Growth and metabolism in mycelial fungi

A mathematical model for the growth and morphogenesis in colonies of mycelial fungi is given. The model consists of partial differential equations for accumulation of hyphae by apical growth, uptake of nutrient, and redistribution of a derived metabolite within the mycelium. Mechanisms for nutrient absorption and for metabolite translocation are discussed. An explanation for growth in the form of concentric mycelial rings is offered, based on the hypothesis that repeated metabolite buildup and depletion gives rise to different local branching rates, and thus distinct bands of hyphal densities.     

Species composition of food-spoiling mycelial fungi

We investigated the composition of the microflora that spoils foodstuffs (the surface of hard cheeses and sausages) at agribusiness factories. Mycelial fungi, mostly ascomycetes of the order Eurotiales belonging to the genus Penicillium play the main role in spoiling food. Most representatives of these fungi are mesophiles and possess the capacity for utilizing nutrient substrates in surface and submerged cultures.     

Liposome-mediated mycelial transformation of filamentous fungi

Liposome-mediated transformation is common for cells with no cell wall, but has very limited usage in cells with walls, such as bacteria, fungi, and plants. In this study, we developed a procedure to introduce DNA into mycelium of filamentous fungi, Rhizopus nigricans LH 21 and Pleurotus ostreatus TD 300, by liposome-mediation but with no protoplast preparation. The DNA was transformed into R. nigricans via plasmid pEGFP-C1 and into P. ostreatus via 7.2 kb linear DNA. The mycelia were ground in 0.6 M mannitol without any grinding aids or glass powder for 15 min to make mycelial fragments suspension; the suspension was mixed with a mixture of the DNA and Lipofectamine 2000, and placed on ice for 30 min; 100 μL of the transformation solution was plated on potato dextrose agar (PDA) plate and cultivated at 28 °C for transformant screening. The plasmid and the linear DNA were confirmed to be integrated into the host chromosome, proving the success of transformation. The transformation efficiencies were similar to those of electroporation-mediated protoplast transformation (EMPT) of R. nigricans or PEG/CaCl₂-mediated protoplast transformation (PMT) of P. ostreatus, respectively. The results showed that our procedure was effective, fast, and simple transformation method for filamentous fungi.     

Diversity of facultatively anaerobic microscopic mycelial fungi in soils

The numbers of microscopic fungi isolated from soil samples after anaerobic incubation varied from tens to several hundreds of CFU per one gram of soil; a total of 30 species was found. This group is composed primarily of mitotic fungi of the ascomycete affinity belonging to the orders Hypocreales (Fusarium solani, F. oxysporum, Fusarium sp., Clonostachys grammicospora, C. rosea, Acremonium sp., Gliocladium penicilloides, Trichoderma aureoviride, T. harzianum, T. polysporum, T. viride, T. koningii, Lecanicillum lecanii, and Tolypocladium inflatum) and Eurotiales (Aspergillus terreus, A. niger, and Paecilomyces lilacimus), as well as to the phylum Zygomycota, to the order Mucorales (Actinomucor elegans, Absidia glauca, Mucor circinelloides, M. hiemalis, M. racemosus, Mucor sp., Rhizopus oryzae, Zygorrhynchus moelleri, Z. heterogamus, and Umbelopsis isabellina) and the order Mortierellales (Mortierella sp.). As much as 10–30% of the total amount of fungal mycelium remains viable for a long time (one month) under anaerobic conditions.     

Diversity of facultatively anaerobic microscopic mycelial fungi in soils

The numbers of microscopic fungi isolated from soil samples after anaerobic incubation varied from tens to several hundreds of CFU per one gram of soil; a total of 30 species was found. This group is composed primarily of mitotic fungi of the ascomycete affinity belonging to the orders Hypocreales (Fusarium solani, F. oxysporum, Fusarium sp., Clonostachys grammicospora, C. rosea. Acremonium sp., Gliocladium penicilloides, Trichoderma aureoviride, T. harzianum, T. polysporum, T. viride. T. koningii, Lecanicillum lecanii, and Tolypocladium inflatum) and Eurotiales (Aspergillus terreus, A. niger, and Paecilomyces lilacimus), as well as to the phylum Zygomycota, to the order Mucorales (Actinomucor elegans, Absidia glauca, Mucor circinelloides, M. hiemalis, M. racemosus, Mucor sp., Rhizopus oryzae, Zygorrhynchus moelleri, Z. heterogamus, and Umbelopsis isabellina) and the order Mortierellales (Mortierella sp.). As much as 10-30% of the total amount of fungal mycelium remains viable for a long time (one month) under anaerobic conditions.     

Ectomycorrhizal fungi: exploring the mycelial frontier

Ectomycorrhizal (ECM) fungi form mutualistic symbioses with many tree species and are regarded as key organisms in nutrient and carbon cycles in forest ecosystems. Our appreciation of their roles in these processes is hampered by a lack of understanding of their soil-borne mycelial systems. These mycelia represent the vegetative thalli of ECM fungi that link carbon-yielding tree roots with soil nutrients, yet we remain largely ignorant of their distribution, dynamics and activities in forest soils. In this review we consider information derived from investigations of fruiting bodies, ECM root tips and laboratory-based microcosm studies, and conclude that these provide only limited insights into soil-borne ECM mycelial communities. Recent advances in understanding soil-borne mycelia of ECM fungi have arisen from the combined use of molecular technologies and novel field experimentation. These approaches have the potential to provide unprecedented insights into the functioning of ECM mycelia at the ecosystem level, particularly in the context of land-use changes and global climate change.     

Strategies of food substrate colonization by mycelial fungi

This article deals with a new research area related to mycology and the food industry. It is concerned with the strategies used by ascomycete mycelial fungi to utilize and colonize food items. The data of scanning and transmission electron and light microscopy revealed that fungi growing on such food items as cheese and sausage are characterized by the following colonization strategies: (i) spreading growth; (ii) burrowing growth; (iii) growth with the formation of up to 4–5 new branches on the apexes of the old hyphae; (iv) growth with the formation of long strands, and (v) growth with biofilm formation.     

Biosorption of cadmium to mycelial pellets of wood-rotting fungi

Summary Fungal pellets of wood-rotting fungi (diameters ranged from 0.2 to 2 cm) were obtained by submerged cultivation on nutrient rich medium. Biosorption of cadmium (initial concentration, 10 mM) in batch system was followed by HPLC. Of 20 fungal strains tested, high abilities to accumulate cadmium were found in Fomitopsis pinicola (130.2 mg/g) and Trametes versicolor (109.5 mg/g). P. chrysosporium contained 84.5 mg Cd /g dry weight.     

The lipids of mycelial fungi and the prospects for the development of microbial oleo-biotechnology. I. The lipids of mycelial fungi

The importance of mycelial fungi as a source of lipids for development of modern oleo biotechnology is considered. For this purpose the data on fungal lipid composition and the main enzymes of fatty acid synthesis in fungi as compared with procaryotes and higher eucaryotes as well the data on the effect of a number of physicochemical factors on the yield and composition of the lipids of the micromycetes are presented. The information on the fungi producers according to the lipid composition able to substitute the vegetable oil and be the source of linolic, linolenic and arachidonic acids is put forward.     

Germination of spores of mycelial fungi in relation to exogenous dormancy

Comparative analysis of germination of asexual sporulation spores (conidia and sporangiospores) and of specific features of dormancy release was carried out for ascomycete mycelial fungi Aspergillus tamarii VKM F-64 and A. sydowii VKM F-441, as well as for zygomycete fungi Cunninghamella echinulata VKM F-663 and Umbelopsis ramanniana VKM F-582. The spores of these strains were shown to be in a state of exogenous dormancy and differed in lag phase duration and germination rate, which depended on the presence of nutrients in the medium. Only the strain C. echinulata VKM F-663 exhibited 100% spore germination, with the germination rate and lag phase duration not depending on the composition of the medium. While in A. tamarii strain VKM F-64, the total number of spores germinating on rich and poor media was also almost the same, in the absence of nutrients lag phase duration increased and the germination rate decreased. For strains U. ramanniana VKM F-582 and A. sydowii VKM F-441, the degree of spore germination in the absence of nutrients in the medium was considerably lower than on the rich medium, while the lag phase was longer. These data indicate that the spores of C. echinulata VKM F-663 are in the state of exogenous dormancy, which does not require for release any compounds except water. The spores of U. ramanniana strain VKM F-582 and of the Aspergillus strains exhibited another variant of exogenous dormancy, which required for release, apart from water, also the sources of carbon and nitrogen. Thus, the character of dormancy release may differ even within a single genus (Aspergillus).     

