Showing papers on "Mycelium published in 1993"

Ergosterol-to-Biomass Conversion Factors for Aquatic Hyphomycetes

Abstract: Fourteen strains of aquatic hyphomycete species that are common on decaying leaves in running waters were grown in liquid culture and analyzed for total ergosterol contents. Media included an aqueous extract from senescent alder leaves, a malt extract broth, and a glucose-mineral salt solution. Concentrations of ergosterol in fungal mycelium ranged from 2.3 to 11.5 mg/g of dry mass. The overall average was 5.5 mg/g. Differences among both species and growth media were highly significant but followed no systematic pattern. Stationary-phase mycelium had ergosterol contents 10 to 12% lower or higher than mycelium harvested during the growth phase, but these differences were only significant for one of four species examined. Availability of plant sterols in the growth medium had no clear effect on ergosterol concentrations in two species tested. To convert ergosterol contents determined in field samples to biomass values of aquatic hyphomycetes, a general multiplicative factor of 182 is proposed. More accurate estimates would be obtained with species-specific factors. Using these in combination with estimates of the proportion of the dominant species in a naturally established community on leaves resulted in biomass estimates that were typically 20% lower than those obtained with the general conversion factor. Improvements of estimates with species-specific factors may be limited, however, by intraspecific variability in fungal ergosterol content.

Tansley Review No. 45 Wall growth, protein excretion and morphogenesis in fungi

Abstract: SUMMARY With the exception of the unicellular yeasts, fungi typically grow by means of hyphae that extend only at their apices and ramify into a mycelium. This mode of growth provides fungi with a certain mobility and the ability to invade dead and living organic substrata. They are thus the main decomposers of plant residues but they also have established intricate symbiotic relationships with plants, both mutualistic and parasitic. The process of apical growth of a hyphae requires the controlled expansion of the apical wall which must be transformed subsequently into a wall that resists turgor pressure and maintains the tubular shape of the hyphae. Although the driving force for hyphal extension is probably the turgor pressure, a subtle interplay between wall extension and cytoplasmic activity is necessary because only a precise gradient of wall-synthetic activity can maintain uniform wall thickness during expansion. Possibly, the presence in the plasma membrane of mechanico-sensitive proteins plays a role in conjunction with the cytoskeleton at the apex, particularly action. Although the major structural wall polysaccharides are probably manufactured directly on the expanding apical plasma membrane, proteins (and probably some wall components) are delivered to the growing surface by a continuous stream of exocytotic vesicles that fuse with the plasma membrane, at the same time extending its surface. Our analyses of the chemistry of the fungal wall and its biosynthesis and assemblage have disclosed a simple mechanism (though complex in detail) that may explain the transition from a newly formed expandable wall at the apex to a more rigid wall at the base of the hyphal extension zone. Two individual wall polymers, chitin and β-glucan, extruded at the apex are modified within the domain of the wall. Among the modifications observed are the formation of covalent crosslinks between these two polymers and hydrogen bonds between the homologous polymer chains, leading to the formation of chitin microfibrils crosslinked to a glucan matrix. This process is thought to convert an initially plastic wall into a rigid wall as the polymers fall behind the advancing tip. We have called this the steady-state growth theory for apical wall extension because a steady-state amount of plastic wall is always maintained at the growing apex. Excretion of lytic enzymes is a vital process in filamentous fungi because, in nature, they thrive on organic polymers which must be degraded extracellularly. Such enzymes are also necessary for infection processes. Cytological data suggest that such enzymes are extruded by the vesicles that continuously fuse with the plasma membrane at the growing apex. We have shown that a large portion of the excreted enzymes indeed leaves the hypha at the growing apex but another portion may be retained by the wall and is slowly released into the medium. In relation to the steady-state growth theory we hypothesize that enzymes can pass the wall at the apex by bulk flow, that is, by being carried by the flow of plastic wall material, making pores in the wall less important than previously thought. Proteins excreted by filamentous fungi not only serve dissimilatory purposes but are also important for a variety of other activities of the whole mycelium, including morphogenesis. By cloning genes abundantly expressed during formation of aerial hyphae and fruit bodies, we have discovered a class of proteins, named hydrophobins, which are only produced when the mycelium has reached a certain stage of maturity. Whilst excreted by submerged hyphae as monomers into the medium, they self-assemble as insoluble complexes in the walls of emergent hyphae. In aerial hyphae a particular hydrophobin takes the form of rodlets which probably coat the hyphae with an impermeable layer. During fruit-body formation other hydrophobins are produced which may function in the aggregation of hyphae to form a multicellular tissue. Apart from such specific morphogenetic functions, the hydrophobins may play a general role in insulating hyphae from the environment, converting the differentiating structures into sinks for translocation of water and nutrients from the assimilating mycelium.

