bluuebunny/crossref_metadata_2025_split huggingface dataset:
A modeling study of anaerobic biofilm systems: I. Detailed biofilm modeling
Authors: Flora Joseph R. V. , Suidan Makram T. , Biswas Pratim , Sayles Gregory D. 
Published: December 2004

AbstractA detailed model acetate‐utilizing methanogenic biofilms accounting for the diffusion of neutral and ionic species, chemical equilibrium, electroneutrality, gas production within the biofilm, pH‐dependent Monod kinetics, and the presence of a concentration boundary layer is presented. The model qualitatively fits the pH profiles that are reported for acetate‐utilizing methanogenic aggregates. A sensitivity analysis on the biological parameters showed that the flux of acetate is sensitive to the maximum utilization rate, half‐saturation constant, and biofilm density for the bulk conditions investigated. Criteria when traditional biofilm models can be used to predict the flux of acetate into the biofilm are established. If the maximum pH change predicted using a hypothetical system is within ±0.05, the traditional model predicts the flux to within ±5% of the value calculated with the model developed in this study. © 1995 John Wiley & Sons, Inc.
Degradation of quinoline by immobilized Comamonas acidovorans in a three‐phase airlift reactor
Authors: Ulonska A. , Deckwer W.‐D. , Hecht V. 
Published: December 2004

AbstractQuinolie degradation by Comamonas acidovorans was studied in a continuously operated three‐phase airlift reactor. Porous glass beads were applied as support matrix for cell imobilization by colonization. Under steady‐state conditions (S ∼ 0), cell attachment was poor at low dilution rates but imporved considerably with increasing dilution rate. Conversion of quinoline was investigated below and above the washout for suspended culture (Dcrit = μmax = 0.42 h−1). With immobilized cells the reactor could be operated at D > μmax, and complete conversion of quinoline was achieved as long as the specific quinoline feed rate D*S0/X did not exceed the maximum specific degradation rate (rS, max). The biofilm thickness was about 100 μm, and its efficiency was about 54% compared to suspended organisms. If quinoline overloads were supplied to the reactor, quinoline, as overloads were supplied to the reactor, quinoline, as well as its pathway intermediates, appeared in the reactor and conversion was low. Hence, the immobilized microorganisms remained viable and active. They could survive quinoline overloads. If the quinoline feed rate was reduced agains, complete conversion was reestablished. © 1995 John Wiley & Sons, Inc.
Photochemistry of a photosynthetic reaction center immobilized in lipidic cubic phases
Authors: Hochkoeppler Alejandro , Landau Ehud M. , Venturoli Giovanni , Zannoni Davide , Feick Reiner , Luisi Pier Luigi 
Published: December 2004

AbstractPhotosynthetic reaction centers, isolated and purified from the facultative phototrophic bacterium Chloroflexus aurantiacus, were immobilized in optically transparent lipidic cubic phases composed of 42% (w/w) 1‐palmitoyl‐2‐hydroxy‐sn‐glycero‐3‐phosphocholine and 58% (w/w) water. The immobilized photosynthetic protein retains its native properties, as indicated by visible and circular dichroic spectra. The ground state visible spectrum of the immobilized reaction centers is very similar to the corresponding spectrum in aqueous solution, indicating that the protein pigments are not extracted into the lipidic regions of the cubic phase. The secondary structure of the protein is maintained in the immobilized state, as determined by far‐UV circular dichroism spectroscopy in the 200‐ to 250‐nm range. Moreover, immobilized reaction centers retain their photochemical activity: a reversible photo‐oxidation of the primary electron donor (P) is seen upon continuous illumination. Furthermore, the entrappment of reaction centers does not affect the kinetics of charge recombination between the photo‐oxidized primary donor (P+) and the photoreduced primary quinone acceptor, generated by a short flash of light. Reaction centers devoided of the secondary quinone acceptor can be easily reconstituted in cubic phases by means of their coimmobilization with 1,4‐naphtoquinone. Indeed, the kinetics for charge recombination in reconstituted reaction centers is dramatically slower than the corresponding kinetics in the unreconstituted protein. Interestingly, immobilized reaction centers are significantly stabilized as compared with reaction centers in aqueous solution: the integrity of the protein in the cubic phase is maintained for at least 5 months, whereas in water solution 50% of the activity is lost within 2 months. © 1995 John Wiley & Sons, Inc.
Heterogeneity within populations of recombinant Chinese hamster ovary cells expressing human interferon‐γ
Authors: Coppen Steven R. , Newsam Ray , Bull Alan T. , Baines Anthony J. 
Published: December 2004

