搜索结果：Chemical engineering journal (Lausanne, Switzerland : 1996)

A chemically-defined protein-free medium (FMX-Turbodoma) has been improved for the production of monoclonal IgA antibodies by hybridoma cells, using a systematic method. Cell growth rate, IgA production, activity and molecular weight pattern have been used as optimization criteria. Of potentially important supplements, glucose, glutamine, Pluronic acid F-68 as well as several amino acids had significant beneficial effects. A determination of amino acids profiles via HPLC analysis allowed the formulation of a balanced medium. Unbalanced supplementations of amino acids were found undesirable because of the toxicity of some amino acids at high concentration. Compared with the basal medium, the maximum viable cell and final IgA concentrations in the final version of the protein-free medium were increased by 130% and 700%, respectively, whereas the IgA molecular weight pattern and in vitro activity were not affected. The IgA production was even higher than in a serum-containing medium (RPMI 1640 + 10% FCS) and the price of the protein-free medium is about 20% of this serum-containing medium. This makes such a protein-free medium very convenient for laboratory and large-scale production.

Ammonia has been reported to be toxic and inhibitory for mammalian cell cultures for many years. Reduction of growth rates and maximal cell densities in batch cultures, changes in metabolic rates, perturbation of protein processing and virus replication have been reported. However, cellular mechanisms of ammonia toxicity are still the subject of controversy and are presented here. The physical and chemical characteristics of ammonia and ammonium are important, with the former capable of readily diffusing across cellular membranes and the latter competing with other cations for active transport by means of carrier proteins. The main source of the ammonia which accumulates in cell cultures is glutamine, which plays an important role in the metabolism of rapidly growing cells. Strategies to overcome toxic ammonia accumulation include substitution of glutamine by glutamate or other amino acids, nutrient control, i.e., controlled addition of glutamine at low concentrations, or removal of ammonia or ammonium from the culture medium by means of ion-exchange resins, ion-exchange membranes, gas-permeable membranes or electrodialysis.

A system for the independent control of ammonia and glutamine in a hollow-fiber reactor has been developed. On-line analysis of the two chemical species was performed using FIA. A custom-made program has been written to fully automate the FIA, to perform measurements, calibrations and data acquisition, and to activate two peristaltic feed pumps. Diagnostic tests were also automatically performed in order to identify, and in some cases eliminate, erroneous measurements and calibrations due to instrument failures. For this purpose, a visual programming language (LabVIEW) has been chosen. Ammonia concentration was controlled by varying the medium supply rate to the hollow-fiber reactor which was shown to behave like an ideal-stirred tank reactor. The glutamine concentration was controlled through the intermittent activation of a pump delivering a concentrated solution of this species to the reactor. This control system was tested with a culture of hybridoma cells at three different ammonia and one glutamine set-points. The hollow-fiber reactor was successfully operated automatically for more than 1200 h with ammonia and glutamine concentrations accurately controlled at non-limiting levels. The visual programming environment was found to be reliable and highly suitable for the development of custom programs for bioprocess control.

The growth kinetics of the sulfate-reducing bacteria Desulfovibrio desulfuricans Essex 6 was investigated under various conditions for potential use in a microbial fuel cell that recovers electrons generated from the reduction of sulfate to hydrogen sulfide. Hydrogen sulfide was found to inhibit growth and decrease both the growth yields and the sulfate-specific reduction rate. Hydrogen sulfide inhibition was direct, reversible, and not due to limitation by iron deficiency. A high initial lactate concentration also retarded bacterial growth, reduced the specific sulfate reduction rates, and gave variable biomass growth yields. This effect resulted from a bottleneck in the lactate oxidation pathway which induced the production of the secondary product butanol. The use of pyruvate as a carbon source was more advantageous than lactate in terms of growth rate and biomass growth yields, with only a slight decrease in the rate of specific sulfate reduction. For equal biomass, a slightly higher current density was generated from lactate than pyruvate, but pyruvate required nearly 40% less sulfate.

Reproducibility in protein purification by preparative isoelectric focusing depends greatly on temperature control during the separation process. A preparative apparatus is described, including a heat exchanger between compartments with isoelectric membranes. The selectivity of the isoelectric membranes was optimized as a function of isoelectric points of the separated proteins. At 2500 V and 60 W, 0.3 g of horse heart myoglobin from 0.2 g of whale skeletal muscle myoglobin could be separated in 1 h. At a total load of 2 g protein, 97% of bovine hemoglobin (2% initial concentration) was purified from bovine serum albumin (0.15%).

