ISSN:0006-3592    

DOI:10.1002/bit.260371102

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

年代:1991

数据来源: WILEY

摘要:

AbstractDehydrogenation of hydrocortisone by agitated suspensions of free and immobilized cells ofArthrobacter simplexATCC 6946 was investigated under controlled ultrasonic irradiation at a frequency of 20 kHz. The microbial conversion was optimized first with respect to mechanical agitation and subsequently with respect to an additionally superimposed sonication. The optimization of ultrasound intensity and its mode of application were established at a level which maintained the structural integrity of the cells as well as their biocatalytic activity. Various regimes of ultrasound at power densities of 0.030–0.120 W/mL were applied in systems of soluble (0.4 g/L) and excess (1 g/L) hydrocortisone and only a moderate enhancement of the bioconversion by free cells was observed. This result was explained by a better ultrasound‐induced dispersal of microscopic clumps of cells and self‐adhering clusters of the steroids. However, a quite significant enhancement effect was obtained in bioconversion systems of soluble substrate by gel‐entrapped cells. This enhancement was explained by a phonophoretic effect associated with ultrasound‐facilitated diffusion of the substrates—oxygen and hydrocortisone—within

ISSN:0006-3592    

DOI:10.1002/bit.260371103

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

年代:1991

数据来源: WILEY

摘要:

AbstractVarious esters were synthesized in nearly anhydrous hexane from alcohols and carboxylic acids using a lipase fromCandida cylindracea. The enzyme was immobilized on a nylon support and protein loadings as high as 10 mg/g were obtained. The activity of the immobilized enzyme was maximum in a range of temperatures from 25 to 37°C. Ethylpropionate was formed from ethanol and propionic acid at a rate of 0.017 mol/h g immobilized protein. Different esters were formed at comparable rates and equilibrium conversions could generally be approached in less than 10 h in a batch reaction system. The immobilized lipase catalyst was quite stable and retained about one third of the initial activity after repeated experiments during the course of 72 days. A stirred tank continuous flow reactor was used successfully for the continuous production of esters

ISSN:0006-3592    

DOI:10.1002/bit.260371104

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

年代:1991

数据来源: WILEY

摘要:

AbstractA lumped model for cell growth and secondary metabolite production in an immobilized live cell bioreactor has been developed. This model is applied here to simulate the performance of an immobilized bioreactor under steady‐state conditions and under conditions of periodically varying concentration of a growth‐limiting substrate. The results of the simulation study were experimentally verified in the case of the production of the antibiotic candicidin byStreptomyces griseusin an immobilized bioreactor with forced periodic operation. The results of the studies suggest that periodically operated immobilized live cell bioreactors can provide a potent alternative for the production of non‐growth‐associated biochemicals, as compared to free cell fermentations, pulsed fermentations with process cycle regeneration, and nonregenerated bioreactors. This work has demonstrated that by frequent pulsing of the growth limiting nutrient, stable extended production can be obtained at high specific cellular product

ISSN:0006-3592    

DOI:10.1002/bit.260371105

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

年代:1991

数据来源: WILEY

摘要:

AbstractHigh gradient magnetic separation (HGMS) is used to separate nonmagnetic microorganisms from solution by a technique known as seeding. Fine magnetic particles are adhered to the cells' surfaces, making them magnetic and amenable to magnetic separation. Attachment of the sub‐micron, acicular γ‐Fe2O3seed to the yeast surface occurs irrespective of the solution pH and surface charge and is essentially irreversible. A model is developed to predict the separation of yeast in a high gradient magnetic separator. The effective capture radius is assumed to be proportional to the derived magnetic parameter γ for the case where the dominant competing force to magnetic attraction is the magnetic floc's inertia. Using this parameter, yeast separation in an HGMS unit is predicted. The measured separation ofSaccharomyces cerevisiaeat differing magnetic seed concentrations and two flow rates supports the above

ISSN:0006-3592    

DOI:10.1002/bit.260371106

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

年代:1991

数据来源: WILEY

摘要:

