摘要:

AbstractA large number of models concerning cultures of genetically engineered bacteria have been described. Among them, some are specifically adapted to continuous cultures and lead to the determination of two variables: (i) the difference in the specific growth rates between plasmid‐carrying cell and plasmid‐free cells (δμ) and (ii) the frequency of plasmid loss by plasmid‐containing cells (prμ+). Until now, studies have been performed on the global expression prμ+and δμ, whose value during continuous assays have been supposed approximately constant (mean value) and not on separate values of both terms prand μ+, respectively, probability of plasmid loss and specific growth rate of the plasmid‐carrying cells. So far these studies do not allow examination of the relationship between these two last parameters. Experimental results were obtained withEscherichia coliC600 galk (GAPDH), a genetically engineered strain that synthetizes an elevated quantity of glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH). From data obtained during continuous cultures, it is shown that during an assay, δμ, andprμ+do not remain constant. An appropriate mathematical analysis of the expression of μ−(specific growth rate of the plasmid‐free cells) and μ+has been built up. This allows the evaluation of the values of μ+and μ−during the continuous cultures carried out at different dilution rates. Values ofprhave been calculated from these data. Indeed our results show thatprincreases with μ+. A modeling approach which allows correct simulation of this variation is also proposed. This model is derived from the Hill equation regarding cooperative binding of enzymic type react

ISSN:0006-3592    

DOI:10.1002/bit.260410402

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

年代:1993

数据来源: WILEY

摘要:

AbstractRemoval of β‐glucosidase (BG) from cellulase is essential to the enzymatic production of cellobiose from cellulose because of the high reactivity of BG with cellobiose to form glucose. Chitosan is a reversibly soluble‐insoluble polymer depending on pH, and it has an affinity with the other components, endo‐β‐1,4‐glucanase and cellobiohydrolase, or cellulase. The affinity precipitation technique using chitosan is an effective way to fractionate cellulase for the above purpose. Hydrolysis experiments of cellulose with the residual fractionated enzyme gave higher cellobiose contents in the soluble sugar products. © 1993 John Wil

ISSN:0006-3592    

DOI:10.1002/bit.260410403

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

年代:1993

数据来源: WILEY

摘要:

AbstractCytochrome P‐450cammonooxygenase is an important bacterial redox enzyme system with potential commercial value for detoxifying trace hydrocarbon contaminants, catalyzing regiospecific hydroxylations, and amperometric biosensing. The present study was undertaken to increase productivity of this enzyme, which is induced in its host,pseudomonas putidaPpG 786, byD(+)‐camphor. Culture processes were studied in batch, fed‐batch, and continuous modes to evaluate metabolic behavior and develop constitutive equations for specific rate of growth (μ), camphor utilization (qp). Fed‐batch culture was characterized by an extended linear growth phase which is often encountered in hydrocarbon fermentations. Inhibition by the camphor solvent, dimethylformamide, was assessed. Production of the terminal protein of the p‐450camenzyme system, cytochromem, was shown to depend on growth medium iron content in fed‐batch culture and was increased by 130% over previously protocols by eliminating iron deficiency. A continuous process that enables greater production rates was developed by using oxygen enrichment while simultaneously reducing gas throughput. Camphor and oxygen requirements were determined for fedbatch and continuous growth. © 1993 John Wi

ISSN:0006-3592    

DOI:10.1002/bit.260410404

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe ΔS f′of one unit carbon formula weight ofEscherichia coliK‐12 cells, when grown on succinic acid, was calculated to be −80.13 J/deg. This value could then be used to calculate the entropy change accompanying the anabolism and metabolism of succinic acid to be 30.82 J/deg and 32.40 J/mol deg, respectively. The entropy of one unit carbon formula weight of driedE. ColiK‐12 cells is calculated to be 94.40 J/deg, which when divided by the mass of these cells becomes 3.90 J/g deg. The corresponding entropy of succinic acid is 2.77 J/g deg, making it apparent that the entropy per unit mass of the cells is greater than that of the substrate. It might be thought that because the cells appear to be so much more complex than the substrate, the cells should have a lesser entropy per unit mass than the substrate. That this does not appear to be true leads to the conclusion that the macromolecular organization (informational content?) of the cells contributes only in a very minor way to the total physical entropy of cells. © 1993 John Wile

ISSN:0006-3592    

DOI:10.1002/bit.260410405

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

年代:1993

数据来源: WILEY

摘要:

