Publications by Urs von Stockar

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There is an increasing interest by the flavor industry for producing natural aroma compds. through biocatalysts. L-Phenylalanine is transformed by Saccharomyces cerevisiae into 2-phenylethanol, which has a rose-like odor. Unfortunately this product inhibits growth even at low concns. and therefore its max. concn. is 3.9 g/l. This problem of the inhibitory effect of the product on the cell can be tackled by different in-situ product removal (ISPR) techniques. The hydrophobicity of 2-phenylethanol differs fro

The objective of this study was to characterize the dynamic adaptation of the oxidative capacity of Saccharomyces cerevisiae to an increase in the glucose supply rate and its implications for the control of a continuous culture designed to produce biomass without allowing glucose to be diverted into the reductive metab. Continuous cultures subjected to a sudden shift-up in the diln. rate showed that the glucose uptake rate increased immediately to the new feeding rate but that the oxygen consumption could n

The aim of the present work was to investigate whether uncoupling of catabolism from anabolism, which was often obsd. in heterotrophic microorganisms under energy-sufficient growth conditions, also occurs in the autotrophic bacterium M. thermoautotrophicum. For this purpose, M. thermoautotrophicum was cultivated in continuous cultures that were limited by the trace element Fe. The influences of both diln. rate and Fe supply rate on the coupling between anabolism and catabolism were investigated. As compared

The understanding of dynamic metabolic regulations is important for physiol. studies and strain characterization tasks. The present study combined transient expts. with online metabolic flux anal. (MFA) in order to quantify metabolic regulations, namely carbon catabolite repression of respiration and transient acetic-acid prodn., in Saccharomyces cerevisiae during aerobic growth on glucose. The aim was to investigate which addnl. information can be gained from using a small metabolic flux model to study tra

The use of extn. techniques to alleviate product inhibition in bioprocesses is one of a no. of potential sepn. methods. However, the intimate contact of an org. phase with the broth implies that the org. components of this phase may be present in the aq. phase at satn. levels. The quaternary amine Aliquat 336 (trioctyl/decylmethylammonium entity), dissolved in octan-1-ol showed no inhibition on the growth of Pseudomonas putida, at least with respect to mol. toxicity. Nevertheless, it is important to point o

A modified bench scale calorimeter has been employed to det. the heat generated by various microbial strains growing on a range of different substrates, covering degrees of redn. from 3 to 6.13. The results are analyzed and interpreted in the light of coupled enthalpy and elemental balances. The heat released by the microbial cultures has been found to correlate linearly with other process variables, such as biomass generation and oxygen uptake. The ratio between the heat generated and the biomass formed, t

The sulfite oxidn. method was reinvestigated to establish a procedure for the measurement of O2 transfer coeff. (KLa). Co ion catalyzed oxidns., using buffered Na2SO3 solns., were conducted in an aerated, baffled tank which was fitted with a turbine impeller, and in a multistage, countercurrent, bubble column. An empirical procedure to change the Co ion catalyst concn. was used to det. the suitable reaction conditions for KLa measurement. In the correct Co2+ range, the oxidn. rate becomes independent of Co2

A review, with .apprx.43 refs. A review of different types of biol. reaction calorimetry systems currently used together with the operating principles is presented. The av. resoln. of these systems is approx. 20 to 1000 mW l-1, sufficient for studies of a wide range of cell culture processes. Poorly exothermic and endothermic processes require the development of even higher resoln. systems. To this end, the Mettler-Toledo RC1 calorimeter has been extensively studied to det. the factors which limit the resol

A process is provided for the in-situ extn. of a fermn. product esp. for products which result from the transformation of an amino acid and which are sol. in the fermn. broth. The sol. product is then removed from aq. phase by extn. into an org. phase where the solvent used is encapsulated so that the product can freely permeate the capsule but the microorganism can not. The process envisions that the fermn. broth be circulated to a sep. extractor for the sepn. In this manner not only may a toxic end produc

Aerobic chemostat cultures of Saccharomyces cerevisiae were performed under carbon-, nitrogen-, and dual carbon- and nitrogen-limiting conditions. The glucose concn. was kept const., whereas the ammonium concn. was varied among different expts. and different diln. rates. Both glucose and ammonium were consumed at the maximal possible rate, i.e., the feed rate, over a range of medium C/N ratios and diln. rates. To a small extent, this was due to a changing biomass compn., but much more important was the abil

In Saccharomyces cerevisiae, the genes HXK2 and REG1 are believed to play a central role in carbon catabolite repression, acting on multiple pathways in the central metab. The present study aimed at quantifying the effect of deletion of genes HXK2 or REG1, resp., in the S. cerevisiae strain CEN.PK113-7D on the regulation of invertase and respiratory functions.Batch cultivation of the HXK2 deletion mutant on substrate mixts. of sucrose, fructose and glucose and on pure glucose showed an initial high invertas

Equil. aspects in biotechnol. and thermodn. as the main theory underlying them have thus far received relatively little attention. As a consequence, design and development of biotechnogical processes is still carried out today in an relatively empirical way. For this situation to improve, a wider and more systematic use of the thermodn. aspects pertaining to biotechnol. must be encouraged. Recognizing this need, the ESF program on Process Integration in Biotechnol. developed an intensive advanced course whi