Multiple extracellular signals govern the production of a morphogenetic protein involved in aerial mycelium formation by Streptomyces coelicolor.

Abstract: The formation of an aerial mycelium by the filamentous bacterium Streptomyces coelicolor is determined in part by a small morphogenetic protein called SapB. A collection of representative bald (bld) mutants, which are blocked in aerial mycelium formation, are all defective in the production of this protein and regain the capacity to undergo morphological differentiation when SapB is supplied exogenously. We now report that most of the bld mutants are rescued for SapB production and aerial mycelium formation when grown near certain other bld mutants. Extracellular complementation experiments of this kind indicate that morphological differentiation is governed by a hierarchical cascade of at least four kinds of intercellular signals. At least one such signal is present in conditioned medium. It is resistant to boiling and protease treatment, and it remains effective even when diluted up to eightfold in fresh medium.

The effects of cadmium on ectomycorrhizal Pinus sylvestris L.

Abstract: SUMMARY The toxicity of a sublethal cadmium concentration to ectomycorrhizal Pinus sylvestris L. seedlings was studied. Nine mycorrhizal strains, collected from a Zn- and Cd-polluted soil or from an unpolluted area, were compared for their ability to increase Cd tolerance in their host plant. Plants were cultivated in a semi-hydroponic system that allowed visual observation of the root systems. The degree of soil colonization as well as the density of the extramatrical mycelium was determined. The water use of the host plants was carefully monitored during the treatment period. Cadmium concentrations were determined in all plant parts. Although Cd addition resulted in decreases in transpiration in the non-mycorrhizal plants, disturbances in water relations could be more or less pronounced in the mycorrhizal pines. The treatment strongly influenced the growth of the fungi in the substrate: several mycobionts hardly survived in the polluted substrate. Fungi producing a large mycelial biomass showed the greatest effect in overcoming toxicity. Some s trains were even able to increase their turnover growth when treated with cadmium. In a dense extramatrical mycelium the potential for Cd retention increases, while the individual hyphae are exposed to a lower Cd concentration than in a sparse mycelium. A protective effect against cadmium toxicity in the host was observed with all mycobionts, since Cd uptake was highest in the nonmycorrhizal seedlings. The treatment had no effect on the growth of the seedlings or on the concentrations of the other cations, probably due to the relatively low toxicity and the relatively short observation period. The results are discussed in relation to the in vitro Cd tolerance of the fungi.

Mycotic aspects of epizootic ulcerative syndrome (EUS) of Asian fishes

Abstract: A survey of fish affected with epizootic ulcerative syndrome taken from outbreaks in countries throughout South and South-East Asia showed that a morphologically typical fungus was consistently present within lesions. Although the majority of the fungal mycelium was dead in most lesions it proved possible to isolate a very delicate and culturally demanding Aphanomyces from such lesions in a few cases. It also proved relatively easy to isolate other members of the Saprolegniaceae including Aphanomyces from the surface of lesions, but these were considered saprophytes derived from background spore burdens in the water. Sporangium morphology of the putatively pathogenic isolates of Aphanomyces was different from that of saprophytic Aphanomyces strains and they also had a lower thermal tolerance. When a mycelium from these strains was placed below the dermis of healthy fish, it caused an inflammatory response and proceeded to migrate down into the tissues of the fish, inducing severe myonecrosis with chronic epithelial reaction. The saprophytic isolates induced a local host response followed by healing of the induced lesion, and destruction or expulsion of the mycelium. It is considered that the specific slow-growing, thermo-labile Aphanomyces is the pathogenic fungus which causes so much tissue damage in this disease, although it may not be a primary pathogen in its own right.