Investigation of mycelial growth in some gill fungi under laboratory conditions

The effect of the composition, consistence and pH of the media was investigated in 57 species (110 strains) of gill fungi of theAgaricaeae family with respect to the influence of cultivation conditions. The results showed that different genera have diverse nutritional requirements. Wort agar, adjusted to pH 5.5 was suitable for most of the fungi investigated. The growth rate of mycelial colonies was also compared, and the effect of the fungi on the cultivation medium and certain manifestations associated with growth, including fructification. A growth coefficient, expressing the relation of the length, height and density of the aerial mycelium after 14 days of cultivation was used to characterize the manner of growth of the different species. The experiments confirmed that most wood-inhabiting species grow rapidly, terrestrial fungi more slowly, and mycorrhizal fungi the slowest. Strains of the same species preserved similar growth characteristics. Microscopic study of the growth of the aerial mycelium revealed clamp connections in the hyphae in 69% of the fungi investigated and secondary spores in 11%.     

Extracellular proteases of mycelial fungi as participants of pathogenic processes

The interest in proteases secreted by mycelial fungi is due to several reasons of which one of the most important is their involvement in the initiation and development of the pathogenic process. A comparison of saprophytic and phytopathogenic mycelial fungi revealed one characteristic feature, namely, the appearance of a new trypsin-like activity in phytopathogens that is absent in saprophytes. To clear up the question of whether the degree of pathogenicity of a fungus is related to the activity of secreted trypsin-like protease, several species of Fusarium of various pathogenicity were compared. In two species, F. sporotrichioides (which causes ear fusa-riosis of rye) and F. heterosporum (the causative agent of root rot in wheat), a clear correlation between the activity and pathogenicity was revealed: the more pathogenetic F. sporotrichioides exhibited a higher extracellular trypsin-like activity than the less pathogenetic species F. heterosporum. Thus, the presence of trypsin-like activity in a saprotroph-pathogen pair may be an indicator of the pathogenicity of a fungus; in some cases, the value of this activity may indicate the degree of its pathogenicity. This suggests that trypsin-like proteases specific to phytopathogens are directly involved in the pathogenetic process, probably, through interaction with the "sentry" protein or the product of the resistance gene.     

Extracellular proteases of mycelial fungi as participants of pathogenic process

The interest in proteases secreted by mycelial fungi is due to several reasons of which one of the most important is their involvement in the initiation and development of the pathogenic process. A comparison of saprophytic and phytopathogenic mycelial fungi revealed one characteristic feature, namely, the appearance of a new trypsin-like activity in phytopathogens that is absent in saprophytes. To clear up the question of whether the degree of pathogenicity of a fungus is related to the activity of secreted trypsin-like protease, several species of Fusarium of various pathogenicity were compared. In two species, F. sporotrichioides (which causes ear fusariosis of rye) and F. heterosporum (the causative agent of root rot in wheat), a clear correlation between the activity and pathogenicity was revealed: the more pathogenetic F. sporotrichioides exhibited a higher extracellular trypsin-like activity than the less pathogenetic species F. heterosporum. Thus, the presence of trypsin-like activity in a saprotroph-pathogen pair may be an indicator of the pathogenicity of a fungus; in some cases, the value of this activity may indicate the degree of its pathogenicity. This suggests that trypsin-like proteases specific to phytopathogens are directly involved in the pathogenetic process, probably, through interaction with the “sentry” protein or the product of the resistance gene.     

Pseudomonas cepacia causes mycelial deformities and inhibition of conidiation in phytopathogenic fungi

Pseudomonas cepacia, a common soil and rhizosphere inhabitant, showed strong antagonism against several fungal plant pathogens. In dual cultures it greatly restricted the growth and conidial formation in several of these fungi. Growth restriction was associated with the frequent induction of a variety of morphological abnormalities such as chlamydoconidium formation, hyphal swellings, vacuolation and granulation of the mycelial contents, as well as lysis of hyphae and conidia. The induction of these deleterious morphological changes in fungi and inhibition of conidial formation were also found with a crude preparation of an antifungal compound fromP. cepacia. Mutants, defective in the production of this antifungal compound, failed to induce these morphological changes; this suggests that the antifungal compound is responsible for these abnormalities.