Biomedical subjects

Wolfgang Burgstaller

Publications and source records attributed to Wolfgang Burgstaller.

8 recordsLinked to original sources

PubMed2006

Determination of adenine and pyridine nucleotides in glucose-limited chemostat cultures of Penicillium simplicissimum by one-step ethanol extraction and ion-pairing liquid chromatography.

Under specific conditions Penicillium simplicissimum excretes large amounts of organic acids, mainly citrate. As the energetic status of the hyphae might play a role in that respect, we developed a method for the determination of adenine (adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate) and pyridine (nicotinamide adenine dinucleotide and reduced nicotinamide adenine dinucleotide (NADH)) nucleotides in hyphae of P. simplicissimum. An optimum separation of the five compounds in less than 15 min was possible on a C-8 column, utilizing 50 mM aqueous triethylamine-buffer (pH 6.5) and acetonitrile as mobile phase; detection was performed at 254 nm. With the exception of NADH, which could not be determined accurately due to stability problems, the method was sensitive (LOD < or = 0.7 ng on-column), repeatable (sigma(rel) < or = 4.4%), accurate (recovery rates between 97.9 and 104.9%), and precise (intraday variation < or = 9.4%, interday variation < or = 6.2 %). For an optimum extraction of the nucleotides the chemostat samples were directly placed into hot (90 degrees C) 50% ethanol, and shaken for 10 min, followed by evaporation of the solvent and a solid phase extraction cleanup of the redissolved aqueous samples. With this method the nucleotide concentrations in hyphae from a glucose-limited chemostat culture and the respective energy charge were determined. Additionally, the effect of the time lag between sampling and extraction and the effect of a glucose pulse on nucleotide concentrations were determined.

Adenine Nucleotides↗

PubMed2006

Thermodynamic boundary conditions suggest that a passive transport step suffices for citrate excretion in Aspergillus and Penicillium.

Excretion of organic acids, e.g. citrate, by anamorphic fungi is a frequent phenomenon in natural habitats and in laboratory cultures. In biotechnological processes for citrate production with Aspergillus niger extracellular citrate concentrations up to 1 mol l(-1) are achieved. Intracellular citrate concentrations are in the millimolar range. Therefore the question arises whether citrate excretion depends on active transport. In this article thermodynamic calculations are presented for citrate excretion by A. niger at an extracellular pH of 3 and by Penicillium simplicissimum at an extracellular pH of 7. From the results of these calculations it is concluded that in both cases a passive transport step suffices for citrate excretion.

Aspergillus↗

PubMed2004

Changes in properties of glutamate transport in Trichoderma viride vegetative mycelia upon adaptation to glutamate as carbon source.

The U-(14)C-labelled glutamate uptake was measured in both sucrose- and glutamate-grown mycelia of Trichoderma viride. The biomass yield was five-fold lower with glutamate as a sole carbon source. The rate of glutamate transport measured at a glutamate concentration of 1 mM remained unchanged in glutamate-grown mycelia whereas the properties of the glutamate transport were substantially changed compared to sucrose-grown mycelia. The glutamate uptake in both sucrose- and glutamate-grown mycelia was inhibited by an uncoupler (3,3',4',5-tetrachlorosalicylanilide) but the inhibitory efficiency was higher in the latter. The affinity of the permease to glutamate increased approximately five-fold in the glutamate-grown mycelia (about 76 microM compared to about 16 microM). The pH optimum for glutamate uptake was 4 in sucrose-grown mycelia but the glutamate-grown mycelia had two pH optima, one at pH 4 and the second between pH 6 and 7. The inhibition of glutamate uptake by other amino acids yielded different inhibitory patterns in the two mycelia under study. The glutamate uptake in mycelia of different ages also showed differences in both transport rate and temporal pattern. The results show that the growth of mycelia on glutamate led to the appearance of an additional permease with different properties and suggest that only this permease is operating in mycelia grown on glutamate.

Adaptation, Physiological↗

PubMed2003

A faster method for 3D/2D medical image registration--a simulation study.

3D/2D patient-to-computed-tomography (CT) registration is a method to determine a transformation that maps two coordinate systems by comparing a projection image rendered from CT to a real projection image. Iterative variation of the CT's position between rendering steps finally leads to exact registration. Applications include exact patient positioning in radiation therapy, calibration of surgical robots, and pose estimation in computer-aided surgery. One of the problems associated with 3D/2D registration is the fact that finding a registration includes solving a minimization problem in six degrees of freedom (dof) in motion. This results in considerable time requirements since for each iteration step at least one volume rendering has to be computed. We show that by choosing an appropriate world coordinate system and by applying a 2D/2D registration method in each iteration step, the number of iterations can be grossly reduced from n6 to n5. Here, n is the number of discrete variations around a given coordinate. Depending on the configuration of the optimization algorithm, this reduces the total number of iterations necessary to at least 1/3 of it's original value. The method was implemented and extensively tested on simulated x-ray images of a tibia, a pelvis and a skull base. When using one projective image and a discrete full parameter space search for solving the optimization problem, average accuracy was found to be 1.0 +/- 0.6(degrees) and 4.1 +/- 1.9 (mm) for a registration in six parameters, and 1.0 +/- 0.7(degrees) and 4.2 +/- 1.6 (mm) when using the 5 + 1 dof method described in this paper. Time requirements were reduced by a factor 3.1. We conclude that this hardware-independent optimization of 3D/2D registration is a step towards increasing the acceptance of this promising method for a wide number of clinical applications.

Algorithms↗

PubMed2003

Characterization of the Penicillium chrysogenum antifungal protein PAF.

The filamentous fungus Penicillium chrysogenum abundantly secretes the small, highly basic and cysteine-rich protein PAF ( Penicillium antifungal protein). In this study, the antifungal activity of PAF is described. PAF inhibited the growth of a variety of filamentous fungi, including opportunistic human pathogenic and phytopathogenic fungi, whereas bacterial and yeast cells were unaffected. PAF reduced the conidial germination and hyphal extension rates in a dose-dependent manner and induced severe changes in cell morphology that resulted in crippled and distorted hyphae and atypical branching. Growth-affected hyphae suffered from oxidative stress, plasma membrane leakage, and metabolic inactivity, which points to an induction of multifactorial effects in sensitive fungi. In contrast to other known antifungal proteins, the effects of PAF were only partially antagonized by cations.

Antifungal Agents↗

PubMed2002

Characterization of an inducible citrate uptake system in Penicillium simplicissimum.

When citrate was used as a sole source of carbon, citrate uptake by Penicillium simplicissimum increased 267-fold (if glucose-grown mycelium was adapted to citrate) or 1400-fold (if the fungus was grown on citrate) compared to glucose-grown mycelium. Inhibition of macromolecular synthesis prevented this stimulation of citrate uptake. Citrate uptake by glucose-grown mycelium was low (0.0015 nmol min(-1) (mg DW)(-1)) and most probably due to diffusion of undissociated citric acid. Citrate-adapted mycelium had a K(M) of 65 micromol l(-1) and a V(max) of 0.34 nmol min(-1) (mg DW)(-1). In citrate-grown mycelium K(M) was 318 micromol l(-1) and V(max) was 8.5 nmol min(-1) (mg DW)(-1). Citrate uptake was inhibited by sodium azide and uncouplers (TCS, 3,3',4',5-tetrachlorosalicylanilide; FCCP, carbonyl cyanide p-trifluoromethoxyphenyl-hydrazone). Because of this we postulate that the induced citrate uptake must be an active transport process. The pH optimum of citrate uptake was between pH 6 and 7. EDTA and Mg2+, Mn2+, Cu2+, Zn2+, Fe2+, Ca2+ only weakly influenced the induced citrate uptake. The properties of citrate uptake by Aspergillus niger and P. simplicissimum are compared.

Biological Transport↗

PubMed2002

Succinate synthesis and excretion by Penicillium simplicissimum under aerobic and anaerobic conditions.

Succinate is an interesting chemical for industries producing food and pharmaceutical products, surfactants, detergents and biodegradable plastics. Succinate is produced mainly by a mixed-acid fermentation process using anaerobically growing bacteria. However, succinate excretion is also widespread among fungi. In this article we report results on the intracellular concentration and the excretion of succinate by Penicillium simplicissimum under aerobic and anaerobic conditions. The intracellular concentration of succinate increased slightly with the specific growth rate and strongly if the respiratory chain was inhibited by sodium azide or anaerobic conditions (N(2)). A strong increase of succinate excretion was observed if the respiratory chain was inhibited. It is suggested that succinate synthesis under functional (sodium azide) or environmental (N(2)) anaerobic conditions occurs via the reductive part of the tricarboxylic acid cycle. Succinate is then excreted because the oxidative part of the tricarboxylic acid cycle is inactive. A possible role of succinate synthesis in the regeneration of NAD ('fumarate respiration') is discussed.

Adenosine Triphosphate↗

PubMed2002

Efflux of organic acids in Penicillium simplicissimum is an energy-spilling process, adjusting the catabolic carbon flow to the nutrient supply and the activity of catabolic pathways.

Continuous cultivation was used to study the effect of glucose, ammonium, nitrate or phosphate limitation on the excretion of tricarboxylic acid (TCA) cycle intermediates by Penicillium simplicissimum. Additionally, the effect of benzoic acid, salicylhydroxamic acid (SHAM) and 2,4-dinitrophenol on TCA cycle intermediates was studied. The physiological state of the fungus was characterized by its glucose and O(2) consumption, its CO(2) production, its intra- and extracellular concentrations of TCA cycle intermediates, as well as by its biomass yield, its maintenance coefficient and its respiratory quotient. The excretion of TCA cycle intermediates was observed during ammonium-, nitrate- and phosphate-limited growth. The highest productivity was found with phosphate-limited growth. The respiratory quotient was 1.3 under ammonium limitation and 0.7 under phosphate limitation. Citrate was always the main excreted intermediate. This justifies calling this excretion an energy-spilling process, because citrate excretion avoids the synthesis of too much NADH. The addition of benzoic acid further increased the excretion of TCA cycle intermediates by ammonium-limited hyphae. A SHAM-sensitive respiration was constitutively present during ammonium-limited growth of the fungus. The sum of the excreted organic acids was negatively correlated with the biomass yield (Y(GlcX)).

Benzoic Acid↗