摘要:

AbstractSemicontinuous fermentations, in which a fraction of a culture is replaced with fresh media at regular intervals, have been previously used as a means of approximating continuous growth. In most cases deviations from continuous operation were erroneously estimated using Fencl's model, which is only valid when the specific growth rate is independent of the substrate concentration. An approach to modeling Semicontinuous growth that incorporates the same kinetics followed in batch and continuous growth was developed and tested for Monod's expression for the specific growth rate. A dimensionless form of the model was used to simulate Semicontinuous fermentations for comparison to continuous growth. Differences between Semicontinuous and continuous growth were found to depend on three dimensionless variables: feed concentration, replacement rate, and time between replacements. For given values of the dimensionless feed concentration and time between replacements, a range of dimensionless replacement rates can be determined over which semi‐continuous cultures are approximately continuou

ISSN:0006-3592    

DOI:10.1002/bit.260350502

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

年代:1990

数据来源: WILEY

摘要:

AbstractBatch xanthan fermentations byXanthomonas campestrisNRRL B‐1459 at various temperatures ranging between 22°C and 35°C were studied. At 24°C or lower, xanthan formation lagged significantly behind cell growth, resembling typical secondary metabolism. However, at 27°C and higher, xanthan biosynthesis followed cell growth from the beginning of the exponential phase and continued into the stationary phase. Cell growth at 35°C was very slow; the specific growth rate was near zero. The specific growth rate had a maximum value of 0.26 h−1at temperatures between 27°C and 31°C. Cell yield decreased from 0.53 g/g glucose at 22°C to 0.28 g/g glucose at 33°C, whereas xanthan yield increased from 54% at 22°C to 90% at 33°C. The specific xanthan formation rate also increased with increasing temperature. The pyruvate content of xanthan produced at various temperatures ranged between 1.9% and 4.5%, with the maximum occurring between 27°C and 30°C. These results suggest that the optimal temperatures for cell growth are between 24°C and 27°C, whereas those for xanthan formation are between 30°C and 33°C. For single‐stage batch fermentation, the optimal temperature for xanthan fermentation is thus dependent on the design criteria (i. e., fermentation rate, xanthan yield, and gum qualities). However, a two‐stage fermentation process with temperature shift‐up from 27°C to 32°C is suggested to optimize both cell growth and xanthan formation, respectively, at each stage, and thus to improve

ISSN:0006-3592    

DOI:10.1002/bit.260350503

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

年代:1990

数据来源: WILEY

摘要:

AbstractTwo hybridoma lines, HB8178 and AFP‐27, were grown in continuous culture. The concentrations of viable cells as well as those of various nutrients and metabolites reached steady‐state values. The concentrations of either total IgG or antigen‐specific antibody, however, failed to reach steady‐state values but rather continuously decreased over the course of the cultures. The fraction of antibody‐producing cells in the total cellular population also continuously decreased in the AFP‐27 cultures. Comparison of the specific antibody productivity based on either the entire population or the antibody‐producing fraction of the population over time suggests that the decrease in productivity was at least partly due to the occurrence of a nonproducing subpopula

ISSN:0006-3592    

DOI:10.1002/bit.260350504

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

年代:1990

数据来源: WILEY

摘要:

AbstractA thermodynamic model was used in this study to predict the adhesion ofPhanerochaete chrysosporiumINA‐12 as conidiospores or mycelium to various solid carriers. Theoretical predictions were closely reflected by experimental results. Amount of immobilized mycelium was higher for hydrophobic (polypropylene and polyurethane) than for hydrophilic carrier (stainless steel and grey). Lignin peroxidase production was stimulated in the same way. However, better results were obtained with polyurethane than with polypropylene and with grey than with stainless steel. These results were attributed to roughness effects of solid surfaces. Surface morphology characterization showed that the surface roughness parameterRAwas higher for polyurethane and grey as compared to polypropylene and stainless steel, respectively. On the other hand, polyurethane is not simply rugous; it has an intraparticle porosity as well as a higher total surface area as compared to polypropylen

ISSN:0006-3592    

DOI:10.1002/bit.260350505

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

年代:1990

数据来源: WILEY

摘要:

AbstractGas holdups and volumetric mass transfer coefficients were measured in a concentric tube airlift reactor designed for the microbial desulfurization of coal. The solutions studied were comprised of an acidified basal salts solution containing thirteen different weight percentages (0 to 40) of coal (74 μm Ohio #1) at three different temperatures (30, 50, and 72°C). Gas holdup ϵGdecreased with solids loading for the entire range studied. An enhancement in the volumetric mass transfer coefficientKLawith respect to that in pure solution was observed from zero to approximately 5 wt % (solids volume fraction ϵs= 0.035), the maximum enhancement occurring at approximately 2 wt % (ϵs= 0.014). At higher solids fractions, the mass transfer coefficient decreased with further solids additions. Gas holdups and the mass transfer coefficients increased with temperature over the studied range. TheKLaand ϵGwere correlated to three process variables separately and the separate correlations combined to yield generalized correlations for the mass transfer coefficient and gas holdup for this system. The correlations may be used for design, operation, and ost estimation of such sy

ISSN:0006-3592    

DOI:10.1002/bit.260350506

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

年代:1990

数据来源: WILEY

摘要:

