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Fungal exudates. I. Characteristics of hyphal exudates in Fusarium culmorum

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Abstract

Exudates have been observed on a number of fungi as liquid droplets adhering to the hyphae, and detailed investigation with Fusarium culmorum shows a definite pattern to the distribution of the droplets in relation to colony morphology. This suggests that the process of exudation is of physiological significance and specific properties of the droplets, absorption, and reexudation, their apparent role in spore formation, and their biochemical contents support this premise. Droplets appear to be closely associated with colony aging and their properties change as this process occurs. Initially they are transparent and water-like but become granular and opaque, and in some instances packed with spores as the colony develops. The sequence of droplet development and a mechanism for the release of these droplets and their function in normal physiological functioning of the organism is discussed.

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... Its ecological role, however, was undervalued and ignored in research for a long time. The first study on its putative functions was provided by McPhee and Colotelo [12]. They suggested that guttation enables the accumulation of metabolite reserves and removal of SMs or toxic byproducts of metabolism [12]. ...
... The first study on its putative functions was provided by McPhee and Colotelo [12]. They suggested that guttation enables the accumulation of metabolite reserves and removal of SMs or toxic byproducts of metabolism [12]. It was also suggested that the guttation process is linked to mycelium maturation [13], and that formation of exudates might serve as a water reservoir, allowing constant growth of aerial hyphae from afar (of their substrates) [14]. ...
... Excretion of nutrients collected outside of mycelium, e.g., inositol, mannitol, trehalose, lauric or heptadecanoic acid, is expected to regulate internal physiological mechanisms, and accompany the development of structures, such as sclerotia [42,48]. Therefore, guttation seems to be an important step in the colony maturation process, e.g., linked to cell death [12,13]. Another hypothesis is that fungi remove metabolic byproducts by their secretion, which partially explains a complex composition of exudates, illustrated in biochemical investigations [8,12,18,34]. ...
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Guttation is a common phenomenon in the fungal kingdom. Its occurrence and intensity depend largely on culture conditions, such as growth medium composition or incubation temperature. As filamentous fungi are a rich source of compounds, possessing various biological activities, guttation exudates could also contain bioactive substances. Among such molecules, researchers have already found numerous mycotoxins, antimicrobials, insecticides, bioherbicides, antiviral, and anticancer agents in exudate droplets. They belong to either secondary metabolites (SMs) or proteins and are secreted with different intensities. The background of guttation, in terms of its biological role, in vivo, and promoting factors, has been explored only partially. In this review, we describe the metabolites present in fungal exudates, their diversity, and bioactivities. Pointing to the significance of fungal ecology and natural products discovery, selected aspects of guttation in the fungi are discussed.
... In 1991, Jennings proposed guttation to be a sort of water reservoir, allowing growth of hyphae from afar of their primary substrate (Jennings 1991). A clear ecological function of fungal guttation droplets was described in two studies for Fusarium culmorum (McPhee and Colotelo 1977) and Sclerotinia sclerotorium (Colotelo 1978). The exudates were shown to possess a degrading ability on plant tissues, demonstrating a high enzyme activity. ...
... The main production of guttation fluids took place between day 7 and day 14 of cultivation, which corresponded to the main growth period of the fungal mycelia. A similar relationship was observed in former studies concerning fungal exudation properties (McPhee and Colotelo 1977). ...
... As discussed earlier, the exudation droplets may also serve as a kind of water (Jennings 1991) or nutrient reservoir (Colotelo 1978;McPhee and Colotelo 1977;Sprecher 1959). Thus, the competition of fungal colonies against each other possibly triggers the building-up of reserves in terms of exudates. ...