AbstractThe Chinese hamster ovary (CHO) cell line has great commercial importance in the production of recombinant human proteins, especially those for therapeutic use. Much attention has been paid to CHO cell population physiology in order to define factors affecting product fidelity and yield. Such studies have revealed that recombinant proteins, including human interferon‐γ (IFN‐γ), can be heterogeneous both in glycosylation and in proteolytic processing. The type of heterogeneity observed depends on the growth physiology of the cell population, although the relationship between them is complex. In this article we report results of a cytological study of the CHO320 line which expresses recombinant human IFN‐γ. When grown in suspension culture, this cell line exhibited three types of heterogeneity: (1) heterogeneity of the production of IFN‐γ within the cell population, (2) heterogeneity of the number of nuclei and mitotic spindles in dividing cells, and (3) heterogeneity of cellular environment. The last of these arises from cell aggregates which form in suspension culture: Some cells are exposed to the culture medium; others are fully enclosed within the mass with little or no direct access to the medium. Thus, live cells producing IFN‐γ are heterogeneous in their environment, with variable access to O2 and nutrients. Within the aggregates, it appears that live cells proliferate on a dead cell mass. The layer of live cells can be several cells deep. Specific cell–cell attachments are observed between the living cells in these aggregates. Two proteins, known to be required for the formation of certain types of intercellular junctions, spectrin and vinculin, have been localized to the regions of cell–cell contact. The aggregation of the cells appears to be an active process requiring protein synthesis. © 1995 John Wiley & Sons, Inc.
The oxidation of chiral alcohols catalyzed by catalase in organic solvents
Authors: Magner Edmond , Klibanov Alexander M. 
Published: December 2004

AbstractThe catalytic properties of bovine liver catalase have been investigated in organic solvents. In tetrahydrofuran, dioxane, and acetone (all containing 1% to 3% of water), the enzyme breaks down tert‐butyl hydroperoxide several fold faster than in pure water. Furthermore, the rate of catalase‐catalyzed production of tert‐butanol from tert‐butyl hydroperoxide increases more than 400‐fold upon transition from aqueous buffer to ethanol as the reaction medium. The mechanistic rationale for this striking effect is that in aqueous buffer the rate‐limiting step of the enzymatic process involves the reduction of catalase's compound I by tert‐butyl hydroperoxide. In ethanol, and additional step in the reaction scheme becomes available in which ethanol, greatly outcompeting the hydroperoxide, is oxidized by compound I regenerating the free enzyme. In solvents, such as acetonitrile or tetrahydrofuran, which themselves are not oxidizable by compound I, catalase catalyzes the oxidation of numerous primary and secondary alcohols with tert‐butyl hydroperoxide to the corresponding aldehydes or ketones. The enzymatic oxidation of some chiral alcohols (2,3‐butanediol, citronellol, and menthol) under these conditions occurs enantioselectively. Examination of the enantioselectivity for the oxidation of 2,3‐butanediol in a series of organic solvents reveals a considerable solvent dependence. © 1995 John Wiley & Sons, Inc.
A cometabolic kinetics model incoroporating enzyme inhibition, inactivation, and recovery: II. Trichloroethylene degradaation experiments
Authors: Ely Roger L. , Hyman Michael R. , Arp Daniel J. , Guenther Ronald B. , Williamson Kenneth J. 
Published: December 2004

