Biomedical subjects

J Tramper

Publications and source records attributed to J Tramper.

At least 55 records · Page 3Linked to original sources

PubMed2000

Growth and sporulation stoichiometry and kinetics of Coniothyrium minitans on agar media.

Coniothyrium minitans was cultivated on agar media with different concentrations of starch, urea, and trace elements. By means of elemental balances, the stoichiometry of growth and sporulation was established. C. minitans produced byproducts on all media, especially in the medium with high urea concentrations, where 30% of the starch was converted into byproducts. Simple empirical models were used to describe the kinetics of growth, sporulation, CO(2) production, and substrate consumption on all media. Total biomass and mycelium could be described reasonably well with the logistic law. Starch, urea, and oxygen consumption and CO(2) production could be described as a function of total biomass by the linear-growth model of Pirt. There were almost no differences between media for the estimates of yield coefficients and maintenance coefficients. Only at high urea concentrations were maintenance coefficients much higher. Similar to substrate consumption and CO(2) production, the kinetics of sporulation could be described as a function of mycelium production with the linear-growth model. It is shown that sporulation of C. minitans is growth-associated. Based on kinetics, the process costs for producing spores are roughly calculated. In addition, it is shown that fermentor costs represent the majority of production costs.

Agar↗

PubMed2000

Regulation of aspartate-derived amino-acid metabolism in Zygosaccharomyces rouxii compared to Saccharomyces cerevisiae.

To elucidate the growth inhibitory effect of threonine, the regulation of the aspartate-derived amino-acid metabolism in Zygosaccharomyces rouxii, an important yeast for the flavor development in soy sauce, was investigated. It was shown that threonine inhibited the growth of Z. rouxii by blocking the methionine synthesis. It seemed that threonine blocked this synthesis by inhibiting the conversion of aspartate. In addition, it was shown that the growth of Z. rouxii, unlike that of Saccharomyces cerevisiae, was not inhibited by the herbicide sulfometuron methyl (SMM). From enzyme assays, it was concluded that the acetohydroxy acid synthase in Z. rouxii, unlike that in S. cerevisiae, was not sensitive to SMM. Furthermore, the enzyme assays demonstrated that the activity of threonine deaminase in Z. rouxii, like in S. cerevisiae, was strongly inhibited by isoleucine and stimulated by valine. From this work, it is clear that the aspartate-derived amino-acid metabolism in Z. rouxii only partly resembles that in S. cerevisiae.

Journal Article↗

PubMed2000

Immobilized soy-sauce yeasts: development and characterization of a new polyethylene-oxide support.

Entrapment of cells in alginate gel is a widely used mild immobilization procedure. However, alginate gel is not very suitable for use in long-term continuous soy-sauce processes because alginate is sensitive to abrasion and chemically unstable towards the high salt content of soy-sauce medium. Therefore, a chemically crosslinked polyethylene-oxide gel was used instead. The disadvantage of this gel was that due to the crosslinking reaction, the viability of the cells after immobilization was poor. For this reason, a new mild procedure for immobilizing soy-sauce yeasts in polyethylene-oxide gel was developed, resulting in high survival percentages of the soy-sauce yeasts Zygosaccharomyces rouxii and Candida versatilis. This newly developed polyethylene-oxide gel, unlike alginate gel, appeared not to be sensitive to abrasion, even in the presence of high salt concentrations. Therefore, we concluded that this newly developed polyethylene-oxide gel is more suitable than alginate gel for use as immobilization material in long-term processes with a high salt content, like soy-sauce processes.

Candida↗

PubMed2000

D-malate production by permeabilized Pseudomonas pseudoalcaligenes; optimization of conversion and biocatalyst productivity.

For the development of a continuous process for the production of solid D-malate from a Ca-maleate suspension by permeabilized Pseudomonas pseudoalcaligenes, it is important to understand the effect of appropriate process parameters on the stability and activity of the biocatalyst. Previously, we quantified the effect of product (D-malate2 -) concentration on both the first-order biocatalyst inactivation rate and on the biocatalytic conversion rate. The effects of the remaining process parameters (ionic strength, and substrate and Ca2 + concentration) on biocatalyst activity are reported here. At (common) ionic strengths below 2 M, biocatalyst activity was unaffected. At high substrate concentrations, inhibition occurred. Ca2+ concentration did not affect biocatalyst activity. The kinetic parameters (both for conversion and inactivation) were determined as a function of temperature by fitting the complete kinetic model, featuring substrate inhibition, competitive product inhibition and first-order irreversible biocatalyst inactivation, at different temperatures simultaneously through three extended data sets of substrate concentration versus time. Temperature affected both the conversion and inactivation parameters. The final model was used to calculate the substrate and biocatalyst costs per mmol of product in a continuous system with biocatalyst replenishment and biocatalyst recycling. Despite the effect of temperature on each kinetic parameter separately, the overall effect of temperature on the costs was found to be negligible (between 293 and 308 K). Within pertinent ranges, the sum of the substrate and biocatalyst costs per mmol of product was calculated to decrease with the influent substrate concentration and the residence time. The sum of the costs showed a minimum as a function of the influent biocatalyst concentration.

