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Biomedical subjects

F J Weber

Publications and source records attributed to F J Weber.

At least 19 recordsLinked to original sources
PubMed2004

Limitations of membrane cultures as a model solid-state fermentation system.

AIMS: To examine the reliability of membrane cultures as a model solid-state fermentation (SSF) system. METHODS AND RESULTS: In overcultures of Aspergillus oryzae on sterilized wheat flour discs overlaid with a polycarbonate membrane, we demonstrated that the presence of membrane filters reduced the maximum respiration rate (up to 50%), and biomass and alpha-amylase production. We also show that the advantage of membrane cultures, i.e. total recovery of biomass, is not very evident for the system used, while the changes in metabolism and kinetics are serious drawbacks. CONCLUSIONS: The use of membrane cultures is artificial and without substantial benefits and therefore has to be carefully considered. SIGNIFICANCE AND IMPACT OF THE STUDY: In future studies on kinetics and stoichiometry of SSF, one should not completely rely on experiments using membrane cultures as a model SSF system.

Aspergillus oryzae↗
PubMed2003

Substrate aggregation due to aerial hyphae during discontinuously mixed solid-state fermentation with Aspergillus oryzae: experiments and modeling.

Solid-state fermentation (SSF) is prone to process failure due to channeling caused by evaporative cooling and the formation of an interparticle mycelium network. Mixing is needed to break the mycelium network and to avoid such failure. This study presents the first attempt to quantify and predict the effect of mycelium bonds on particle mixing and vice versa. We developed a novel experimental set-up to measure the tensile strength of hyphal bonds in SSF: Aspergillus oryzae was cultivated between two wheat-dough disks and the tensile strength of the aerial mycelium was measured with a texture analyzer. Tensile strength at different incubation times was related to oxygen consumption, to allow a translation to a rotating drum with A. oryzae cultivated on wheat grain. We performed several discontinuously mixed solid-state fermentations in the drum fermentor and measured the number and size of grain-aggregates remaining after the first mixing action. We integrated data on mycelium tensile strength into a previously developed two-dimensional discrete-particle model that calculates forces acting on individual substrate particles and the resulting radial-particle movements. The discrete-particle model predicted the quantity and size of the aggregates remaining after mixing successfully. The results show that the first mixing event in SSF with A. oryzae is needed to break mycelium to avoid aggregate formation in the grain bed, and not to distribute water added to compensate for evaporation losses, or smooth out temperature gradients.

Aspergillus↗
PubMed2003

Heat and water transfer in a rotating drum containing solid substrate particles.

In previous work we reported on the simulation of mixing behavior of a slowly rotating drum for solid-state fermentation (SSF) using a discrete particle model. In this investigation the discrete particle model is extended with heat and moisture transfer. Heat transfer is implemented in the model via interparticle contacts and the interparticle heat transfer coefficient is determined experimentally. The model is shown to accurately predict heat transfer and resulting temperature gradients in a mixed wheat grain bed. In addition to heat transfer, the addition and subsequent distribution of water in the substrate bed is also studied. The water is added to the bed via spray nozzles to overcome desiccation of the bed during evaporative cooling. The development of moisture profiles in the bed during spraying and mixing are studied experimentally with a water-soluble fluorescent tracer. Two processes that affect the water distribution are considered in the model: the intraparticle absorption process, and the interparticle transfer of free water. It is found that optimum distribution can be achieved when the free water present at the surface of the grains is quickly distributed in the bed, for example, by fast mixing. Alternatively, a short spraying period, followed by a period of mixing without water addition, can be applied. The discrete particle model developed is used successfully to examine the influence of process operation on the moisture distribution (e.g., fill level and rotation rate). It is concluded that the extended discrete particle model can be used as a powerful predictive tool to derive operating strategies and criteria for design and scale-up for mixed SSF and other processes with granular media.

Absorption↗
PubMed2002

Three-dimensional simulation of grain mixing in three different rotating drum designs for solid-state fermentation.