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The formation of guttation droplets is a long-known property of various fungi. However, their composition, biological function and metabolism in fungi have hardly attracted deeper research interest. The highly toxic mould Stachybotrys (S.) chartarum chemotype S is supposed to play-amongst other factors such as endotoxins and microbial volatile organic compounds (MVOCs)-an important role in indoor air toxicity, mainly after water damage. The way of toxins becoming airborne and leading to exposure via inhalation, however, is still under discussion. We hypothesised that guttation may be a factor for exudation of toxins into the environment. Therefore, selected isolates (n = 15) of our own culture collection of Stachybotrys spp. (S. chartarum chemotype S, S. chartarum chemotype A, S. chlorohalonta) originating from various habitats were cultivated on malt extract agar for 3 weeks. All strains but one produced different amounts of guttation droplets, which were collected quantitatively and subjected to various independent analytical techniques like ELISA, effect-based bioassay (MTT cell culture test) and tandem mass spectrometry (LC-MS/MS). Actually, the toxigenic isolates (n = 5) produced highly toxic guttation droplets, which was confirmed by all methods. The concentration of macrocyclic trichothecenes, such as satratoxin G and H, ranged between the LOD and 7,160 ng/ml exudate and 280 and 4,610 ng/ml as determined by LC-MS/MS, respectively. According to our knowledge, the ability of S. chartarum to produce toxic exudates is reported for the first time, which possibly plays an important role regarding its toxic potential in indoor environments.
... Coletelo [47] suggested that exudates are associated with actively growing mycelia and McPhee [48] that the process of exudation is of physiological significance and closely associated with colony aging. The exudation of liquid droplets is common for Ulocladium chartarum as well as for other fungal species like Sclerotinia sclerotiorum [48,49]. A proteome-level study revealed that proteins present in the exudates could be classified into several functional categories including secondary metabolism [49].Different secondary metabolites have been isolated from different species of Ulocladium: botralin (Ulocladium botrytis) [50], curvularins (Ulocladium atrum) [51], ulocladol A and ulocladol B (Ulocladium chartarum) [52]. ...
... Exudates or liquid droplets were found on the surface of colonies in all experimental conditions but they were larger and numerous in flight than on ground. Coletelo [47] suggested that exudates are associated with actively growing mycelia and McPhee [48] that the process of exudation is of physiological significance and closely associated with colony aging. The exudation of liquid droplets is common for Ulocladium chartarum as well as for other fungal species like Sclerotinia sclerotiorum [48,49]. ...
... Coletelo [47] suggested that exudates are associated with actively growing mycelia and McPhee [48] that the process of exudation is of physiological significance and closely associated with colony aging. The exudation of liquid droplets is common for Ulocladium chartarum as well as for other fungal species like Sclerotinia sclerotiorum [48,49]. A proteome-level study revealed that proteins present in the exudates could be classified into several functional categories including secondary metabolism [49]. ...
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Space biology is a young and rapidly developing discipline comprising basic research and biotechnology. With the prospect of longer space missions and the construction of the International Space Station several aspects of biotechnology will play a prominent role in space. In fact, biotechnological processes allowing the recycling of vital elements, such as oxygen or water, and the in-flight production of food becomes essential when considering the financial and logistic standpoint. Every kilogram which, having been recycled or produced in space, does not have to be uploaded will drastically reduce the cost of space missions. In addition, the scientific community is offered a better opportunity to investigate long-term biotechnological processes performing experiments with a duration ranging from weeks to months. Therefore, there is an increasing demand for sophisticated instrumentation to satisfy the requirements of future projects in space biology. The carryover of knowledge from conventional bioreactor technology to miniature space bioreactors for a monitored and controlled cell culturing is one of the key elements for this new dimension in space life science. The first space bioreactors were developed and flown at the end of the last century. It has been demonstrated that cells of different types, from bacteria to mammalian cells, can be successfully grown in this type of culture vessel. This chapter presents different generations of bioreactors developed so far, their performances in space and their potential for the future, as well as the activities of the European Space Agency (ESA) in this domain. A dedicated chapter by Lisa Freed on the rotating wall vessel reactor and the latest NASA bioreactor research is also part of this volume.
... Recent findings showed that guttation is a common phenomenon in many of the mushrooms, such as Chamaemyces fracidus, Hebeloma crustiliniforme, Hydnellum peckii, Lacrymaria lacrymabunda, Lactarius chrysorrheus, Limacella guttata, Paneolus guttulatus, Russula sardonia, Sarcodon lundelli, Suillus granulates, and Tricholoma pessundatum (Halbwachs et al. 2016). Even though the guttation phenomenon was suggested as a function of growing aerial hypha, i.e., it acts as a reservoir of water for maintaining constant growth (Jennings 1991), the exudates also were reported to possess many secondary metabolites and enzymes (McPhee and Colotelo 1977). Colotelo (1978) while examining liquid droplets of various fungi found that the droplet production was associated with actively growing mycelia, including fruiting structure. ...
