Biomedical subjects

Johannes Tramper

Publications and source records attributed to Johannes Tramper.

At least 19 recordsLinked to original sources

PubMed2007

Prediction of volumetric productivity of an outdoor photobioreactor.

Volumetric productivity of Monodus subterraneus cultivated in an outdoor pilot-plant bubble column was predicted with a mathematical model. Two border cases to model the photobioreactor were chosen. Firstly, a model with no light integration in which it is assumed that microalgae can adapt immediately to local light conditions. Secondly, full light integration implicating that microalga can convert all absorbed light with a photosynthetic yield based on average light intensity. Because temperature and light conditions in our photobioreactor changed during the day, photosynthetic yields at any combination of temperature and light intensity were needed. These were determined in repeated-batch lab-scale experiments with an experimental design. The model was evaluated in an outdoor bubble column at different natural light conditions and different temperatures. Volumetric productivities in the bubble column were predicted and compared with experimental volumetric productivities. The light integration model over-estimated productivity, while the model in which we assumed no light integration under-estimated productivity. Light integration occurred partly (47%) during the period investigated. The average observed biomass yield on light was 0.60 g.mol(-1). The model of partly light integration predicted an average biomass yield on light of 0.57 g.mol(-1) and predicted that productivity could have been increased by 19% if culture temperature would have been maintained at 24 degrees C.

Bioreactors↗

PubMed2006

Controlling light-use by Rhodobacter capsulatus continuous cultures in a flat-panel photobioreactor.

The main bottleneck in scale-up of phototrophic fermentation is the low efficiency of light energy conversion to the desired product, which is caused by an excessive dissipation of light energy to heat. The photoheterotrophic formation of hydrogen from acetate and light energy by the microorganism Rhodobacter capsulatus NCIMB 11773 was chosen as a case study in this work. A light energy balance was set up, in which the total bacterial light energy absorption is split up and attributed to its destinations. These are biomass growth and maintenance, generation of hydrogen and photosynthetic heat dissipation. The constants defined in the light energy balance were determined experimentally using a flat-panel photobioreactor with a 3-cm optical path. An experimental method called D-stat was applied. Continuous cultures were kept in a so-called pseudo steady state, while the dilution rate was reduced slowly and smoothly. The biomass yield and maintenance coefficients of Rhodobacter capsulatus biomass on light energy were determined at 12.4 W/m(2) (400-950 nm) and amounted to 2.58 x 10(-8) +/- 0.04 x 10(-8) kg/J and 102 +/- 3.5 W/kg, respectively. The fraction of the absorbed light energy that was dissipated to heat at 473 W/m(2) depended on the biomass concentration in the reactor and varied between 0.80 and 0.88, as the biomass concentration was increased from 2.0 to 8.0 kg/m(3). The process conditions were estimated at which a 3.7% conversion efficiency of absorbed light energy to produced hydrogen energy should be attainable at 473 W/m(2).

Biomass↗

PubMed2006

Application of a continuous bioreactor cascade to study the effect of linoleic acid on hybridoma cell physiology.

The aim of the present study is to demonstrate the use of controlled bioreactors for toxicological studies. As a model system the effect of linoleic acid on hybridoma cells is studied in two well-controlled continuously operated bioreactors placed in series. In the first reactor the effect on rapid proliferating cells can be studied, while in the second reactor a special steady state is created, which allows studying the effect on apoptotic cells. Experiments are done at 0, 25, and 50 microM linoleic acid. At the end of the experiment with 50 microM linoleic acid, the concentration of linoleic acid is increased stepwise to determine the cytotoxic level. For rapid proliferating cells exposed to 25 and 50 microM stimulation of growth was observed. At 50 microM there was at the same time an increase in cell death through apoptosis. For stressed apoptotic cells linoleic acid caused partial growth inhibition at 25 and 50 microM and arrest of cell proliferation in the G(2)/M phase at 50 microM. For both, rapid proliferating cells and stressed apoptotic cells, complete growth inhibition occurred at 85 microM, with cells being arrested in the G(2)/M phase and dying mainly through necrosis. Cells in the bioreactor system appeared to be more sensitive towards linoleic acid than cells grown in multi-well plates. (IC(50) = 300 microM; IC(100) = 400 microM). Altogether the results of the present study reveal that the biostat experiments allow detailed analysis of the effect of a bioactive ingredient on cell physiology and behavior.

