Advanced Materials From Fungal Mycelium: Fabrication and Tuning of Physical Properties

In this work is presented a new category of self-growing, fibrous, natural composite materials with controlled physical properties that can be produced in large quantities and over wide areas, based on mycelium, the main body of fungi. Mycelia from two types of edible, medicinal fungi, Ganoderma lucidum and Pleurotus ostreatus, have been carefully cultivated, being fed by two bio-substrates: cellulose and cellulose/potato-dextrose, the second being easier to digest by mycelium due to presence of simple sugars in its composition. After specific growing times the mycelia have been processed in order to cease their growth. Depending on their feeding substrate, the final fibrous structures showed different relative concentrations in polysaccharides, lipids, proteins and chitin. Such differences are reflected as alterations in morphology and mechanical properties. The materials grown on cellulose contained more chitin and showed higher Young's modulus and lower elongation than those grown on dextrose-containing substrates, indicating that the mycelium materials get stiffer when their feeding substrate is harder to digest. All the developed fibrous materials were hydrophobic with water contact angles higher than 120°. The possibility of tailoring mycelium materials' properties by properly choosing their nutrient substrates paves the way for their use in various scale applications.

Production of mycelial biomass by the Amazonian edible mushroom Pleurotus albidus

Edible mushroom species are considered as an adequate source of food in a healthy diet due to high content of protein, fiber, vitamins, and a variety of minerals. The representatives of Pleurotus genus are characterized by distinct gastronomic, nutritional, and medicinal properties among the edible mushrooms commercialized worldwide. In the present study, the growth of mycelial biomass of Pleurotus albidus cultivated in submerged fermentation was evaluated. Saccharose, fructose, and maltose were the three main carbon sources for mycelial biomass formation with corresponding yields of 7.28 g L⁻¹, 7.07 g L⁻¹, and 6.99 g L⁻¹. Inorganic nitrogen sources did not stimulate growth and the optimal yield was significantly higher with yeast extract (7.98 g L⁻¹). The factorial design used to evaluate the influence of saccharose and yeast extract concentration, agitation speed, and initial pH indicated that all variables significantly influenced the production of biomass, especially the concentration of saccharose. The greater amount of saccharose resulted in the production of significantly more biomass. The highest mycelial biomass production (9.81 g L⁻¹) was reached in the medium formulated with 30.0 g L⁻¹ saccharose, 2.5 g L⁻¹ yeast extract, pH 7.0, and a speed of agitation at 180 rpm. Furthermore, P. albidus manifested different aspects of morphology and physiology under the growth conditions employed. Media composition affected mycelial biomass production indicating that the diversification of carbon sources promoted its improvement and can be used as food or supplement.

Abiotic and biotic degradation of oxo-biodegradable plastic bags by Pleurotus ostreatus

In this study, we evaluated the growth of Pleurotus ostreatus PLO6 using oxo-biodegradable plastics as a carbon and energy source. Oxo-biodegradable polymers contain pro-oxidants that accelerate their physical and biological degradation. These polymers were developed to decrease the accumulation of plastic waste in landfills. To study the degradation of the plastic polymers, oxo-biodegradable plastic bags were exposed to sunlight for up to 120 days, and fragments of these bags were used as substrates for P. ostreatus. We observed that physical treatment alone was not sufficient to initiate degradation. Instead, mechanical modifications and reduced titanium oxide (TiO2) concentrations caused by sunlight exposure triggered microbial degradation. The low specificity of lignocellulolytic enzymes and presence of endomycotic nitrogen-fixing microorganisms were also contributing factors in this process.

Pleurotus ostreatus biofilms exhibit higher tolerance to toxicants than free-floating counterparts

The MBEC(TM)-High Throughput Assay based on the Calgary Biofilm Device was used to produce and to characterize Pleurotus ostreatus biofilms. Hydroxyapatite coating of pegs was required to enable biofilm attachment; biofilm amounts and homogeneity of distribution were markedly improved upon removal of non-sessile biomass after 48 h from inoculation. Scanning electron microscopy showed surface-associated and multi-layered growth stabilized by the presence of an extracellular matrix (ECM). Biofilms had higher contents of total sugars and ECM than their free-floating counterparts. Tolerance to Cr(VI) in the former was about twice that of the latter as inferred by the respective inhibitory concentrations (48.4 vs 24.1 mM and 114.5 vs 61.0 mM in 4- and 7-d-old cultures, respectively). Biofilms also displayed superior olive-mill wastewater (OMW) treatment efficiency along 5 consecutive batches leading to chemical oxygen demand and total phenol removals higher than 50 and 90%, respectively. Laccase activity peaks in biofilm cultures grown on OMW were significantly higher than those in free-floating cultures.

Investigation of growth responses in saprophytic fungi to charred biomass

We present the results of a study testing the response of two saprophytic white-rot fungi species, Pleurotus pulmonarius and Coriolus versicolor, to charred biomass (charcoal) as a growth substrate. We used a combination of optical microscopy, scanning electron microscopy, elemental abundance measurements, and isotope ratio mass spectrometry ((13)C and (15)N) to investigate fungal colonisation of control and incubated samples of Scots Pine (Pinus sylvestris) wood, and charcoal from the same species produced at 300 degrees C and 400 degrees C. Both species of fungi colonise the surface and interior of wood and charcoals over time periods of less than 70 days; however, distinctly different growth forms are evident between the exterior and interior of the charcoal substrate, with hyphal penetration concentrated along lines of structural weakness. Although the fungi were able to degrade and metabolise the pine wood, charcoal does not form a readily available source of fungal nutrients at least for these species under the conditions used in this study.

[Morphogenesis and ultrastructure of basidiomycetes Agaricus and Pleurotus mitochondria]

Mitochondrial morphogenesis in 31 strains of 9 species of Agaricus--A. arvensis Schaeff., A. bisporus (Lange) Imbach, A. bitorquis (Quel.) Sacc., A. campestris L., A. excellens (F. H. Moller) F. H. Moller, A. macrocarpus (F. H. Möller) F. H. Möller, A. silvaticus Schaeff., A. silvicola (Vittad.) Peck, A. xanthodermus Genev--and 2 strains of Pleurotus--P. ostreatus (Jacg.) P. Kumm., P. pulmonarius (Fr.) Quel.--has many common features in mitochondria distribution under favorable growth conditions (type 1) and in reconstruction of chondriom (fission or fragmentation) under unfavorable growth conditions and aging (type 2). The first type of mitochondria distribution was observed in heterokaryotic mycelium of some Agaricus strains and Pleurotus grown in agar medium during 7-14 days, and also in submerged mycelium of some Agaricus strains and Pleurotus. The second type of mitochondria distribution was observed in homokaryotic Agaricus strains under condition of starvation, in aging mycelium (28 days of growth), and in submerged mycelium of most of Agaricus strains. The first type of chondriom consists of small granular mitochondria in the apical cells and long snake-like network in subapical cells, and restores almost completely the mitochondrial network in the aging mycelium cells. The second type of chondriom consists of small granular mitochondria in all cells of mycelium. The surface of chondriom type 2 mitochondrial membrane was usually closely associated with ribosomes and changed crists. Such mycelium cells in A. bisporus strain Bs94 were TUNEL positive. So, the types of mitochondria morphogenesis in the Agaricus and Pleurotus mycelium cells are similar at different time and growth conditions and depend on complex of physiological and biochemical process in the mycelium cells.

Accumulation and localization of cesium in edible mushroom (Pleurotus ostreatus) mycelia

The characteristics of Cs accumulation and localization in edible mushrooms were examined using the mycelia of Pleurotus ostreatus-Y1. Scanning electron microscope images revealed the existence of white spots, and energy dispersive X-ray microanalyzer analysis indicated the presence of larger amounts of Cs and P in these spots in mycelia cultured on medium containing 25 mM CsCl. The (137)Cs activities in the mycelia were approximately 4-6 times higher than those in water used for (137)Cs elution. Higher Cs concentrations in the sediment fraction including vacuolar pellets were obtained compared to the upper fractions. It was observed that yellowish spots caused by the fluorescence of 4',6-diamidino-2-phenylindole (DAPI)-stained polyphosphate were localized in the mycelia. The higher fluorescence intensity of the yellowish-grained spots was measured in comparison with other regions in the mycelium. These results suggested that Cs in the mycelia was trapped by polyphosphate in vacuoles or other organelles.

Microscopic observations of the early development of Pleurotus pulmonarius fruit bodies

From observations made by light microscopy, transmission electron microscopy, environmental-scanning and cryoscanning electron microscopy we conclude that the expansion of the young fruit body of Pleurotus pulmonarius involves considerable vacuolation of hyphae but no marked inflation of cell dimensions. There is evidence for an extensive extracellular matrix (ECM), the components of which must be under the control of the hyphae which the ECM surrounds. However the ECM in these fruit bodies is a dilute material. It is easily lost during specimen preparation and is evident only when certain techniques are used to preserve the fluid surface of the hyphae. Observations of the hyphal and fruit body structures with a range of conventional microscopic techniques are crucial to complement the information obtained through physiological and molecular studies for understanding the cellular changes that occur during mushroom development.

[Comparative analysis of Pleurotus ostreatus natural isolates]

A comparative analysis is performed of the polymorphism of the Pleurotus ostreatus (Fr.) Kumm naturally occurring strains isolated from the natural substrates found in two geographically remote Russian natural preserves, the Central Arboreal Biosphere Tver State Preserve (CABTSP) and the Moscow State University Zvenigorod Biological Station (ZBS, Moscow oblast), and within the city of Moscow. The results of the frequency analysis for the isozyme loci alleles and for the sexual and vegetative incompatibility groups are presented; the genetic structure and the interpopulation relations among 58 P. ostreatus dikaryotic strains are estimated. The natural samples from the Moscow and Tver oblasts are shown to have a high degree of polymorphism with a genetic differentiation of 0.743; in spite of their territorial remoteness, they are, however, actively exchanging genetic material. The natural fungal isolates form two reproductively isolated groups.

Influence of the substrate on the ultrastructure of Pleurotus pulmonarius fruit body primordia

Pleurotus pulmonarius fruit body primordia (FBP) formed on potato extract agar (PEA) and wheat straw-based media (WS) were studied. When grown on PEA, FBP hyphae had a large number of vacuoles and less stainable cytoplasmic material. In contrast, when grown on WS, there was abundant cytoplasmic material and fewer vacuoles. FBP grown on WS had a more well-defined mushroom shape than those grown on PEA. The average hyphal diameters on PEA and WS were 4.15 and 3.52 micro m, respectively; the average hyphal lengths were 11.75 and 11.80 micro m, respectively. The control mechanisms regulating formation of the normal shape and size of FBP might be more dependent on the amount of cytoplasmic material than on the physical volume of the hyphal compartment. Since the ultrastructure of the hyphal compartment, which makes up the substance of the FBP, depends on the substrate in which the FBP has been grown, the composition of the substrate may be important for manipulating the nutritive and organoleptic characteristics of the mushroom crop.

Simple staining detects ultrastructural and biochemical differentiation of vegetative hyphae and fruit body initials in colonies of Pleurotus pulmonarius

AIMS

To know the ultrastructural and biochemical differences of vegetative hyphae and fruit body initials in colonies of Pleurotus pulmonarius.

METHODS AND RESULTS

Feulgen reagent was used to detects differentiation of hyphae. The intracellular laccases, proteases and beta-1,3-glucanases activity, content of cytoplasmic protein, glycogen and glucans in the cell wall were evaluated in hyphae of fruit body initials and in vegetative hyphae. The thickness of hyphal walls of the vegetative hyphae was also evaluated. Substantial biochemical changes were observed in hyphae of different zones of the fruiting colony. Hyphae at the periphery had thinner walls than in the centre of the colony.

CONCLUSION, SIGNIFICANCE AND IMPACT OF THE STUDY

Staining correlated with the enzymatic activity, protein, glycogen and glucans, in mycelium and in fruit body initials. The implications are that hyphal maturity in P. pulmonarius involves storage of glucans, in part at least, in the form of a thickened hyphal wall.

[Ultrastructure of the cell wall in vegetative mycelia of Agaricus bisporus (Lange) Imbach]

A comparative description of the cell wall ultrastructure was made for vegetative mycelia in Agaricus bisporus, other species of Agaricus, and Pleurotus ostreatus. Apart from well known ultrastructural features of cell walls of the examined strains, inclusions of different kinds were observed. The cell wall thickness varied in different Agaricus strains. Maximum differences between the examined strains were 1.4 times. The cell wall thickness in P. ostreatus strains was by 3 to 4 times less than that in Agaricus strains. Using electron micrographs, a brief description of mycelia and A. bisporus basidia ultrastructure was composed.