AbstractTheSaccharomyces cerevisiaestrain Mc16/p520 has an unstable plasmid, p520, which directs production of a wheat α‐amylase. The effects of immobilizing this microorganism on the plasmid stability and the specific productivity of the secreted α‐amylase were investigated. Small gelatin beads were used as the support in both fluidized and packed bed configurations, and the yeast cells were attached by covalent cross‐linking with glutaraldehyde. These data were then compared to those for nonimmobilized, suspension cells.Plasmid stability was increased for the immobilized cells during continuous culture at dilution rates both above and below washout. Continuous suspension cultures were not stable and rapidly lost the plasmid. Immobilization caused an increase in specific and volumetric productivity during continuous culture, with a packed bed design resulting in the highest specific produ

ISSN:0006-3592    

DOI:10.1002/bit.260371107

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

年代:1991

数据来源: WILEY

摘要:

AbstractMuch more information concerning the biodegradation kinetics of mixtures of common industrial chemicals, such as organic solvents, needs to be gathered before wastewater biotreatment process performance can become a matter of design. Here, the biooxidation of a solvent mixture comprizing methanol, acetone, isopropanol, and methylene chloride is examined. The fact that the enrichment culture obtained comprized only two solvent‐utilizing strains, together with only minor percentages of nonsolvent utilizing satellite strains, was contrary to the theory of microbial competition. In addition, the complex relationship between the two solvent‐utilizing strains indicates that further work is necessary on the pathways involved in isopropanol and acetone biooxidation and on the effects of operating conditions on the fluxes along such pathw

ISSN:0006-3592    

DOI:10.1002/bit.260371108

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

年代:1991

数据来源: WILEY

摘要:

AbstractA new fluorescent bioreactor monitoring probe—multiple excitation fluorometric system (MEFS)—has been developed. This probe was compared to the commercially available BioChem Technology FluroMeasure system (NADH probe). In this task the fluorescence behavior of three model fermentation systems, ethanol fermentation byCandida utilis, phenol fermentation byPseudomonas putida, and glucose fermentation bySaccharomyces cerevisiae, were examined. The results indicated that the fluorescence intensity and behavior of various cellular fluorophors vary significantly between the different fermentation systems. Monitoring a fermentation process using only NAD(P)H fluorescence provided limited information. The NAD(P)H fluorescence was found not to be the best fluorescence signal for monitoring cell concentrations. The best way of monitoring a bioreactor by fluorometry may be to monitor several fluorophors in the whole culture broth simultaneously and to relate these fluorescence signals to various biological paramet

ISSN:0006-3592    

DOI:10.1002/bit.260371109

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

年代:1991

数据来源: WILEY

摘要:

AbstractOxygen consumption by hybridoma cells immobilized in 1‐ and 3.9‐mm‐diameter calcium alginate beads was measured. The entrapped cells consumed oxygen at about 10 μmol/min per 109cells, regardless of the bead size and cell loading. In contrast, the same cells in suspension culture respire at specific rates of 3–8 μmol/min per 109cells (depending on the cell density). The growth rate of the immobilized cells was significantly reduced, while specific antibody production was comparable to that of f

ISSN:0006-3592    

DOI:10.1002/bit.260371110

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

年代:1991

数据来源: WILEY

摘要:

AbstractApplication of bioreactors is dominated by industrial production with the consequence that bioreactors also for scientific purposes are mainly used following an empiric pragmatic approach. For the sake of a breakthrough in biotechnology in general, and especially for advanced process development, a more systematic approach is emphasized here. This methodology in bioreactor performance studies is explained and the meaning clarified in a case study of a new type of tubular bioreactor. The central role of so‐called “model bioreactors” in bench‐scale applications is illustrated as a powerful contribution to the optimal design of bioreactors in technical scale. Pilot plant data in case of a tubular reactor for the production of ethanol withZymomonasand biopesticides withBacillus thuringiensisare pr

ISSN:0006-3592    

DOI:10.1002/bit.260371111

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

年代:1991

数据来源: WILEY