Research Interests:
Research Interests: Technology, Water, Biology, Fungi, Medicine, and 15 moreAspergillus, Biological Sciences, Environmental Sciences, Archaea, Bacteria, Staphylococcus aureus, Temperature, Artifacts, Water Activity, CARBOHYDRATES, Water Microbiology, Ascomycota, Sodium Chloride, Halobacterium, and Adaptation in extreme environment
Water activity, temperature and pH are determinants for biotic activity of cellular systems, biosphere function and, indeed, for all life processes. This study was carried out at high concentrations of glycerol, which concurrently reduces... more
Water activity, temperature and pH are determinants for biotic activity of cellular systems, biosphere function and, indeed, for all life processes. This study was carried out at high concentrations of glycerol, which concurrently reduces water activity and acts as a stress protectant, to characterize the biophysical capabilities of the most extremely xerophilic organisms known. These were the fungal xerophiles: Xeromyces bisporus (FRR 0025), Aspergillus penicillioides (JH06THJ) and Eurotium halophilicum (FRR 2471). High-glycerol spores were produced and germination was determined using 38 media in the 0.995-0.637 water activity range, 33 media in the 2.80-9.80 pH range and 10 incubation temperatures, from 2 to 50°C. Water activity was modified by supplementing media with glycerol+sucrose, glycerol+NaCl and glycerol+NaCl+sucrose which are known to be biologically permissive for X. bisporus, A. penicillioides and E. halophilicum respectively. The windows and rates for spore germinati...
Research Interests:
Water availability acts as the most-stringent constraint for life on Earth. Thus, understanding the water relations of microbial extremophiles is imperative to our ability to increase agricultural productivity (e.g., by enhancing the... more
Water availability acts as the most-stringent constraint for life on Earth. Thus, understanding the water relations of microbial extremophiles is imperative to our ability to increase agricultural productivity (e.g., by enhancing the processing and turnover of dead organic matter in soils of arid regions); reduce human exposure to mycotoxins in buildings and our food-supply chain; prevent the spoilage of foods/animal feeds, books, museum specimens and artworks; and better control microbiology of industrial fermentations. Only a small number of microbial systems can retain activity at < 0.710 water activity (ISME J 2015 9,1333-1351), and the most resilient of these is Xeromyces bisporus which inhabits sugar-rich substrates (Appl Environ Microbiol 1968 16,1853-1858). The current study focused on germination of Aspergillus penicillioides, a xerophile which is also able to grow under low humidity and saline conditions. Investigations of germination differed from those reported earlie...
Research Interests:
Ascospores of Talaromyces.macrosporus belong to the most stress resistant eukaryotic cells and show a constitutive dormancy, i.e., no germination occurs in the presence of rich growth medium. Only an extreme trigger as very high... more
Ascospores of Talaromyces.macrosporus belong to the most stress resistant eukaryotic cells and show a constitutive dormancy, i.e., no germination occurs in the presence of rich growth medium. Only an extreme trigger as very high temperature or pressure is able to evoke synchronized germination. In this study, several changes within the thick cell wall of these cells are observed after a heat treatment: (i.) a change in its structure as shown with EPR and X-ray diffraction; (ii.) a release of an abundant protein into the supernatant, which is proportional to the extent of heat activation; (iii.) a change in the permeability of the cell wall as judged by fluorescence studies in which staining of the interior of the cell wall correlates with germination of individual ascospores. The gene encoding the protein, dubbed ICARUS, was studied in detail and was expressed under growth conditions that showed intense ascomata (fruit body) and ascospore formation. It encodes a small 7–14 kD protei...
Research Interests: Biology, Fungi, Medicine, Germination, Cell Wall, and 3 moreDormancy, Stress Resistance, and food spoilage
Conidia of Aspergillus niger are produced on conidiophores. Here, maturation of conidia on these asexual reproductive structures was studied. Pigmented conidia that had developed on conidiophores for 2, 5, and 8days were similarly... more
Conidia of Aspergillus niger are produced on conidiophores. Here, maturation of conidia on these asexual reproductive structures was studied. Pigmented conidia that had developed on conidiophores for 2, 5, and 8days were similarly resistant to heat and were metabolically active as shown by CO2 release and conversion of the metabolic probe Tempone. A total number of 645-2421 genes showed a ⩾2-fold change in expression when 2-day-old conidia were compared to 5- and 8-day-old spores. Melanin was extracted more easily from the cell wall of 2-day-old conidia when compared to the older spores. In addition, mannitol content and germination rate of the 2-day-old conidia were higher. Dispersal efficiency by water was lower in the case of the 8-day-old conidia but no differences were observed in dispersal by wind and a hydrophobic moving object. These data and the fact that only a minor fraction of the conidia on a conidiophore were dispersed in the assays imply that a single colony of A. nig...
Research Interests:
ABSTRACTIndoor fungi cause damage in houses and are a potential threat to human health. Indoor fungal growth requires water, for which the terms water activity (aw) and relative humidity (RH) are used. The ability of the fungiAspergillus... more
ABSTRACTIndoor fungi cause damage in houses and are a potential threat to human health. Indoor fungal growth requires water, for which the terms water activity (aw) and relative humidity (RH) are used. The ability of the fungiAspergillus niger,Cladosporium halotolerans, andPenicillium rubensat different developmental stages to survive changes in awdynamics was studied. Fungi grown on media with high awwere transferred to a controlled environment with low RH and incubated for 1 week. Growth of all developmental stages was halted during incubation at RHs below 75%, while growth continued at 84% RH. Swollen conidia, germlings, and microcolonies ofA. nigerandP. rubenscould not reinitiate growth when retransferred from an RH below 75% to a medium with high aw. All developmental stages ofC. halotoleransshowed growth after retransfer from 75% RH. Dormant conidia survived retransfer to medium with high awin all cases. In addition, retransfer from 84% RH to medium with high awresulted in bur...
Research Interests:
Spores are an integral part of the life cycle of the gross majority of fungi. Their morphology and the mode of formation are both highly variable among the fungi, as is their resistance to stressors. The main aim for spores is to be... more
Spores are an integral part of the life cycle of the gross majority of fungi. Their morphology and the mode of formation are both highly variable among the fungi, as is their resistance to stressors. The main aim for spores is to be dispersed, both in space, by various mechanisms or in time, by an extended period of dormancy. Some fungal ascospores belong to the most stress-resistant eukaryotic cells described to date. Stabilization is a process in which biomolecules and complexes thereof are protected by different types of molecules against heat, drought, or other molecules. This review discusses the most important compounds that are known to protect fungal spores and also addresses the biophysics of cell protection. It further covers the phenomena of dormancy, breaking of dormancy, and early germination. Germination is the transition from a dormant cell toward a vegetative cell and includes a number of specific changes. Finally, the applied aspects of spore biology are discussed.
Research Interests:
Research Interests:
Research Interests:
... two nematophagous fungi during infection and digestion of the nematode Panagrellus redivivus JAN DIJKSTERHUIS, KLAAS A. SJOLLEMA ... and growth conditions Arthrobotrys oligospora ATCC 24927 (obtained from Professor Nordbring-Hertz,... more
... two nematophagous fungi during infection and digestion of the nematode Panagrellus redivivus JAN DIJKSTERHUIS, KLAAS A. SJOLLEMA ... and growth conditions Arthrobotrys oligospora ATCC 24927 (obtained from Professor Nordbring-Hertz, University of Lund, Sweden) was ...
