摘要:

AbstractThe mode ofn‐hexadecane uptake by two organisms—PseudomonasM 1 andPseudomonasN 1—was studied. During the growth ofPseudomonasM 1 onn‐hexadecane, no extracellular biosurfactant/bioemulsifier was produced, no significantn‐hexadecane pseudosolubilization was observed, and the reduction of surface and interfacial tensions in the cell‐free culture broth was negligible. EDTA, a known inhibitor of hydrocarbon pseudosolubilization, did not inhibit the growth of the organism onn‐hexadecane. Normal hexadecane‐grown cells showed strong surface‐active properties and capacity to adhere firmly to hydrocarbon phase. It was concluded that in this organism, surface‐active properties of the cells facilitate attachment of cells to the hydrocarbon–water interface generated by agitation, and promote substrate uptake and growth; no hydrocarbon pseudosolubilization or extracellular mediator is involved in the substrate uptake.PseudomonasN 1 grew onn‐hexadecane much faster thanPseudomonasM 1. Growth of this organism onn‐hexadecane was associated with the extracellular production of biosurfactant–bioemulsifier andn‐hexadecane pseudosolubilizing factor; the growth was strongly inhibited by 5 mMEDTA, indicating that hydrocarbon pseudosolubilization was the dominant factor in substrate uptake. The rate ofn‐hexadecane pseudosolubilization was high enough to account for the substrate up take rate. Hydrocarbon emulsifying andn‐hexadecane pseudosolubilizing factors were isolated and tentatively characterized as lipoprotein and glycoprotein, respectively. Both factors act in a synergistic manner to provide enhanced hydrocarbon transport to cells through pseudosolubilization. It is proposed that this facility of mediated hydrocarbon transport is the basis for the relatively fast rate of growt

ISSN:0006-3592    

DOI:10.1002/bit.260370103

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe ability ofL‐sorbose to stimulate cellulase production In shake flask culture ofTrichoderma reeseiwas examined in mineral salts media (initial pH 5.0) containing either 1.0%D‐xylose, 1.0% cellulose, and/or 0.1, 0.3, or 0.5%L‐sorbose. When sorbose was the only carbon source, growth was limited, little substrate was utilized, pH increased, and cellulase activity was not apparent. The other carbon sources promoted good growth, pH dropped sharply to 2.5–3.0, substrate was utilized rapidly, and cellulase activity was detected. After three weeks of fermentation, twice as much cellulase activity was detected in the medium containing only cellulose as the carbon source, as compared to xylose as the carbon source. Cellulase activity was higher when media contained xylose supplemented with sorbose compared to xylose as the only carbon source. At 0.3 and 0.5% levels of sorbose supplementation of xylose‐based media, cellulase activity was similar to that in cellulose‐

ISSN:0006-3592    

DOI:10.1002/bit.260370104

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

年代:1991

数据来源: WILEY

摘要:

AbstractBacterial biofilm removal processes due to shear and catastrophic sloughing have been investigated in a turbulent flow system under conditions of carbon versus oxygen substrate limitations and varying aqueous phase calcium concentrations. Biofilm cellular and extracellular polymer carbon, total biofilm carbon and mass, and biofilm calcium concentrations are measured for pure culture biofilms of the facultative aerobe,Pseudomonas putidaATCC 11172. Results indicate oxygen‐limited biofilms reach a higher steady‐state biofilm organic carbon level than carbon‐limited biofilms. Oxygen‐limited biofilms also exhibit (1) a higher extracellular polymer‐carbon: cell‐carbon ratio throughout biofilm development and (2) a higher biofilm calcium content than carbon‐limited biofilms. Increasing aqueous phase calcium concentrations increase the amount of biofilm calcium in both cases; the rate of calcium accumulation in oxygen‐limited biofilms increases with increasing liquid phase calcium concentrations over the entire range studied while the rates of calcium accumulation in carbon‐limited biofilms appear independent of aqueous phase calcium concentrations above 11.0 mg/L. Oxygen‐limited biofilms with their higher extracellular polymer and calcium content exhibit shear removal rates that are 20–40% of those observed for carbon‐limited biofilms. However, it is the oxygen‐limited biofilms that experience catastrophic sloughing events. The carbon‐limited biofilms studied here never sloughed even if subjected to intentional long‐term deprivation of all nutrients. Reduced shear removal and the susceptibility to sloughing of the oxygen‐limited biofilms are attributed to their more cohesive structure bought about by their relatively greater e