Synchronized populations of Saccharomyces cerevisiae CBS 426 are characterized by autonomous oscillations of process variables. CO2 evolution rate, O2 uptake rate and heat production rate varied by a factor of 2 for a continuous culture grown at a dilution rate of 0.10 h-1. Elemental analysis showed that the carbon mass fraction of biomass did not change. Since the reactor is not at steady state, the elemental and energy balances were calculated on cumulated quantities, i.e. the integral of the reaction rates. It was possible to show that carbon, degree of reduction and energy balances matched. Application of simple mass balance principles for non-steady state systems indicated that oscillations were basically characterized by changes in biomass production rate. In addition, the amount of intermediates, e.g. ethanol or acetate, produced or consumed was negligible. Growth rate was low during the S-phase (0.075 h-1) and high during the G2, M and G1 phases (0.125 h-1) for a constant dilution rate of 0.10 h-1. However, nitrogen, ash, sulfur and potassium content showed systematic increases during the S-phase (bud initiation). Cell component analyses showed that changes in cellular fractions during oscillations (storage carbohydrate content decreased during the S-phase) were due to changes in production rates, particularly for protein and carbohydrates. Nevertheless, using the data evaluation techniques for dynamic systems presented here, it was shown that storage carbohydrates are not consumed during the S-phase. Only the synthesis rate of the different cell components changed depending on position in cell cycle. The growth process may be divided into two phenomena: the formation of new cells during mitosis with a low yield, and size increase of new born cells with high yield. Both kinetic and stoichiometric coefficients varied with the position in the oscillation: the results showed that biomass structure changed and that specific growth rate, as well as biomass yield, varied by +/- 25% during the oscillation.

Quantum fluid droplets made of helium-3 (3He) or helium-4 (4He) isotopes have long been considered as ideal cryogenic nanolabs, enabling unique ultracold chemistry and spectroscopy applications. The droplets were believed to provide a homogeneous environment in which dopant atoms and molecules could move and react almost as in free space but at temperatures close to absolute zero. Here, we report ultrafast x-ray diffraction experiments on xenon-doped 3He and 4He nanodroplets, demonstrating that the unavoidable rotational excitation of isolated droplets leads to highly anisotropic and inhomogeneous interactions between the host matrix and enclosed dopants. Superfluid 4He droplets are laced with quantum vortices that trap the embedded particles, leading to the formation of filament-shaped clusters. In comparison, dopants in 3He droplets gather in diffuse, ring-shaped structures along the equator. The shapes of droplets carrying filaments or rings are direct evidence that rotational excitation is the root cause for the inhomogeneous dopant distributions.

This article presents a simple, unstructured mathematical model describing microbial growth in continuous culture limited by a gaseous substrate. The model predicts constant gas conversion rates and a decreasing biomass concentration with increasing dilution rate. It has been found that the parameters influencing growth are primarily the gas transfer rate and the dilution rate. Furthermore, it is shown that, for correct simulation of growth, the influence of gaseous substrate consumption on the effective gas flow through the system has to be taken into account.Continuous cultures of Methanobacterium thermoautotrophicum were performed at three different gassing rates. In addition to the measurement of the rates of biomass production, product formation, and substrate consumption, microbial heat dissipation was assessed using a reaction calorimeter. For the on-line measurement of the concentration of the growth-limiting substrate, H(2), a specially developed probe has been used. Experimental data from continuous cultures were in good agreement with the model simulations. An increase in gassing rate enhanced gaseous substrate consumption and methane production rates. However, the biomass yield as well as the specific conversion rates remained constant, irrespective of the gassing rate. It was found that growth performance in continuous culture limited by a gaseous substrate is substantially different from "classic" continuous culture in which the limiting substrate is provided by the liquid feed. In this report, the differences between both continuous culture systems are discussed.

Scientists are testing two promising ways to destroy PFAS, the stubborn “forever chemicals” that can accumulate in water and resist normal treatment。 One method uses collapsing vapor bubbles to generate extreme heat and reactive molecules, while the other uses cold plasma and rising gas bubbles to pull PFAS to the surface and break them apart

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