摘要:

AbstractTwo‐ and three‐phase mixing studies were carried out in a 44‐L concentric draft tube gas‐lift fermentor. It was proposed to use the fermentor for the production of solvents using immobilized bacteria. Bubble size, gas holdup, liquid velocities, circulation, and mixing times were determined for various superficial gas velocities in distilled water, starch, carboxymethyl cellulose, and ethanol solutions. The observed trends for two phase mixing were similar to other studies but the results were found to be more sensitive to liquid properties. This was possibly due to the large value of downcomer to riser area used in this study. Mixing in three phases highlighted the difficulty in predicting the effect of adding solids to the gas‐liquid system. Results showed that the gas‐lift fermentor was ideally suited to dealing with three phases but more work is necessary before accurate models can be developed to account for the effec

ISSN:0006-3592    

DOI:10.1002/bit.260381102

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn order to investigate how plasmid content, transcription efficiency, and translation efficiency affect the productivity of a cloned gene protein, a new vector (pPLc‐RP4.5) was constructed. The vector has PLpromoter andlacZas a structure gene 4.5S RNA gene between PLpromoter andlacZgene. We took advantage of the characteristic that the 4.5S RNA is accumulated insideE. colicells and can be quantitatively measured. A two‐stage continuous culture system in combination with a temperature‐sensitive gene switching system was used to study the performance of the recombinant fermentation. It was found that the plasmid content as varied by the dilution rate in the production stage showed a different pattern from that in the growth stage. The result showed that promoter strength had a greater influence on the overall gene expression efficiency of a cloned gene than the plasmid content, and the overall gene expression efficiency was largely dependent upon translation efficiency when a multicopy plasmid (pBR322 derivative androp‐) and a strong promoter (PL) were used to express a heterologous protein in

ISSN:0006-3592    

DOI:10.1002/bit.260381103

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe progress of reductive biotransformations of a variety of earbonyl compounds by whole cells of baker's yeast was monitored with time. Biotransformations rates ranged from 0.11 to 112.12 mg product formed per g dry yeast per h. While rapid biotransformations of citronellal and ethyl benzoylformate were observed, complete conversion of substrate to product did not occur. Reductive conversions of ethyl‐ and methyl‐acetoacetate went to completion in 6 and 12 h respectively. Ethyl mandelate was produced stereoselectively, favoring the (R)‐ stereoisomer and ethyl and methyl‐3‐hydroxybutyrate were produced with (S)‐enantiospecificity. Yeast crude extract and resuspended presence of NAD(P)H. Ethyl benzoylformate and methyl‐and ethyl‐acetoacetate were preferentially reduced by yeast crude extract as compared to resuspended pellet and, in the case of the former two substrates, the reaction manifested a preference for

ISSN:0006-3592    

DOI:10.1002/bit.260381104

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe plantTripterygium wilfordiiproduces di‐ and triterpenes of interest for male contraception and treatment of arthritis and skin disorders. Cell line TRP4a obtained form this plant in 1981 was reported to produce these valuable compounds at yields (∼0.04% of the biomass dry weight) higher than found in the plant (0.001%). In order to improve this production, studies were carried out to determine the feasibility of eliminating the troublesome component of coconut milk originally used to culture this cell line. A defined formulation suitable for growth ad maintenance has been developed. This medium consisted of Gamborg's PRL4 or B5 medium supplemented with 2 mg L−12,4‐dichlorophenoxyacetic acid and 20 g L−1sucrose. Furthermore, monitoring of carbohydrate uptake revealed thatT. wilfordiicells, contrary to many plant cell species, did not hydrolyze sucrose extra‐cellularly before uptake. Replacement of this disaccharide by glucose or fructose increased specific growth rate from 0.15 to 0.25 day−1. As tripdiolide is reported to be present in broth extract in significant amounts, plant cell immobilization technology offers a promising alternative to suspension cultures, especially in view to on line harvesting of the product. Surface immobilizedT. wilfordiicell cultures were successfully carried out in 2‐L bioreactors. Their biomass production and carbohydrate uptake were comparable to those observed for shake flask grown suspension cultures. Higher nitrate and ammonium uptake were found in immob

ISSN:0006-3592    

DOI:10.1002/bit.260381105

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

年代:1991

数据来源: WILEY

摘要:

AbstractA biosensor model was developed for a commercial NADH fluorescence probe to describe the single‐frequency excitation and emission fluorescence behavior of an aqueous mixture of fluorophores. This model is essential in correlating the measured signals to the concentrations of fluorescent compounds in a bioreactor. In addition to the concentrations of fluorescent components, the relevant parameters of the model are the absorbance at both the excitation and the emission frequencies by the solvent and other absorbing species, the background signals, the light path length of the bioreactor vessel, the fluorescence yield, and the lampdetector configuration. Due to inner‐filter effects and other interferences, the probe signal is intrinsically nonlinear in both the fluorophore concentration and the path length. An important parameter in the model is the geometric constant,S, which accounts for variations in the monitoring efficiency throughout the sample because fluorescent light is emitted in all directions. Previous models, derived from an unrealistic assumption that fluorescent light is emitted only in one direction parallel to the probe axis, are shown to be seriously deficient. The validity of the model was verified experimentally for a single‐component solution in which both the fluorophore concentration and path length were v

ISSN:0006-3592    

DOI:10.1002/bit.260381106

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

年代:1991

数据来源: WILEY

摘要:

