摘要:

AbstractIn a continuous fermentation, significant advantages may be gained by immobilization of microbial cells. Immobilization allows cells to be retained in the fermenter or to be readily recovered and recycled. Therefore, the hydraulic retention time and the biomass retention time are decoupled. A novel cell immobilization has been developed for the immobilization of autotrophic bacteria by coculture with floc‐forming heterotrophic bacteria with growth of the latter limited by the availability of organic carbon. The result is an immobilization matrix which grows along with the immobilized autotroph. We have previously demonstrated the utility of this approach by immobilizing the chemoautotrophThiobacillus denitrificansin macroscopic floc by coculture with floc‐forming heterotrophs from an activated sludge treatment facility. Floc with excellent settling characteristics were produced. These floc have now been used to remove H2S from a gas stream bubbled through continuous cultures. The stoichiometry and kinetics of H2S oxidation by immobilizedT. denitrificanswere comparable to that reported previously for free‐cell cultures. Oxygen uptake measurements indicated the growth of bothT. denitrificansand the heterotrophs although the medium contained no added organic carbon. Continuous cultures with total biomass recycle were maintained for up to four months indicating the long‐term stability of the commensal relationship between the immobilized autotroph and the heterotrophs which composed the immobilization matrix. It was observed that at any given H2S loading the biomass concentration reached a maximum and leveled out. The ultimate biomass concentration was dependent upon the H2S fe

ISSN:0006-3592    

DOI:10.1002/bit.260370602

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe effect of interfacial surfactant molecules on oxygen transfer through oil/water phase boundary has been studied in FlurO2TMemulsions, i.e., perfluorocarbon (PFC) emulsions developed as oxygen carriers in cell culture. Measurements of oxygen permeability were made with a polarographic oxygen electrode in pure PFCs and in emulsions with various PFC volume fractions. Comparison of the experimental results with the theoretically derived values of relative oxygen permeability clearly indicates that the mass transfer resistance caused by the interfacial surfactant layer in PFC emulsions is insignificant. Therefore, oxygen dissolved in the enclosed PFC phase is readily available to cells growing in the aqueous media and FlurO2emulsions with very fine emulsion particles (<0.2 μm) can be used to effectively enhance gas/liquid interfacial oxygen transfer in bioreactors. The inadequacy in describing mass transfer in heterogeneous systems, such as the PFC emulsions, by conventional concentration‐based oxygen diffusion coefficients has also been discuss

ISSN:0006-3592    

DOI:10.1002/bit.260370603

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

年代:1991

数据来源: WILEY

摘要:

AbstractPseudomonas putidabiofilms were developed on and biofilm accumulation rate data were obtained for the following two classes of support materials: charged surfaces and noncharged hydrophobic and hydrophilic surfaces. The effects of surface roughness and porosity on the rate of microbial attachment were also examined.Materials bearing a net positive or negative surface charge supported the greatest biofilm accumulation and the highest biofilm accumulation rate. Uncharged hydrophobic materials achieved the next greatest biofilm accumulation, averaging approximately 50% of the total biomass which was accumulated on the charged surface materials after 16 days. Uncharged hydrophilic materials supported very little biofilm development. In general, biofilm accumulation increased with decreased surface roughness. The effect of pore size on biofilm accumulation was not conclusive.The biofilm accumulation kinetics showed an exponential accumulation rate for the charged surfaces and an approximately linear accumulation rate for the hydrophobic materials. This difference in accumulation kinetics is consistent with proposed differences in the physicochemical mechanism governing attachment to these two types of surface materials.

ISSN:0006-3592    

DOI:10.1002/bit.260370604

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

年代:1991

数据来源: WILEY

摘要:

AbstractSynthesis of N‐CBZ‐(N‐Carbobenzoxy)‐1‐amino‐acid methyl esters from N‐CBZ‐amino acids and methanol has been used as an assay to examine the properties of papain in organic solvents containing small amounts of water. Papain is active in solvents ranging in polarity from acetonitrile to tetrachloromethane. The optimal activity in each solvent varied only about three to four fold, but the amount of added water required to achieve it varied from 4% (v/v) in acetonitrile to 0.05% (v/v) in tetrachloromethane. The enzyme was generally more stable in hydrophobic solvents and at lower water contents. The apparentKmvalue of CBZ‐glycine was 26 times higher in acetonitrile than in toluene due to differential partitioning of the substrate between aqueous and organic phases. The substrate specificity of the enzyme was qualitatively little different from that in aqueous solution, with amino acid derivatives still the best substrates. Nitrile analogs of substrates inhibited the enzyme, as they do in aqueous solution, and inhibition by a variety of substituted aromatic hydrocarbons showed that the main specificity of papain for hydrophobic side chains at its S2subsite, was little affected. The results show that papain can catalyze reactions under a variety of conditions in organic solvents but its substrate specificity is little changed from that

ISSN:0006-3592    

DOI:10.1002/bit.260370605

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

年代:1991

数据来源: WILEY

摘要:

AbstractMaintenance of high cell viability was the main characteristic of our new strains of thermotolerantSaccharomyces.Total sugar conversion to ethanol was observed for sugarcane juice fermentation at 38–40°C in less than 10 h and without continuous aeration of the culture. Invertase activity differed among the selected strains and increased during fermentation but was not dependent on cell viability. Invertase activity of the cells and optimum temperature for growth, as well as velocity of ethanol formation, were dependent on medium composition and the type of strain used. At high sugarcane syrup concentrations, the best temperature for ethanol formation by strain 781 was 35°C. Distinct differences among the velocities of ethanol production using selected strains were also observed in sugarcane syrup at 35