AbstractA miniature fuel cell, using a hydrophobic Teflon® membrane, designed to continuously measure dissolved H2in nonbiological media, was tested for use in anaerobic digestion conditions. In water, this detector responds quickly and efficiently to variation of hydrogen concentration in the range from 80 to 770 nMThe media used, and the metabolites or products found in anaerobic digestion media, i. e. inorganic carbon and phosphate buffers, formate, acetate, and dissolved methane, did not interfere with the signal of the detector cell. Dissolved hydrogen sulfide did not poison the cell but was detected. In spite of the detector's high sensitivity to hydrogen (about 21,000 times higher for hydrogen than for hydrogen sulfide), interferences can occur in media containing high sulfide levels.In a methanogenic reactor, the detector cell response to dissolved hydrogen was fast and reliable with time. The observed values ranged values ranged from 2 to 3.5μM. Dissolved hydrogen concentrations were 40 to 70 times higher than values calculated from measured hydrogen partial pressures and Henry's coefficient, suggesting a limitation of the process in the hydrogen transfer from the liquid to the gaseous phas

ISSN:0006-3592    

DOI:10.1002/bit.260350507

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe results of numerical simulations for a growing biological film are presented to justify the use of steady‐state biofilm models for approximating the behavior of both unlimited and shear‐limited biofilms. For an unlimited biofilm we show that although the total biofilm thickness may continue to increase over time, the active biofilm volume will reach a constant value. We also show that the profile of active microorganisms within the biofilm will become constant with respect to the biofilm/fluid interface and simply move outward as the biofilm thickness increases. For a shear‐limited biofilm we similarly show that once a “limiting” thickness has been reached the active biofilm volume, substrate consumption, and profile of active microorganisms within the biofilm will also be independent of the biofilm

ISSN:0006-3592    

DOI:10.1002/bit.260350508

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

年代:1990

数据来源: WILEY

摘要:

AbstractThis article describes the characteristics of silk fibroin membranes and glucose oxidase, immobilized in membranes as determined by a variety of physical methods, mainly the spin‐label electron spin resonance (ESR) method. The properties of membranes insolubilized by different methods, i. e., immersion in 80% methanol aqueous solution, uniaxially drawing by placing on a stretcher, and hydration by placing in a desiccator of 96% relative humidity (RH) for 17 h, are compared. The results are also analyzed in relation to ESR spectra of spin‐labeled immobilized glucose oxidase and 4‐hydroxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy as a model of the substrate. It is concluded that the heterogeneous structures of the swollen membranes in water differ locally among membranes insolubilized by different methods, but the immobilized state of the enzyme in such membranes is mostly similar. This is correlated to the fact that the thermal or pH stabilities are essentially same among glucose‐oxidase‐immobilized silk fibroin membranes insolubilized by

ISSN:0006-3592    

DOI:10.1002/bit.260350509

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

年代:1990

数据来源: WILEY

摘要:

AbstractWater‐insoluble proteases were prepared by immobilizing papain and chymotrypsin onto the surface of polyacrolein microspheres with and without oligoglycines as spacer. The activity of immobilized proteases was found to be still high toward small ester substrates, but very low toward casein, a high‐molecular‐weight substrate. The relative activity of the immobilized proteases without spacer decreased gradually with the decreasing surface concentration of the immobilized proteases on the microspheres. On the contrary, the immobilized proteases with oligoglycine spacers gave an almost constant activity for the substrate hydrolysis within the surface concentration region studied and gave a much higher relative activity than those without any spacer. With the longer spacer, the immobilized enzymes showed a higher activity toward casein hydrolysis, whereas there was an optimum length for the spacer when hydrolysis was carried out toward the low‐molecular‐weight substrate. The thermal stability of the immobilized proteases was higher than that of the respective native proteases. The initial enzymatic activity of the immobilized proteases maintained almost unchanged without any elimination and inactivation of proteases, when the batch enzyme reaction was performed repeatedly, indicating the excellent d

ISSN:0006-3592    

DOI:10.1002/bit.260350510

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

年代:1990

数据来源: WILEY

摘要:

AbstractA quantitative assay of β‐galactosidase activity in single cells ofSaccharomyces cerevisiaehas been developed using a fluorogenic substrate and flow cytometry [reported in Wittrup&Bailey,Cytometry, 9,394 (1988)]. The β‐galactosidase activity is expressed in yeast from theEscherichia coli lacZgene under the control of the yeastGAL10promoter, and is used as a marker for multicopy plasmid content. A nonfluorescent fluorogenic substrate is enzymatically cleaved by intracellular β‐galactosidase to form a fluorescent product. The accumulation of fluorescent product in single cells was found to depend on bulk substrate concentration and single‐cell enzyme activity in a fashion that could not be described by a Michaelis–Menten kinetic rate form. It has been demonstrated that diffusion limitation rather than enzyme activity can determine the level of single‐cell fluorescence under certain assay conditions, and a mathematical model has; been formulated which accounts for substrate and product diffusion. Guided by the mathematical model, the assay conditions were modified to allow measurement of single‐cell enzyme activity rather than

ISSN:0006-3592    

DOI:10.1002/bit.260350511

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

年代:1990

数据来源: WILEY