AbstractA Cometabolism enzyme kinetics model has been presented which takes into account changes in bacterial activity associated with enzyme inhibitiion, inactivation, inactivation of enzyme resulting from product toxicty, and respondent synthesis of new enzyme. Although this process is inherently unsteady‐state, the model assumes that cometabolic degradation of a compound exhibiting product toxicity can be modeled as pseudo‐steady‐staate under certain conditions. In its simplified from, the model also assumes that enzyme inactivation is directly propoertional to nongrawth substrate oxidation, and that recovery is directly proportionla to growth substrate oxidation. In part 1, model drivation, simplification, and analyses were described. In this articles, model assuptiions are tested by analyzing data from experiments exmining trichloroethylene (TCE) degradation by the ammoniaoxidizing baceterium Nitrosomonas europaea in a quasisteady‐state bioreactor. Model solution results showed steady‐state bioreactor. Model solution results showed TCE to be a competitive inhibitoer of ammonia oxidation, with TCE affinity for ammonia monooxygenase (AMO) being about four times greater than that of ammonia for the enzyme. Inhibition was independent fo TCE oxidation and occurred essentially instantly upon exposure to TCE. In contrast, inactivation of AMO occurred more gradually and was proportional to the rate and amount of TCE oxidized. Evaluation of other O2‐dependent enzymes and electron transport proteins suggested that TCE‐related damage was predominantly confined to AMO. In response to inhibition and/or inactivation, bacterial recovery was initiated, even in the presence of TCE, implying that membranes adn protein synthesis systems were functioning. Analysis of data and comparison of model results showed the inhibition/inactivation/recovery concept to provide a reasonable basis for understandign the effects fo TCE on AMO function and bacterial response. The model assumptions were verified except tht questions remain regarding the factores controlling recovery and its role in the long term. © 1995 John Wiley & Sons, Inc.
Detachment of biomass from suspended nongrowing spherical biofilms in airlift reactors
Authors: Gjaltema A. , Tijhuis L. , van Loosdrecht M. C. M. , Heijnen J. J. 
Published: December 2004

AbstractIn three‐phase internal loop airlift reactors, the detachment of biomass from suspended biofilm pellets in the presence of bare carrier particles was investigated under nongrowth conditions. The detachment rate was dominated by collisions between bare carrier particles and biofilm pellets. The concentration of bare carrier particles and the carrier roughness strongly influenced the detachment rate. A change in flow regime from bubbling to slug flow considerably increased the detachment rate. Otherwise, the superficial gas velocity did not directly affect the detachment rate. The influence of particle size was not clear. The bottom clearance did not affect the detachment rate within the tested range. Other aspects of reactor geometry might be important. The main detachment processes were abrasion and breakage of biofilm pellets. During the detachment process, two phases could be distinguished. In the first phase the detachment was relatively high, and both breakage and abrasion of biofilm pellets occurred. During the second phase, breakage dominated and the detachment rate was lower. The two‐phase behavior is explained by differences in strength between the inner and outer biofilm layers, possibly caused by variations in local growth rates during biofilm formation. Differences in growth history might also explain the various detachment rates observed with different biofilm batches. © 1995 John Wiley & Sons, Inc.
Propane‐Induced biodegradation of vapor phase trichoroethylene
Authors: Wilcox Donnell W. , Autenrieth Robin L. , Bonner James S. 
Published: December 2004

AbstractMicrobial degradation of trichloroethylene (TCE) has been demonstrated under aerobic conditions with propane. The primary objective of this research was to evaluate the feasibility of introducing a vapor phase form of TCE in the presence of propane to batch bioreactors containing a liquid phase suspension of Mycobacterium vaccae JOB5 to accomplish degradation. The reactor system consisted of three phases: a vapor phase introducing air, propane, and TCE; a liquid phase of the microbial suspension; and a solid phase in the form of the microorganisms. Long‐term and initial rate experiments were conducted on three culture sets to evaluate microbial response. In two long‐term test fed propane and approximately 0.1 mg/L and 1 mg/L of TCE, respectively, propane utilization was more efficient at the high TCE concentration (600 mmol propane/mmol TCE versus 11,900 mmol propane/mmol TCE), because the propane degradation rate was approximately the same for both tests (6.73 mg/L · h and 7.85 mg/L · h for the high and low tests). In addition, TCE utilization decreased after complete propane consumption. Initial rate tests on culture sets fed propane only revealed that cells with a history of exposure to a high concentration of TCE had the highest specific growth rate, but the lowest half‐saturation constant (7.60e−3 h−1 and 0.10 mg/L, respectively). Tests fed variable TCE concentrations (0.031 to 5.378 mg/L in the liquid phase) with no propane showed TCE depletion but no biomass growth. The tests revealed that the TCE removal increased as the TCE concentration increased, indicating a greater removal efficiency at the higher concentrations. Tests with a constant initial propane concentration and variable liquid phase TCE concentration revealed that specific propane utilization was essentially the same. © 1995 John Wiley & Sons, Inc.
Pathway engineering for production of aromatics in Escherichia coli: Confirmation of stoichiometric analysis by independent modulation of AroG, TktA, and Pps activities
Authors: Patnaik Ranjan , Spitzer Richard G. , Liao James C. 
Published: December 2004