... The guttation droplets produced by a wild edible mushroom, S. bovines, possess natural antioxidant (Pereira et al. 2012). Assessment of physiological function of hyphal exudates in Fusarium culmorum showed that they have both enzymatic and nonenzymatic properties and that plays potential role in pathogenesis (McPhee and Colotelo 1977). Hutwimmer et al. (2010) while analyzing the exudation in droplets of Metarhizium anisopliae found that they were produced on media with more than one carbon source and exuded droplets contained destruxin, a toxin that plays a major role in pathogenesis. ...
... In both cases, the transparent droplets formed earlier turned into opaque orange due to the merger of droplets and sporulation structure. It was reported that the hyphal tips are a very active metabolic region that uses the droplet system as reservoir for many kinds of secondary metabolites and by-products (McPhee and Colotelo 1977). These authors also reported that the region and time sequence of development of droplets in F. culmorum cultures was in accordance with sporulation, i.e., production of macroconidia is always preceded by the presence of guttation droplets in that area. ...
Article
Production of guttation droplets in the cultures of Colletotrichum falcatum was often noticed. Hence, formation of guttation droplets, exudation of toxin in guttation, and guttation droplet chemical composition were assessed to find the ecological importance of guttation. Among the tested culture media, more guttation was noticed in oat meal agar medium and host extracts broth medium. Assessing the effect of five different carbon sources on guttation of C. falcatum showed that among solid media, sparse guttation droplets were noticed in glucose-, fructose-, and starch-amended media, whereas in broth cultures except fructose-amended media no other carbon sources induced guttation in mycelium. The guttation phenomenon was noticed only in sporulating mycelia, and it also followed a specific pattern in connection with sporulation. Bioassay of guttation exudates on sugarcane leaves produced pronounced necrotic lesions with large, yellow halo similar to positive control, thus confirming the presence of toxin. The guttation fluid initiated browning symptom on sugarcane leaves at a concentration of 1000 ppm and produced pronounced necrotic lesions of 3.7 cm at 10 000 ppm. The toxicity of crude fraction was thermostable up to 60 C. The gas chromatography-mass spectrometry (GC-MS) analysis of crude guttation droplets identified the presence of 24 compounds belonging to fatty acids, derivatives of fatty acids, flavonoids, flavonoid glycosides, sterols, quinone derivatives, amides, and glycol ethers, and among them fatty acids were dominant. The two compounds, viz., hexadecanoic acid methyl ester and 9-octadecenoic acid (Z) methyl ester, were abundant (18.14% and 17.98%, respectively) and identified as probable toxic compounds.
... Streptomyces colonies with droplets on their aerial mycelium are frequently depicted and droplet production was even used as a criterion for the classification of Streptomyces strains [59] . Microbial droplet formation has been compared to the release of droplets by higher plants (guttation) and is favoured at high humidity [147,149,150] or during a particular time of the day [151] . In addition, droplet formation by fungi and streptomycetes strongly depends on the respective growth stage. ...
... In addition, droplet formation by fungi and streptomycetes strongly depends on the respective growth stage. [150,[152][153][154][155] The ecological function of the droplets on the aerial mycelium of fungi and streptomycetes is so far virtually unknown. ...
... Droplets of Sclerotinia sclerotiorum consist of enzymes and various solutes, which have distinct temporal dynamics attributed to culture age and development (Colotelo 1973, 1978; Colotelo et al 1971). Hyphal exudates of Fusarium culmorum show definite distribution patterns in relation to colony morphology and vary in their appearance from transparent to granular and opaque (McPhee and Colotelo 1977). Clear scientific evidence on the function of droplets and their ecological role is lacking. ...
... It was argued that guttation droplets might function as a reservoir of water for maintaining constant growth of aerial hyphae. The droplets could mitigate suboptimal or stressful conditions due to unfavorable water potentials of cultivation media (Jennings 1991), but it also was suggested that guttations function as a reservoir of metabolic byproducts, metabolite reserves , secondary metabolites or enzymes (Colotelo 1978, McPhee and Colotelo 1977). Because exudates are possibly of cytoplasmatic origin they also were linked to cell death and the rupture of cytoplasmic membranes in the development of sclerotia in Sclerotinia sp. and Sclerotium sp. ...
Article
Nutritional conditions causing droplet exudation by Metarhizium anisopliae var. anisopliae were studied. Exudation in droplets occurred only on media with more than one carbon source and was highly dependent on the ratio of a well metabolized sugar such as trehalose and a nonpreferred sugar, in particular arabinose. Exuded droplets contained destruxin A, B and E in concentrations similar to those on submerged culture on Czapek Dox medium with equivalent C:N ratios but was clearly less than previously reported on standard Czapek Dox or Sabouraud dextrose broth. Destruxins also were found in agar samples from directly below mycelium and from up to 2 cm from the colony edge. Exudates retrieved from different media were proven to have Pr1 protease-related enzyme activity. Additional HPLC analysis indicated that droplets from diverse media did not differ in their sugar and acid content. A hypothesis is presented regarding the trigger for guttation in Metarhizium during growth under these conditions.
... Coletelo [47] suggested that exudates are associated with actively growing mycelia and McPhee [48] that the process of exudation is of physiological significance and closely associated with colony aging. The exudation of liquid droplets is common for Ulocladium chartarum as well as for other fungal species like Sclerotinia sclerotiorum [48], [49]. A proteome-level study revealed that proteins present in the exudates could be classified into several functional categories including secondary metabolism [49]. ...
... Exudates or liquid droplets were found on the surface of colonies in all experimental conditions but they were larger and numerous in flight than on ground. Coletelo [47] suggested that exudates are associated with actively growing mycelia and McPhee [48] that the process of exudation is of physiological significance and closely associated with colony aging. The exudation of liquid droplets is common for Ulocladium chartarum as well as for other fungal species like Sclerotinia sclerotiorum [48], [49]. ...
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The objectives of this 14 days experiment were to investigate the effect of spaceflight on the growth of Ulocladium chartarum, to study the viability of the aerial and submerged mycelium and to put in evidence changes at the cellular level. U. chartarum was chosen for the spaceflight experiment because it is well known to be involved in biodeterioration of organic and inorganic substrates covered with organic deposits and expected to be a possible contaminant in Spaceships. Colonies grown on the International Space Station (ISS) and on Earth were analysed post-flight. This study clearly indicates that U. chartarum is able to grow under spaceflight conditions developing, as a response, a complex colony morphotype never mentioned previously. We observed that spaceflight reduced the rate of growth of aerial mycelium, but stimulated the growth of submerged mycelium and of new microcolonies. In Spaceships and Space Stations U. chartarum and other fungal species could find a favourable environment to grow invasively unnoticed in the depth of surfaces containing very small amount of substrate, posing a risk factor for biodegradation of structural components, as well as a direct threat for crew health. The colony growth cycle of U. chartarum provides a useful eukaryotic system for the study of fungal growth under spaceflight conditions.
... For mycologists, formation of droplets on the aerial parts of fungal mycelium is an everyday experience (Jennings 1991). Fungal exudates or guttation droplets have been described in the literature as physiological important processes (Colotelo 1978;McPhee and Colotelo 1977), for instance, in the maintenance of growth rates under unfavorable water conditions (Jennings 1991). Interestingly, the formation of droplets was observed before the production of macroconidia in Fusarium culmorum, suggesting their involvement in colony growth and maturation but also as a reservoir of secondary metabolites (McPhee and Colotelo 1977). ...
... Fungal exudates or guttation droplets have been described in the literature as physiological important processes (Colotelo 1978;McPhee and Colotelo 1977), for instance, in the maintenance of growth rates under unfavorable water conditions (Jennings 1991). Interestingly, the formation of droplets was observed before the production of macroconidia in Fusarium culmorum, suggesting their involvement in colony growth and maturation but also as a reservoir of secondary metabolites (McPhee and Colotelo 1977). Secondary metabolites, such as gliotoxin in Aspergillus fumigatus (Grovel et al. 2003), ochratoxins in Penicillium (Gareis and Gareis 2007) and destruxins in Metarhizium anisopliae (Hutwimmer et al. 2010), have been found in fungal guttates. ...