ISSN:0006-3592    

DOI:10.1002/bit.260370606

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe effect of surface properties on the adsorption of bovine γ‐globulin, a model protein for antibody, was studied. Polystyrene latex (PS), hydrophilic copolymer lattices of styrene/2‐hydroxyethyl methacrylate [P(S/HEMA)], styrene/ methacrylic acid [P(S/MAA)]and methyl methacrylate/ 2‐hydroxyethyl methacrylate [P(MMA/HEMA)], and colloidal silica were used. The adsorption isotherms of γ‐globulin on these colloidal particles were measured as a function of pH and ionic strength. The hydrophilic particles showed low affinities for γ‐globulin at alkaline pH, while PS showed high affinities for γ‐globulin over the whole range of pH and ionic strength. The γ‐globulin adsorption on hydrophilic particles was highly reversible with respect to the pH and ionic strength compared with that on PS. These differences indicate that the dominant driving forces of adsorption are related to the hydrophilicity of particles. The adsorption isotherms of all colloidal particles showed the plateau values, and the order of maximum values of plateau adsorption was P(S/MAA)>PS or P(S/HEMA), silica>P(MMA/HEMA). Thus, they were also affected by the charged groups and the hydrophilicity of the surfaces. On the other hand, the plateau values of all colloidal particles were more or less symmetrical with a maximum at around the isoelectric point of γ‐globulin at an ionic strength of 0.01. This behavior is attributed to the important role of the lateral interaction between the adsorbed molecules

ISSN:0006-3592    

DOI:10.1002/bit.260370607

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe use of immobilization in extractive lactic acid fermentation byLactobacillus delbrueckiiis preferred. In this article, the mathematical simulations to examine the influences of substrate and product transport were performed to assess the overall performance. The simulations showed that transport of the substrate ink‐carrageenan beads was not a rate limiting factor. However, the model observed significant buildup of inhibitory product in large beads. The model was validated through comparisons with the experimental results. Finally, the model was used to predict the performance of the extractive fermentation under different operating strategie

ISSN:0006-3592    

DOI:10.1002/bit.260370608

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe DEAE‐cellulose linked cells ofMethylosinus trichosporiumdisplaying high specific methane mono‐oxygenase activity (66 μmol methane oxidized/h mg cells) were used for methanol biosynthesis from biogas derived methane in a batch and a continuous cell reactor. The optimum cell‐to‐carrier ratio was determined to be 0.5 g cells/g dry weight cellulose. Batch experiments indicated that 100 mMphosphate ion concentration was necessary to inhibit further oxidation of methanol; excess oxygen supply favored methanol accumulation with an increase in methane conversion efficiency to 27%. A pulse of 40 mMsodium formate at the end of 6 h resulted in restoration of methanol accumulation by regenerating NADH2required for the sustained activity of methane mono‐oxygenase. Maximum methanol level of 50 μmol/mg cells was obtained in the batch reactor. In a standard 50‐mL ultrafiltration continuous reactor, the covalently linked cells produced methanol at a continuous rate of 100 μmol/h for the first 10 h, after which the methanol accumulation rate fell low due to the depletion of NADH2. The methanol accumulation could be stimulated by supplying sodium formate (40 mM) in either 20 or 100 mMphosphate buffer. Maximum methanol accumulation rate of 267 μmol/h was obtained when 20 mMformate was supplied in the feed stream containing 100 mMphosphate ions, and this level of biosynthesis was maintained for over 72 h. The stoichiometric balance made at various points of formate addition indicated that the molar amount of methanol generated at steady state is dependent on the equimolar addition of sodium formate to the feed. The half‐lifet1/2and thermal denaturation rate constant Kdwere computed to be 108 h and 6.42 × 10

ISSN:0006-3592    

DOI:10.1002/bit.260370609

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe effect of various operating variables such as initial inoculum circulation, dilution rate, chemical oxygen demand (COD) loading rate, and quantity and quality of inoculum on the process of film formation on sand surface and reactor performance were studied using synthetic glucose based wastewater. It was found that the film formation process is favored by a high dilution rate, a large quantity of inoculum, and an inoculum having high methane producing capacity. Experimental observations indicate that the biofilm formation process is initiated by methanogenic bacteria.

ISSN:0006-3592    

DOI:10.1002/bit.260370610

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

年代:1991

数据来源: WILEY

摘要:

AbstractBatch fermentation kinetics of xanthan gum production from glucose byXanthomonas campestrisat temperatures between 22°C and 35°C were studied to evaluate temperature effects on cell growth and xanthan formation. These batch xanthan fermentations were modeled by the logistic equation for cell growth, the Luedeking–Piret equation for xanthan production, and a modified Luedeking–Piret equation for glucose consumption. Temperature dependence of the parameters in this model was evaluated. Growth‐associated rate constants increased to a maximum at ∼30°C and then decreased to zero at ∼35°C. This temperature effect can be modeled using a square‐root model. On the contrary, non‐growth‐associated rate constants increased with increasing temperature, following the Arrhenius relationship, in the entire temperature range studied. The model developed in this work fits the experimental data very well and can be used in a simulation study. However, due to the empirical nature of the model, the parameter values need to be reevaluated if the model is to be applied to differen

ISSN:0006-3592    

DOI:10.1002/bit.260370611

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

年代:1991

数据来源: WILEY