Mycelium

Fungal micelio seen in a calicata.

Micelio and carpophores Agaricus bisporus.

The mycelium is a fungal structure with a root-like appearance, consisting of a mass of branched, thread-like hyphae, which form the vegetative part of multicellular fungi such as mushrooms and molds. Fungal colonies composed of mycelium can be found in or on the soil, as well as on many other substrates. A typical single spore germinates on a monokaryotic mycelium, which cannot reproduce sexually. When two compatible monokaryotic mycelium unite and form a dikaryotic mycelium, the mycelium can form fruiting bodies, such as mushrooms. A mycelium can be tiny, forming a colony that is too small to see with the naked eye, or it can grow to number hundreds. hectares, as is the case of the honey fungus.

The vegetative bodies of most fungi (and therefore lichens) are made up of multicellular filaments called hyphae. The hyphae grow only apically at the apex. The hyphae can grow very rapidly, up to more than 1 mm per hour. For this reason and due to the frequent ramifications, a tangle of hyphae with an enormous surface area arises in the substrate: the mycelium.

Through the mycelium, a fungus absorbs nutrients from its environment. It does so in a two-stage process. First, the hyphae secrete enzymes onto or into the food source, which break down biopolymers into smaller units such as monomers. These monomers are then taken up by the mycelium via facilitated diffusion and active transport.

Since the hyphae are not cutinized, the mycelium is very sensitive to desiccation, but, on the other hand, they are highly capable of osmotrophically absorbing dissolved substances. This fact is used by many higher plants forming symbiosis with fungi.

The hyphae of the lower fungi are not septate (they do not present divisions), with a siphonal organization.

The hyphae of the higher fungi present septa, divided into chambers and cells; but with perforations, so that also in these fungi the plasma forms a continuum.

Mycelia are vital in terrestrial and aquatic ecosystems for their role in breaking down plant material. They contribute to the organic fraction of the soil and their growth releases carbon dioxide into the atmosphere (see carbon cycle). The ectomycorrhizal extramatric mycelium, as well as the mycelium of arbuscular mycorrhizal fungi, increase the efficiency of water and nutrient uptake of most plants and confer resistance to some plant pathogens. The mycelium is an important food source for many soil invertebrates. They are vital to agriculture and are important to almost all plant species, many species co-evolving with fungi. Mycelium is a major factor in the health, nutrient intake and growth of a plant, with mycelium being an important factor in plant fitness.

Networks of mycelia can transport water and electrical potential spikes.

Sclerotia consist of compact or hard masses of mycelium.

Uses

One of the main functions of fungi in an ecosystem is to break down organic compounds. Petroleum products and some pesticides (typical soil contaminants) are organic molecules (ie built on a carbon framework) and therefore show a potential carbon source for fungi. Therefore, fungi have the potential to eradicate such contaminants from their environment unless the chemicals are toxic to the fungus. This biological degradation is a process known as bioremediation.

Mycelial mats have been suggested to have potential as biological filters, removing chemicals and microorganisms from soil and water. The use of fungal mycelium to achieve this has been termed mycofiltration.

Knowledge of the relationship between mycorrhizal fungi and plants suggests new ways to improve crop yields.

When spread on logging roads, the mycelium can act as a binder, holding the disturbed new soil in place and preventing it from washing away until woody plants can establish roots.

Alternatives to Styrofoam and plastic packaging can be produced by growing mycelium in agricultural waste. The two ingredients are mixed and placed in a mold for 3-5 days so that they become a durable material. Depending on the strain of mycelium used, many different varieties of the material are possible, such as water absorbent, flame retardant, and dielectric.

The mycelium has also been used as a material in furniture, bricks, and artificial leather.

Fungi are essential for composting biomass, as they break down feedstock components, such as lignin, that many other composting microorganisms cannot. Turning over a compost pile commonly exposes visible webs of mycelia that have formed on the decaying organic material inside. Compost is an essential fertilizer and soil amendment for organic farming and gardening. Composting can divert a substantial fraction of municipal solid waste from landfills.

Biology

In fungi, the germination of a spore gives rise to a haploid mycelial filament (chromosomes) called the primary mycelium. But the latter remains sterile. You must meet another primary filament that you carry of the opposite sex. This encounter will give a fertile secondary mycelium carrying cells with two nuclei (2 chromosomes). The mycelial filaments branch and diverge in all directions. Under ideal conditions, the mycelium forms a disk on the surface of the substrate.

In bacteria, on a solid support, the germination of a spore leads to the formation of a primary mycelium that extends to the surface of the substrate to take advantage of its nutritional resources. Aerial hyphae emerge from this vegetative mycelium, forming the secondary mycelium that covers the surface and sporulating colonies (asexual reproduction), which gives it a fungal appearance. The primary mycelium lyses, releasing recycled nutrients for the growth of these hyphae.

When a mycelium has accumulated sufficient reserves and a thermohydric shock occurs, a primordium develops to form a sporophore (visible part of the fungus resulting from the fusion of mycelium filaments) which in turn will give rise to spores.

Properties and characteristics

The mycelium has a great power of penetration and dissemination in the substrate. The extension of the mycelial network, favored by the small diameter of the hyphae (5 to 10 μm in most species), ensures a maximum contact surface between the fungus and the environment from which it derives its subsistence. Thus, in the tree, this set of hyphae increases the root capacity by a factor of a thousand. This surface area maximization explains why a mycelium can hold 3,000 times its weight and that the human foot covers an average of 400 km of mycelium.

Ten cubic centimeters of fertile soil very rich in organic matter can contain up to 1 km of mycelial filaments with an average diameter of 10 micrometers, which corresponds to 200 m of mycelium per gram of soil. Its growth rate can reach several centimeters per day under optimal conditions (humidity, temperature, nutrient medium). Its growth always occurs in length and not in thickness, in order to increase its absorption capacity.

Mycorrhizal fungi are very abundant in certain soils, where their mycelium represents on average 60% of the total soil microbial biomass (% rootless age) and up to 30% of root biomass.

In 2000, in Oregon, a mycelium of Armillari ostoyae, a giant fungus measuring 5.5 km in diameter and spreading over an area of 890 hectares of forest, was discovered. The fungus it was over 2,400 years old.