Apoptosis↗

PubMed2006

Fed-batch cultivation of Bordetella pertussis: metabolism and Pertussis Toxin production.

The production of acellular pertussis in comparison with whole cell pertussis vaccines demands 5-25 times the amount of Bordetella pertussis' virulence factors, such as Pertussis Toxin (PT), to produce the same number of vaccine doses. An increase in the volumetric productivity by employing fed-batch rather than the currently used batch cultivations of B. pertussis could reduce the cost price of acellular pertussis vaccines. This study defined the conditions that enable fed-batch cultivations at high specific PT production. A solution containing lactate and glutamate was fed to the cultures at various rates. The feed rate and whether or not the fed substrates were completely consumed, significantly influenced cellular metabolism. If lactate was detectable in the culture broth while glutamate was not, poly-hydroxy-butyrate (PHB) was formed. Any PHB present was metabolized when glutamate became detectable again in the culture liquid. At higher lactate and glutamate concentrations, free fatty acids were produced. Though toxic, free fatty acids were not the reason the cultures stopped growing. By choosing appropriate conditions, a cell density of 6.5 g/L dry weight was reached, i.e. a 7-fold increase compared to batch culture. The metabolic mechanisms behind the formation of PHB and fatty acids are discussed, as well as how to increase the cell density further. The PT production stopped at 12 mg/L, well before growth stopped, indicating that regulatory mechanisms of PT production may be involved.

Bacteriological Techniques↗

PubMed2006

Effect of relevant culture parameters on Pertussis Toxin expression by Bordetella pertussis.

Whooping cough vaccines are produced using different ranges of cultivation conditions and medium compositions, which are known to influence growth rate, virulence factor production and degradation, as well as the virulence factors' association to the cell. This study quantifies the impact of individual parameters on Pertussis Toxin (PT) production, using an optimized chemically defined medium as starting point, rather than a complex medium. A number of chemicals that are identified affect both growth rate and virulence factor production, which occur at similar levels in various commonly used production media. Also, degradation by proteolytic activity is shown to be an important parameter to monitor, since it significantly affects the PT yield. Low sodium concentrations, i.e. 50-75 mM rather than the conventional 100-140 mM, significantly increase the growth rate of the organism, the final optical density, as well as the association of PT to the cells. The absolute amount of biomass produced measured as dry weight, is similar for all sodium concentrations tested, contrary to earlier work. While it is known that high iron concentrations inhibit virulence factor production, it is shown here that iron-limited growth results in very high specific PT production. This finding may be used to produce a whole-cell vaccine with little biomass per dose, reducing whole-cell vaccine toxicity. The Bordetella pertussis strain 509 used here produces 30% more PT at 34 than at 37 degrees C, a commonly used cultivation temperature. The data in this study show that existing production processes for cellular and acellular vaccines can in principle be optimised considerably by taking simple measures.

Bordetella pertussis↗

PubMed2006

Virtual parameter-estimation experiments in Bioprocess-Engineering education.

Cell growth kinetics and reactor concepts constitute essential knowledge for Bioprocess-Engineering students. Traditional learning of these concepts is supported by lectures, tutorials, and practicals: ICT offers opportunities for improvement. A virtual-experiment environment was developed that supports both model-related and experimenting-related learning objectives. Students have to design experiments to estimate model parameters: they choose initial conditions and 'measure' output variables. The results contain experimental error, which is an important constraint for experimental design. Students learn from these results and use the new knowledge to re-design their experiment. Within a couple of hours, students design and run many experiments that would take weeks in reality. Usage was evaluated in two courses with questionnaires and in the final exam. The faculties involved in the two courses are convinced that the experiment environment supports essential learning objectives well.

Biomedical Engineering↗

PubMed2006

Hypothesized kinetic models for describing the growth of globular and encrusting demosponges.

The marine sponges Dysidea avara and Chondrosia reniformis (globular forms) were cultured in the laboratory on a diet of viable Phaeodactylum tricornutum cells and dissolved nutrients (algae and fish powders). Our growth data were combined with literature data for Pseudosuberites andrewsi (a globular sponge) and for the encrusting sponges Oscarella lobularis, Hemimycale columella, and Crambe crambe. The suitability of three growth models-linear, exponential, and radial accretive-for describing the growth of globular and encrusting sponges was assessed. Radial accretive growth was determined to be the best model to describe growth of both encrusting and globular sponges. Average growth rates of 0.051+/-0.016 and 0.019+/-0.003 mm/day (calculated as the increase of the radius of the sponge per day) were obtained experimentally for D. avara and C. reniformis, respectively.