Research Interests:
Interaction between microbes affects the growth, metabolism and differentiation of members of the microbial community. While direct and indirect competition, like antagonism and nutrient consumption have a negative effect on the... more
Interaction between microbes affects the growth, metabolism and differentiation of members of the microbial community. While direct and indirect competition, like antagonism and nutrient consumption have a negative effect on the interacting members of the population, microbes have also evolved in nature not only to fight, but in some cases to adapt to or support each other, while increasing the fitness of the community. The presence of bacteria and fungi in soil results in various interactions including mutualism. Bacilli attach to the plant root and form complex communities in the rhizosphere. Bacillus subtilis, when grown in the presence of Aspergillus niger, interacts similarly with the fungus, by attaching and growing on the hyphae. Based on data obtained in a dual transcriptome experiment, we suggest that both fungi and bacteria alter their metabolism during this interaction. Interestingly, the transcription of genes related to the antifungal and putative antibacterial defence mechanism of B. subtilis and A. niger, respectively, are decreased upon attachment of bacteria to the mycelia. Analysis of the culture supernatant suggests that surfactin production by B. subtilis was reduced when the bacterium was co-cultivated with the fungus. Our experiments provide new insights into the interaction between a bacterium and a fungus.
Research Interests:
Research Interests:
Section 4. Control of fungi and mycotoxins in foods Inactivation of fruit spoilage yeasts and moulds using high pressure process-ing Ailsa D. Hocking, Mariam Begum and Cindy M. Stewart Activation of ascospores by novel food preservation... more
Section 4. Control of fungi and mycotoxins in foods Inactivation of fruit spoilage yeasts and moulds using high pressure process-ing Ailsa D. Hocking, Mariam Begum and Cindy M. Stewart Activation of ascospores by novel food preservation techniques Jan Dijksterhuis and Robert A. ...
Research Interests:
ABSTRACT Food products are a rich nutrient source that will attract both bacterial and fungal colonizers. Food spoilage is a major threat for our food stock and is responsible for enormous losses worldwide, which makes it a research area... more
ABSTRACT Food products are a rich nutrient source that will attract both bacterial and fungal colonizers. Food spoilage is a major threat for our food stock and is responsible for enormous losses worldwide, which makes it a research area that is very relevant with respect to the increasing demand on food during the next decennia. This chapter will highlight fungal spoilage, including the fact that it deals mostly with plant-based food products. Firstly, the relationship between the living crop and fungi will be illustrated. Between host and pathogen there exists a surprisingly complex communication, and successful intervention may result in novel strategies to prevent post-harvest diseases. Then the association of fungi with different types of processed food will be described. Over time, different preservation techniques have been developed with the aim of discouraging fungal development in the food product. These include fermentation, addition of salts or high concentrations of sugars, pickling, drying, cooling, the addition of preservatives or a heating treatment before packaging. Only fungi that can survive these adverse conditions can successfully spoil processed food. Different aspects of stress resistance are addressed in this chapter, including osmo- and xerotolerance, protective compounds inside cells, and heat-resistant structures. Food parameters are often surprisingly restrictive to the spectrum of fungal species which are able to grow and thus spoil the individual food types. Normally, less than ten and often one to three species are responsible for spoilage. Careful elucidation of the specific aspects of food spoilage may lead to novel tailor-made methods to decrease the enormous portion of our food that is lost.
Research Interests:
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... more
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.
Research Interests:
Research Interests:
Research Interests:
ABSTRACT
Research Interests:
Research Interests:
Research Interests:
Aspergillus species are highly abundant fungi worldwide. Their conidia are among the most dominant fungal spores in the air. Conidia are formed in chains on the vesicle of the asexual reproductive structure called the conidiophore. Here,... more
Aspergillus species are highly abundant fungi worldwide. Their conidia are among the most dominant fungal spores in the air. Conidia are formed in chains on the vesicle of the asexual reproductive structure called the conidiophore. Here, it is shown that the velvet protein VeA of Aspergillus niger maximizes the diameter of the vesicle and the spore chain length. The length and width of the conidiophore stalk and vesicle were reduced nearly twofold in a ΔveA strain. The latter implies a fourfold reduced surface area to develop chains of spores. Over and above this, the conidial chain length was approximately fivefold reduced. The calculated 20-fold reduction in formation of conidia by ΔveA fits the 8- to 17-fold decrease in counted spore numbers. Notably, morphology of the ΔveA conidiophores of A. niger was very similar to that of wild-type Aspergillus sydowii. This suggests that VeA is key in conidiophore architecture diversity in the fungal kingdom. The finding that biomass formati...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
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... more
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.