Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Physical gels based on charge-driven bridging of nanoparticles by triblock copolymers
Lemmers, M. ; Spruijt, E. ; Akerboom, S. ; Voets, I.K. ; Aelst, A.C. van; Cohen Stuart, M.A. ; Gucht, J. van der - \ 2012
Langmuir 28 (2012)33. - ISSN 0743-7463 - p. 12311 - 12318.
dynamic light-scattering - shear-induced gelation - nanocomposite hydrogels - formulation process - colloidal silica - aqueous-solution - reversible gels - micelles - macromolecules - adsorption
We have prepared an aqueous physical gel consisting of negatively charged silica nanoparticles bridged by ABA triblock copolymers, in which the A blocks are positively charged and the B block is neutral and water-soluble. Irreversible aggregation of the silica nanoparticles was prevented by precoating them with a neutral hydrophilic polymer. Both the elastic plateau modulus and the relaxation time increase slowly as the gel ages, indicating an increase both in the number of active bridges and in the strength with which the end blocks are adsorbed. The rate of this aging process can be increased significantly by applying a small shear stress to the sample. Our results indicate that charge-driven bridging of nanoparticles by triblock copolymers is a promising strategy for thickening of aqueous particle containing materials, such as water-based coatings.
Relation between Gelation Conditions and the Physical Properties of Whey Protein Particles
Saglam, D. ; Venema, P. ; Vries, R.J. de; Aelst, A.C. van; Linden, E. van der - \ 2012
Langmuir 28 (2012)16. - ISSN 0743-7463 - p. 6551 - 6560.
beta-lactoglobulin - isolate gels - structural-properties - particulate gels - water emulsions - ph - emulsification - microstructure - microscopy - rheology
We have developed a robust procedure for preparing protein micro-particles with a high internal protein content ([small tilde]20 % w/w). Such protein micro-particles, having controlled size, protein content, and surface composition can be useful in the development of novel food products with high protein content. Protein particles were formed through emulsification of a WPI (whey protein isolate) solution (25% w/w) in sunflower oil containing 2.5 % (w/w) PGPR (Polyglycerol Polyricinoleate) as an oil-soluble emulsifier. The emulsion (w/o) was heated to induce gelation of the protein inside the emulsion droplets. Oil was removed through successive centrifugation and washing steps. This resulted in micron-sized protein particles dispersed in an aqueous phase. The average diameter of the particles was in the order of a few [mu]m, depending on the mixing speeds applied in the primary emulsification step. CLSM (Confocal laser scanning microscopy) analysis of protein particles indicated that there is oil associated with the particles, either surrounding the particles and/or distributed throughout the particles. NMR analysis showed that this amount of oil does not exceed 1.8% (w/w).
Opzuigen van eikenprocessierupsen; Onderzoek naar aanwezigheid van brandharen in de uitstromende lucht
Spijker, J.H. ; Aelst, A.C. van; Berg, C.A. van den; Niemeijer, C.M. - \ 2010
Wageningen : Alterra (Alterra-rapport 2106) - 26
thaumetopoea processionea - brandharen - stofzuigers - evaluatie - urticating hairs - vacuum cleaners - evaluation
De microharen van de eikenprocessierups vormen een risico voor de volksgezondheid. Alterra heeft een onderzoek uitgevoerd naar het opzuigen van microharen door de EPR-compactunit. Hierbij is onderzocht of de opgezogen haren door de EPR-compactunit zodanig worden opgevangen, dat deze niet met de uitstromende lucht de unit weer kunnen verlaten.
Bioaugmentation of UASB reactors with immobilized Sulfurospirillum barnesii for simultaneous selenate and nitrate removal
Lenz, M. ; Enright, A.M. ; O’Flaherty, V. ; Aelst, A.C. van; Lens, P.N.L. - \ 2009
Applied Microbiology and Biotechnology 83 (2009)2. - ISSN 0175-7598 - p. 377 - 388.