AbstractThe synthesis of 3‐deoxy‐D‐arabino‐heptulosonate‐7‐phosphate (DAHP) is the first commitment of resources toward aromatics production in Escherichia coli. DAHP is produced during a condensation reaction between phosphoenolpyruvate (PEP) and erythrose 4‐phosphate (E4P) catalyzed by DAHP synthases (coded by aroF, aroG, and aroH). Stoichiometric analysis has shown a severe PEP limitation in the theoretical yield of DAHP production from glucose due to the phosphotransferase system (PTS) for sugar uptake. This limitation can be relieved by (i) the recycling of pyruvate from PEP using PEP synthase (Pps) or (ii) use of non‐PTS sugars such as xylose. Previous studies have shown the usefulness of overexpressing tktA (encoding transketolase), aroG, and pps (PEP synthase) for DAHP production in an aroB strain unable to utilize DAHP further. In the present study we confirm the predictions of the stoichiometric analysis by introducing pps, tktA, and aroG into vectors under independently controlled promoters. In glucose medium, although TktA has some positive effect on the final DAHP concentration, it has no effect on the yield (percent conversion). With Pps overexpression, the DAHP concentration produced from glucose is increased almost twofold and the yield is approaching the theoretical maximum, as predicted by the stoichiometric analysis. However, this Pps effect is observed only in the presence of both increased AroG and TktA. In xylose mimimal medium, the final DAHP concentration and the yield are completely determined by the AroG activity. TktA and Pps play no or insignificant roles, and the yield can reach the theoretical maximum without overexpression of these two enzymes. The results shown here are important for both rational design of metabolic pathways and industrial production of aromatics such as tryptophan, phenylalanine, indigo, quinic acid, and catechol.
Effects of subzero temperatures on the kinetics of protease catalyzed dipeptide synthesis in organic media
Authors: Jönsson Åsa , Adlercreutz Patrick , Mattiasson Bo 
Published: December 2004

AbstractA depeptide synthesis was drastically influenced by the reaction temperature, in the range from −30° to 25°C. This article shows the kinetic reasons of this effect. α‐Chymotrypsin was immobilized on celite and used in four different water‐miscible solvents containing small amounts of water‐miscible solvents containing small amounts of water. The reaction studied was the aminolysis of N‐acetyl‐L‐phenylalanine ethyl ester (Ac‐PheOEt) with L‐alaninamide (Ala‐NH2) and water for the acylenzyme complex, the nucleophile was favoured by low reaction temperatures. This effect (quantified as p‐values) was observed in all four solvents, and it was greatest in acetonitrile and tetrahydrofuran. The esterase and amidase activities of the enzyme were studies using AcPheOEt and N‐acetyl‐L‐phenylalanyl‐L‐ananinamide (AcPheAla‐NH2) as substrates. The Michaelis–Menten parameters, Km,app and Vmax, were determined for ester hydrolysis and dipeptide hydrolysis. Both Km,app and Vmax tended to increase with increasing temperature. Secondary hydrolysis was reduced at subzero temperatures because ester hydrolysis was favoured in relation to depeptide hydrolysis. Depeptide synthesis was thus favored by low temperatures in two ways: first, in the competition between the nucleophile and water for the acyl enzyme; and, second, in the competition between the ester substrate and the peptide substrate for the free enzyme. As a result, in acetonitrile containing 10% water, the maximal yield was 99% at −20%C compared with 84% at 25°C. © 1995 John Wiley & Sons, Inc.
An autoclavable glucose biosensor for microbial fermentation monitoring and control
Authors: Phelps Michael R. , Hobbs John B. , Kilburn Douglas G. , Turner Robin F. B. 
Published: December 2004

AbstractThe design, construction, and characterization of a prototype‐regenerable glucose biosensor based on the reversible immobilization of glucose oxidase (GOx) using cellulose binding domain (CBD) technology is described. GOx, chemically linked to CBD, is immobilized by binding to a cellulose matrix on the sensor‐indicating electode. Enzyme immobilization can be reversed by perfusing the cellulose matrix with a suitable eluting solution. An autocavable sensor membrane system is employed which is shown to be practical for use in real microbial fermentations. The prototype glucose biosensor was used without failure or deterioration during fed‐batch fermentations of Escherichia coli reaching a maximum cell density of 85 g (dry weight)/L. Medium glucose concentration based on sensor output correlated closely with off‐line glucose analysis and was controlled manually at 0.44 ± 0.2 g/L for 2 h based on glucose sensor output. The sensor enzyme component could be eluted and replaced without interrupting the fermentation. To our knowledge, no other in situ biosensor has been used for such an extended period of time in such a high‐cell‐density fermentation. © 1995 John Wiley & Sons, Inc.
Biofilm parameters influencing biocide efficacy
Authors: Srinivasan Rohini , Stewart Philip S. , Griebe Thomas , Chen Ching‐I. , Xu Xiaoming 
Published: December 2004

