摘要:

AbstractWe have examined the effect of genetically engineered charge modifications on the partitioning behavior of proteins in dextran/polyethylene glycol two‐phase systems containing potassium phosphate. By genetically altering a protein's charge, the role of charge on partitioning can be assessed directly without the need to modify the phase system. The charge modifications used are of two types: Charged tails of polyaspartic acid fused to β‐galactosidase and charge‐change point mutations of T4 lysozyme which replace positive lysine residues with negative glutamic acids. The partition coefficientKpfor these proteins was related to measured interfacial potential differences Δϕ using the simple thermodynamic model, InKp= InKo+(F/RT)Zpδϕ. The protein net chargeZpwas determined using the Henderson–Hasselbalch relationship with modifications based on experimentally determined titration and isoelectric point data. It was found that when the electropartitioning termZpδϕ was varied by changing the pH, the partitioning of T4 lysozyme was quantitatively described by the thermodynamic model. The β‐galactosidase fusions displayed qualitative agreement, and although less than predicted, the partitioning increased more than two orders of magnitude for the pH range examined. Changes in the partitioning of lysozyme due to the various mutations agreed qualitatively with the thermodynamic model, but with a smaller than expected dependence on the estimated charge differences. The β‐galactosidase fusions, on the other hand, did not display a consistent charge based trend, which is likely due either to the enzyme's large size and complexity or to nonelectrostatic contributions from the tails. The lack of quantitative fit with the model described above suggests that the assumptions made in developing this model are oversimplified. © 1994

ISSN:0006-3592    

DOI:10.1002/bit.260440202

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper presents a new formulation for the analysis of growth kinetics on multiple nutrients. The baseline for the theory is the concept that a noninteractive growth process occurs among perfectly substitutable nutrients if the locus of points of the substrate concentrations producing equal growth rate is linear. A deviation function is then defined with respect to this base case, and several models for this function are suggested. The underlying theory is taken by analogy with mixture thermodynamics. The proposed formulation is tested against data in the literature on growth under substitutable and complementary substrate mixtures. © 1994 John Wiley&Sons, Inc

ISSN:0006-3592    

DOI:10.1002/bit.260440203

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn Industrial production of penicillin there is a noticeable loss of the product through degradation reactions. It is shown that the degradation of penicillin‐V, both in a complex and in a chemically defined medium, can be separated into a phosphate‐catalyzed conversion of penicillin‐V to penicilloic‐V acid, overlaid by at least one other reaction in which penicillin V is degraded to as yet unknown products. Parameter values for the phosphatecatalyzed degradation are found to be independent of the type of fermentation medium. The rate of formation of other degradation products of penicillin‐V is found to be significantly higher in a complex fermentation medium with corn‐steep liquor in a chemically defined medium. © 1994 John Wil

ISSN:0006-3592    

DOI:10.1002/bit.260440204

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe on‐line determination of the physiological state of a cell culture process requires reliable on‐line measurements of various parameters and calculations of specific rates from these measurements. The cell concentration of a hybridoma culture was estimated on‐line by measuring optical density (OD) with a laser turbidity probe. The oxygen uptake rate (OUR) was determined by monitoring dynamically dissolved oxygen concentration profiles and closing oxygen balances in the culture. The base addition for neutralizing lactate produced by cells was also monitored on‐line via a balance. Using OD and OUR measurements, the specific growth and specific oxygen consumption rates were determined on‐line. By combining predetermined stoichiometric relationships among oxygen and glucose consumption and lactate production, the specific glucose consumption and lactate production rates were also calculated on‐line. Using these on‐line measurements and calculations, the hybridoma culture process was characterized on‐line by identifying the physiological states. They will also facilitate the implementation of nutrient feeding strategies for fed‐batch and perfusion cultures. © 1994 Jo

ISSN:0006-3592    

DOI:10.1002/bit.260440205

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe potential of thylakoid membranes immobilized in an albumin‐glutaraldehyde crosslinked matrix in a fast bioassay for phytotoxicity measurements in aqueous samples is studied. Free and immobilized preparations are compared for their electron transport activity measured as the initial rate of oxygen evolution with 2,5‐cichlorobenzoquinone as the artificial electron acceptor. Immobilized thylakoids were much stable under storage conditions; in the dark, at 4°C, they were fully stable in terms of photosynthetic activity for a period of 200 h. The immobilized membranes were as sensitive as the free thylakoids for the detection of most of the compounds tested (metal cations, sulfite, nitrite, and herbicides), all known as inhibitors of photosynthetic electron transport. In some instances, the immobilized preparations were even more sensitive than the free counterparts. The sensitivity could be further increased by lowering chlorophyll concentration in the assay. The short incubation period required (∼10 to 15 min) and the small volume of the assay (3 mL) suggest that this type of material should be useful in the detection of locations or effluents with phytotoxic character. © 1994 John Wiley&So

ISSN:0006-3592    

DOI:10.1002/bit.260440206

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe intracellular pool of UDP‐N‐acetylglucosamine and UDP‐N‐acetylgalactosamine has been shown to act as a central target during the inhibitory action of ammonium ions in vitro cultivated mammalian cell cultures. This pool has been demonstrated to be elevated at the end of a batch cultivation and very quickly as a response to exogenously applied ammonium chloride by using four different cell lines (hybridoma, BHK, CHO, and Ltk−929). The amount of enlarged UDP aminohexoses is correlated to the inhibitor concentration and additionally dependent on the cell line. The formation of the UDP sugars is associated with a transient reduction of the UTP pool. Moreover, the quick formation of UDP‐GNAc is strictly dependent on the presence of glucose and ammonium. Both metabolites act as biochemical precursors. Additionally, the formation of UDP‐GNAc after ammonium application has been shown to increase with an elevated cultivation pH and to be independent of the inhibition of transcription and translation processes. The intracellular amount of UDP‐GNAc correlates with the level of growth inhibition in mammalian cell lines. © 1994 John

ISSN:0006-3592    

DOI:10.1002/bit.260440207

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

年代:1994

数据来源: WILEY

摘要:

AbstractA rotating annular reactor (Roto Torque) was used for qualitative and quantitative studied on biofilm heterogeneity. In contrast to the classic image of biofilms as smooth, homogeneous layers of biomass on a substratum, studies using various pure and mixed cultures consistently revealed more‐dimensional structures that resembled dunes and ridges, among others. These heterogeneities were categorized and their underlying causes analyzed. Contrary to expectations, motility of the microorganisms not a decisive factor in determining biofilm homogeneity. Small Variations in substratum geometry homogeneity. Small variations in substratum geometry and flow patterns were clearly reflected in the biofilm pattern. Nonhomogeneous flow and shear patterns in the reactor, together with inadequate mixing resulted in significant, position‐dependent differences in surface growth. It was therefore not possible to take representative samples of the attached biomass. Like many other types of reactors, the Roto Torque reactor is valuable for qualitative and morphological biofilm experiments but less suitable for quantitative physiological and kinetics studies using attached microorganisms. © 1994 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260440208

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

年代:1994

数据来源: WILEY

摘要:

AbstractCell culture ofTaxus cuspidatamay represent an alternative to extraction of bark as a source of taxol and related taxanes. Cell suspensions of a cell line ofT. cuspidatawere grown for 44 days in shake flasks containing B5C2 medium. Throughout the growth cycle, fresh and dry weight accumulation, taxol yield on a dry weight basis, taxol accumulation in the medium, pH and pigmentation variation in the medium, as well as the uptake of sucrose, glucose, fructose, nitrate, and inorganic phosphate from the culture medium were examined. The results showed that the growth was relatively slow (doubling times of 17 and 20 days for fresh and dry weight, respectively), and taxol accumulation in the cells was non‐growth related (higher in the stationary phase) and at relatively low levels (up to 4 μg/g of the extracted dry weight). Taxol concentration in the medium had two peaks: one during the early (0.4μg/mL) and another during the late (0.1‐μg/mL) parts of the growth cycle. On a volumetric basis, the average total amount of taxol produced during the stationary phase (day 38) was 0.15 μg/mL, of which approximately 66% was in the medium and 34% was in the cells. Total carbohydrate uptake was closely associated with the increase in dry biomass. Sucrose was apparently extracellularly hydrolyzed after the first 6 days of culture; glucose was used before fructose. Nitrate was assimilated throughout the growth cycle, but phosphate was absorbed within the first week of culture. The pH variation showed an initial drop followed by a trend toward alkalinization for most of the growth period. Dark pigmentation in the medium increased progressively, particularly during the stationary phase. © 1994 John Wiley&S

ISSN:0006-3592    

DOI:10.1002/bit.260440209

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

年代:1994

数据来源: WILEY

摘要:

AbstractA denitrifying consortium capable of transforming carbon tetrachloride (CCI4) was cultured from an aquifer soil sample from the U.S. Department of Energy's Hanford Site in southeastern Washington State. A mathematical description of the kinetics of CCI4destruction by this microbial consortium is presented, and its prediction are compared to experimental data. The model successfully predicted the concentrations of acetate, nitrate, nitrite, biomass, and CCI4for all 12 experiments (a total of 60 concentration‐vs.‐time data sets). In addition, no statistically significant interactions exist between parameter values and individual test conditions. The ability of the model to predict the results of a treatability test for CCI4degradation in Hanford groundwater, without adjusting any model parameters, is discussed. © 1994 John Wiley&Sons,

ISSN:0006-3592    

DOI:10.1002/bit.260440210

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

年代:1994

数据来源: WILEY

摘要:

AbstractAdsorbent surfaces in natural and engineered systems are frequently modifies by bacterial attachment, growth of a biofilm, and bacterial production of extracellular polymer. Attached cells or sorbed polymers may alter the metal‐binding characteristics of the supporting substratum and influence metal partitioning. The interdependent behavior of toxic trace metal partitioning and biofilm development requires description of the interaction between cell growth with its accompanying polymer production and metal speciation. In this article, the first of a two part series, a mechanistic model is developed to describe the growth of a film‐forming bacterium which adheres to a substratum through the production of extracellular biopolymers. Each bacterial cell was modeled as a two‐component structure consisting of active cell mass and biopolymer. The biopolymer component was further divided into cell‐associated and dissolved categories to distinguish which remained naturally bound to cell surfaces from that which did not. Use of this structured model permitted independent description of the dynamics of cell growth, and polymer production, both of which may influence trace metal behavior. Employing parameters obtained from independent experiments as well as published values, the model satisfactorily predicts experimental observations of bacterial growth, attachment and detachment, biopolymer production, and adsorption of polymer onto solid (glass) surfaces. The model stimulated transient and steady‐state biofilm systems equally well. In the second article in this series, we describe how this model may be extended and utilized to make predictions of the behavior of transient and steady‐state biofilm systems in the presence of a toxic transition metal(Pb). © 1994 John Wil

ISSN:0006-3592    

DOI:10.1002/bit.260440211

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

年代:1994

数据来源: WILEY