Analysis of Variance↗

PubMed2005

Modeling conversion and transport phenomena in solid-state fermentation: a review and perspectives.

Solid-state fermentation (SSF) is accompanied inevitably by development of concentration and temperature gradients within the substrate particles and microbial biofilms. These gradients are needed for driving the transport of substrates and products. In addition, concentration gradients have been suggested to be crucial for obtaining the characteristics that define the products of SSF; nevertheless, gradients are also known to result in reduced productivity and unwanted side reactions. Solid-state fermentations are generally batch processes and this further complicates their understanding as conditions change with time. Mathematical models are therefore needed for improving the understanding of SSF processes and allowing their manipulation to achieve the desired outcomes. Existing models of SSF processes describe coupled substrate conversion and diffusion and the consequent microbial growth. Existing models disregard many of the significant phenomena that are known to influence SSF. As a result, available models cannot explain the generation of the numerous products that form during any SSF process and the outcome of the process in terms of the characteristics of the final product. This review critically evaluates the proposed models and their experimental validation. In addition, important issues that need to be resolved for improved modeling of SSF are discussed.

Algorithms↗

PubMed2005

Stable hybridoma cultivation in a pilot-scale acoustic perfusion system: long-term process performance and effect of recirculation rate.

Perfusion systems have the possibility to be operated continuously for several months. It is important that the performance of the cell retention device does not limit the operation time of a perfusion process used in the production of active pharmaceutical ingredients. Therefore, the aim of this study was to investigate the reliability and long-term stability of an acoustic perfusion process using the 200 L/d BioSep. As the BioSep is an external device, it is possible that dependent on the recirculation rate nutrient gradients occur in the external loop, which could affect the cell metabolism. Therefore, the effect of possible nutrient gradients on cell metabolism, viability and productivity was studied by varying the recirculation rate. In this study, it is shown that a perfusion process using a pilot-scale acoustic cell-retention device (200 L/d) is reliable and simple to operate, resulting in a stable 75-day cultivation of a hybridoma cell line producing a monoclonal antibody. The recirculation rate had a significant effect on the oxygen concentration in the external loop, with oxygen being depleted within the cell-retention device at recirculation rates below 6 m3/m(reactor)3.d (=600 L/d). The oxygen depletion at low circulation rates correlated with a slightly increased lactate production rate. For all other parameters no effect of the recirculation rate was observed, including cell death measured through the release of lactate dehydrogenase and specific productivity. A maximum specific productivity of 12 pg/cell.d was reached.

Antibodies, Monoclonal↗

PubMed2005

Large-scale production of pharmaceuticals by marine sponges: sea, cell, or synthesis?

Marine sponges are known to produce an overwhelming array of secondary metabolites with pharmaceutical potential. The technical and economical potential of using marine sponges for large-scale production of these compounds was assessed for two cases: the anticancer molecule halichondrin B from a Lissodendoryx sp., and avarol from Dysidea avara for its antipsoriasis activity. An economic and technical analysis was done for three potential production methods: mariculture, ex situ culture (in tanks), and cell culture. We concluded that avarol produced by mariculture or ex situ culture could become a viable alternative to currently used pharmaceuticals for the treatment of psoriasis. Production of halichondrin B from sponge biomass was found to not be a feasible process, mainly due to the extremely low concentration of the compound in the sponge. Technical feasibility was also analyzed for five alternatives: chemical synthesis, wild harvest, primmorph culture, genetic modification and semi-synthesis. It was concluded that the latter two approaches could prove to be valuable methods for the production of pharmaceuticals, based on chemical structures of secondary metabolites present in trace amounts in marine sponges.

Animals↗

PubMed2005

Marine sponges as pharmacy.