Calcium↗

PubMed2000

Efficiency of light utilization of Chlamydomonas reinhardtii under medium-duration light/dark cycles.

The light regime inside a photobioreactor is characterized by a light gradient with full (sun)light at the light-exposed surface and darkness in the interior of the bioreactor. Consequently, depending on the mixing characteristics, algae will be exposed to certain light/dark cycles. In this study the green alga Chlamydomonas reinhardtii was cultivated under five different light regimes: (1) continuous illumination; (2) a square-wave light/dark cycle with a light fraction (epsilon) of 0.5 and a duration (t(c)) of 6.1 s; (3) epsilon=0.5, t(c)=14.5 s; (4) epsilon=0.5, t(c)=24.3 s and (5) epsilon=0.8, t(c)=15.2 s. The biomass yield on light energy, protein per photons, decreased under light/dark cycles (epsilon=0. 5) in comparison to continuous light (CL), from 0.207 (CL) to 0.117-0.153 g mol(-1) (epsilon=0.5). Concomitantly, the maximal specific photosynthetic activity, oxygen production per protein, decreased from 0.94 (CL) to 0.64-0.66 g g(-1) h(-1) (epsilon=0.5). Also the quantum yield of photochemistry, yield of the conversion of light energy into chemical energy, decreased from 0.47 (CL) to 0. 23 (epsilon=0.5, t(c)=24.3 s). Apparently, C. reinhardtii is not able to maintain a high photosynthetic capacity under medium-duration light/dark cycles and since specific light absorption did not change, light utilization efficiency decreased in comparison to continuous illumination.

Animals↗

PubMed2000

Effect of threonine, cystathionine, and the branched-chain amino acids on the metabolism of Zygosaccharomyces rouxii*

Zygosaccharomyces rouxii is an important yeast in the formation of flavor in soy sauce. In this study, we investigated the separate effects of exogenous threonine, cystathionine, and the branched-chain amino acids on the metabolism of Z. rouxii. The addition of these amino acids had significant effects on both Z. rouxii growth and glycerol and higher alcohol production. It also seemed that Z. rouxii displayed the Crabtree effect, which was independent of the added amino acids. Furthermore, we investigated the regulation of the metabolism of alpha-ketobutyrate, which is a key-intermediate in Z. rouxii amino acid metabolism. Threonine and cystathionine were introduced separately to stimulate the formation rate of alpha-ketobutyrate and the branched-chain amino acids to inhibit its conversion rate. Enzyme activities showed that these amino acids had a significant effect on the formation and conversion rate of alpha-ketobutyrate but that the alpha-ketobutyrate pool size in Z. rouxii was in balance all the time. The latter was confirmed by the absence of alpha-ketobutyrate accumulation.

Journal Article↗

PubMed2000

Defined media and inert supports: their potential as solid-state fermentation production systems.

Solid-state fermentation (SSF) using inert supports impregnated with chemically defined liquid media has several potential applications in both scientific studies and in the industrial production of high-value products, such as metabolites, biological control agents and enzymes. As a result of its more defined system, SSF on inert supports offers numerous advantages, such as improved process control and monitoring, and enhanced process consistency, compared with cultivation on natural solid substrates.

Biotechnology↗

PubMed1999

A simplified material and energy balance approach for process development and scale-up of Coniothyrium minitans conidia production by solid-state cultivation in a packed-bed reactor.

