摘要:

AbstractA technique of continuous water activity control was used to examine the effects of water activity on enzyme catalysis in organic media. Esterification catalyzed byRhizopus arrhizuslipase was preferably carried out at a water activity of 0.33, which resulted in both maximal initial reaction rate and a high yield. WhenPseudomonaslipase was used as catalyst it was beneficial to start the reaction at high water activity (giving the optimal reaction rate with this enzyme) and then shift to a lower water activity toward the end of the reaction to obtain a high yield. The apparent equilibrium constant of the reaction was influenced by the water activity of the organic solvent. © 1994 John Wiley&Sons, Inc

ISSN:0006-3592    

DOI:10.1002/bit.260440502

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractInvertase as well as as amyloglucosidase were immobilized within asymmetyric ultrafiltration membranes that were prepared from polysulfone or homogeneously modified polysulfone. The chemical modification was carried out by sulfonation and halomethylation. This additional change of the surface properties of the capillaries within the membrane offers the possibilities for various types of enzyme fixation, namely adsorption, charge interactions, or covalent bonding. By variation of the immobilization conditions the distribution of the enzyme could be adjusted over the membrane's cross section. At a distinct enzyme concentration in the loading solution a homogeneous enzyme distribution within the membrane could be verified. This was shown by diffusion experiments. Under ultrafiltration conditions using a solution that contains membrane‐impermeable macromolecules as well as a membrane‐permeable solute like saccharose the residence time within the membrane was increased due to gel formation atop the membrane yet the kinetic was no affected. The nonpermeable soluble starch was not reacted by the amyloglucosidase membrane, indicating that the skin layer was free of enzymes. © 1994 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260440503

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractPrimary metabolism of a murine hybridoma was probed with13C nuclear magnetic resonance (NMR) spectroscopy. Cells cultured in a hollow fiber bioreactor were serially infused with [1−13C] glucose, [2−13C] glucose, and [3−13C] glutamine. In vivo spectroscopy of the culture was used in conjunction with off‐line spectroscopy of the medium to determine the intracellular concentration of several metabolic intermediates and to determine fluxes for primary metabolic pathways. Intracellular concentrations of pyruvate and alanine were very high relative to levels observed in normal quiescent mammalian cells. Estimates made from labeling patterns in lactate indicate that 76% of pyruvate is derived directly from glycolysis; some is also derived from the malate shunt, the pyruvate/melate shuttle associated with lipid synthesis and the pentose phosphate pathway. The rate of formation of pyruvate from the pentose phosphate pathway was estimated to be 4% of that from glycolysis; This value is a lower limit and the actual value may be higher. Incorporation of pyruvate into the tricarboxylic acid (TCA) cycle appears to occur through only pyruvate dehydrogenase; no pyruvate carboxylase activity was detected. The malate shunt rate was approximately equal to the rate of glutamine uptake. The rate of incorporation of glucosederived acetyl‐CoA into lipids was 4% of the glucose uptake rate. The TCA cycle rate between isocitrate and α‐ketoglutarate was 110% of the glutamine uptake rate. © 1994 John Wi

ISSN:0006-3592    

DOI:10.1002/bit.260440504

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractFeasibility and engineering aspects of biological sulphate reduction in gas‐lift reactors were studied. Hydrogen and carbon dioxide were used as energy and carbon source. Attention was paid to biofilm formation, sulphide toxicity, sulphate conversion rate optimization, and gasliquid mass transfer limitations. Sulphate‐reducing bacteria formed stable biofilms on pumice particles. Biofilm formation was not observed when basalt particles were used. However, use of basalt particles led to the formation of granules of sulphate‐reducing biomass. The sulphate‐reducing bacteria, grown on pumice, easily adapted to free H2S concentrations up to 450 mg/L. Biofilm growth rate then equilibrated biomass loss rate. These high free H2S concentrations caused reversible inhibition rather than acute toxicity. When free H2S concentrations were kept below 450 mg/L, a maximum sulphate conversion rate of 30 g SO42−/L · d could be achieved after only 10 days of operation. Gas‐to‐liquid hydrogen mass transfer capacity of the reactor determined the maximum sulphate conversion rate. © 1994 John