Marine sponges have been considered as a gold mine during the past 50 years, with respect to the diversity of their secondary metabolites. The biological effects of new metabolites from sponges have been reported in hundreds of scientific papers, and they are reviewed here. Sponges have the potential to provide future drugs against important diseases, such as cancer, a range of viral diseases, malaria, and inflammations. Although the molecular mode of action of most metabolites is still unclear, for a substantial number of compounds the mechanisms by which they interfere with the pathogenesis of a wide range of diseases have been reported. This knowledge is one of the key factors necessary to transform bioactive compounds into medicines. Sponges produce a plethora of chemical compounds with widely varying carbon skeletons, which have been found to interfere with pathogenesis at many different points. The fact that a particular disease can be fought at different points increases the chance of developing selective drugs for specific targets.

Animals↗

PubMed2005

Effect of low oxygen concentrations on growth and alpha-amylase production of Aspergillus oryzae in model solid-state fermentation systems.

Oxygen transfer in the fungal mat is a major concern in solid-state fermentation (SSF). Oxygen supply into the mycelial layers is hampered by diffusion limitation. For aerobic fungi, like Aspergillus oryzae, this oxygen depletion can be a severely limiting factor for growth and metabolite production. This paper describes the effects of a low oxygen concentration on growth at the levels of individual hyphae, colonies and overcultures, and on alpha-amylase production in overcultures. PDA medium was used to study the effect of a low oxygen concentration on hyphal elongation rate and branching frequency of hyphae, and radial extension rate of colonies of A. oryzae. We found similar saturation constants (K(O2)) of 0.1% (v/v in the gas phase) for oxygen concentration described with Monod kinetics, for branching frequency of hyphae and colony extension rate. When A. oryzae was grown as an over-culture on wheat-flour model substrate at 0.25% (v/v) oxygen concentration, the reduction in growth was more pronounced than as individual hyphae and a colony on PDA medium. Experimental results also showed that the specific alpha-amylase production rate under the condition of 0.25% (v/v) oxygen was reduced. Because the value of K(O2) is relatively low, it is reasonable to simplify the kinetics of growth of A. oryzae to zero-order kinetics in coupled diffusion/reaction models.

Aspergillus oryzae↗

PubMed2005

Significance of bed porosity, bran and specific surface area in solid-state cultivation of Aspergillus oryzae.

In this paper, the effects of bed porosity, bran and specific surface area on the oxygen uptake rate and alpha-amylase production during growth of Aspergillus oryzae on wheat grain and wheat-flour substrate are reported. The high oxygen uptake rate found during cultivation of A. oryzae on wheat-flour substrate was not reached on wheat grain. This is mainly due to the bran of the wheat grain. Using wheat-flour substrates, it was shown that extra bed porosity increased the alpha-amylase production and oxygen uptake rates. Furthermore, the peak oxygen uptake rate decreased with increasing surface area-volume ratio of the substrate particles, while the alpha-amylase production and the cumulative oxygen uptake per gram of initial substrate dry matter increased. The present work does not support a direct correlation between aerial mycelia and enzyme production. There is, however, a correlation between the alpha-amylase yield and the cumulative oxygen uptake (not the uptake rate). This implies that aerial mycelia could accelerate alpha-amylase production even if they do not increase the yield.

Aspergillus oryzae↗

PubMed2004

Effect of feed and bleed rate on hybridoma cells in an acoustic perfusion bioreactor: part I. Cell density, viability, and cell-cycle distribution.

For the development of optimal perfusion processes the effect of the feed and bleed rate on cell growth in a perfusion bioreactor was studied. The viable-cell density, viability, growth, death, and lysis rate and cell-cycle distribution of a hybridoma cell line producing an IgG1 were studied over a range of specific feed and bleed rates. It was found that the feed and bleed rates applied in the different cultures could be divided into two regions based on the viable-cell density and cell-cycle distribution. The cultures in the first region, low feed rates (0.5 and 1.0 d(-1)) combined with low bleed rates (0.05 and 0.10 d(-1)), were nutrient-limited, as an increase in the feed rate resulted in an increase in the viable-cell density. The cultures in the second region, high feed and bleed rates, were nonnutrient-limited. In this region the viable-cell density decreased more or less linearly with an increase in the bleed rate and was independent of the feed rate. This suggests that the cells were limited by a cell-related factor. Comparison of Trypan-blue dye-exclusion measurements and lactate-dehydrogenase activity measurements revealed that cell lysis was not negligible in this bioreactor set-up. Therefore, lactate-dehydrogenase activity measurements were essential to measure the death rate accurately. The specific growth rate was nearly constant for all tested conditions. The viability increased with an increase of the bleed rate and was independent of the feed rate. Furthermore, the specific productivity of monoclonal antibody was constant under all tested conditions. For the optimal design of a perfusion process it should first be established whether viability is an important parameter. If not, a bleed rate as low as possible should be chosen. If low viabilities are to be avoided, the bleed rate chosen should be higher, with the value depending on the desired viability. Next, the feed rate should be set at such a rate that the cells are just in the nonnutrient-limited region.