Nitrogen translocation between Alnus glutinosa (L.) Gaertn. seedlings inoculated with Frankia sp. and Pinus contorta Doug, ex Loud seedlings connected by a common ectomycorrhizal mycelium

Abstract: Uptake and translocation of nitrogen was studied in laboratory microcosms consisting of Alnus glutinosa (L.) Gaertn., Frankia sp., Paxillus involutus (Fr.) Fr. and Pinus contorta Dougl. ex Loud. P. involutus was shown to form a fully functional ectomycorrhizal association with alder as well as pine, and the seedlings thus became interconnected by a common mycelium. When microcosms were exposed to N-15(2) gas, interplant translocation of N-15 was observed in two out of three experiments. N-15(2) was fixed by Frankia and translocated to all other parts of the system. In the two experiments in which interplant translocation occurred, between 5 and 15 % of the N-15 recovered was found in the pine seedlings. Within seven days, fixed N2 was incorporated into amino acids in the Frankia nodules, translocated to both the A. glutinosa and P. contorta seedlings and incorporated into macromolecules. In alder seedlings, citrulline and ornithine were the free amino acids that had both the highest N-15 enrichment levels and concentrations. In pine, glutamine and citrulline had the highest N-15 concentrations, and glutamine had the highest level of N-15 enrichment. N-15 enrichment levels were greatest in the nodules, at between 5.5 and 29 % in the different amino acids and 12 % in the macromolecular fraction. Enrichment levels decreased with increasing distance from the nodules. The uptake and translocation of N-15 applied as (NH4Cl)-N-15 to the mycelium was also studied. N-15 was incorporated into amino acids in the mycelium and translocated further in this form. Generally, free amino acids had high N-15 enrichment levels in the mycelium, decreasing along the translocation pathway. Citrulline and glutamine were the amino acids with highest N-15 concentrations in all parts of the system. N-15 was also found in the macromolecular fraction. (Less)

Polysaccharides in Fungi. XXXII. Hypoglycemic Activity and Chemical Properties of a Polysaccharide from the Cultural Mycelium of Cordyceps sinensis.

Abstract: Crude polysaccharides were obtained from a hot-water extract and alkaline extracts of the cultural mycelium of Cordyceps sinensis. They showed significant activity in normal mice and streptozotocin-induced diabetic mice as a result of intraperitoneal (i.p.) injection. A crude polysaccharide (CS-OHEP) obtained from 5% sodium hydroxide extract slightly lowered the plasma glucose level in normal mice by oral (p.o.) administration. A neutral polysaccharide (CS-F30) exhibited higher hypoglycemic activity than its crude polysaccharide (CS-OHEP), exhibited by i.p. injection, and it significantly lowered the glucose level by p.o. administration (50 mg/kg). However, it hardly affected the plasma insulin level in normal mice. CS-F30 ([α]D +21°in water) is composed of galactose, glucose and mannose (molar percent, 62 : 28 : 10), and its molecular weight is about 45000.

Fruiting in the higher fungi.

