PubMed Health⌕ Search

Biomedical subjects

J Dijksterhuis

Publications and source records attributed to J Dijksterhuis.

12 recordsLinked to original sources
PubMed2006

High viscosity and anisotropy characterize the cytoplasm of fungal dormant stress-resistant spores.

Ascospores of the fungus Talaromyces macrosporus are dormant and extremely stress resistant, whereas fungal conidia--the main airborne vehicles of distribution--are not. Here, physical parameters of the cytoplasm of these types of spores were compared. Cytoplasmic viscosity and level of anisotropy as judged by spin probe studies (electron spin resonance) were extremely high in dormant ascospores and during early germination and decreased only partly after trehalose degradation and glucose efflux. Upon prosilition (ejection of the spore), these parameters fell sharply to values characteristic of vegetative cells. These changes occurred without major volume changes that suggest dramatic changes in cytoplasmic organization. Azide reversibly inhibited prosilition as well as the decline in cytoplasmic parameters. No organelle structures were observed in etched, cryoplaned specimens of ascospores by low-temperature scanning electron microscopy (LTSEM), confirming the high cytoplasmic viscosity. However, cell structures became visible upon prosilition, indicating reduced viscosity. The viscosity of fresh conidia of different Penicillium species was lower, namely, 3.5 to 4.8 cP, than that of ascospores, near 15 cP. In addition the level of anisotropic motion was markedly lower in these cells (h(0)/h(+1) = 1.16 versus 1.4). This was confirmed by LTSEM images showing cell structures. The decline of cytoplasmic viscosity in conidia during germination was linked with a gradual increase in cell volume. These data show that mechanisms of cytoplasm conservation during germination differ markedly between ascospores and conidia.

Anisotropy↗
PubMed2004

Dormant ascospores of Talaromyces macrosporus are activated to germinate after treatment with ultra high pressure.

AIMS: Ascospores of Talaromyces macrosporus are constitutively dormant and germinate after a strong external shock, classically a heat treatment. This fungus is used as a model system to study heat resistance leading to food spoilage after pasteurization. This study evaluates the effect of high pressure on the germination behaviour of these spores. METHODS AND RESULTS: Ascospore containing bags were subjected to ultra high pressure and spores were plated out on agar surfaces. Untreated suspensions showed invariably very low germination. Increased germination of ascospores occurred after short treatments at very high pressure (between 400 and 800 MPa). Activation is partial compared with heat activation and did not exceed 6.9% (65 times that of untreated suspensions) of the spore population. Maximum activation was attained shortly (10 s-3 min) after the pressure was applied and accompanied by cell wall deformations as judged by scanning electron microscopy. The spores observed in this study were harvested from cultures that were 39-58 days old. The maturity of spores at similar developmental stages was measured by assessing the heat resistance of ascospores. Between 20 and 40 days heat resistance increased 2.4-fold, but only an additional increase of 1.3-fold was observed at later stages (40-67 days). CONCLUSIONS: Our investigations show that high pressure constitutes a second type of shock that can activate heat-resistant ascospores to germinate. Activation is maximal after very short treatments and accompanied with changes in the cell wall structure. High-pressure activation is not the result of immaturity of the ascospores. SIGNIFICANCE AND IMPACT OF THE STUDY: These observations are relevant for the application of high pressure as a novel pasteurization method.

Food Microbiology↗
PubMed2004

The SC15 protein of Schizophyllum commune mediates formation of aerial hyphae and attachment in the absence of the SC3 hydrophobin.

Disruption of the SC3 gene in the basidiomycete Schizophyllum commune affected not only formation of aerial hyphae but also attachment to hydrophobic surfaces. However, these processes were not completely abolished, indicating involvement of other molecules. We here show that the SC15 protein mediates formation of aerial hyphae and attachment in the absence of SC3. SC15 is a secreted protein of 191 aa with a hydrophilic N-terminal half and a highly hydrophobic C-terminal half. It is not a hydrophobin as it lacks the eight conserved cysteine residues found in these proteins. Besides being secreted into the medium, SC15 was localized in the cell wall and the mucilage that binds aerial hyphae together. In a strain in which the SC15 gene was deleted (DeltaSC15) formation of aerial hyphae and attachment were not affected. However, these processes were almost completely abolished when the SC15 gene was deleted in the DeltaSC3 background. The absence of aerial hyphae in the DeltaSC3DeltaSC15 strain can be explained by the inability of the strain to lower the water surface tension and to make aerial hyphae hydrophobic.

