摘要:

AbstractCyclodextrin glycosyltransferase (CGTase) was found to be severely inhibited by cyclodextrins. In order to increase the conversion yield by reducing product inhibition and reuse the CGTase in the production of cyclodextrins from milled corn starch, an ultrafiltration membrane bioreactor system was employed. In a batch operation with ultrafiltration, the conversion yield was increased 57% compared with that without ultrafiltration. Operating conditions for the continuous production of cyclodextrins in the membrane bioreactor were optimized by taking into consideration the filtration rate and the conversion yield as follows: initial starch concentration, 7% (w/v); starch feeding rate, 240 mg/h; CGTase loading, 350 units/initial gram starch. When cyclodextrins were continuously produced in the membrane bioreactor under optimized conditions, 340 units of CGTase was require to produce 1 g of cyclodextrins for 48 h, while in the case of conventional batch operation, 1 g of cyclodextrins was produced for 24 h by 1410 units of CGTase. © 1993 John Wiley&Sons, Inc

ISSN:0006-3592    

DOI:10.1002/bit.260410112

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe effect of organic solvents on the equilibrium position of lipase‐catalyzed esterification of glycerol and decanoic acid has been investigated. The reaction is carried out in an aqueous‐organic two‐phase system. In polar solvents, high mole fractions of monoacylglycerol and low mole fractions of triacylglycerol and measured, while in nonpolar solvents, the measured differences in the mole fractions of monodi‐, and triacylglycerols are less. There is a good correlation between the ester mole fractions at equilibrium and the logPof the solvent (partition coefficient inn‐octanolwater), however, only if the group of tertiary alcohols is excluded. In the plot of the easter mole fractions as a function of the logarithm of hte solubility of water in the organic solvent, the tertiary alcohols can be included; however, in this case other deviations appear.For the prediction of the effect of organic solvents on the ester mole fractions at reaction equilibrium in nondilute reaction systems with a water activity below 1, the program TREP (Two‐phase Reaction Equilibrium Prediction) is developed, which is based on the UNIFAC group contribution method. With this model the equilibrium data are essentially predicted from basic thermodynamic data. The required equilibrium constants are estimated from experiments without an organic solvent in the reaction medium. The mole fractions calculated by TREP show the same trends as the experimentally measured mole fractions; however, some variation is observed in the absolute values. These deviations may be due to inaccuracies in the UNIFAC group contribution method. TREP is found to be a correct method to predict within some limits the ester mole fractions at equilibrium for all mixtures of solvents, substrates, and products. The production of monoester can be enhanced in reaction system with a sufficient high concentration of a polar solvent. In experiments with a triglymeto‐decanoic acid ratio of 5, almost no di‐and triesters can be detected at equilibrium. © 1993 John

ISSN:0006-3592    

DOI:10.1002/bit.260410113

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe death process of baculovirus‐infected insect cells was divided into two phases: a constant viability (or delay) phase characterized by a delay time (td) and a first‐order death phase characterized by a half‐life (t1/2). These two parameters were used in conjunction with then‐target theory to classify the kinetics of cell death under various conditions, including different multiplicity of infection (MOI), host cell lines, virus types, incubation volumes, cell density and extracellularL(+)‐lactate and ammonium concentrations. Two groups of kinetic effects were found: one characterized by a constant number of hypothetical targets and the other by decreased numbers of hypothetical targets. The first group includes effects such as MOI, virus types, and host cell lines. The second includes the effects of environmental perturbations, such as incubation volume, cell density, and extracellular concentrations ofL(+)‐lactate and ammonium. Although the underlying mechanisms of these effects are as yet unknown, the death kinetics of infected cells significantly affects the recombinant protein production. In general, foreign protein production does not correlate with the cell life after infection © 1993 John Wil

ISSN:0006-3592    

DOI:10.1002/bit.260410114

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

年代:1993

数据来源: WILEY

摘要:

AbstractA general mathematical framework for modeling biofilm detachment is presented. The approach is founded on a material balance on biomass that equates the detachment rate to the product of a detachment frequency and a detaching particle mass. The model provides a theoretical basis for deriving many of the empirical detachment rate expressions in common use and can thus lend some insight into their physical and biological significance. By allowing for variation in the detachment frequency with depth in the biofilm, the model permits derivation of detachment expressions that reflect a dependence on chemical or physiological gradients in the biofilm. Analysis of literature data sets from two different biofilm systems suggests, in both cases, that detachment is a growth‐associated phenomenon. © 1993 John Wiley&Sons, I

ISSN:0006-3592    

DOI:10.1002/bit.260410115

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

年代:1993

数据来源: WILEY

摘要:

AbstractA method has been developed to continuously measure the intracellular pH (pHi) of cells cultivated in a bioreactor in an on‐line fashion over extend time periods. The methods is attractive in its simplicity and involves the use of a fluorescent pHiindicator 9‐aminoacridine (9A A) which is a week base. An expression has been derived to calculate changes in pHifrom measured 9AA‐fluorescence changes. The indicator 9AA was found t be nontoxic to yeast cells at concentrations used to measure pHi(7 μM). The fluorescence of nicotinamide adenine dinucleotide (NADH) molecules did not interfere significantly with the measurement of 9AA‐fluorescence. The pHichange in yeast cell following the addition of a proton ionophore carbonyl cyanidem‐chlorophenyl hydrazone (CCCP) measured by 9AA compared favorably with that measured by the well‐established pHi, indicator (which is however unsuitable for on‐line applications in a bioreactor) bis‐carboxyethyl carboxy fluorescein (BCECF). The pHiof yeast under substrate starved conditions was 6.4 units. The responses of pHiof yeast cells to induced metabolic transitions were studied. Under aerobic condition, pHiincreased by 0.12 unit following a 100‐ppm glucose pulse addition and by 0.25 unit following a 300‐ppm ethanol pulse addition. Under anaerobic condition, pHiincreased by 0.1 unit following a 500‐ppm glucose pulse addition. Comparison of pHiwith other indicators of cellular metabolic state suggests that pHiis a cellular metabolic state indicator. © 19

ISSN:0006-3592    

DOI:10.1002/bit.260410116

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

年代:1993

数据来源: WILEY

摘要:

AbstractKinetics of bacterial reduction of toxic hexavalent chromium (chromate: CrO42−) was investigated using batch and fedbatch cultures ofEnterobacter cloacaestrain HO1. In fedbatch cultures, the CrO42−feed was controlled on the basis of the rate of pH change. This control strategy has proven to be useful for avoiding toxic CrO42−overload. A simple mathematical model was developed to describe the bacterial process of CrO42−reduction. In this model, two types of bacterial cells were considered: induced, CrO42−‐resistant cells and uninduced, sensitive ones. Only resistant cells were assumed to be able to reduce CrO42−. These fundamental ideas were supported by the model predictions which well approximated all experimental data. In a simulation study, the model was also used to optimize fed‐batch cultures, instead of lengthy and expensive laboratory experiments. © 1993 John

ISSN:0006-3592    

DOI:10.1002/bit.260410117

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe results of a study of the optimization of the experimental conditions for maximum production rate in overloaded elution and displacement chromatography are discussed. This study is based on the use of the equilibrium‐dispersive model of chromatography and the competitive Langmuir isotherms to calculate individual band profiles in the elution and displacement modes, and of a simplex algorithm to optimize the production rate. The operating parameters (sample size, mobile phase velocity, and the displacer concentration in the displacement model) and the column design parameters (column length and average particle diameter) are optimized simultaneously. Binary mixtures having relative concentrations 3:1 and 1:3, and separation factors of 1.2 to 1.8 are investigated. One of our major results is that, in both modes of chromatography, the maximum production rate is achieved at very low values of the retention factors,k′, much lower than those used in current practice. In all cases, unlessk′ exceeds greatly that optimum value, the production rate is higher in overloaded elution than in displacement chromatography. This is particularly true for the extraction of a minor component, which is eluted second. © 1993 John Wiley&Son

ISSN:0006-3592    

DOI:10.1002/bit.260410118

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

年代:1993

数据来源: WILEY

摘要:

AbstractPlasmid plJ303 stability inStreptomyces lividanscultures has been studied by measuring plasmid copy number under various growth conditions. An increase in mean plasmid copy number was normally seen during early rapid growth in both shaken culture and stirred vessel fermentations at 28°C. Maximum copy numbers were consistently attained in early stationary phase followed by a decline (of variable amount) upon further incubation. The imposition of environmental stress (high growth temperature, i.e., 37°C, and low dissolved oxygen tension, i.e.,<5% air saturation) led to a plasmid copy number of zero and a 50% reduction, respectively. Interestingly, the relative proportions of plasmid topoisomers changed with time since progressively more supercoiled forms were observed throughout the stationary phase. Plasmid dimers were also observed in some cultures, and no evidence of structural plasmid instability was found. In general, this host‐vector system seemed remarkably stable under normal growth conditions. However, copious organic acid production by the host was observed and was thought to be undesirable for good heterologous gene expression of a secreted protein. © 1993 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260410119

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

年代:1993

数据来源: WILEY

摘要:

AbstractAlcohol dehydrogenase (LADH) was studied in aqueous solutions of surfactants to determine its structural and catalytic characteristics. Fluorescence, circular dichroism (CD), and electron paramagnetic resonance (ERP) techniques were used to study structural changes to the enzyme. The activity of LADH in catalyzing the oxidation of ethanol was investigated. Short‐chain alkyl sulfonates and sulfates did not deactivate LADH or alter its structure. Longer and branched alkyl sulfates and sulfonates, as well as a cationic surfactant (CTAB), affected both LADH activity and conformation. © 1993 John Wiley&Sons, I

ISSN:0006-3592    

DOI:10.1002/bit.260410120

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

年代:1993

数据来源: WILEY

摘要:

AbstractSamples from fed‐batch fermentations ofPenicillium chrysogenumon complex medium are rheologically characterized. The behavior is well described by a power law model for which the parameters are estimates. Furthermore, two types of model media are characterized and compared with the real fermentation samples. Xanthan solutions are found to mimic the rheological properties of the filamentous fungi much better than carboxymethyl cellulose (CMC) solutions. © 1993 John Wiley&Sons, I

ISSN:0006-3592    

DOI:10.1002/bit.260410121

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

年代:1993

数据来源: WILEY