ISSN:0006-3592    

DOI:10.1002/bit.260370105

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

年代:1991

数据来源: WILEY

摘要:

AbstractAn alternative to estimation of cell growth kinetics via continuous culture experiments is proposed in this article. The method employed is based on batch culture experiments with very small inocula (initial cell concentrations being typically less than 5000 cells/mL). Such low initial cell concentrations result in extended exponential cell growth phase during which culture conditions remain unchanged, thereby permitting precise estimation of specific cell growth rates from batch experiments especially for fast‐growing microorganisms such asBacillusspecies. The effectiveness and utility of this approach are demonstrated via several experiments conducted with a wild‐type strain (Bacillus subtilisTN106) and a recombinant strain (B. subtilisTN106[pAT5]). True establishment of exponential growth phase requires insignificant variance of most of the culture conditions during the initial growth phase. Satisfaction of this requirement is demonstrated for microbial systems investigated here. This approach is especially well suited for recombinant microorganisms containing segregationally unstable plasmids, since estimation of growth kinetics of these from continuous cultures is very difficult and highly unreliable due to continual reversion of recombinant ceils to plasmid‐free host cells unless some selection pressure is applied at levels sufficient to keep the presence of plasmid‐free cells

ISSN:0006-3592    

DOI:10.1002/bit.260370106

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

年代:1991

数据来源: WILEY

摘要:

AbstractTwo murine hybridoma cell lines (167.4G5.3 and S3H5/γ2bA2) were adapted to grow in low‐serum and serum‐free media by a weaning procedure. The changes in cell growth, metabolic, and antibody production rates with adaptation were examined using biochemical and flow cytometric analyses. After adaptation to a particular serum level, the short‐term serum response of the cells was experimentally determined. Specific growth rates, glucose and glutamine uptake and lactate and ammonia production rates, and specific antibody production rates were evaluated from the data. For both cell lines, an improvement in cell growth was observed after adaptation, and both higher growth rates and higher cell concentrations were obtained. The specific glucose and glutamine uptake rates and the lactate and ammonia production rates changed insignificantly with adaptation. Conversely, changes in the specific antibody production rate of the two cell lines differed. Cell line 167.4G5.3 showed a loss in antibody productivity at low serum levels, while the S3H5/γ2bA2 kept its original productivity in low‐serum‐containing media. The intracellular antibody content for S3H5/γ2bA2 cells remained unaltered by adaptation, but a low antibody containing cell population appeared in the 167.4G5.3 culture. The loss of specific antibody productivity in this cell line was due to the appearance of thi

ISSN:0006-3592    

DOI:10.1002/bit.260370107

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

年代:1991

数据来源: WILEY

摘要:

AbstractPlasmid‐encoded mercuric reduction involves transfer of Hg2+across the cellular envelope and reduction to Hg0by the cytoplasmic mercuric reductase using NADPH. A mathematical model was developed for the binding and transfer of Hg2+by transport proteins and the subsequent reduction of Hg2+. The values of the model parameters were determined using experimental data. The derived rate expressions were similar to the previously experimentally determined ones. The model predicted that a differential amplification of the transport protein relative to mercuric reductase expression levels may enhance the Hg2+reduction rate in whole cell