AbstractThe influence of biofilm areal cell density, species composition, and the presence of abiotic particles on the disinfection and removal of bacterial biofilms by monochloramine was investigated. Mono‐ and binary population biofilms of Pseudomonas aeruginosa and Klebsiella pneumoniae were grown on stainless‐steel slides in a continuous flow annular reactor. Biofilms were treated in the reactor with a pulse/step dose of 4 mg/L monochloramine for 2 h. Biofilm samples were disaggregated and assayed for colony formation on R2A agar and for total cell numbers by acridine orange direct counts. These data were used to determine apparent first order rate coefficients for the processes of disinfection and detachment. Disinfection rate coefficients exceeded detachment rate coefficients by as much as an order of magnitude and the two coefficients were poorly correlated (r = 0.272). The overall decay rate coefficient (disinfection plus detachment) depended strongly on the initial biofilm areal cell density. It displayed a parabolic dependence on cell density with a maximum near 108 cfu/cm2. This result points to multiple factors influencing biofilm susceptibility to antimicrobial challenge. Decay rates of K. pneumoniae measured in binary population biofilms were comparable with those measured in monopopulation biofilms (p = 0.61). P. aeruginosa decayed more slowly in biofilsm dominated by K. pneumoniae (p = 0.028), indicating some interaction between species. The presence of kaolin and calcium carbonate particles in the biofilm reduced disinfection efficacy. © 1995 John Wiley & Sons, Inc.
Synthesis of aspartame precursor with an immobilized thermolysin in mixed organic solvents
Authors: Miyanaga Masamitsu , Tanaka Takaaki , Sakiyama Takaharu , Nakanishi Kazuhiro 
Published: December 2004

AbstractN‐(benzyloxycarbonyl)‐L‐aspartyl‐L‐phenylalanine methyl ester, a precursor of the synthetic sweetener, aspartame, was synthesized from N‐(benzyloxycarbonyl)‐L‐aspartic acid and L‐phenylalanine methyl ester with an immobilized thermolysin (EC 3.4.24.4) in the mixed organic solvent system of tert‐amyl alcohol and ethyl acetate. A mixed solvent consisting of tert‐amyl alcohol and ethyl acetate at a ratio of 33:67 (v/v) was found to be the most suitable with respect to synthetic rate and stability of the immobilized enzyme. The reaction continued to proceed quite successfully in a column reactor at 40°C and at a space velocity of 3.6 h−1 with a yield of 99%, using 40 mM Z‐Asp and 200 mM PheOMe dissolved in the mixed solvent as the substrate. © 1995 John Wiley & Sons, Inc.
Transport of lactate and acetate through the energized cytoplasmic membrane of Escherichia coli
Authors: Axe Douglas D. , Bailey James E. 
Published: December 2004

AbstractEscherichia coli produces lactate and acetate in significant amounts during both aerobic and anaerobic glycolysis. A model describing the mechanism of protein mediated lactate transport has previously bee proposed. A simple theoretical analysis here indicates that the proposed model would be drain cellular energy resources by catalytically dissipating the proton‐motive force. An experimental analysis of lactate and acetate transport employ nuclear magnetic resonance (NMR) spectroscopy to measure the relative concentration of these end products on the two sides of the cytoplasmic membrane of anaerobically glycolyzing cells. Comparison of measured concentration rations to those expected at equilibrium for various transport modes indicates that acetate is a classical uncoupling agent, permeating the membrane oat comparable rates in the dissociated and undissociated forms. The lactate concentration ratio changes market markedly after an initial period of sustained glycolysis. This change is most readily explained as resulting from a lactate transport system that responds to an indicator of glycolytic activity. The data further indicates that lactate permeates the membrane in both dissociated and undissociated forms. Both acids, then are capable of catalytically dissipating the proton‐motives force. © 1995 John Wiley & Sons, Inc.