anaerobic granular sludge - waste-water treatment - respiring bacteria - elemental selenium - sulfate reduction - precipitation - remediation - bioreactors - chain - se
Whole-cell immobilization of selenate-respiring Sulfurospirillum barnesii in polyacrylamide gels was investigated to allow the treatment of selenate contaminated (790¿µg Se¿×¿L-1) synthetic wastewater with a high molar excess of nitrate (1,500 times) and sulfate (200 times). Gel-immobilized S. barnesii cells were used to inoculate a mesophilic (30°C) bioreactor fed with lactate as electron donor at an organic loading rate of 5 g chemical oxygen demand (COD)¿×¿L-1 day-1. Selenate was reduced efficiently (>97%) in the nitrate and sulfate fed bioreactor, and a minimal effluent concentration of 39¿µg Se¿×¿L-1 was obtained. Scanning electron microscopy with energy dispersive X-ray (SEM–EDX) analysis revealed spherical bioprecipitates of =2¿µm diameter mostly on the gel surface, consisting of selenium with a minor contribution of sulfur. To validate the bioaugmentation success under microbial competition, gel cubes with immobilized S. barnesii cells were added to an Upflow Anaerobic Sludge Bed (UASB) reactor, resulting in earlier selenate (24 hydraulic retention times (HRTs)) and sulfate (44 HRTs) removal and higher nitrate/nitrite removal efficiencies compared to a non-bioaugmented control reactor. S. barnesii was efficiently immobilized inside the UASB bioreactors as the selenate-reducing activity was maintained during long-term operation (58 days), and molecular analysis showed that S. barnesii was present in both the sludge bed and the effluent. This demonstrates that gel immobilization of specialized bacterial strains can supersede wash-out and out-competition of newly introduced strains in continuous bioaugmented systems. Eventually, proliferation of a selenium-respiring specialist occurred in the non-bioaugmented control reactor, resulting in simultaneous nitrate and selenate removal during a later phase of operation
Biological alkylation and colloid formation of selenium in methanogenic UASB reactors
Lenz, M. ; Smit, M.P.J. ; Binder, P. ; Aelst, A.C. van; Lens, P.N.L. - \ 2008
Journal of Environmental Quality 37 (2008)5. - ISSN 0047-2425 - p. 1691 - 1700.
enterobacter-cloacae sld1a-1 - anaerobic granular sludge - agricultural drainage sediment - selenate-reducing bacterium - bacillus sp sf-1 - elemental selenium - dimethyl selenone - bed reactors - waste-water - toxicity
Bioalkylation and colloid formation of selenium during selenate removal in upflow anaerobic sludge bed (UASB) bioreactors was investigated, The mesophilic (30 degrees C) UASB reactor (pH = 7.0) was operated for 175 d with lactate as electron donor at an organic loading rate of 2 g COD L-1 d(-1) and a selenium loading rate of 3.16 mg Se L-1 d(-1). Combining sequential filtration with ion chromatographic analysis for selenium oxyanions and solid phase micro extraction gas chromatography mass spectrometry (SPME-GC-MS) for alkylated selenium compounds allowed to entirely close the selenium mass balance in the liquid phase for most of the UASB operational runtime. Although selenate was removed to more than 98.6% from the liquid phase, a less efficient removal of dissolved selenium was observed due to the presence of dissolved alkylated selenium species (dimethylselenide and dimethyldiselenide) and colloidal selenium particles in the effluent. The alkylated and the colloidal fractions contributed LIP to 15 and 31%, respectively, to the dissolved selenium concentration. The size fractions Of the colloidal dispersion were: 4 to 0.45 mu m: up to 21%, 0.45 to 0.2 mu m: up to 11%, and particles smaller than 0.2 mu m: up to 8%. Particles of 4 to 0.45 pin were formed in the external settler, but did not settle. SEM-EDX analysis showed that microorganisms form these Selenium containing colloidal particles extracellularly on their Surface. Lowering the temperature by 10 degrees C for 6 h resulted in drastically reduced selenare removal efficiencies (after a delay of 1.5 d), accompanied by the temporary formation of all unknown, soluble, organic selenium species. This study shows that a careful process control is a prerequisite for selenium treatment in UASB bioreactors, as disturbances in the operational conditions induce elevated selenium effluent concentrations by alkylation and colloid formation.