Chemical potentials (molar Gibbs energies) are usually extrapolated to the remote physical–chemical reference state and then stored. Subsequent use under in vivo conditions requires a similarly substantial, reverse extrapolation, again with significant potential errors. In order to shrink both extrapolations drastically and thereby enhance both biological meaning and accuracy, we propose a transformation to a more biological reference state: pH = 7, pMg = 3, 99.5% water, with 1 m m each of the additional ‘p

Addnl. data considered in abstracting and indexing are available from a source cited in the original document. Nonisothermal gas absorption in plate columns was studied and the data were compared with the values computed by the procedure developed in Part I. In addn. to the usual phys. chem. data, the 3 Murphree plate efficiencies were required. These were detd. as functions of the operating variables in a 1-plate absorber. The conditions used in the absorption expts. included feed gas concns. of 0-12% NH3,

Growth of Methanobacterium thermoautotrophicum, an anaerobic archaebacterium using methanogenesis as the catabolic pathway, is characterized by large heat prodn. rates, up to 13 W g-1, and low biomass yields, in the order of 0.02 C-mol mol-1 H2 consumed. These values, indicating a possibly "inefficient" growth mechanism, warrant a thermodn. anal. to obtain a better understanding of the growth process. The growth-assocd. heat prodn. (DrHX0,min) and the growth-assocd. Gibbs energy dissipation per mol biomas

In view of the prime importance of the biomass yield in microbial growth for research, for environmental and for industrial applications some thermodynamic concepts are reviewed that were developed over the years in order to understand the large variations ...

Continuous cultures of a hybridoma cell line (Zac3) were performed in a stirred tank reactor with protein-free media. At steady state the medium was replaced by one contg. U-14C-labeled glucose. The fluxes leaving the reactor were analyzed with a scintillation counter to det. the specific activity of each. The gas and solid phases allowed detn. of the oxidn. and the assimilation ratio of the consumed glucose. The liq. phase was sepd. chromatog. to det. quant. the different species consumed or formed by the

This article presents a simple, unstructured math. model describing microbial growth in continuous culture limited by a gaseous substrate. The model predicts const. gas conversion rates and a decreasing biomass concn. with increasing diln. rate. The parameters influencing growth are primarily the gas transfer rate and the diln. rate. Furthermore, 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. Continu

The effect of diln. rate on the prodn. of lactic acid from whey permeate by L. helveticus was investigated. In the 1st chemostat of a 2-stage system, total conversion (98.1%) and max. lactic acid concn. (43.7 g/L) were obtained at a diln. rate (D1tot) of 0.06/h. Max. volumetric productivities of lactic acid (8.27 g/L-h) and biomass (1.90 g/L-h) occurred at D1tot of 0.40/h. The fraction of L-lactate in the product increased with diln. rate and reached a max. of 66% at the same diln. rate. The max. sp. growth

Deletion mutants with either deletion of HXK2 and REG1 of the wild-type strain Saccharomyces cerevisiae CEN.PK113-7D were quant. analyzed for the impact on carbon catabolite repression and the short-term effect of the oxidative metab. Therefore, continuous cultures and transient expts. were performed, which were followed by high frequency online anal. of multiple compds.It could be demonstrated that either deletion of HXK2 or REG1 alleviated repression of respiratory functions in steady state conditions. Th

Urs von Stockar

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Comparison of different in situ product-removal methods to enhance the production of the aroma compound 2-phenylethanol

Identification and control of oxidative metabolism in Saccharomyces cerevisiae during transient growth using calorimetric measurements

The coupling between catabolism and anabolism of Methanobacterium thermoautotrophicum in H2- and iron-limited continuous cultures

A small metabolic flux model to identify transient metabolic regulations in Saccharomyces cerevisiae

Factors influencing the potential use of Aliquat 336 for the in situ extraction of carboxylic acids from cultures of Pseudomonas putida

Calorimetric investigation of aerobic fermentations

Practical guidelines for the determination of oxygen transfer coefficients (KLa) with the sulfite oxidation method

Biological reaction calorimetry: development of high sensitivity bio-calorimeters

A process for the in-situ extraction of fermentation broths

Growth and metabolism of Saccharomyces cerevisiae in chemostat cultures under carbon-, nitrogen-, or carbon- and nitrogen-limiting conditions

Quantitative analysis of the impact of HXK2 and REG1 deletion in Saccharomyces cerevisiae on invertase expression and respiration

Thermodynamics in biochemical engineering

Metabolic thermodynamics: pertinent reference state and energy potentials

Gas absorption with heat effects. II. Experimental results

Thermodynamic analysis of growth of Methanobacterium thermoautotrophicum

Can microbial growth yield be estimated using simple thermodynamic analogies to technical processes?

Development of carbon balances for continuous animal cell cultures using 14C-labeled glucose

Continuous cultures limited by a gaseous substrate: development of a simple, unstructure mathematical model and experimental verification with Methanobacterium thermoautotrophicum

Continuous production of lactic acid from whey permeate by Lactobacillus helveticus in two chemostats in series

Quantitative analysis of the oxidative metabolism in HXK2- and REG1-deletion mutants of Saccharomyces cerevisiae