Abstract: Publisher Summary Large elaborate fruit bodies of higher fungi called mushrooms (brackets or toadstools), have attracted attention and are the objects of taxonomic and morphological studies. In the fruit bodies, specialized cells are generated that have genetically different haploid nuclei fuse to form diploid nuclei. The diploid cells do not propagate but undergo meiosis to form haploid spores. The vegetative mycelium colonizes the substrate, and its growth depends on regularly branching hyphae. In the heterothallic basidiomycetes, fruiting is observed regularly or exclusively in the heterokaryon, also called the secondary mycelium, that arises from a mating between two compatible homokaryons. It ensures that diploid cells (basidia) that are formed in fruit bodies produce recombinant meiotic progeny (basidiospores). Haploid fruiting may occur spontaneously, only under stress conditions such as transfer to nutritionally deficient media or injury, or only after applying fruit-body formation-inducing substances. The chapter describes molecular and biochemical indices of fruiting. Environmental conditions such as light, temperature and ambient carbon dioxide concentrations, affect the initiation and further development of fruit bodies in basidiomycetes. Formation of large fruit bodies in basidiomycetes and some members of the ascomycetes can be considered as a special case of emergent growth in fungi. The commercially most valuable mushrooms—those mostly appreciated for their taste—are borne on mycelia that live in mutual symbiosis with the roots of trees.

Day/night and circadian rhythm control of con gene expression in Neurospora.

Abstract: In the filamentous fungus Neurospora crassa, several events in the process of conidiation are influenced by light. Two genes, con-6 and con-10, which were previously shown to be transcriptionally activated during conidiation and by exposure to light, were found to be unexpressed in mycelium maintained in constant darkness or in constant light. However, when mycelium was shifted from darkness to light, transcripts of both genes appeared and were abundant. Upon further illumination both transcripts disappeared--i.e., their continued production was light repressed. When dark-grown mycelium was exposed to a light pulse and reincubated in the dark, expression of con-6 and con-10 exhibited a 20-hr circadian periodicity. Both genes were photoinducible throughout the stages of the circadian cycle. In the mutant strains bd and bd;frq9, con-6 and con-10 were light inducible but were not normally light repressible. Mutant genes such as acon-2, acon-3, and fl that block developmental expression of con-6 and/or con-10 did not prevent their photoinduction.

A New Actinomycete Species, Nocardiopsis lucentensis sp. nov.

Abstract: A new species of the genus Nocardiopsis, for which we propose the name Nocardiopsis lucentensis sp. nov. (type strain, strain DSM 44048), was isolated from a salt marsh soil sample near Alicante, Spain. Whole-cell hydrolysates contain the meso isomer of diaminopimelic acid and no characteristic sugar; thus, the cell wall composition is type III. Menaquinone MK-10(H8) is the major menaquinone, and the phospholipid type is type PIII (phosphatidylcholine present). Spore chains are rectiflexibilis, and in the early stages of sporulation zig-zag-shaped aerial hyphae are observed. This microorganism produces compatible solutes of the ectoine type and is characterized by a yellowish to yellowish brown substrate mycelium and a white aerial mycelium. This organism exhibits only 40 to 50% DNA relatedness to other Nocardiopsis spp.

Hemibiotrophic infection of Pisum sativum by Colletotrichum truncatum

Abstract: The infection of pea (Pisum sativum) by Colletotrichum truncatum was studied by light and electron microscopy. These investigations were facilitated by use of an Argenteum pea mutant, which has a readily detachable epidermis. Infection pegs emerging from appressoria penetrated epidermal cells directly. Large intracellular primary hyphae formed a dense stromatic mycelium confined within a single epidermal cell. Primary mycelia gave rise to thinner secondary hyphae which radiated into surrounding cells and caused extensive wall dissolution. Melanized sclerotia developed in the centre of chlorotic water-soaked lesions. Acervuli were not observed. Epidermal cells survived initial penetration by primary hyphae, as shown by their ability to plasmolyse and accumulate Neutral red, but all infected cells were dead when the secondary hyphae had formed. Six cultivars of pea were susceptible, but seven other legumes were resistant. A single isoform of polygalacturonase with a pI of 8·3 and apparent Mr of 40000 was purified from culture filtrates and the TV-terminal amino acid sequence determined. The relevance of the results to the taxonomy of C. truncatum and the relationships between infection process and host range are discussed.

Transmission of Pythium aphanidermatum to greenhouse cucumber by the fungus gnat Bradysia impatiens (Diptera: Sciaridae)

Abstract: Summary The fungus gnat (Bradysia impatiens) was examined for its ability to transmit Pythium aphanidermatum to cucumber plants. Larvae that had ingested oospores and mycelium, and then fed on the roots of young cucumber plants growing in rockwool readily introduced the fungus to them. Trans-stadial transmission of oospores from the larval to the adult stage of B. impatiens was demonstrated, although decreasing to a very low level (1.67%) in adults. However, external transmission of P. aphanidermatum on the surface of adults could not be shown. These results suggest that the larval stages of fungus gnats play a role in the dissemination of the fungus between cucumber plants but that adults probably play only a minor role.

Inhibition of the fungal asexual reproduction stages by three Moroccan essential oils

Abstract: The effect of oregano (Origanum compactum Benth.), mugwort (Artemisia herba-alba Asso) and eucalyptus (Eucalyptus globulus Labill.) oils on spore germination, mycelial elongation and sporulation were studied in three fungi. All three stages of fungal asexual reproduction were affected, but mycelium growth was the most sensitive, followed by spore germination and then sporulation. Of the three fungi studied, Zygorrhynchus sp. was found to be the most sensitive followed by Aspergillus niger and then Penicillium italicum. Oregano oil was observed to be the most active on the three phenomena studied, followed by mugwort at spore germination and sporulation stages and eucalyptus oil when mycelial elongation was considered. The antifungal activity at all three stages of asexual reproduction was shown to be related to oil composition.

Characterization of streptomycetes causing russet scab in Québec.

Abstract: Strains of actinomycetes causing russet scab on potato tubers were different from Streptomyces scabies and S. acidiscabies. The russet scab-inducing organisms were characterized by a bright yellow mycelium on yeast malt extract (YME) which turned brown with age, and by aerial mycelium forming flexuous spore chains which appeared as a gray mass on the colonies. The organisms utilized L-arabinose, D-fructose, D-glucose, D-mannitol, raffinose, rhamnose, sucrose, and D-xylose. They degraded xanthine and xylan, but did not produce melanin

Regulation of production of a trypsin-like protease by the insect pathogenic fungus Metarhizium anisopliae

Abstract: The entomopathogenic fungus metarhizium anisopliae produces several cuticle-degrading proteases which may play a role in pathogenesis. The regulation of one of these, a trypsin-like protease PR2, has been investigated using depressed mycelia. Three insoluble protein sources, insect cuticle, elastin and collagen, as well as two soluble proteins, BSA and gelatin, induced PR2. The polymeric carbon sources cellulose and xylan resulted in depressed basal levels but not induced production of PR2. An approximately 15-fold increase in PR2 activity per mg dry weight of mycelium was observed when the fungus was grown in the presence of bovine serum albumin (BSA), as compared with conditions of depression alone. This indicates that PR2 is induced by BSA, and probably by other proteins. Basal levels of PR2 were detected after 8 h when mycelium was starved for both carbon and nitrogen but only after 16 h when starved for either nitrogen or carbon. In the presence of a protein source, nitrogen strongly repressed PR2 whereas carbon had little effect. There was no effect of sulphur on PR2 production.

Accumulation of intracellular carbon reserves in relation to chloramphenicol biosynthesis by Streptomyces venezuelae.

Abstract: Two chloramphenicol-producing strains of Streptomyces venezuelae accumulated small amounts of polyhydroxybutyrate during exponential growth; the compound disappeared from the mycelium as the cultures entered stationary phase. Depletion of polyhydroxybutyrate coincided with chloramphenicol production but the amount of polymer stored in the mycelium was insufficient to supply the precursor requirement for biosynthesis of the antibiotic. Accumulation of polyhydroxybutyrate in the S. venezuelae strains was appreciably lower than in two other streptomycetes examined. Glycogen and lipids accumulated in the mycelium of S. venezuelae 13s during the stationary phase, after nitrogen depletion; under the culture conditions used, they were the principal storage compounds in S. venezuelae. Trehalose was absent from the mycelium in vegetative cultures grown under nonsporulating conditions but it was abundant in spores obtained from submerged and surface cultures. Glycogen and polyhydroxybutyrate were absent from spores.

