on glucose was Y_G,X = 0.85 C-mol·C-mol^–1 and maintenance requirements were negligible. Assuming a constant coupling between energy generation and biomass formation for both respirative and respiro-fermentative breakdown of glucose, the biomass yield from ATP (Y_ATP) and the efficiency of oxidative phosphorylation (P/O ratio) could be determined as 9.8 g biomass·mol ATP and 1.28 mol ATP·atom of O₂, respectively. Correspondence to: A. Pareilleux     

Seasonal course of translocation and distribution of 14C-labelled photoassimilate in young trees of Larix decidua Mill

Summary Young trees of Larix decidua, in their 4th and 5th year of development, were permitted to photoassimilate a pulse of ¹⁴CO₂ at different times throughout the growing season. After chase periods between 1 h and 7 days, the distribution of ¹⁴C in these plants was determined. CO₂ fixation followed a maximum curve with highest rates of photosynthesis of 123 ± 4 mol CO₂·h^-1·mg chl^-1 in June. Translocation of ¹⁴C assimilate was observed throughout the growing season. The main quantity of fixed ¹⁴C was always retained in the fed leaves. Radiocarbon moved basipetally into the roots at all times, particularly in spring and late summer. Sprouting young shoots and leaves at the stem apex attracted assimilate in spring. Incorporation of ¹⁴C into soluble low-molecular-weight substances prevailed; less radioactivity was incorporated into insoluble polymeric compounds. Distribution of ¹⁴C among the sugar, amino acid and organic acid fraction was determined. Labelled free sugars were analysed.     

Continuous production of gibberellic acid in a fixed-bed reactor by immobilized mycelia of Gibberella fujikuroi in calcium alginate beads

Summary The continuous production of gibberellic acid with immobilized mycelia of Gibberella fujikuroi was maintained over a hundred days in a tubular fixed-bed reactor. Free mycelium at the beginning of the storage phase was harvested from G. fujikuroi shake-flask culture and was immobilized by ionotropic gelation in calcium alginate beads.The continuous recycle production system consisted of a fixed-bed reactor, a container in which the culture medium was heated, stirred and aerated, and valves for sample withdrawal or reactant addition during the first 1320 h (55 days). A two-phase continuous extractor was then added for the last 960 hours (40 days). Free and immobilized mycelium shake-flask cultures with the same strain used in the continuous culture system were also realized to compare growth, maintenance and production parameters. The results show about the same gibberellic acid productivity in both free and immobilized mycelium shakeflask cultures: 0.384 and 0.408 mgGA₃·gBiomass^-1 ·day^-1, respectively, whereas in the continuous system the gibberellic acid production is about twice as large for a similar biomass: 0.768 mgGA₃·gBiomass^-1·day^-1. Several factors affecting the overall productivity of the immobilized systems were found to be: the quality and the quantity of mycelia in the biocatalyst beads and the immobilization conditions.