ISSN:0006-3592    

DOI:10.1002/bit.260440505

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractIn this article, the conditions for aerobic biofilm formation on suspended particles, the dynamics of biofilm formation, and the biomass production during the start‐up of a Biofilm Airlift Suspension reactor (BAS reactor) have been studied. The dynamics of biofilm formation during start up in the biofilm airlift suspension reactor follows three consecutive stages: bare carrier, microcolonies or patchy biofilms on the carrier, and biofilms completely covering the carrier. The effect of hydraulic retention time and of substrate loading rate on the formation of biofilms were investigated. To obtain in a BAS reactor a high biomass concentration and predominantly continuous biofilms, which completely surround the carrier, the hydraulic retention time must be shorter than the inverse of the maximum growth rate of the suspended bacteria. At longer hydraulic retention times, a low amount of attached biomass can be present on the carrier material as patchy biofilms. During the start‐up at short hydraulic retention times the bare carrier concentration decreases, the amount of biomass per biofilm particle remains constant, and biomass increase in the reactor is due to increasing numbers of biofilm particles. The substrate surface loading rate has effect only on the amount of biomass on the biofilm particle. A higher surface load leads to a thicker biofilm.A strong nonlinear increase of the concentration of attached biomass in time was observed. This can be explained by a decreased abrasion of the biofilm particles due to the decreasing concentration of bare carriers. The detachment rate per biofilm area during the start‐up is independent of the substrate loading rate, but depends strongly upon the bare carrier concentration.The Pirt‐maintenance concept is applicable to BAS reactors. Surplus biomass production is diminished at high biomass concentrations. The average maximal yield of biomass on substrate during the experiments presented in this article was 0.44 ± 0.08 C‐mol/C‐mol, the maintenance value 0.019 ± 0.012 C‐mol/(C‐mol h). The lowest actual biomass yield measured in this study was 0.15 C‐mol/C‐mol. © 199

ISSN:0006-3592    

DOI:10.1002/bit.260440506

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe establishment of prolific long‐term human bone marrow cultures has led to the development of hematopoietic bioreactor systems. A single batch expansion of bone marrow mononuclear cell populations leads to a 10‐ to 30‐fold increase in total cell number and in the number of colony forming units‐granulocyte/macrophage (CFU‐GMs), and a four‐ to tenfold increase in the number of long‐term culture initiating cells (LTC‐ICs). In principle, unlimited expansion of cells should be attainable from a pool of stem cells if all the necessary requirements leading to stem cell maintenance and division are met. In this article, we take the first step toward the identification of factors that limit single batch expansion of ex vivo bone marrow cells in perfusion‐based bioreactor systems. One possible constraint is the size of the growth surface area required. This constraint can be overcome by harvesting half the cell population periodically. We found that harvesting cells every 3 to 4 days, beginning on day 11 of culture, led to an extended growth period. Overall calculated cell expansion exceeded 100‐fold and the CFU‐GM expansion exceeded 30‐fold over a 27‐day period. These calculated values are based on growth that could be obtained from the harvested cell population. Growth of the adherent cell layer was stable, whereas the nonadherent cell population diminished with increasing number of passages. These results show that the bioreactor protocols published to date are suboptimal for long‐term cultivation, and that further definition and refinement is likely to lead to even greater expansion of hematopoietic cell populations obtained from bone marrow. More importantly, these results show that the LTC‐IC measured during the single pass expansion do have further expansion potential that can be realized by frequent harvesting. Finally, the present culture conditions provide a basis for an assay system for the identifications provide a basis for an assay system for the identification of the factors that determine the long‐term maintenance and replication of human stem cells ex vi