Amino Acid Sequence↗
PubMed2003

Confocal microscopy of Spitzenkörper dynamics during growth and differentiation of rust fungi.

The membrane-selective fluorescent dye FM4-64, N-(3-triethylammoniumpropyl)-4-(6-(4-(diethylamino)phenyl)hexatrienyl)pyridium dibromide, was used to stain the apical vesicle cluster within the specialized Spitzenkörper of the germ tube of the rust fungi Uromyces vignae and Puccinia graminis f. sp. tritici grown on glass surfaces. The Spitzenkörper stained within 15 min following addition of the dye. Optical sectioning by confocal microscopy of stained hyphal tips showed that the Spitzenkörper was asymmetrically positioned close to the cell-substratum interface during germ tube growth. The Spitzenkörper showed variations in shape and positioning over short (5 s) time intervals. The movement to a new location in the hyphal dome was followed by new growth in that region, consistent with the view that the Spitzenkörper supplies secretory vesicles for germ tube growth. A pronounced Spitzenkörper disappeared at the onset of appressorium differentiation during swelling of the germ tube. However, a stained structure, similar in appearance to a Spitzenkörper, was again observed during the formation of the highly polarized penetration peg.

Basidiomycota↗
PubMed2003

Defective zoospore encystment and suppressed cyst germination of Phytophthora palmivora caused by transient leaching treatments.

The behaviour of encysting zoospores of Phytophthora palmivora during leaching conditions was studied. Zoospores encysted and germinated successfully on polycarbonate membranes after mechanical agitation. Transient (10 min) leaching treatments with nutrient-free buffer underneath the membranes resulted in abnormal encystment and poor germination. The disruption was greatest when leaching was applied during the first minutes after start of encystment and not observed after 20 min. The early sensitivity of cells to leaching coincided with the period when alkali-resistant cell walls were formed (2-6 min after mechanical agitation). Effects of calcium and organic nutrients on encystment during leaching and germination after these treatments were studied. The disruption of encystment by early leaching treatments, but not the suppression of cyst germination, was overcome by adding calcium chloride during mechanical agitation of zoospores. Leaching with calcium containing buffer resulted in suppressed cyst germination as was the case with buffer alone. Leaching with 0.1% peptone containing buffer promoted consistently high encystment and germination.

Buffers↗
PubMed2002

High-oxygen and high-carbon dioxide containing atmospheres inhibit growth of food associated moulds.

AIMS: The objective of this study was to determine the relationship between the growth of three foodborne fungi and high-oxygen modified atmosphere. METHODS AND RESULTS: Petri dishes were incubated in a series of connected flasks, which were placed in a climatized room and flushed continuously with the desired gas atmosphere. A combination of 80% oxygen and 20% carbon dioxide resulted in reduced growth of Rhizopus stolonifer, Botrytis cinerea and Penicillium discolor compared with ambient atmosphere conditions. Combining 80% oxygen and 20% carbon dioxide at 10 degrees C arrested growth of B. cinerea for 17 d while an elevated carbon dioxide concentration only inhibited growth up to 11 d. In addition, the peroxidase activity was doubled at 80% oxygen and decreased when 10% carbon dioxide was present. IMPACT OF THE STUDY: This study demonstrates the potential use of elevated oxygen levels in a modified atmosphere to inhibit food-associated mould growth.

Atmosphere↗
PubMed2000

Confocal microscopy of FM4-64 as a tool for analysing endocytosis and vesicle trafficking in living fungal hyphae.

Confocal microscopy of amphiphilic styryl dyes has been used to investigate endocytosis and vesicle trafficking in living fungal hyphae. Hyphae were treated with FM4-64, FM1-43 or TMA-DPH, three of the most commonly used membrane-selective dyes reported as markers of endocytosis. All three dyes were rapidly internalized within hyphae. FM4-64 was found best for imaging the dynamic changes in size, morphology and position of the apical vesicle cluster within growing hyphal tips because of its staining pattern, greater photostability and low cytotoxicity. FM4-64 was taken up into both the apical and subapical compartments of living hyphae in a time-dependent manner. The pattern of stain distribution was broadly similar in a range of fungal species tested (Aspergillus nidulans, Botrytis cinerea, Magnaporthe grisea, Neurospora crassa, Phycomyces blakesleeanus, Puccinia graminis, Rhizoctonia solani, Sclerotinia sclerotiorum and Trichoderma viride). With time, FM4-64 was internalized from the plasma membrane appearing in structures corresponding to putative endosomes, the apical vesicle cluster, the vacuolar membrane and mitochondria. These observations are consistent with dye internalization by endocytosis. A speculative model of the vesicle trafficking network within growing hyphae is presented.

Diphenylhexatriene↗
PubMed1999

Antibiosis plays a role in the context of direct interaction during antagonism of Paenibacillus polymyxa towards Fusarium oxysporum.

Interaction of Fusarium oxysporum and Paenibacillus polymyxa starts with polar attachment of bacteria to the fungal hyphae followed by the formation of a large cluster of non-motile cells embedded in an extracellular matrix in which the bacteria develop endospores. Enumeration of fungal viable counts showed that less than one of 36,000 colony-forming units survived in paired cultures for 71 h. Effective antagonism was not observed below pH5 and was specific for the bacterial species. Development of F. oxysporum was inhibited in cell-free filtrates derived from cultures of P. polymyxa, but was much more strongly repressed in the presence of living bacteria. Furthermore, recovery of fungal growth started immediately after addition of antibiotics to paired cultures. Restoration of fungal growth was enhanced in filtrates that were supplemented with MgCl2, which suggests that anti-fungal compounds produced by the bacteria were counteracted by magnesium ions. In paired cultures, fungal counts remained very low, even in the presence of the magnesium salt. This study clearly showed that P. polymyxa antagonizes the plant pathogenic fungus F. oxysporum in liquid medium by means of an interaction process in which the presence of living bacteria is a prerequisite for continuous suppression of fungal growth.

Antibiosis↗
PubMed1993

Antibodies to skeletal muscle in myasthenia gravis. Part 1. Diagnostic value for the detection of thymoma.

The role of anti-muscle antibodies (AMA) in the diagnosis of thymoma in patients with myasthenia gravis (MG) is evaluated. We compared ELISA and Western blot assay for antibodies to citric acid muscle extract (a-CAE) with an immunofluorescence assay (IF). Sera from 234 selected MG patients and 123 controls were tested. There was no essential difference between ELISA and IF. Western blot was superior in young onset patients but less useful in patients with an onset beyond the age of 40 years. Unusually high post-test probabilities were found by our patient selection criteria which seem most realistic for clinical practice. Western blot revealed no differences in specificity of AMA in thymoma and non-thymoma patients irrespective of age at onset of disease.

Adult↗
PubMed1992

Adhesive knob formation by conidia of the nematophagous fungus Drechmeria coniospora.

We studied conidiogenesis and adhesive knob formation (maturation) by newly developed conidia of the nematophagous fungus Drechmeria coniospora. Upon conidiogenesis on infected nematodes or during saprophytic growth of the fungus in axenic cultures compact clusters of conidia developed. Less than 10% of such clustered conidia matured; mature conidia were invariably located on the periphery of the clusters. The kinetics and rate of maturation of conidia were studied in in vitro systems and in soil. In both cases adhesive knobs were formed; the rate at which knobs were formed appeared to be determined by the age of the conidia, the temperature and the soil moisture. In addition, knob formation was suppressed at increasing conidial densities. Under favorable conditions, however, over 90% of the conidia matured within a period of 3 days. The rate of knob formation was neither influenced by the presence of nematodes nor by that of exogenous nutrients, which suggests that maturation is an autonomous process. Electron-microscopical analysis indicated that budding of the conidia at the initial stage of maturation occurred simultaneously with the deposition of the sticky, adhesive layer around the wall of the developing knob. The ecological significance of the time- and spatially separated maturation of conidia after conidiogenesis is discussed with respect to survival of the conidia.

Adhesiveness↗
PubMedDate not supplied

The hyphomycete Teberdinia hygrophila gen. nov., sp. nov. and related anamorphs of Pseudeurotium species.

A hyphomycetous fungus isolated from montane fen soil in the Caucasus Mountains, Russia, had obscurely sympodial conidiogenous cells that suggested a link to the heterogeneous genus Leptodontidium. Sequence analysis of the nuclear ribosomal small subunit and internal transcribed spacer region, however, disclosed that the fungus was an anamorphic member of a clade containing the cleistothecial ascomycetous genus Pseudeurotium. Teberdinia, gen. nov., is proposed for the blastic, generally sympodially proliferating anamorphs in this group, and Teberdinia hygrophila, sp. nov., is proposed for the species from upland fens. Binomials are not proposed for the remaining Teberdinia anamorphs of Pseudeurotium species. Purely anamorphic isolates in this clade are difficult to recognize using current morphological keys and might be more widely distributed and ecologically significant than is currently evident.

Ascomycota↗