Acoustics↗

PubMed2003

Microalgae cultivation in air-lift reactors: modeling biomass yield and growth rate as a function of mixing frequency.

The slow development of microalgal biotechnology stems from the failure in the design of large-scale photobioreactors where light energy is efficiently utilized. Due to the light gradient inside the reactor and depending on the mixing properties, algae are subjected to certain light/dark cycles where the light period is characterized by a light gradient. These light/dark cycles will determine productivity and biomass yield on light energy. Air-lift reactors can be used for microalgae cultivation and medium-frequency light/dark cycles will be found in these systems. Light/dark cycles are associated with two basic parameters: first, the light fraction, i.e., the ratio between the light period and the cycle time and second, the frequency of the light/dark cycle. In the present work, light/dark cycles found in air-lift reactors were simulated taking into account the light gradient during the light period. The effect of medium-frequency cycle time (10-100 s) and light fraction (0.1-1) on growth rate and biomass yield on light energy of the microalgae Dunaliella tertiolecta was studied. The biomass yield and growth rates were mainly affected by the light fraction, while cycle time had little influence. Response surface methodology was used and a statistical model describing the effect of light fraction and cycle time on growth rate and biomass yield on light energy was developed. The use of the model as a reactor design criterion is discussed.

Biomass↗

PubMed2003

Progress towards a controlled culture of the marine sponge Pseudosuberites andrewsi in a bioreactor.

Explants of the tropical sponge Pseudosuberites andrewsi were fed with the marine diatom Phaeodactylum tricornotum. The food was supplied either as intact algae or as a filtered crude extract. Growth (measured as an increase in underwater weight) was found in both experiments. The explants fed with intact algae increased to an average underwater weight of 255% of the initial weight in 45-60 days. The explants fed with crude extract increased to an average of 200% of the initial weight in 30 days. These results show that it is possible to grow a sponge using a single microorganism species as a food source. In addition, it was demonstrated that sponges are also capable of growing on non-particulate food. Therefore, this study is an important step forward towards the development of controlled, in vivo sponge cultures.

Animal Feed↗

PubMed2003

Enclosed outdoor photobioreactors: light regime, photosynthetic efficiency, scale-up, and future prospects.

Enclosed outdoor photobioreactors need to be developed and designed for large-scale production of phototrophic microorganisms. Both light regime and photosynthetic efficiency were analyzed in characteristic examples of state-of-the-art pilot-scale photobioreactors. In this study it is shown that productivity of photobioreactors is determined by the light regime inside the bioreactors. In addition to light regime, oxygen accumulation and shear stress limit productivity in certain designs. In short light-path systems, high efficiencies, 10% to 20% based on photosynthetic active radiation (PAR 400 to 700 nm), can be reached at high biomass concentrations (>5 kg [dry weight] m(-3)). It is demonstrated, however, that these and other photobioreactor designs are poorly scalable (maximal unit size 0.1 to 10 m(3)), and/or not applicable for cultivation of monocultures. This is why a new photobioreactor design is proposed in which light capture is physically separated from photoautotrophic cultivation. This system can possibly be scaled to larger unit sizes, 10 to >100 m(3), and the reactor liquid as a whole is mixed and aerated. It is deduced that high photosynthetic efficiencies, 15% on a PAR-basis, can be achieved. Future designs from optical engineers should be used to collect, concentrate, and transport sunlight, followed by redistribution in a large-scale photobioreactor.

Biomass↗

PubMed2003

What can spores do for us?

Many organisms have the ability to form spores, a remarkable phase in their life cycles. Compared with vegetative cells, spores have several advantages (e.g. resistance to toxic compounds, temperature, desiccation and radiation) making them well suited to various applications. The applications of spores that first spring to mind are bio-warfare and the related, but more positive, field of biological control. Although they are often considered metabolically inert, spores can also be used as biocatalysts. Other uses for spores are found in the fields of probiotics, tumour detection and treatment, biosensing and in the "war against drugs".

Animals↗