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Microorganisms interact with each other via metabolic exchange. Several studies have revealed that microbial metabolites may act as mediators of microbial interactions. During our previous work with endophytes isolated from the Brazilian medicinal plant Lychnophora ericoides, we demonstrated that the well-known antifungal compound amphotericin B, produced by the endophytic actinobacterium Streptomyces albospinus RLe7, may trigger chemical responses in endophytic fungi. In this study, we cultured endophytic fungi in amphotericin B-enriched media to verify whether other chemical responses could be induced. Interestingly, one fungal strain showed a differential response under the tested conditions. When the fungus Xylaria cubensis FLe9 was cultured in amphotericin B-enriched media, a mycelial guttate was observed. Investigation of the fungal extracts from X. cubensis FLe9 and purification of fungal metabolites were performed using high-performance liquid chromatography coupled to a diode array detector. Isolated compounds were characterized on the basis of nuclear magnetic resonance and mass spectrometry data. Therefore, we report on the overproduction of the fungal metabolites griseofulvin (1) and dechlorogriseofulvin (2) when the endophytic fungus Xylaria cubensis FLe9 was exposed to amphotericin B. Both fungal compounds 1 and 2 were also detected in the mycelial guttate produced when X. cubensis FLe9 was exposed to amphotericin B. Since the amphotericin B-producing actinobacterium S. albospinus RLe7 and the griseofulvin-producing fungus X. cubensis FLe9 are endophytes from the same host, biosynthetic induction of fungal compounds may suggest a potential signaling role for amphotericin B in natural environments. However, this hypothesis needs to be further investigated in field experiments.
... classification of Streptomyces strains (Waksman and Lechevalier 1953). Microbial droplet formation has been compared to the release of droplets by higher plants (guttation) and is favoured at high humidity (Atkinson 1900;Sprecher 1959;McPhee and Colotelo 1977) or during a particular time of the day (Wilson 1948). In addition, droplet formation by fungi and streptomycetes strongly depends on the respective growth stage (Williams and McCoy 1953;Waters et al. 1975;McPhee and Colotelo 1977;Schrempf et al. 2011;Gareis and Gottschalk 2014). ...
... Microbial droplet formation has been compared to the release of droplets by higher plants (guttation) and is favoured at high humidity (Atkinson 1900;Sprecher 1959;McPhee and Colotelo 1977) or during a particular time of the day (Wilson 1948). In addition, droplet formation by fungi and streptomycetes strongly depends on the respective growth stage (Williams and McCoy 1953;Waters et al. 1975;McPhee and Colotelo 1977;Schrempf et al. 2011;Gareis and Gottschalk 2014). The ecological function of the droplets on the aerial mycelium of fungi and streptomycetes is so far virtually unknown. ...
Article
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Streptomyces violaceoruber grown in co-culture with Streptomyces aburaviensis produces an about 17-fold higher volume of droplets on its aerial mycelium than in single-culture. Physical separation of the Streptomyces strains by either a plastic barrier or by a dialysis membrane, which allowed communication only by the exchange of volatile compounds or diffusible compounds in the medium, respectively, still resulted in enhanced droplet formation. The application of molecular sieves to bioassays resulted in the attenuation of the droplet-inducing effect of S. aburaviensis indicating the absorption of the compound. ¹H-NMR analysis of molecular-sieve extracts and the selective indophenol-blue reaction revealed that the volatile droplet-inducing compound is ammonia. The external supply of ammonia in biologically relevant concentrations of ≥8 mM enhanced droplet formation in S. violaceoruber in a similar way to S. aburaviensis. Ammonia appears to trigger droplet production in many Streptomyces strains because four out of six Streptomyces strains exposed to ammonia exhibited induced droplet production.
... Generally, fungal exudates contain secondary metabolites, enzymes and other by-products that are assumed to support cell survival under unfavorable environmental conditions. These liquid reservoirs can be reabsorbed when needed [43]. Indeed, these droplets and the exudate below the colony disappeared with longer incubation. ...
Article
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Small, cysteine-rich and cationic antimicrobial proteins (AMPs) from filamentous ascomycetes promise treatment alternatives to licensed antifungal drugs. In this study, we characterized the Penicillium chrysogenum Q176 antifungal protein C (PAFC), which is phylogenetically distinct to the other two Penicillium antifungal proteins, PAF and PAFB, that are expressed by this biotechnologically important ascomycete. PAFC is secreted into the culture broth and is co-expressed with PAF and PAFB in the exudates of surface cultures. This observation is in line with the suggested role of AMPs in the adaptive response of the host to endogenous and/or environmental stimuli. The in silico structural model predicted five β-strands stabilized by four intramolecular disulfide bonds in PAFC. The functional characterization of recombinant PAFC provided evidence for a promising new molecule in anti-Candida therapy. The thermotolerant PAFC killed planktonic cells and reduced the metabolic activity of sessile cells in pre-established biofilms of two Candidaalbicans strains, one of which was a fluconazole-resistant clinical isolate showing higher PAFC sensitivity than the fluconazole-sensitive strain. Candidacidal activity was linked to severe cell morphology changes, PAFC internalization, induction of intracellular reactive oxygen species and plasma membrane disintegration. The lack of hemolytic activity further corroborates the potential applicability of PAFC in clinical therapy.
... The ecological functions of exudates in nature are under debate. Jennings [30] believes that the exudates could act as a water reservoir for aerial hyphal growth in unfavourable conditions; whereas McPhee and Colotelo [31] suggest that exudate droplets might function as a reservoir of metabolic by-products, secondary metabolites, or metabolite reserves. The guttation droplets from Fusarium culmorum and Sclerotinia sclerotiorum, two plant fungal pathogens, have been shown to rapidly degrade plant tissue suggesting that exudate droplets may play a role in pathogenicity [32]. ...
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Pseudogymnoascus destructans is the causative agent of an emerging infectious disease that threatens populations of several North American bat species. The fungal disease was first observed in 2006 and has since caused the death of nearly six million bats. The disease, commonly known as white-nose syndrome, is characterized by a cutaneous infection with P. destructans causing erosions and ulcers in the skin of nose, ears and/or wings of bats. Previous studies based on sequences from eight loci have found that isolates of P. destructans from bats in the US all belong to one multilocus genotype. Using the same multilocus sequence typing method, we found that isolates from eastern and central Canada also had the same genotype as those from the US, consistent with the clonal expansion of P. destructans into Canada. However, our PCR fingerprinting revealed that among the 112 North American isolates we analyzed, three, all from Canada, showed minor genetic variation. Furthermore, we found significant variations among isolates in mycelial growth rate; the production of mycelial exudates; and pigment production and diffusion into agar media. These phenotypic differences were influenced by culture medium and incubation temperature, indicating significant variation in environmental condition - dependent phenotypic expression among isolates of the clonal P. destructans genotype in North America.
... Fungal guttation is a well-known phenomenon in the literature [35,38,39]. It has been suggested that these guttates or exudates play different ecological roles such as water reservoirs, excretion systems, or to degrade plant tissues [40][41][42]. Regardless of their role, guttates can be a rich source of secondary metabolites [17,[43][44][45]. Due to the relatively small amount of material that these exudates provide, the isolation of secondary metabolites often occurs from the extract of the whole fungal culture rather than the guttate itself. ...
Article
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Abstract: Two new species, Penicillium krskae (isolated from the air as a lab contaminant in Tulln (Austria, EU)) and Penicillium silybi (isolated as an endophyte from asymptomatic milk thistle (Silybum marianum) stems from Josephine County (Oregon, USA)) are described. The new taxa are well supported by phenotypic (especially conidial ornamentation under SEM, production of red exudate and red pigments), physiological (growth at 37°C, response to cycloheximide and CREA), chemotaxonomic (production of specific extrolites), and multilocus phylogenetic analy-sis using RNA-polymerase II second largest subunit (RPB2), partial tubulin (benA), and calmodu-lin (CaM). Both new taxa are resolved within the section Exilicaulis in series Restricta and show phylogenetic affiliation to P. restrictum sensu stricto. They produce a large spectrum of toxic an-thraquinoid pigments, namely, monomeric anthraquinones related to emodic and chloremodic acids and other interesting bioactive extrolites (i.e., endocrocin, paxilline, pestalotin, and 7-hydroxypestalotin). Of note, two bianthraquinones (i.e., skyrin and oxyskyrin) were detected in a culture extract of P. silybi. Two new chloroemodic acid derivatives (2-chloro-isorhodoptilometrin and 2-chloro-desmethyldermoquinone) isolated from the exudate of P. krskae ex-type culture were analyzed by nuclear magnetic resonance (NMR) and liquid chromatography–mass spectrometry (LC–MS). Keywords: cycloheximide tolerance; Penicillium restrictum group; milk thistle; red exudate; sec-ondary metabolites; mycotoxins
... Consistent with the present results, these droplets are produced on aerial parts of the mycelia (Sprecher, 1959) and exit the cell by exocytosis (Read, 2011), and contain enzymes (W. J. McPhee and 1977) and secondary metabolites (Gareis and Gareis, 2007;Munoz et al., 2011;Castagnoli et al., 2018). Interestingly, in our settings, the surface of these capsules had a visible film that probably provided the reservoir for the solvent necessary for the biochemical reactions involving hydrolytic enzymes and H 2 O 2 on the aerial hyphae. ...
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When resources are limited, the hypocrealean fungus Trichoderma guizhouense can overgrow another hypocrealean fungus Fusarium oxysporum, cause sporadic cell death and arrest growth. A transcriptomic analysis of this interaction shows that T. guizhouense undergoes a succession of metabolic stresses while F. oxysporum responded relatively neutrally but used the constitutive expression of several toxin‐encoding genes as a protective strategy. Because of these toxins, T. guizhouense cannot approach it's potential host on the substrate surface and attacks F. oxysporum from above. The success of T. guizhouense is secured by the excessive production of hydrogen peroxide (H2O2), which is stored in microscopic bag‐like guttation droplets hanging on the contacting hyphae. The deletion of NADPH oxidase nox1 and its regulator, nor1 in T. guizhouense led to a substantial decrease in H2O2 formation with concomitant loss of antagonistic activity. We envision the role of NOX proteins in the antagonism of T. guizhouense as an example of metabolic exaptation evolved in this fungus because the primary function of these ancient proteins was probably not linked to interfungal relationships. In support of this, F. oxysporum showed almost no transcriptional response to T. guizhouense ∆nox1 strain indicating the role of NOX/H2O2 in signaling and fungal communication. This article is protected by copyright. All rights reserved.
... In analogy to a similar plant phenomenon, these excretions are called guttation droplets. Regarding their function, external storage of secondary metabolites and water to cope with the unfavorable environment of the growth media were discussed (McPhee & Colotelo 1977, Jennings 1991. The presence of griseofulvin in guttation droplets at an even higher concentration than in the mycelium was observed by Sica et al. (2016) for Xylaria cubensis. ...
Article
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Screening of fungal endophytes from five Costa Rican Palicourea and three Psychotria species (Rubiaceae) growing in the surroundings of the Tropical Rainforest Station La Gamba resulted in the identification of strains belonging to the genera Xylaria, Arthrinium, Fusarium, Clonostachys and Colletotrichum. Metabolic profiles of isolated fungi were analyzed. Several cytochalasin derivatives, piliformic acid as well as the antifungal agents griseofulvin and its derivative 7-dechlorogriseofulvin were identified. Additionally, griseofulvin and its 7-dechloro form were found to be sequestered in the guttation droplets of four strains. Growth inhibiting effects against various microbial test organisms highlight the potential of the isolated fungi to produce powerful antibiotic agents.
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Modified media for Pleurotus sajor-caju and Pleurotus ostreatus was formulated and investigated in terms of its suitability and effect on the mycelial growth rate of the Pleurotus spp. strains. The modified media was of various whole-wheat grain: media (Malt extract agar[MEA] or Potato dextrose agar [PDA]) ratios of 1:1 to 1:5. Polyethylene (PEG) 6000 was also added as its effects on growth rate at minute concentrations were noted in earlier work. The 1:1 ratio mixture resulted in the drying of the wheat grain by the 8 th day. The water content of the media formulations were all significantly different from the water content of conventional Malt Extract Agar (MEA, 3 %) (97.9 % water) and Potato dextrose Agar (PDA, 3 %) (97.9 % water). The water contents generally ranged from 14.3 % (1:2 MEA) to 57.4 % (1:4 PDA). There was no clear-cut trend for the water contents of the media formulations. The growth rate generally initially decreased below that obtained for normal media (MEA and PDA). However the growth rate increased above that for normal media for the 1:2 to 1:5 for MEA and 1:3 to 1:5 for PDA. The water content of the mixtures cannot be used to predict the growth rates. Generally mushrooms are taken to require adequate water however surprisingly growth higher than that for normal media was obtained for media with low water content. The increase in growth rate is attributed to the richness in terms of nutrients. PEG amended MEA media generally resulted in higher growth rates than non-amended media. This has been the case in earlier work done. The crushed wheat grain : media formulations ranging from 1:2 to 1:15 with PDA and no PDA treatments (the media formulation comprised only of distilled water and crushed grain) induced luxuriant mycelial growth and prolific fruiting of the Pleurotus spp. The water content of the crushed wheat grain: media formulations ranged from 75 % to 97 %. Water content generally increased from 1: 2 media to 1:15 media. Growth rate was highest for 1: 5 + PDA media. 1:2 – PDA had the lowest growth rate. The low –cost media formulations 1:3 to 1:5 (whole wheat grain) and 1:3 to 1:15 (crushed wheat grain) have potential use as low-cost alternatives to culture Pleurotus spp. for culture maintenance, spawn production, mushroom cultivation and bioremediation.