A previously published two-dimensional discrete particle simulation model for radial mixing behavior of various slowly rotating drums for solid-state fermentation (SSF) has been extended to a three-dimensional model that also predicts axial mixing. Radial and axial mixing characteristics were predicted for three different drum designs: (1) without baffles; (2) with straight baffles; and (3) with curved baffles. The axial mixing behavior was studied experimentally with video- and image-analysis techniques. In the drum without baffles and with curved baffles the predicted mixing behavior matched the observed behavior adequately. The predicted axial mixing behavior in the drum with straight baffles was predicted less accurately, and it appeared to be strongly dependent on particle rotation, which was in contrast to the other drum designs. In the drum with curved baffles complete mixing in the radial and axial direction was achieved much faster than in the other designs; that is, it was already achieved after three to four rotations. This drum design may therefore be very well suited to SSF. It is concluded that discrete particle simulations provide valuable detailed knowledge about particle transport processes, and this may help to understand and optimize related heat and mass transfer processes in SSF.

Air Movements↗
PubMed2001

Discrete particle simulations predicting mixing behavior of solid substrate particles in a rotating drum fermenter.

A soft-sphere discrete particle model was used to simulate mixing behavior of solid substrate particles in a slow rotating drum for solid-state fermentation. In this approach, forces acting on and subsequent motion of individual particles can be predicted. The (2D) simulations were qualitatively and quantitatively validated by mixing experiments using video and image analysis techniques. It was found that the simulations successfully predicted the mixing progress as a function of the degree of filling and size of the drum. It is shown that only relatively large, straight baffles perpendicular to the drum wall (67% of the drum radius) increase the mixing performance of the rotating drum. Considering the different aspects of mixing dealt with in this work, it is concluded that the soft sphere discrete particle model can serve as a valuable tool for investigating mixing of solid substrate particles. Finally, it is expected that this model may evolve into a potential tool for design and scale-up of mixed solid-state fermenters.

Bioreactors↗
PubMed2001

The fungal biocontrol agent Coniothyrium minitans: production by solid-state fermentation, application and marketing.

Biological control agents (BCAs) are potential alternatives for the chemical fungicides presently used in agriculture to fight plant diseases. Coniothyrium minitans is an example of a promising fungal BCA. It is a naturally occurring parasite of the fungus Sclerotinia sclerotiorum, a wide-spread pathogen which substantially reduces the yield of many crops. This review describes, exemplified by C. minitans, the studies that need to be carried out before a fungal BCA is successfully introduced into the market. The main aspects considered are the biology of C. minitans, the development of a product by mass production of spores using solid-state fermentation technology, its biocontrol activity and marketing of the final product.

Ascomycota↗
PubMed2001

An outline of the 1994-1998 European inspection and maintenance study: part I-design, tests, and results of experimental methods.

This paper provides an overview and the main results of a study aiming to evaluate current and alternative inspection and maintenance (I/M) programs to control emissions from in-use cars in Europe. For this purpose, a large number of passenger cars from five countries (France, Germany, Greece, the Netherlands, and the United Kingdom) were tested according to a common test protocol that included a variety of driving cycles and short tests, both legislative and specifically developed for this exercise. Evaluation of all test results was conducted with the objective of defining effective I/M test procedures and examining the potential of periodic I/M programs to reduce pollutant emissions and improve fuel economy of in-use cars. The results indicate that the current idle test used for catalyst-equipped cars in Europe is probably ineffective, while short transient loaded testing was found to offer higher potential in environmental terms. Regarding conventional gasoline cars, it is concluded that the idle test is sufficient, provided that the CO cut point is reduced and an HC test is added at high idle. Finally, the effectiveness of the free acceleration smoke test for diesels is questioned, while a transient cycle with continuous opacity measurement was found to be very promising. A companion paper further uses these results to analyze the likely cost-effectiveness on a per-country basis and discusses the possible effect of maintenance on emissions.

Air Pollution↗
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↗
PubMed1995

Growth of the fungus Cladosporium sphaerospermum with toluene as the sole carbon and energy source.

The fungus Cladosporium sphaerospermum was isolated from a biofilter used for the removal of toluene from waste gases. This is the first report describing growth of a eukaryotic organism with toluene as the sole source of carbon and energy. The oxygen consumption rates, as well as the measured enzyme activities, of toluene-grown C. sphaerospermum indicate that toluene is degraded by an initial attack on the methyl group.

Biodegradation, Environmental↗
PubMed1994

Cis/trans isomerization of fatty acids as a defence mechanism of Pseudomonas putida strains to toxic concentrations of toluene.

Defence mechanisms of three Pseudomonas putida strains growing in the presence of toluene up to 50% (v/v) were investigated. The three strains reacted to toxic concentrations of toluene by accumulating trans unsaturated fatty acids in the membrane instead of the cis isomers. The membranes of the toluene-adapted cells possessed a higher trans/cis ratio and had a higher lipid-ordering since the transition temperature was about 7 centigrade degrees higher compared to the non-adapted cells.

Drug Resistance, Microbial↗
PubMed1992

Purification and properties of the NADH reductase component of alkene monooxygenase from Mycobacterium strain E3.

Alkene monooxygenase, a multicomponent enzyme system which catalyzes the epoxidation of short-chain alkenes, is induced in Mycobacterium strain E3 when it is grown on ethene. We purified the NADH reductase component of this enzyme system to homogeneity. Recovery of the enzyme was 19%, with a purification factor of 920-fold. The enzyme is a monomer with a molecular mass of 56 kDa as determined by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It is yellow-red with absorption maxima at 384, 410, and 460 nm. Flavin adenine dinucleotide (FAD) was identified as a prosthetic group at a FAD-protein ratio of 1:1. Tween 80 prevented irreversible dissociation of FAD from the enzyme during chromatographic purification steps. Colorimetric analysis revealed 2 mol each of iron and acid-labile sulfide, indicating the presence of a [2Fe-2S] cluster. The presence of this cluster was confirmed by electron paramagnetic resonance spectroscopy (g values at 2.011, 1.921, and 1.876). Anaerobic reduction of the reductase by NADH resulted in formation of a flavin semiquinone.

Alkenes↗
PubMed1991

Alkene monooxygenase from Mycobacterium: a multicomponent enzyme.

A NADH- or NADPH-dependent alkene monooxygenase (AMO) activity has been detected in cell-free extracts of the ethene-utilizing Mycobacterium E3 and Mycobacterium aurum L1. The activity was not linear with protein concentration in the assay suggesting AMO is a multicomponent enzyme. The inhibition pattern of AMO activity was very similar to the inhibition patterns published for the three-component soluble methane monooxygenases. Fractionation of crude extracts revealed that combination of two fractions was required to restore alkene monooxygenase activity. The first fraction was inhibited by acetylene, indicating it contained an oxygenase component. The second fraction contained reductase activity which was absent from non-induced cells. This reductase activity is probably the NADH-acceptor reductase of AMO.

Chromatography, Gel↗
PubMed1980

The binding of tumor localizing porphyrins to a fibrin matrix and their effects following photoirradiation.

The binding of two tumor localizing porphyrins, meso-tetra (4-carboxyphenyl) porphine (TCPP) and meso-tetra (4-sulfonatophenyl) porphine (TPPS4) to fibrin clots was determined in vitro. Both TCPP and TPPS4 were found to bind extensively, although weakly, to fibrin. No appreciable binding by Hematoporphyrin IX to the fibrin matrix was detectable. Similar results were obtained whether the clot was non-crosslinked or crosslinked with factor XIII. Photoirradiation of a porphyrin-impregnated non-crosslinked clot rendered it urea insoluble. Electrophoretic analysis indicated that the alpha chain of the fibrinogen molecule was most affected by photoirradiation. This was manifested as a loss of the alpha chain intensity and a concomitant increase of high molecular weight components, suggesting the formation of crosslinks. No substantial differences were noted in susceptibility to plasmin lysis between photoirradiated and non-irradiated clots. Photoirradiated clots were, however, significantly more resistant to lysis induced by the plasminogen activators urokinase and streptokinase, suggesting that inactivation of plasminogen within the clot matrix had occurred during photoirradiation. The relevance of porphyrin binding to fibrin with regard to tumor localization and destruction is also discussed.

Binding Sites↗