Polymer Microcapsules with a Fiber-Reinforced Nanocomposite Shell
Sagis, L.M.C. ; Ruiter, R. de; Rossier Miranda, F.J. ; Ruiter, J. de; Schroën, C.G.P.H. ; Aelst, A.C. van; Kieft, H. ; Boom, R.M. ; Linden, E. van der - \ 2008
Langmuir 24 (2008)5. - ISSN 0743-7463 - p. 1608 - 1612.
human serum-albumin - amyloid fibrils - vesicles - nanocapsules - stability - ph - permeability - fabrication - emulsions - capsules
Polymer microcapsules can be used as controlled release systems in drugs or in foods. Using layer-by-layer adsorption of common food proteins and polysaccharides, we produced a new type of microcapsule with tunable strength and permeability. The shell consists of alternating layers of pectin and whey protein fibrils, yielding a fiber-reinforced nanocomposite shell. The strength can be tightly controlled by varying the number of layers or the density and length of the fibrils in the protein layers. The mechanical stability of these microcapsules appears to be superior to that of currently available multilayer capsules. The method involves only standard unit operations and has the potential for scaling up to industrial production volumes.
Lipophilic and hydrophilic moisturizers show different actions on human skin as revealed by cryo scanning electron microscopy
Caussin, J. ; Groenink, H.W.W. ; Graaff, A.M. de; Gooris, G.S. ; Wiechers, J.W. ; Aelst, A.C. van; Bouwstra, J.A. - \ 2007
Experimental Dermatology 16 (2007)11. - ISSN 0906-6705 - p. 891 - 898.
stratum-corneum hydration - double-blind - barrier - degradation - maturation - filaggrin - epidermis - xerosis - acid - mice
To study the mode of action of moisturizers on human skin, hydrophilic moisturizers in water and neat lipophilic moisturizers were applied on excised skin for 24 h at 32°C. Samples of the treated skin were subsequently visualized in a cryoscanning electron microscope. The stratum corneum (SC) appeared as a region of swollen corneocytes (the swollen region) sandwiched between two layers of relatively dry corneocytes (the upper and lower non-swelling regions respectively). Lipophilic moisturizers increased the water content of the SC, whereas hydrophilic moisturizers can also reduce the water content of the SC. When focusing on the effect of the moisturizers on the three different regions, it was observed that cells in the swelling region are most sensitive to the application of the moisturizers and that the change in SC thickness is most influenced by the change in the thickness of the swelling region. Summarizing, SC cells are not equally sensitive to moisturizer application: centrally located corneocytes are more sensitive than corneocytes in the upper and the lowest regions of the SC.
Onderzoek naar de mogelijke besmetting van een partij hooi met haren van de eikenprocessierups
Spijker, J.H. ; Aelst, A.C. van; Niemeijer, C.M. - \ 2007
Wageningen : Alterra (Alterra-rapport 1606) - 25
hooi - voer - paardenvoeding - paarden - besmetting - insecten - thaumetopoea processionea - tortricidae - insectenplagen - bomen - voederveiligheid - hay - feeds - horse feeding - horses - contamination - insects - insect pests - trees - feed safety
Mogelijk effect van dierziekte bij paarden als gevolg van het voorkomen van restatnten van de eikenprocessierups in diervoeder, namelijk hooi
Visualization studies of human skin in vitro/in vivo under the influence of an electrical field
Fatouros, N.E. ; Groenink, H.W.M. ; Graaff, A.M. de; Aelst, A.C. van; Koerten, H.K. ; Bouwstra, J.A. - \ 2006
European Journal of Pharmaceutical Sciences 29 (2006)2. - ISSN 0928-0987 - p. 160 - 170.
human stratum-corneum - in-vitro - transdermal iontophoresis - basic principles - drug-delivery - microscopy - ultrastructure - pretreatment - apomorphine - temperature
The aim of this study was to investigate the local changes in the ultrastructure of human skin after iontophoresis, using cryo-scanning, transmission and freeze fracture electron microscopy in human skin in vitro and in vivo. Human dermatomed skin was subjected to passive diffusion for 6 hours followed by nine hours of iontophoresis at 0.5 mA/cm2. The skin was processed and examined using both cryo-scanning electron microscopy (Cryo-SEM) and transmission electron microscopy (TEM). In addition, iontophoresis patches were applied to healthy volunteers for 3.5 h with 0.5 h of passive delivery followed by 3 h of iontophoresis at a current density of 0.25 mA/cm2. Subsequently, a series of tape stripping were performed, which were visualized by freeze fracture transmission electron microscopy (FFTEM). In vitro, the cryo-scanning electron microscopy study revealed that electric current induced changes in the water distribution in the stratum corneum. Transmission electron microscopy showed no local changes in the ultrastructure of the stratum corneum; however, layers of detached corneocytes were frequently observed especially at the anodal site. In vivo, there was no evidence of perturbation of the stratum corneum lipid organization; however, changes in the fracture were noticed deeper in the stratum corneum at the anodal side, indicating a weakening of the desmosomal structure. The in vitro/in vivo studies suggest that iontophoresis results in the formation of intercellular water pools (in vitro observation) and a weakening of the desmosomal structure (in vivo observation) only in the upper part of the stratum corneum. However, no changes in the lipid organization were observed in vitro and in vivo at the current densities of 0.5 and 0.25 mA/cm2, respectively. Therefore, even at relatively high current densities, no drastic changes in the ultrastructure of the stratum corneum are observed. As far as structural changes in stratum corneum are concerned iontophoresis is therefore a safe method at the experimental conditions we used
Description of Pratylenchus dunensis sp. n. (Nematoda: Pratylenchidae), a root-lesion nematode associated with the dune grass Ammophila arenaria (L.) Link
Peña, E. de la; Moens, M. ; Aelst, A.C. van; Karssen, G. - \ 2006
Nematology 8 (2006)1. - ISSN 1388-5545 - p. 79 - 88.
dutch coastal foredunes - molecular characterization - knot nematode - competition - descriptions - morphology - morphometrics - new species - plant pests - ribosomal DNA - wild relatives - Ammophila arenaria - Elymus farctus - Pratylenchus - Ammophila - Poaceae - Cyperales - monocotyledons - angiosperms - Spermatophyta - plants - eukaryotes - Elymus - invertebrates - animals - Pratylenchidae - nucleotide sequences - plant parasitic nematodes - nematoda - restriction fragment length polymorphism - intergenic DNA - taxonomy - beschrijvingen - morfologie - morfometrie - nieuwe soorten - plantenplagen - ribosomaal DNA - wilde verwanten - eenzaadlobbigen - bedektzadigen - planten - eukaryoten - ongewervelde dieren - dieren - nucleotidenvolgordes - plantenparasitaire nematoden - Nematoda - restrictiefragmentlengtepolymorfisme - intergeen DNA - taxonomie
A root-lesion nematode, Pratylenchus dunensis sp. n., is described and illustrated from Ammophila arenaria (L.) Link, a grass occurring abundantly in coastal dunes of Atlantic Europe. The new species is characterised by medium sized (454-579 ¿ m) slender, vermiform, females and males having two lip annuli (sometimes three to four; incomplete incisures only visible with scanning electron microscopy), medium to robust stylet (ca 16 ¿ m) with robust stylet knobs slightly set off, long pharyngeal glands (ca 42 ¿ m), lateral field with four parallel, non-equidistant, lines, the middle ridge being narrower than the outer ones, lateral field with partial areolation and lines converging posterior to the phasmid which is located between the two inner lines of the lateral field in the posterior half of the tail, round spermatheca filled with round sperm, vulva at 78% of total body length and with protruding vulval lips, posterior uterine sac relatively short (ca 19 ¿ m), cylindrical tail (ca 33 ¿ m) narrowing in the posterior third with smooth tail tip and with conspicuous hyaline part (ca 2 ¿ m). Males occur abundantly and present similar characteristics except for smaller dimensions for all morphological characters, but the head region is more truncated in outline than the female, spicule length is ca 15 ¿ m and testis length is ca 195 ¿ m. Nucleotide sequences of the rDNA expansion region D2D3 differed from the morphologically similar species P. penetrans and P. brzeskii that also occur in coastal dunes. These differences are supported by PCR-RFLP of the ITS-rDNA. Pratylenchus dunensis sp. n. was also found parasitising roots of Elymus farctus Viv.
Topdrukte in de plantencel
Schel, J.H.N. ; Aelst, A.C. van; Simons, Th. ; Lever-De Vries, C. - \ 2005
NVOX Tijdschrift voor Natuurwetenschap op School 30 (2005)8. - ISSN 0929-757X - p. 435 - 437.
Field-emission scanning electron microscopy analysis of morphology and enzyme distribution within an industrial biocatalytic particle
Roon, J.L. van; Aelst, A.C. van; Schroën, C.G.P.H. ; Tramper, J. ; Beeftink, H.H. - \ 2005
Scanning 27 (2005)4. - ISSN 0161-0457 - p. 181 - 189.
Field-emission scanning electron microscopy (FESEM) was used in a technical feasibility study to obtain insight into the internal morphology and the intraparticle enzyme distribution of Assemblase®, an industrial biocatalytic particle containing immobilized penicillin-G acylase. The results were compared with previous studies based on light and transmission electron microscopic techniques. The integrated FESEM approach yielded the same quantitative results as the microscopic techniques used previously. Given this technical equivalence, the integrated approach offers several advantages. First, the single preparation method and detection system avoids interpretation discrepancies between corresponding areas that were examined for different properties with different detection techniques in different samples. Second, the specimen size suitable for whole particle study is virtually unlimited, which simplifies sectioning and puts less stringent demands on the embedding technique. Furthermore, the sensitivity toward enzyme presence and distribution increases because the epitopes inside thick sections become available for labeling. Quick and unambiguous analysis of the relation between particle morphology and enzyme distribution is important because this information may be used in the future for the design of enzyme distributions in which the particle morphology can be used as a control parameter
Abscisic acid controls embryo growth potential and endosperm cap weakening during coffee (Coffea arabica cv. Rubi) seed germination
Silva, E.A.A. da; Toorop, P.E. ; Aelst, A.C. van; Hilhorst, H.W.M. - \ 2004
Planta 220 (2004)2. - ISSN 0032-0935 - p. 251 - 261.
endo-beta-mannanase - celery apium-graveolens - tomato seeds - radicle protrusion - water relations - cell-walls - beta-1,3-glucanases - imbibition - dormancy - expression
The mechanism and regulation of coffee seed germination were studied in Coffea arabica L. cv. Rubi. The coffee embryo grew inside the endosperm prior to radicle protrusion and abscisic acid (ABA) inhibited the increase in its pressure potential. There were two steps of endosperm cap weakening. An increase in cellulase activity coincided with the first step and an increase in endo-beta-mannanase (EBM) activity with the second step. ABA inhibited the second step of endosperm cap weakening, presumably by inhibiting the activities of at least two EBM isoforms and/or, indirectly, by inhibiting the pressure force of the radicle. The increase in the activities of EBM and cellulase coincided with the decrease in the force required to puncture the endosperm and with the appearance of porosity in the cell walls as observed by low-temperature scanning electronic microscopy. Tissue printing showed that EBM activity was spatially regulated in the endosperm. Activity was initiated in the endosperm cap whereas later during germination it could also be detected in the remainder of the endosperm. Tissue printing revealed that ABA inhibited most of the EBM activity in the endosperm cap, but not in the remainder of the endosperm. ABA did not inhibit cellulase activity. There was a transient rise in ABA content in the embryo during imbibition, which was likely to be responsible for slow germination, suggesting that endogenous ABA also may control embryo growth potential and the second step of endosperm cap weakening during coffee seed germination.
Description of Meloidogyne minor n.sp. (Nematoda: Meloidogynidae), a root-knot nematode associated with yellow patch disease in golf courses
Karssen, G. ; Bolk, R.J. ; Aelst, A.C. van; Beld, I. van den; Kox, L.F.F. ; Korthals, G.W. ; Molendijk, L.P.G. ; Zijlstra, C. ; Hoof, R.A. van; Cook, R. - \ 2004
Nematology 6 (2004)1. - ISSN 1388-5545 - p. 59 - 72.
m-fallax - heteroderidae - chitwoodi - identification - hapla - rdna - pcr
A relatively small root-knot nematode, Meloidogyne minor n. sp., is described and illustrated from tomato from the Netherlands. This new species is characterised by the following features: female with dorsally curved stylet, 14 Pm long, with transversely ovoid knobs slightly sloping backwards from the shaft; perineal pattern rounded; male stylet 18 mum long, large transversely ovoid knobs slightly sloping backwards from the shaft; head region not set off, labial disc elevated, lateral lips prominent; and second-stage juvenile 377 mum long, with hemizonid posterior adjacent to excretory pore; tail 54 mum long; and a distinct hyaline tail terminus 16 pm long. Additionally, distinguishing information on isozymes, DNA, cytogenetics and host plants is presented. Meloidogyne minor n. sp. has so far been found on potato in the Netherlands and has been detected in the British Isles on several golf courses, associated with yellow patches, often together with M. naasi.
Antennal sensilla of two parasitoid wasps: A comparative scanning electron microscopy study
Bleeker, M.A.K. ; Smid, H.M. ; Aelst, A.C. van; Loon, J.J.A. van; Vet, L.E.M. - \ 2004
Microscopy Research and Technique 63 (2004)5. - ISSN 1059-910X - p. 266 - 273.
olfactory receptor neurons - multiporous plate sensilla - cotesia-glomerata - apanteles-glomeratus - anomala-cuprea - scarab beetle - hymenoptera - braconidae - morphology - volatiles
Two closely related parasitoid wasp species, Cotesia glomerata (L.) and Cotesia rubecula (Marshall) (Hymenoptera:Braconidae), are different in their associative learning of plant odors. To provide a solid basis for our research on the mechanisms that underlie this difference, we described the morphology of the antennal sensilla of these two species using scanning electron microscopy complemented with transmission electron microscopy. Female and male antennae of both species have the same six types of sensilla. We classified these sensilla as sensilla trichodea without pores, sensilla trichodea with a tip pore, sensilla trichodea with wall pores, sensilla coeloconica type I, sensilla coeloconica type II, and sensilla placodea. We conclude that the morphology, numbers, and distribution of the sensory receptors are highly similar in these two closely related wasp species. Differences between species and sexes occurred only in sensilla placodea numbers. C. rubecula has more sensilla placodea than C. glomerata and males of both species have a larger number and a higher density of sensilla placodea compared to females of the same species. (C) 2004 Wiley-Liss, Inc.
Diffusional properties of methanogenic granular sludge: 1H-NMR Characterisation
Lens, P.N.L. ; Gastesi, R. ; Vergeldt, F. ; Aelst, A.C. van; Pisabarro, G. ; As, H. van - \ 2003
Applied and Environmental Microbiology 69 (2003)11. - ISSN 0099-2240 - p. 6644 - 6649.
nuclear-magnetic-resonance - fatty-acid degradation - mass-transfer - transport processes - molecular-diffusion - porous-media - spin-echo - biofilms - nmr - coefficients
The diffusive properties of anaerobic methanogenic and sulfidogenic aggregates present in wastewater treatment bioreactors were studied using diffusion analysis by relaxation time-separated pulsed-field gradient nuclear magnetic resonance (NMR) spectroscopy and NMR imaging. NMR spectroscopy measurements were performed at 22degreesC with 10 ml of granular sludge at a magnetic field strength of 0.5 T (20 MHz resonance frequency for protons). Self-diffusion coefficients of H2O in the investigated series of mesophilic aggregates were found to be 51 to 78% lower than the self-diffusion coefficient of free water. Interestingly, self-diffusion coefficients of H2O were independent of the aggregate size for the size fractions investigated. Diffusional transport occurred faster in aggregates growing under nutrient-rich conditions (e.g., the bottom of a reactor) or at high (55degreesC) temperatures than in aggregates cultivated in nutrient-poor conditions or at low (10degreesC) temperatures. Exposure of aggregates to 2.5% glutaraldehyde or heat (70 or 90degreesC for 30 min) modified the diffusional transport up to 20%. In contrast, deactivation of aggregates by HgCl2 did not affect the H2O self-diffusion coefficient in aggregates. Analysis of NMR images of a single aggregate shows that methanogenic aggregates possess a spin-spin relaxation time and self-diffusion coefficient distribution, which are due to both physical (porosity) and chemical (metal sulfide precipitates) factors.
Cellulose microfibrils in root hairs of Arabidopsis: A TEM study
Franssen-Verheijen, M.A.W. ; Aelst, A.C. van; Emons, A.M.C. ; Schel, J.H.N. - \ 2003
In: Proceedings NVvM Meeting, Papendal, December 2003, The Netherlands - p. 110 - 110.
Cellulose microfibrils in root hairs of Arabidopsis - a TEM study
Franssen-Verheijen, M.A.W. ; Aelst, A.C. van; Emons, A.M.C. ; Schel, J.H.N. - \ 2003
In: Abstracts of the 7th International Botanical Microscopy Meeting Plant Cell Biology Saturday 12 - Thursday 17 April 2003 Lisbon : Royal Microscopical Society - p. 50 - 50.
An antifungal compound produced by Bacillus subtilis YM 10-20 inhibits germination of Penicillium roqueforti conidiospores
Chitarra, G.S. ; Breeuwer, P. ; Nout, M.J.R. ; Aelst, A.C. van; Rombouts, F.M. ; Abee, T. - \ 2003
Journal of Applied Microbiology 94 (2003). - ISSN 1364-5072 - p. 159 - 166.
iturin-a - saccharomyces-cerevisiae - sorbic acid - lipopeptide - antibiotics - viability - growth - fungi - cells - maize
Aims: To identify and characterize an antifungal compound produced by Bacillus subtilis YM 10-20 which prevents spore germination of Penicillium roqueforti . Methods and Results: The antifungal compound was isolated by acid precipitation with HCl. This compound inhibited fungal germination and growth. Identification by HPLC and mass spectrometry analysis showed high similarity to iturin A. Permeabilization and morphological changes in P. roqueforti conidia in the presence of the inhibitor were revealed by fluorescence staining and SEM, respectively. Conclusions: The iturin-like compound produced by B. subtilis YM 10-20 permeabilizes fungal spores and blocks germination. Significance and Impact of the Study: Fluorescence staining in combination with flow cytometry and scanning electron microscopy are efficient tools for assessing the action of antifungal compounds against spores. Iturin-like compounds may permeabilize fungal spores and inhibit their germination.
Water distribution and related morphology in human stratum corneum at different hydration levels
Bouwstra, J.A. ; Graaff, A. de; Gooris, G.S. ; Nijsse, J. ; Wiechers, J.W. ; Aelst, A.C. van - \ 2003
Journal of Investigative Dermatology 120 (2003). - ISSN 0022-202X - p. 750 - 758.
x-ray-diffraction - lipid organization - human-skin - temperature - microscopy - diffusion
This study focused on the water distribution in human stratum corneum and on the swelling of the corneocytes. For this purpose stratum corneum was hydrated to various levels and used either for Fourier transform infrared spectroscopy or for cryo-scanning electron microscopy. The images were analyzed with respect to water localization and cell shape. The Fourier transform infrared spectra were measured to study the water-lipid interactions. The results show that water only slightly changes the lipid transitions in the stratum corneum even at a hydration level of 300% wt/wt compared to stratum corneum and that water is inhomogeneously distributed in the stratum corneum. No gradual increase in water level was observed in depth. At 57%-87% wt/wt water content the hydration level in the central part of stratum corneum is higher than in the superficial and deeper cell layers. Water domains are mainly present within the corneocytes and not in the intercellular regions. At a very high hydration level (300% wt/wt), the corneocytes are strongly swollen except for the deepest cell layers adjacent to the viable epidermis. The corneocytes in these layers are not swollen. At 300% wt/wt hydration level water domains are also present in intercellular regions. Between 17% wt/wt and 300% wt/wt the cell thickness increases linearly with the hydration level suggesting that swelling of cells mainly occurs in the direction perpendicular to the skin surface. At an increased hydration level, the corneocyte envelope more efficiently surrounds the cell content compensating for the increased cell volume. The changes in stratum corneum morphology with increasing water level have also been observed in dermatomed skin.
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