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Thesis research directed by: Cell Biology & Molecular Genetics. Title from t.p. of PDF. Thesis (Ph. D.) -- University of Maryland, College Park, 2006. Includes bibliographical references. Text.
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Sclerotia are loosely described as morphologically variable, nutrient-rich, multihyphal structures which can remain dormant or quiescent when their environment is adverse and then, when conditions improve, germinate to reproduce the fungus. A narrower concept of sclerotia distinguishes between ‘true sclerotia’ and ‘sclerotioid structures’, with the former tuber-like and detachable from the substratum at maturity. The possibility of ‘true sclerotia’ originating from sporogenous tissue is discussed. There are three main types of sclerotial ontogeny — loose, terminal and lateral. Many endogenous and exogenous factors are involved in sclerotial initiation, and these are generally similar to those involved in initiation of other multihyphal structures. Metabolic changes in the vegetative mycelium may cause a flux in a single, organic, carbon compound, which could then become the major carbon translocate from the nutrient source and provide the trigger for sclerotial initiation. Translocation is probably by turgor-driven mass flow along physiologically specialized conducting hyphae. Exudation of liquid droplets is characteristic of developing sclerotia. It may be involved in the maintenance of internal physiological balance. However, exudation is probably primarily concerned with the expulsion of water and not directly in the removal of organic and inorganic materials from sclerotial hyphae. Soluble compounds not needed for structural growth of sclerotia are converted to insoluble forms and deposited both intra- and extracellularly in sclerotial tissues. These deposits are utilized during periods of rest and germination. The physiological processes of initiation, translocation and exudation are reviewed. Sclerotia usually consist of a peripheral rind which encases a broad medulla of loosely interwoven hyphae. Sometimes a narrow cortex of close-fitting hyphae is present between the rind and medulla. The rind is a continuous layer of tightly packed hyphal tips. Reduction in rind permeability corresponds with wall thickening and pigmentation rather than formation of the rind as a continuous surface layer. The cortex, if present, is a region where reserves accumulate. Some cortical cell walls may be pigmented. The medulla forms the main part of the sclerotium. Intracellular reserves are present in medullary hyphae, and an extracellular matrix, which may be continuous or contain lacunae, is usually a characteristic feature of the medulla. Considerable data have accumulated on the ultrastructure and histochemistry of sclerotia. Until recently most studies have involved the use of chemical fixation techniques, but current freeze-substitution methods are providing new insights into sclerotial ultrastructure and histochemistry. The main cytoplasmic reserves present in sclerotia are glycogen, protein, polyphosphate and lipid. Sclerotial cell walls contain chitin and glucans, and the extracellular matrix contains glucans. The structure, composition and functions of sclerotial reserves are reviewed and discussed. Although sclerotia are alike functionally they have probably developed due to convergent evolution. Studies on sclerotia and conidia of the family Sclerotiniaceae could indicate that there are only two types of true sclerotia produced by this family: the tuberoid sclerotium characteristic of Sclerotinia sclerotiorum; and the plano-convexoid sclerotium characteristic of Botryotinia (form genus Botrytis). The derivation of these two types of sclerotia is discussed and compared with that of resting stromatic structures produced by other sclerotiniaceous genera, including Monilinia, and of sclerotia of some genera of the Basidiomycotina and Deuteromycotina.
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