Production of conidia of the biocontrol fungus Coniothyrium minitans by solid-state cultivation in a packed-bed reactor on an industrial scale is feasible. Spore yield and oxygen consumption rate of C. minitans during cultivation on oats and three inert solids (hemp, perlite, and bagasse) saturated with a liquid medium were determined in laboratory-scale experiments. The sensitivity of the fungus to reduced aw, and the water desorption isotherms of the four solid materials were also determined. C. minitans is very sensitive to reduced aw: 50% inhibition of respiration was found at aw 0.95, spore formation was completely inhibited at aw 0.97. A simplified mathematical model taking into account convective and evaporative cooling was used to simulate temperature and moisture gradients in the bed during cultivation. Adequate temperature control can be achieved with acceptable air flow rates for all four solid matrices. Moisture control is the limiting factor for cultivation in a packed bed. Oats cannot be used due to the shrinkage and aw reduction caused by evaporative cooling. Of the three inert supports tested, hemp provides the best spore yield and control of water activity, due to its high water uptake capacity. A spore yield of 9 x 10(14) conidia per m(3) packed bed can be achieved in 18 days, using hemp impregnated with a solution containing 100 g dm(-3) glucose and 20 g dm(-3) potato extract. Sufficient water is predicted to be available after 18 days, to allow a higher initial nutrient concentration, which may lead to higher spore yields.

Bioreactors↗

PubMed1999

Rational medium design for Bordetella pertussis: basic metabolism.

In current Bordetella pertussis media ammonium accumulates because of an imbalance in the nitrogen:carbon ratio of the substrates used, which is one of the factors limiting cell density in fed-batch cultures. The aim of this study was to map B. pertussis catabolic and anabolic capabilities, in order to design a medium that avoids ammonium accumulation, while substrates are metabolised completely. Besides the known dysfunctional glycolysis, B. pertussis also possessed a partially dysfunctional citric-acid cycle. Although ammonium accumulation was avoided by adding various carbon sources to medium with glutamate, nuclear magnetic resonance (NMR) showed excretion of acetate, acetoacetate and beta-hydroxy-butyrate, thereby reducing the biomass yield. Acetoacetate and beta-hydroxy-butyrate were also formed in Verwey, B2 and modified Stainer-Scholte medium. Electron microscopy in combination with NMR showed that cells early on in these cultures contained poly-hydroxy-butyrate (PHB) globules, which disappeared later during the culture, coinciding with the appearance of beta-hydroxy-butyrate and/or acetoacetate. No globules nor metabolite excretion was detected when lactate in combination with glutamate were used as substrates. Thus, metabolite excretion and ammonium accumulation were avoided, while the yield of 8.8 g C-mol-1 compared favourably with literature values, averaging 6.5 g C-mol-1. Optimisation of this medium for pertussis toxin production will be reported in a separate article.

Bordetella pertussis↗

PubMed1999

Medium optimization for spore production of coniothyrium minitans using statistically-based experimental designs

Statistically-based experimental designs were used to optimize a chemically defined solid medium for the spore production of Coniothyrium minitans. In the first optimization step the influence of starch, urea, phosphate, magnesium, calcium, thiamin and trace elements on spore production was evaluated using a fractional factorial design. Starch and trace elements influenced spore production positively while urea affected spore production negatively. The other components had no significant influence on spore production. In the second and third steps the concentrations of starch, urea and trace elements were further optimized using central composite designs and response surface analysis. This optimization strategy allowed the spore production to be increased by a factor 7 from 4 x 10(9) to almost 3 x 10(10) spores per Petri dish of 9 cm diameter. Copyright 1999 John Wiley & Sons, Inc.

Journal Article↗

PubMed1999

Effect of temperature on the saccharide composition obtained after alpha-amylolysis of starch

The hydrolysis of starch to low-molecular-weight products (normally characterised by their dextrose equivalent (DE), which is directly related to the number-average molecular mass) was studied at different temperatures. Amylopectin potato starch, lacking amylose, was selected because of its low tendency towards retrogradation at lower temperatures. Bacillus licheniformis alpha-amylase was added to 10% [w/w] gelatinised starch solutions. The hydrolysis experiments were done at 50, 70, and 90 degrees C. Samples were taken at defined DE values and these were analysed with respect to their saccharide composition. At the same DE the oligosaccharide composition depended on the hydrolysis temperature. This implies that at the same net number of bonds hydrolysed by the enzyme, the saccharide composition was different. The hydrolysis temperature also influenced the initial overall molecular-weight distribution. Higher temperatures led to a more homogenous molecular weight distribution. Similar effects were observed for alpha-amylases from other microbial sources such as Bacillus amyloliquefaciens and Bacillus stearothermophilus. Varying the pH (5.1, 6.2, and 7.6) at 70 degrees C did not significantly influence the saccharide composition obtained during B. licheniformis alpha-amylase hydrolysis. The underlying mechanisms for B. licheniformis alpha-amylase were studied using pure linear oligosaccharides, ranging from maltotriose to maltoheptaose as substrates. Activation energies for the hydrolysis of individual oligosaccharides were calculated from Arrhenius plots at 60, 70, 80, and 90 degrees C. Oligosaccharides with a degree of polymerisation exceeding that of the substrate could be detected. The contribution of these oligosaccharides increased as the degree of polymerisation of the substrate decreased and the temperature of hydrolysis increased. The product specificity decreased with increasing temperature of hydrolysis, which led to a more equal distribution between the possible products formed. Calculations with the subsite map as determined for the closely related alpha-amylase from B. amyloliquefaciens reconfirmed this finding of a decreased substrate specificity with increased temperature of hydrolysis. Copyright 1999 John Wiley & Sons, Inc.