ISSN:0006-3592    

DOI:10.1002/bit.260370108

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe kinetic behavior of a nonproducing hybridoma clone AFP‐27‐NP was investigated in continuous culture under glucose‐limited conditions. A total of more than 21, 000 h of cultures were operated at dilution rates ranging from 0.01 to 0.06 h−1. The viable cell concentrations, dead cell concentrations, and cell volumes all varied with the dilution rate. A steady‐state model was developed based on the biomass concentration and the glucose concentration. The specific growth rate as a function of glucose concentration is described by a model similar to the Monod model with a threshold glucose concentration and a minimum specific growth rate incorporated; the model is meaningful only at glucose concentrations and specific growth rates above these levels. A death rate is included in the model which is described by an inverted Monod‐type function of glucose concentration. The yield coefficient based on glucose is constant in the lower range of specific growth rates and changes to a new constant value in the upper region of specific growth rates. No maintenance term for glucose consumption was needed; in the plot of specific glucose consumption rate vs. specific growth rate, the line intercepted the specific growth rate axis at a value close to the minimum growth rate. The values for the model parameters were determined from regression analysis of the steady‐state data. The model predictions and experimental results

ISSN:0006-3592    

DOI:10.1002/bit.260370109

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe effect of isotherm parameters of a displacer on the efficiency of desorption Chromatography has been investigated numerically. A general nonlinear multicomponent rate equation model with Langmuir isotherm was used in this study. It was found that the best displacer in this kind of operation is usually not the one that is more strongly adsorbed than the adsorbates when the operation is to displace and concentrate the adsorbates from a saturated or partially saturated column and to minimize the amount of displacer used. The desorption Chromatography is different from the classical displacement development in both operational purpose and the requirement for the displacer. The desorption Chromatography in industrial practice was also analyzed and discussed for the case in which the displacer is introduced in either the same or the reverse flow direction after an incomplete frontal adsorption operation.

ISSN:0006-3592    

DOI:10.1002/bit.260370110

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

年代:1991

数据来源: WILEY

摘要:

AbstractEscherichia coliHB101 harboring an expression plasmid that bears the calf prochymosin gene controlled by thetacpromoter was cultivated under different conditions in order to find an optimal fermentation arrangement that would lead to maximal prochymosin yield. Our results indicate that it is advantageous to use lactose in the double role of inducer and carbon/energy source when foreign gene expression is controlled by thetacpromoter and the gene product is only moderately toxic owing to its accumulation in the form of an intracellular body. Glucose, on the other hand, may be used when expression should be repressed. Growth temperature substantially influenced the specific rate of prochymosin and β‐lactamase gene expression and the plasmid copy number. Three phases were distinguished in the time course of the fermentation on lactose: exponential growth practically without prochymosin synthesis, linear growth with prochymosin synthesis, and prochymosin synthesis without growth of biomass. The synthesis of prochymosin in the form of intracellular inclusion body was accompanied by the loss of respiratory activity of the cell and the loss of its ability to multiply. Sixteen hours cultivation at 37°C in a complex medium with lactose as inducer and carbon/energy source resulted in up to 30% of the volume and 48% of the total protein of biomass being accumulated for as prochymosin inclusion bodies. The concentration of extractable enzymatically active chymosin in the culture reached 12

ISSN:0006-3592    

DOI:10.1002/bit.260370111

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

年代:1991

数据来源: WILEY

摘要:

AbstractAxial and radial oxygen depletion are believed to be critical scale‐limiting factors in the design of cell culture hollow fiber bioreactors. A mathematical analysis of oxygen depletion has been performed in order to develop effectiveness factor plots to aid in the scaling of hollow fiber bioreactors with cells immobilized in the shell‐side. Considerations of the lumen mass transport resistances and the axial gradients were added to previous analyses of this immobilization geometry. An order of magnitude analysis was used to evaluate the impact of the shell‐side convective fluxes on the oxygen transport. A modified Thiele modulus and a lumen and membrane resistance factor have been derived from the model. Use of these terms in the effectiveness factor plots results in a considerable simplification of the presentation and use of the model. Design criteria such as fiber dimensions and spacing, reactor lengths, and recycle flow rates can be selected using these plots. Model predictions of the oxygen limitations were compared to experimental measurements of the axial cell distributions in a severely oxygen limited hollow fiber bioreactor. Despite considerable uncertainty in our parameters and nonidealities in hollow fiber geometry, the cell distribution correlated well with the modeling re

ISSN:0006-3592    

DOI:10.1002/bit.260370112

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

年代:1991

数据来源: WILEY