ISSN:0006-3592    

DOI:10.1002/bit.260440507

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractPolarographic microcoaxial needle electrodes were used to measure internal profiles of dissolved oxygen tension (Po2) within single Ca‐alginate beads of different diameter containing entrapped cells ofSaccharomyces cerevisiae.For the investigations, single beads coming from variable growing conditions and distinct cultivation stages were fixed in a special holding device. In dependence on microbial growth steep oxygen gradients were observed. The Oxygen penetration depth at steady state lay between 50 and 100 μm. After 8 h of cultivation time, the anaerobic space within the beads (ϕ 2 mm; cultivation in a packed bed reactor) is beginning at ∼ 130 μm, whereas the anaerobic space within the beads (ϕ 2 mm) coming from the shaker flask culture is located ∼440 μm below the bead surface. Surprisingly, steep gradients were also observed, when recording profiles from cell‐free Ca‐alginate beads of different diameter and alginate concentrations. The steep oxygen gradients apparently had to be interpreted as pseudo‐Po2‐gradients. These results were borne by several effects, such as formation of artifacts and diffusion barriers in front of the electrode tip or oxygen “availability” at the tip and consumption of oxygen by the electrode itself. These phenomena could be documented by microscopic observation and photography. Thus, to obtain real Po2‐profiles it is important to be exactly informed about the physical, chemical, and biological properties of the material to be investigated. Furthermore, it is necessary to apply a special stepwise puncture technique with distinct step‐in/step‐out movements of the electrode: e.g.,unidirectionalorcontradirectionalpuncture techniques.

ISSN:0006-3592    

DOI:10.1002/bit.260440508

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe behavior of a series of pure proteins partitioned in aqueous two‐phase systems is compared with their behavior during mild hydrophobic interaction chromatography (HIC). A simple theoretical rationale for this comparison is presented based upon solvophobic theory. Similarities were found in the behavior of the model proteins in the two forms of partition chromatography. This indicates that HIC may be employed as a rapid instrumental technique for the broad characterization of protein behavior, which may be of benefit in the development of liquid‐liquid partitioning strategies. However, it has proved difficult to completely account for this behavior on the basis of the known physical and structural properties of the proteins used. The variety in the detailed partitioning behavior of this small sample of protein types suggests that partition in aqueous two‐phase systems is uniquely sensitive to subtle differences in surface properties of complex macromolecules. © 1994 John Wiley&Son

ISSN:0006-3592    

DOI:10.1002/bit.260440509

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractLiquid flow was studied in aerobic biofilms, consisting of microbial cell clusters (discrete aggregates of densely packed cells) and interstitial voids. Fluorescein microinjection was used as a qualitative technique to determine the presence of flow in cell clusters and voids. Flow velocity profiles were determined by tracking fluorescent latex spheres using confocal microscopy. Liquid was flowing through the voids and was stagnant in the cell clusters. Consequently, in voids both diffusion and convection may contribute to mass transfer, whereas in cell clusters diffusion is the dominant factor. The flow velocity in the biofilm depended on the average flow velocity of the bulk liquid. The velocity profiles in biofilms were linear and the velocity was zero at the substratum surface. The velocity gradients within biofilms were 50% of that near walls without biofilm coverage. The influence of the biofilm roughness on the flow velocity profiles was similar to that caused by rigid roughness elements. © 1994 John Wiley&Sons, Inc

ISSN:0006-3592    

DOI:10.1002/bit.260440510

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractA packed granular activated carbon (GAC) biobed, inoculated with the ethane‐degrading strainMycobacteriumE3, was used to study ethene removal from a synthetic waste gas. Ethene, for which the dimensionless partition coefficient for an air‐water system at 20°C is about 7.6, was used as a model compound for poorly water soluble gaseous pollutants. In a first mode or operation, the GAC biobed was sprinkled intermittently and the waste gas influent was continuously pre‐humidified, establishing relatively moist conditions (water content>40% to 45%). A volumetric ethene removal rate of 0.382 kg COD · m−3· d−1(0.112 kg ethene · m−3· d−1) was obtained for an influent concentration of 125 ppm, a superficial waste gas velocity of 3.6E−3 m · s−1and a pseudo residence time of 45 s. However, in the second mode of operation, omitting the pre‐humidification of the waste gas influent and establishing a “dry” biobed (water content<40% to 45%), and thus obtaining better mass transfer to the biofilm, the ethene removal could be doubled for otherwise comparable operating parameters. Furthermore, under decreased wetting and for the given experimental conditions (influent concentration 125 to 816 ppm, waste gas superficial velocity 3.0E−3 m ·s−1, pseudo waste gas residence time 43 s), the ethene removal was not limited by mass transfer of ethene through the water layer covering the bi

ISSN:0006-3592    

DOI:10.1002/bit.260440511

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY