摘要:

AbstractBy feeding ethanol at various high rates to low cell density cultures ofSaccharomyces cerevisiaeit was shown that the sharp fall in viability when ethanol is produced during rapid fermentations is in part a direct consequence of the high rate of change of extracellular ethanol concentration. Nevertheless, the fall in viability in high cell density rapid fermentations which produced 98 g L−1ethanol in 3 h considerably exceeded that of control low cell density cultures to which ethanol was added at the same rate. This difference was shown to be not due to intracellular ethanol accumulation or to differences in glucose concentration between the cultures. The concentrations of a range of potentially toxic fatty acids, higher alcohols, and esters were measured during rapid fermentations, but when added at these concentrations to control cultures in the presence of ethanol they had no significant toxic effect. However, when rapid fermentations were conducted in rich medium containing 80 g L−1yeast extract, the apparent difference in toxicity of produced and added ethanol virtually disappeared. Magnesium was shown to be the component of yeast extract primarily responsible for this effect. The high rate of fall of viability when ethanol is rapidly produced is suggested to be partly due to the inability of the cells to adapt quickly enough to the rising ethanol concentration and partly to an increased demand for magnesium at higher ethanol concentrations which cannot be met in Mg‐unsupplemented high cell density fermenta

ISSN:0006-3592    

DOI:10.1002/bit.260350202

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

年代:1990

数据来源: WILEY

摘要:

AbstractA carrier‐mediated counter transport process is proposed to separate and to purify an amino acid produced by microbial fermentation. The case ofL‐valine permeation through a liquid membrane, constituted by a solution of Aliquat 336 in decanol and supported by a hydrophobic microporous membrane, is reported. A mathematical model was developed to estimate distribution coefficients and permeabilities and to predict the influence of hydrodynamic and pH conditions on supported liquid membrane (SLM) performances. Optimum conditions for the transport and the concentration of valine were achieved with synthetic aqueous valine solutions. Series of experiments on fermentation broths, where molasses and biomass contents were varied, permitted pointing out the role of the broth composition on the kinetics and yields of separation. The selectivity of transport of valine by an Aliquat 336/decanol liquid membrane was about 10 toward molasses dyes, 100 toward glucose, and beyond 1000 toward sucrose. This allowed us to achieve the recovery and one step of purification of the product in a single operation. The stability of the Aliquat 336/decanol liquid membrane was sufficient to ensure a selective transport of valine during a continuous run lasting 18 d

ISSN:0006-3592    

DOI:10.1002/bit.260350203

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

年代:1990

数据来源: WILEY

摘要:

AbstractSix different types of materials including PVC, chitosan, chitin, agarose, Sepharose, and Trisacryl were evaluated for their lipase‐coupling efficiencies. Among those tested, chitosan yielded the highest amount of lipase (79 mg/mL packed gel) immobilized but with lowest oil hydrolytic activity (0.03 mg eq/mL gel). The amount of lipase immobilized was affected by the length of the hydrocarbon chain attached to the PVC matrix but not by the pore size of the supports used. On the other hand, the specific activity of the immobilized lipase was affected by the pore size but not by the chain length of the hydrocarbon attached to the support. After immobilization, the optimal reaction pH was shifted from 7.5 to 8.5 and the optimal reaction temperature from 35 to 45‐55°C. Lipase immobilized on PVC exhibited higher thermal stability than that on agarose. The half‐life of the PVC immobilized lipase operating at 30°C in a packed‐bed reactor was estimated to be ab

ISSN:0006-3592    

DOI:10.1002/bit.260350204

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

年代:1990

数据来源: WILEY

摘要:

AbstractPirt's maintenance model has been widely accepted for the effects of growth rate and maintenance on growth yield. However, the interpretation of parameters in Pirt's model as biological constants is difficult for energy‐sufficient culture growth. In this study, a mechanistic model for the growth energetics of energy‐sufficient chemostat cultures is proposed and verified with literature data. In the model, the overutilization of the energy substrate in energy‐sufficient culture growth is attributed to the defective regulation of the energy substrate metabolism and energy uncoupling. The model also uses an “energy surplus” concept to collectively represent the effects of energy excessiveness. The proposed model provides a better quantitative understanding of the maximum growth yield and maintenance of energy‐sufficient cultures. It also explains the glucose concentration effect reported in the

ISSN:0006-3592    

DOI:10.1002/bit.260350205

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe effects of charged residues in peptide antigens on the binding characteristics of polyclonal antipeptide antibodies were studied using immunoadsorbents prepared by coupling the antibodies to CNBr‐activated Sepharose 4B. Among the antipeptide antibodies, an antibody to the peptide without charged residues showed the most stable interaction with the peptide to the changes in pH. Conversely, the binding affinity of antibodies to the pep‐tides with histidine residues having a unique pKa value of 6.0 decreased steeply with pH at around 6.0. The binding affinity of an antibody to the peptide with many charged residues decreased steeply with an increase in the ionic strength (adjusted by NaCl). Since circular dichroism (CD) spectrum measurements indicate that these peptides show disordered structures in the pH range of adsorption measurement, the dependence of peptide‐antibody interaction on environmental conditions is attributed to the characteristics of side chains of the peptides. These results indicate that the dependence of the binding affinity of antipeptide antibodies on pH and the ionic strength is dominantly affected by the number and the pKa values of charged residues in the pep

ISSN:0006-3592    

DOI:10.1002/bit.260350206

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

年代:1990

数据来源: WILEY

摘要:

AbstractArthrobacter simplexcells, which convert the steroid hydrocortisone to prednisolone, have been entrapped in a thermally reversible hydrogel. Such hydrogels exhibit a lower critical solution temperature (LCST) wherein the gel shrinks and deswells when it is warmed through its LCST, and then reversibly expands and reswells when it is cooled below the LCST. The immobilized cell‐hydrogel system has been thermally cycled between two temperatures, each below the LCST. The upper temperature was selected to be just below the LCST, where the gel deswells but does not collapse, as it does at the LCST. The thermal cycling acts like a “hydraulic pump” which enhances mass transfer of the substrate (hydrocortisone) in and the product (prednisolone) out of the gel, thereby increasing steroid conversion dramatically relative to isothermal operation at either the upper or lower temperature. The increased conversion can also be due in part to reduced product inhibition. Mass transfer resistance and product inhibition are among the most serious problems in immobilized biocatalyst technology and thermal cycling of LCST hydrogels is both a novel and useful approach to minimizing these pro

ISSN:0006-3592    

DOI:10.1002/bit.260350207

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

年代:1990

数据来源: WILEY

摘要:

AbstractA mathematical model for the growth process of the bacteriumBacillus subtilisis described. The model is a highly structured one. The driving motivation for development of the model and explicit accounting of major interactions of metabolic networks in the model is related to our eventual goal that the model will be used in the analysis of complex biological patterns.Bacillus subtiliswas chosen in our study due to the interesting sporulation process that these cells undergo in response to adverse environmental conditions including nutrient limitation. Sporulation process inB. subtilisrepresents a primordial prototype of cellular differentiation in higher cellular systems. Thus a model for theB. subtilisgrowth process should prove extremely useful for understanding questions of developmental biology. The model is capable of simulating the transition between the exponential and stationary phase of growth in a batch culture. Since during the transition period the growth process and the metabolism become decoupled and many transient processes are taking place, such predictions are a severe test for the validity of any model. A strategy to examine the leading hypothesis onB. subtillssporulation implementing GTP as a component which signals sporulation initiation is described.

ISSN:0006-3592    

DOI:10.1002/bit.260350208

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

年代:1990

数据来源: WILEY

摘要:

AbstractA mathematical model of the tryptophan operon is analyzed to investigate the regulatory effects of feedback repression and the demand for tryptophan in the cell. In this model, feedback repression is considered to be a two‐step process. First, the endproduct tryptophan combines with the inactive repressor produced by the regulatory genes to yield an active complex. This complex subsequently binds to the operator and prevents transcription of the structural genes into mRNA. The demand for tryptophan in the cell is modeled by a hyperbolic saturation function of the Michaelis‐Menten type. Results are obtained for the expression of the tryptophan operon inEscherichia coliand their applicability to tryptophan production by microbial fermentation is discussed. It is shown that, depending on the strain level of the operon and the rate of utilization of tryptophan in the cell, an overproduction of tryptophan can be achieved under stable operating conditions; in other circumstances, the operon may become stable or unstable, and may lead to a periodic synthe

ISSN:0006-3592    

DOI:10.1002/bit.260350209

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

年代:1990

数据来源: WILEY

摘要:

AbstractImmobilizedMucor mieheilipase catalyzes synthesis reactions between glycerol and oleic acid. No organic solvent is necessary to solubilize the substrates, which allows for the use of a reaction medium solely composed of the necessary substrates. Water produced in the reaction evaporates due to the high temperature used for the process. A conversion of 86% of oleic acid into triolein is obtained when using the substrates in stoichiometric amounts. Varying the ratio of glycerol over oleic acid allows for the preferential synthesis of one of the glycerides. Some batch reactors have been set up using different means of removing the water: spontaneous evaporation, molecular sieves, vacuum, and dry air bubbling.

ISSN:0006-3592    

DOI:10.1002/bit.260350210

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe fermentation of glucose by a strain ofSaccharomyces cerevisiaewas studied in a continuous single‐stage process with recycle of the cells via cross‐flow micro‐filtration membranes. Operating conditions were selected such that the culture was not carbon limited and inhibition by ethanol and cell death were minimized.Steady states were obtained for various biomass bleeding rates, i.e., various specific growth rates. From the experimental data, the stoichiometry of the simultaneous reactions, cell growth, ethanol production and maintenance were established using mass and degree of reduction balance relative to substrates (carbon source and oxygen) and products (biomass, ethanol, carbon dioxide etc.), and the growth parameters, yields, and maintenance cofficients were determined. It was shown that the oxygen consumption was not linked to the kinetics of the fermentation. The calculated growth constants were discussed and compared to the currently reported v

ISSN:0006-3592    

DOI:10.1002/bit.260350211

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

年代:1990

数据来源: WILEY