AbstractTo study the effects of the growth rate of the hybridoma cell Mn12 on productivity, cell cycle, cell size, and shear sensitivity, six continuous cultures were run at dilution rate of 0.011, 0.021, 0.023, 0.030, 0.042, and 0.058 h−1. This particular hybridoma cell appeared to be unstable in continuous culture with respect to specific productivity, as a sudden drop occurred after about 30 generations in continuous culture, accompanied by the appearance of two populations with respect to the cytoplasmic lgG content. The specific productivity increased with increasing growth rate. The shear sensitivity of the cell, as measured in a small air‐lift loop reactor, increased with increasing growth rate. The mean relative cell size, as determined with a flow cytometer, increased with increasing growth rates. Furthermore, the fraction of cells in the S phase increased, and the fraction of cells in the G1/G0 phase decreased with increasing growth rates. © 1993 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260410406

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

年代:1993

数据来源: WILEY

摘要:

AbstractPhanerochaete chrysosporiumand cultivated both mechanically agitated and pneumatic bioreactors. In the pneumatic devices, the yields of lignin and manganese peroxidases as well as extracellular protein, were considerably increased as compared with mechanically agitated bioreactors. Lignin peroxidase and manganese peroxidase activities as high as 4500 U · L−1and 1812 U · L−1respectively, were produced in an airlift bioreactor. By using enzyme markers, the secretion pathway and the respiration were shown to be dramatically activated in pneumatic bioreactors. The general metabolism of the fungus, when cultivated in the conventional fermentors, is oriented toward the synthesis of biomass at the expense of the synthesis of peroxidases. The use of pneumatic devices for the production of extracellular peroxidases byP. chrysosporium, avoids shear effects due to turbine agitator in the conventional fermentors, and provides a good example for the production of shear‐sensitive metabolites. © 1993 John Wiley&S

ISSN:0006-3592    

DOI:10.1002/bit.260410407

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe effect of substrate protection on enzyme deactivation was studied in a differential bed and a packed bed reactor using a commercial immobilized glucose isomerase (Swetase, Nagase Co.). Experimental data obtained from differential bed reactor were analyzed based on Briggs‐Haldane kinetics in which enzyme deactivation accompanying the protection of substrate was considered. The deactivation constant of the enzyme‐substrate complex was found to be about half of that of the free enzyme. The mathematical analysis describing the performance of a packed bed reactor under the considerations of the effects of substrate protection, diffusion resistance, and enzyme deactivation was studied. The system equations for the packed bed reactor were solved using an orthogonal collocation method. The presence of substrate protection and the diffusion effect within the enzyme particles resulted in an axial variation of effectiveness factor, ηD, along the length of the packed bed. The axial distribution profile of ηDwas found to be dependent on the operation temperature, Based on the effect of substrate protection, a better substrate feed policy could be theoretically found for promoting productivity in long‐term operation. © 1993 John Wiley&S

ISSN:0006-3592    

DOI:10.1002/bit.260410408

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe effect of carbon dioxide concentration on the bacterial leaching of a pyrite‐arsenopyrite ore concentrate was studied in continuous‐flow reactors. Steady‐state operation with two feed slurry densities, 6 wt% and 16 wt% solids, were tested for the effect of carbon dioxide concentration. Bacterial growth rates were estimated via the measurement of carbon dioxide consumption rates. Aqueous‐phase carbon dioxide concentrations in excess of 10 mg/L were found to be inhibitory to bacterial growth. © 1993 John Wiley&S

ISSN:0006-3592    

DOI:10.1002/bit.260410409

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

年代:1993

数据来源: WILEY

摘要:

AbstractCyanidase, an immobilized enzyme preparation for hydrolyzing cyanide to ammonia and formate, was applied for the treatment of cyanide‐containing waste waters from the food industry. Apricot seed extract was chosen as a model effluent. The enzymatic hydrolysis of pure amygdalin, the main cyanogenic glycoside in the extract, and the degradation of the cyanide formed was investigated and compared with the behavior of the real extract in a batch slurry reactor. A diffusional‐type, flat‐membrane reactor with immobilized cyanidase was developed, where the enzyme is effectively protected from adverse effects of high molecular components contained in the extract. For monitoring continuous‐membrane reactor operation, a new unsegmented ammonia measurement system was developed and applied. In continuous operation the cyanidase retained its original activity for more than 400 hours on steam. © 1993 John Wiley&S

ISSN:0006-3592    

DOI:10.1002/bit.260410410

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

年代:1993

数据来源: WILEY

摘要:

AbstractCatalase has been immobilized within sandwich membranes prepared by the photoinduced grafting of an epoxy‐diacrylate prepolymer onto commercial asymmetric cellulose membranes. The enzymatic activity of the membrane composite of hydrogen peroxide decomposition has been studied in a recirculation apparatus under tangential flow conditions without ultrafiltration. The enzymatic membranes were exposed to very low mechanical stresses and showed a very good catalytic performance and durability. Initial reaction rates, measured at 25°C as a function of both substrate concentration and enzyme amount immobilized per unit membrane surface, indicate that the mechanism of action of catalase is not altered after immobilization, although substrate diffusion through the original thin layer of membranes may become rate controlling. © 1993 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260410411

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

年代:1993

数据来源: WILEY