AbstractSelective separation and purification of two lipases formChromobacterium viscosumwere carried out by liquid‐liquid extraction using a reversed micellar system. Optimum parameters for extraction were determined using a 250 mMAOT micellar solution in isooctane. Complete separation of the two lipases was achieved at pH 6.0 with a 50mMpotassium phosphate buffer solution containing 50 mMKCI. By adding 2.5% by volume of ethanol to the lipase‐loaded micellar solution, 85% of the extracted lipase could be recovered in a new aqueous phase, 50 mMK2HPO4with 50 mMKCl, at pH 9.0. Lipase A was purified 2.6‐fold with a recovery of 86%, and lipase B by 1.5‐fold with a recovery

ISSN:0006-3592    

DOI:10.1002/bit.260381107

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

年代:1991

数据来源: WILEY

摘要:

AbstractEffects of time, temperature, and pH during the steam explosion of poplar wood were studied with the aim of optimize both pentoses recovery and enzymatic hydrolysis efficiency. Steam explosion of acid impregnated wood chips allowed the recovery of 70% of potential xylose as monomers (217°C, 120 s) Enzymatic hydrolysis of pretreated fiber withTrichoderma reeseiCL‐847 cellulase system increased progressively with the severity of the steam treatment conditions. The best yield in term of glucose recovery after 24 h of enzymatic hydrolysis was 70% of potential glucose (225°C, 120 s). Deactivation by adsorption on lignin ofTrichoderma reeseicellulases and inhibition of these enzymes by low‐molecular‐weight phenols and trihydroxybutyric acids were

ISSN:0006-3592    

DOI:10.1002/bit.260381108

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe glucose metabolism of anEscherichia colistrain bearing mutations abolishing both acetyl phosphotransferase (PTA) and acetate kinase (ACK) activities was studied under aerobic and anaerobic conditions. These studies were conducted in a complex medium with the mutant carrying no plasmid, the mutant carrying the common cloning vector pUC19, and the mutant carrying a plasmid bearing the “pet” operon that encodesZymomonas mobilispyruvate decarboxylase and alcohol dehydrogenase activities. The mutant carrying no plasmid showed lower specific growth and glucose uptake rates relative to the parent wild‐type strain (K‐12), Lactic acid was produced at higher levels than the wild type, and considerable amounts of pyruvic acid were secreted as an unusual byproduct. Analysis of other fermentation products showed low but significant amounts of acetic acid, no accumulation of formic acid, and lower secretion of succinate and ethanol. The maintenance of the plasmid pUC19 in the mutant negatively affected metabolism. Expression of thepetoperon overcame the metabolic stress caused by the plasmid, enhancing growth and glucose uptake rates to the values observed in the plasmidfree mutant. Also, expression of thepetoperon allowed consumption of pyruvate accumulated during the first hours of ferme

ISSN:0006-3592    

DOI:10.1002/bit.260381109

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

年代:1991

数据来源: WILEY

摘要:

AbstractThis study was aimed at determining the degree of biomass homogeneity in the various parts of an internal loop airlift bioreactor, thus verifying the assumption, often made in bioreactor studies, of a well‐mixed liquid‐biomass system. Following characterization of the hydrodynamics of the vessel with water, the axial biomass distribution in the riser and downcomer was determined for plant and yeast cell suspensions of 5.8, 8.5, and 12.5 g DW/LPhaseolus vulgarisand of 30 and 46 g DW/LSaccharomyces cerevisiae. The airlift bioreactor with a surface ratioAD/ADof 1.04 and aspect ratio of 4.95 was investigated under various aeration rates. The yeast cells were found to be distributed practically uniformly throughout the vessel at the aeration rates of 0.1−1.45 vvm. However, in the case of the denser and cluster‐forming plant cells, a clear trend of a gradual bio‐mass accumulation in the downcomer, a slightly lower but uniform biomass loading in the riser, and a slightly higher biomass concentration in the gas‐liquid separator was observed at the lower aeration rates of 0.1−0.61 vvm. In the case of powderized calcium carbonate (55g/L) often used in fermentations of organic acids, a slight trend of a gradual accumulation of solids towards the bottom parts in both the downcomer and riser was observed. A better representative sampling location, in terms of solids and biomass loading, seems to be in the middle part of the vessel. It is suggested that airlift bioreactors with higher aspect ratios (>5) may be prone to a more significant inhomogeneity of solids (biomass a

ISSN:0006-3592    

DOI:10.1002/bit.260381110

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

年代:1991

数据来源: WILEY

摘要:

AbstractA novel imaging sensor system for the determination of plasmid carrying yeast cells was developed. The sensor system consisted of an Silicon Intensifier Target (SIT) video camera, a fluorescent microscope, and a personal computer system equipped with an image memory board. This system was based on the fact that the membrane integrity of only plasmid‐carrying cells is lost following cell growth in 5‐fluoro‐orotic acid (5‐FOA) containing medium, and consequently these target cell can be stained with fluorescent probes and detected. In this study, plasmid‐carrying cells were detected and their fraction determined in a mixture of both plasmid‐carring and plasmid‐free cells. A good correlation was observed between the values determined by this sensor system and the conventional method in the 30%‐80% range, and one assay was possible within 4 h. This sensor system could be used for the monitoring of plasmid‐carrying fraction in recombinant yeast cells d

ISSN:0006-3592    

DOI:10.1002/bit.260381111

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

年代:1991

数据来源: WILEY