Journal Article↗

PubMed1999

The effect of process conditions on the alpha-amylolytic hydrolysis of amylopectin potato starch: An experimental design approach.

The hydrolysis of amylopectin potato starch with Bacillus licheniformis alpha-amylase (Maxamyl) was studied under industrially relevant conditions (i.e. high dry-weight concentrations). The following ranges of process conditions were chosen and investigated by means of an experimental design: pH [5.6-7.6]; calcium addition [0-120 microg/g]; temperature [63-97 degrees C]; dry-weight concentration [3-37% [w/w]]; enzyme dosage [27.6-372.4 microL/kg] and stirring [0-200 rpm]. The rate of hydrolysis was followed as a function of the theoretical dextrose equivalent. The highest rate (at a dextrose equivalent of 10) was observed at high temperature (90 degrees C) and low pH (6). At a higher pH (7.2), the maximum temperature of hydrolysis shifted to a lower value. Also, high levels of calcium resulted in a decrease of the maximum temperature of hydrolysis. The pH, temperature, and the amount of enzyme added showed interactive effects on the observed rate of hydrolysis. No product or substrate inhibition was observed. Stirring did not effect the rate of hydrolysis. The oligosaccharide composition after hydrolysis (at a certain dextrose equivalent) did depend on the reaction temperature. The level of maltopentaose [15-24% [w/w]], a major product of starch hydrolysis by B. licheniformis alpha-amylase, was influenced mostly by temperature.

Amylopectin↗

PubMed1999

Cultivation of Marine Sponges.

There is increasing interest in biotechnological production of marine sponge biomass owing to the discovery of many commercially important secondary metabolites in this group of animals. In this article, different approaches to producing sponge biomass are reviewed, and several factors that possibly influence culture success are evaluated. In situ sponge aquacultures, based on old methods for producing commercial bath sponges, are still the easiest and least expensive way to obtain sponge biomass in bulk. However, success of cultivation with this method strongly depends on the unpredictable and often suboptimal natural environment. Hence, a better-defined production system would be desirable. Some progress has been made with culturing sponges in semicontrolled systems, but these still use unfiltered natural seawater. Cultivation of sponges under completely controlled conditions has remained a problem. When designing an in vitro cultivation method, it is important to determine both qualitatively and quantitatively the nutritional demands of the species that is to be cultured. An adequate supply of food seems to be the key to successful sponge culture. Recently, some progress has been made with sponge cell cultures. The advantage of cell cultures is that they are completely controlled and can easily be manipulated for optimal production of the target metabolites. However, this technique is still in its infancy: a continuous cell line has yet to be established. Axenic cultures of sponge aggregates (primmorphs) may provide an alternative to cell culture. Some sponge metabolites are, in fact, produced by endosymbiotic bacteria or algae that live in the sponge tissue. Only a few of these endosymbionts have been cultivated so far. The biotechnology for the production of sponge metabolites needs further development. Research efforts should be continued to enable commercial exploitation of this valuable natural resource in the near future.

Journal Article↗

PubMed1998

Ethene removal from gas by recycling a water-immiscible solvent through a packed absorber and a bioreactor.