Succinate dehydrogenase activity of external and internal hyphae of a vesicular-arbuscular mycorrhizal fungus, Glomus mosseae (Nicol. & Gerd.) Gerdmann and Trappe, during mycorrhizal colonization of roots of leek ( Allium porrum L.), as revealed by in situ histochemical staining

Abstract: The succinate dehydrogenase (SDH) activity of hyphae of the vesicular-arbuscular (VA) mycorrhizal fungus Glomus mosseae (Nicol. & Gerd.) Gerdmann and Trappe, in symbiotic association with leek (Allium porrum L.) roots, was investigated by histochemical staining in situ. Leek seedlings were transplanted to sand culture and inoculated with spores of G. mosseae placed just below the base of the stem. At intervals (14, 25, 35 and 60 days) after transplanting, the growth medium of seedlings was flooded with nitro blue tetrazolium chloride solution, thereby displacing the nutrient solution. This allowed sites of SDH activity of external and internal fungal structures of the mycorrhizas to be stained without physically disturbing the symbiotic system. After counterstaining harvested roots and mycelium with acid fuchsin, it was possible to differentiate clearly metabolically active and inactive regions of the fungus. The lengths of external hyphae and infected root both increased nearly exponentially, and were in constant proportion (1.4 m hyphae per cm of infected root) for up to 60 days. The percentage length of external hyphae with SDH activity remained almost constant (80%). In each infected length of root there was a gradation of SDH activity from inactive distal (older) hyphae to uniformly active proximal (younger) hyphae. These findings are discussed in relation to the symbiotic activity of the mycobiont.

Biological control of southern blight disease of tomato caused by Sclerotium rolfsii with simplified mycelial formulations of Trichoderma koningii

Abstract: Two simple formulations of an antagonistic strain of Trichoderma koningii were employed against southern blight disease caused by Sclerotium rolfsii in seedling, potted outdoor and field-grown tomatoes (cvs. Ife No. 1 and Ibadan Local). Corn cob germling inoculum and mycelium powder of T. koningii significantly controlled (P≤0·05) symptoms of damping off, blight and wilting in both tomato cultivars. The populations of the antagonist increased from an initial 1 × 104 to about 1 × 106 colony-forming units per g of soil in the protected plants. Moreover, sclerotial counts decreased significantly (P≤0·05) in these soils and those sclerotia found had been parasitized by T. koningii. Trichoderma-protected plants were more vigorous than those in the other treatment categories. The significance of these results is discussed in relation to the use of Trichoderma in appropriately simplified formulations.

Evaluation of a fungal antagonist, Phaeotheca dimorphospora, for biological control of tree diseases.

Abstract: Phaeotheca dimorphospora, which was first isolated from elm wood and found to be antagonistic in vitro against the Dutch elm disease pathogen Ophiostoma ulmi, was tested for antifungal activity in vitro against other tree pathogens by a variation of the agar layer technique. Phaeotheca dimorphospora produced antifungal compounds that were strongly inhibitory against a wide range of tree pathogens in addition to O. ulmi, such as Gremmeniella spp., Armillaria spp., Septoria musiva, Verticillium albo-atrum, Cylindrocladium floridanum, Phytophthora sp., Nectria galligena, and Heterobasidion annosum. Under light and interference microscopy, four types of morphological changes were observed in the pathogens tested: swelling of hyphae, production of resting spores such as chlamydospores and of sclerotia, extrusion of cytoplasm from hyphal tips, and bursting and destruction of mycelium. Chloroform-soluble antagonistic compounds were extracted that showed both fungicidal and fungistatic effects on the test organis...