Publications by Urs von Stockar

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This article is an adapted version of the introductory chapter of a book whose publication is imminent. It bears the title "Biothermodynamics - The role of thermodynamics in biochemical engineering." The aim of the paper is to give a very short overview of ...

Yeasts degrade glucose through different metabolic pathways, where the choice of the pathway is dependent on the nature of the limitation in the various substrates. When oxygen is limiting in addn. to glucose, yeasts often grow according to a mixt. of oxidative and reductive metab. Oxygen may be limiting either by supply or by inherent biol. restrictions such as the respiratory bottleneck in Saccharomyces cerevisiae or by both. A unified model incorporating both supply and biol. limitations is proposed for

The calorimetric response of the yeast Kluyveromyes fragilis was investigated for growth in continuous culture where N limitation was imposed on a C-limited culture. Calorimetric measurements were combined with off gas anal., measurements of biomass, substrate and product concns., elemental biomass compn., and heat prodn. to study the physiol. response of K. fragilis. Regions where both carbon and nitrogen limited growth, were found over a broad range of diln. rates and feed carbon-to-nitrogen ratios. The p

Aerobic chemostat cultures of S. cerevisiae were performed at different diln. rates under energy (glucose) limitation or at various extents of energy excess imposed by a N limitation. Energy excess induced metabolic uncoupling under steady-state conditions. The sp. EtOH prodn. rate was always higher the lower the feed medium N concn. throughout the whole range of diln. rates tested. In addn., the respiratory rate also increased under N limitation, for at least as long as the sp. O2 consumption rate was belo

The heat generated by both batch and continuous cultures of the yeast Kluyveromycs fragilis was studied using a modified bench scale calorimeter. Batch cultures were used to measure the heat dissipation rates and the heat yields during fully aerobic and completely anaerobic growth, whereas continuous cultures also allowed a quant. study of heat dissipation rates during growth on mixed metab. The extent of fermn. vs. respiration could be specified and controlled by O2 limitation. The heat dissipated per unit

A novel heat-flux calorimeter was used to study the aerobic batch growth of the facultative yeast K. fragilis on glucose [50-99-7], galactose [59-23-4], lactose [63-42-3], and deproteinized whey permeate. The calorimetric data enabled optimization of the defined medium compn. with respect to vitamin and trace element requirements. Direct relationship between heat evolved and biomass concn., O2 consumption rate, and CO2 evolution rate were obsd. with values for YQ/X, YQ/O, and YQ/C of 9.43, 440, and 474 kJ/m

The elemental compn. of microorganisms varies widely with respect to the N, S, P, and ash content as well as many trace elements depending on microorganism and growth conditions. As a consequence, the mass of 1 C-mol of biomass can differ considerably from 1 microorganism to another. S is completely volatilized during combustion, so that the calcn. of the mass fraction of O is affected when S is not measured. However, its neglect does not seriously affect the elemental compn. and the degree of redn. of biom

A review and discussion with 59 refs. Schrodinger stated in his landmark book, What is Life, that life feeds on neg. entropy. In this contribution, the validity of this statement is discussed through a careful thermodn. anal. of microbial growth processes. In principle, both feeding on neg. entropy, i.e. yielding products of higher entropy than the substrates, and generating heat can be used by microorganisms to rid themselves of internal entropy prodn. resulting from maintenance and growth processes. Liter

A recombinant avidin-producing Mut(+) Pichia pastoris strain was used as a model organism to study the influence of the methanol feeding strategy on the specific product productivity (q(p)) and protein glycosylation. Fed-batch cultivations performed at var ...

Bubble-free aeration is applied in animal cell culture processes for oxygenation to avoid shear stress and foaming assocd. with direct sparging into the culture. Oxygen mass transfer across PTFE-membranes was detd. in three different reactor systems that may be applied to animal cell cultures. Oxygen was supplied on the aeration side of the membrane by air- or oxygen-satd. aq. liqs., or directly using air or pure oxygen. By using liqs., the bubble-free aeration may be combined with an ammonia removal system

A system for the independent control of ammonia and glutamine in a hollow-fiber reactor has been developed. Online anal. of the two chem. 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. F

A dynamic simulation method was applied to det. the state of a stagewise gas absorption column. The unsteady state heat and mass balances for each real stage were integrated up to the steady state, considering all possible heat effects. The new method resulted in stable convergence of the 2-point boundary value problem. Earlier studies of the influences of typical operating and system variables on the capacity of an absorber were extended. The transport capacity of the gas phase for heat, solvent evapn., th

Due to residual oil retained within it, rapeseed press-cake has been shown to be effective for the removal of atrazine from water through an absorption mechanism. However, it is difficult to put this into practice due to the hygroscopic nature of the press ...

In many microorganisms, flux limitations in oxidative metab. lead to the formation of overflow metabolites even under fully aerobic conditions. This can be avoided if the specific growth rate is controlled at a low enough value. This is usually accomplished by controlling the substrate feeding profile in a fed-batch process. The present work proposes a control concept which is based on the online detection of metabolic state by online calcn. of mass and elemental balances. The advantages of this method are:

Four models taken from the literature, which permit calcn. of heats of combustion from elemental anal., are evaluated from a theor. point of view. In order to obtain exptl. values of heat of combustion with a higher degree of accuracy than that in the literature, an improved sample prepn. technique based on lyophilization of microbial biomass was developed. Heat of combustion was detd. by direct measurement in a calorimeter and compared to calcd. values from each of the literature models. Giese's formula pr

A review, with refs. This contribution analyzes the position of biochem. engineering in general and bioprocess engineering particularly in the force fields between fundamental science and applications, and between academia and industry. By using culture technol. as an example, it can be shown that bioprocess engineering has moved slowly but steadily from an empirical art concerned with mainly know-how to a science elucidating the know-why of culture behavior. Highly powerful monitoring tools enable biochem.

To answer the intriguing question whether or not endothermic microbial growth exists, and in particular, to verify Heijnen and van Dijken's prediction (1992), acetotrophic methanogen, Methanosarcina barkeri, has been cultivated in a highly sensitive bench-scale calorimeter (an improved Bio-RC1 reaction calorimeter) in a pH auxostat fashion. A growth yield of 0.043 C-mol-1 has been obtained and a cell d. as high as 3 g L-1 was attained. Heat uptake during growth has indeed been quant. measured with calorimet

A FIA method has been developed and fully characterized for the simultaneous detection of ammonia and glutamine in culture media. Ammonia detection is based upon a chem. method and does not require an electrode. This species diffuses across a hydrophobic porous membrane into an indicator soln., the absorbance of which is continuously monitored using a LED and a phototransistor. Glutamine was detd. by a difference method in which ammonia was measured before and after passage through a module contg. immobiliz

Carotenoid prodn. by microorganisms, as opposed to chem. synthesis, could fulfill an ever-increasing demand for 'all natural' products. The yeast Phaffia rhodozyma has received considerable attention because it produces the red pigment astaxanthin, commonly used as an animal feed supplement. In order to have a better understanding of its metab., labeling expts. with [1-13C]glucose were conducted with the wildtype strain (CBS5905 T) and a hyper-producing carotenoid strain (J4-3) in order to det. their metabo

This work evaluates three techniques of calibrating capacitance (dielectric) spectrometers used for on-line monitoring of biomass: modeling of cell properties using the theoretical Cole-Cole equation, linear regression of dual-frequency capacitance measure ...

Urs von Stockar

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The role of thermodynamics in biochemical engineering

A unified stoichiometric model for oxidative and oxidoreductive growth of yeasts

Calorimetric and stoichiometric analysis of growth of Kluyveromyces fragilis in continuous culture. Nitrogen limitation imposed upon carbon-limited growth

Metabolic uncoupling in Saccharomyces cerevisiae

The heat generated by yeast cultures with a mixed metabolism in the transition between respiration and fermentation

A calorimetric investigation of the aerobic cultivation of Kluyveromyces fragilis on various substrates

Measurements of sulfur, phosphorus and other ions in microbial biomass: influence on correct determination of elemental composition and degree of reduction

Does microbial life always feed on negative entropy? Thermodynamic analysis of microbial growth

Influence of specific growth rate on specific productivity and glycosylation of a recombinant avidin produced by a Pichia pastoris Mut(+) strain

Bubble-free oxygenation by means of hydrophobic porous membranes

Development of an online control system for the cultivation of animal cells in a hollow-fiber reactor using flow injection analysis and a visual programming language

Gas absorption with heat effects. I. New computational method

Immobilization of rapeseed press-cake in an alginate matrix for the sorption of atrazine

Generally applicable fed-batch culture concept based on the detection of metabolic state by on-line balancing

The relationship between elemental composition and heat of combustion of microbial biomass

Know-how and know-why in biochemical engineering

Microbial growth by a net heat up-take: a calorimetric and thermodynamic study on acetotrophic methanogenesis by Methanosarcina barkeri

Online simultaneous monitoring of ammonia and glutamine in a hollow-fiber reactor using flow injection analysis

Metabolic network analysis on Phaffia rhodozyma yeast using 13C-labeled glucose and gas chromatography-mass spectrometry

Cole-Cole, linear and multivariate modeling of capacitance data for on-line monitoring of biomass