Hydrophobic pollutants in waste gases are difficult to remove with the conventional biological treatment techniques because of the slow gas/water mass transfer rate. A two-stage system with a water-immiscible solvent as intermediate liquid was developed. This system consisted of a packed absorber for transfer of the model pollutant, ethene, from gas to solvent and a stirred-tank reactor (mixer) for solvent/water transfer and subsequent degradation by Mycobacterium parafortuitum. The solvent FC40, a perfluorocarbon, was recycled between these two compartments. The stability of the system was shown during a run of 10 days. The elimination efficiency was found to be a function of the solvent flow: 9% and 15% elimination were obtained at solvent flows of 6 x 10(-8) m3.s-1 and 11.3 x 10(-8) m3.s-1, respectively. Ethene removal remained constant at increasing solvent hold-ups up to 50% (v/v). In spite of the low elimination efficiencies caused by an inefficient use of the column, the feasibility of the system to remove ethene has been demonstrated. The system's performance was described by a steady-state mathematical model. Simulated ethene removal efficiencies agreed well with the experimental data. Based on this, the model was used to optimise the dimensions and operating conditions. Furthermore, the model was used to compare the performance of the combined system (PA/MS) with the performance of a similar system without solvent. It was found that the use of solvent as intermediate liquid can improve substantially the removal efficiency of hydrophobic gaseous pollutants compared with the system without solvent. This is dependent however, on the solubility of the pollutant in the solvent, on the dimensions of the system and on the operating conditions.

Absorption↗

PubMed1998

Extractive bioconversions in aqueous two-phase systems

Although extractive bioconversions in aqueous two-phase systems (ATPSs) have been studied for over a decade, this has not yet resulted in widespread industrial application. The main reasons are the cost of the phase-forming polymers and the complexity of ATPS behavior. A number of recent developments may give a new impetus to this technology. First of all, the use of extractive bioconversions in ATPSs has recently been extended to high-value protein products, while in the meantime the development of low-cost ATPSs is ongoing. Furthermore, novel chromatographic methods enable the analysis of polymer and metabolite compositions in complex ATPS mixtures, and recently employed statistical experimental designs provide a tool for efficient data gathering, while they also reveal synergistic effects between process parameters. Together, these developments open the way towards improved modeling of partitioning behavior in ATPSs.

Journal Article↗

PubMed1998

Activity of glutamate dehydrogenase is increased in ammonia-stressed hybridoma cells.

The effect of added ammonia on the intracellular fluxes in hybridoma cells was investigated by metabolic-flux balancing techniques. It was found that, in ammonia-stressed hybridoma cells, the glutamate-dehydrogenase flux is in the reverse direction compared to control cells. This demonstrates that hybridoma cells are able to prevent the accumulation of ammonia by converting ammonia and alpha-ketoglutarate into glutamate. The additional glutamate that is produced by this flux, as compared to the control culture, is converted by the reactions catalyzed by alanine aminotransferase (45% of the extra glutamate) and aspartate aminotransferase (37%), and a small amount is used for the biosynthesis of proline (6%). The remaining 12% of the extra glutamate is secreted into the culture medium. The data suggest that glutamate dehydrogenase is a potential target for metabolic engineering to prevent ammonia accumulation in high-cell-density culture.

Amino Acids↗

PubMed1998

Shear sensitivity of animal cells from a culture-medium perspective.

Recently, several groups have published data on the shear sensitivity of suspended animal cells and the protective effect of certain polymers. These findings did not, at the time, seem to have great practical application because shear sensitivity did not cause great problems for large-scale applications in sparged and stirred-tank reactors using the then-current culture media and fermentation procedures. However, two recent developments might require renewed attention in sparged animal-cell cultures--protein-free media and new fermentation techniques.

Biotechnology↗

PubMed1998

IgG and hybridoma partitioning in aqueous two-phase systems containing a dye-ligand.

The effect of the important ATPS- and buffer parameters on IgG and hybridoma partitioning in ATPSs containing a PEG-dye-ligand was studied. Objective was to establish selection criteria for effective ligands for extractive fermentations with animal cells in ATPSs. In the presence of 1% PEG-dye-ligand the binding of IgG to the PEG-ligand was affected severely by the Na-chloride concentration. The tie-line length and pH affected IgG partitioning to a lesser extent. The desired partitioning of IgG into the top phase, was only obtained when, in addition to the 10 mmol/kg K-phosphate buffer, no Na-chloride was present. In an ATPS culture medium, with +/- 35 mmol/kg Na-bicarbonate and 60 mmol/kg Na-chloride, increasing the PEG-dye-ligand concentration up to 100% did increase the partition coefficient, but was not effective in concentrating the IgG in the top phase of ATPS culture medium at a pH of 7.8. Furthermore, addition of the PEG-dye-ligand to ATPS culture medium changed the hybridoma cell partitioning from the bottom phase to the interface.

Animals↗