GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

8. FUNGI

8.9. DISTRIBUTION OF FUNGI AND CHARACTERISTICS OF ECOLOGICAL GROUPS

Geographical Distribution of Fungi. Fungi are widely distributed in soil, air, Water bodies, on plants, animals, and humans. Compared to plants and animals, their geographical range is broader. Fungi are most commonly found in soil, air, and partially in water. This is due to the presence of plant substrates, which serve as the most suitable nutritional sources for fungi in nature. Depending on The Nature of the substrate, fungi adapt to it, which leads to the Selection of specialized fungal species or associations and their rapid spread. For instance, woody plants are dominated by specific species of Basidiomycetes—both parasitic and mycorrhizal—whereas herbaceous plants harbor basidiomycetes, ascomycetes, and deuteromycetes. The epiphytic fungal flora of plants differs in composition from the mycoflora inhabiting the roots of the same plants. Desert soils across various geographical regions feature a similar fungal flora dominated by dark-pigmented fungi. Alpine soils contain more micromycetes than macromycetes, whereas bare mountain slopes or slopes covered with shrub and herbaceous vegetation are dominated by basidiomycetes (macromycetes). Consequently, it can be concluded that the geographical range of fungi is closely linked to that of higher plants.

The Biological features of fungi—such as the hyphal growth form, which ensures contact with the environment, active METABOLISM of hyphal Cells, and rapid colonization and Modification of the substrate—play a crucial role in fungal dissemination. Furthermore, fungi exhibit a high level of environmental adaptation.

The science that investigates the life processes of organisms in nature, along with their environmental impacts, interrelationships, and mutual interactions, is called ecology. Fungal ecology, like the ecology of other organisms, examines The Influence of numerous factors on their natural distribution. Fungi constitute an integral element of the ecosystem.

External factors (environmental factors) directly or indirectly influence the distribution of fungi within specific ecological niches. For example, Physical and Chemical factors such as Temperature regulate the cyclical GROWTH AND REPRODUCTION of fungi. Water exerts a direct or indirect effect by dissolving substances that are either nourishing or toxic to fungi. Substrate moisture, particularly atmospheric humidity, alongside temperature, dictates the growth of specific fungal species. Similarly, soil moisture affects soil aeration and metabolism, which in turn determines the presence of particular fungi. In addition to physical and Chemical factors, biotic factors—such as plants, animals, and microorganisms—are of great importance for fungal distribution. Biotic factors can be diverse in nature, including metabolic, symbiotic, parasitic, and antibiotic interactions. Like other organisms, fungi in nature do not grow in isolation, but rather in close interconnection with other living beings. Such interdependent microbial activity is referred to as an association. The nature of fungal associations with other organisms varies and likewise depends on numerous factors. For instance, various insects are affected by multiple fungal species, while at the same time, fungi serve as a food source for many insects. Parasitic fungi, by damaging plant Tissues, create favorable conditions for The Development of saprophytic fungi.

As a result of complex interactions among biotic, physicochemical, and geographical (climatic) factors, specific ecological groups of fungi emerge, consisting of species adapted to particular natural conditions. Let us examine the most important ecological groups of fungi.

Soil fungi. Soil is the primary habitat for the majority of fungi across various taxonomic groups. Fungi exist in the soil not only as sporulation Organs and dormant forms, but also as a physiologically active mycelium.

Soil mycoflora is represented by all major fungal classes: phycomycetes, ascomycetes, basidiomycetes, and deuteromycetes. The most widespread soil fungi belong to the genera Trichoderma, Mucor, Mortierella, Penicillium, Aspergillus, and Fusarium. The soil also harbors spores and other structures of numerous parasitic fungi, such as the chytrid fungus Synchytrium endobioticum, the CAUSATIVE AGENT OF potato wart disease, among others.

The species composition of fungi is influenced by soil type, climate, vegetation, tillage practices, and other factors. In vegetated soils, the mycoflora is represented by mycorrhizal, rhizospheric, parasitic, and saprophytic fungi. Among mycorrhizal fungi, there are both parasites and Saprophytes that utilize plant tissues, organs, and plant residues. Rhizospheric fungi are saprophytes that consume organic and mineral compounds of the soil.

The Role of fungi in the soil is diverse and substantial. Along with other organisms, fungi participate in the decomposition of PLANT AND ANIMAL residues, thereby driving nutrient cycling in nature and contributing to soil fertility. Soil fungi take a direct part in the Nutrition of higher plants while also acting as agents of plant diseases. Soil mycology today constitutes an integral component of soil microbiology.

Due to their structural and metabolic characteristics, fungi play a major role in shaping soil Structure. Specifically, hyphae can adsorb fine soil particles on their surface, forming durable aggregates that facilitate the exchange of the soil's mineral fraction, The conversion of insoluble salts into soluble forms, and the leaching of certain elements. Fungi frequently participate in the Initial Stages of the Hydrolysis of plant polymers (Cellulose, hemicellulose, Lignin), thereby creating favorable conditions for the development of other microorganisms.

Among higher fungi, the most active cellulose degraders are basidiomycetes, ascomycetes, and deuteromycetes. Among the latter, particularly active species include Trichoderma lignorum, Trichoderma koningii, Cladosporium herbarum, and species of the genera Fusarium, Aspergillus, Penicillium, and Stachybotrys.

Lignin in soil is degraded primarily by basidiomycetous fungi and deuteromycetes. However, deuteromycetes are represented by a relatively small number of species. For instance, studies of over 1,500 strains belonging to various species of the genera Trichoderma, Fusarium, Aspergillus, Penicillium, and Mucor isolated from soil have shown that about 30% of them could not utilize lignin as a sole source of carbon and energy.

Soil fungi participate in the synthesis and decomposition of humic acids, which are the primary component of soil humus. Many fungi synthesize Melanins and phenols, which are incorporated into the synthesis of humic acids, while some fungal species are capable of breaking down humic acids.

Consequently, soil fungi are essential components of biocenoses, participating in nutrient cycling through the decomposition of soil organic matter, as well as in soil structure formation and fertility enhancement.

Fungi in the air. Fungi occur in the air in the form of spores (conidia, spores, chlamydospores, ascospores, basidiospores) and mycelial fragments. Their spore counts vary depending on atmospheric altitude, terrain characteristics, season, vegetation composition, and other factors.

In surface-level air up to a height of 2 m, 1 m³ of rural air contains up to 12.5 thousand spores: Cladosporium accounts for 47% of the total amount, Sporobolomyces up to 31%, and basidiospores of edible and inedible mushrooms account for about 3%. As altitude decreases, the concentration of spores increases.

It is believed that the primary source of airborne spores consists of fungi inhabiting cultivated and wild plants, plant residues, and surface soil layers. Fungi spread through the air via passive dissemination (wind, raindrops, etc.) and through specific physical, chemical, and morphological mechanisms designed for spore ejection from fruiting bodies.

The Study of air mycoflora is of significant sanitary, hygienic, and phytopathological importance. Spores of phytopathogenic fungi present in the air can be carried over considerable distances, thereby facilitating the spread of plant diseases.

Elevated levels of airborne fungi in industrial indoor environments during plant raw material Processing pose a hazard to workers' health (triggering allergic conditions). High concentrations of spores of the dry rot fungus Serpula lacrymans, which destroys wooden structures in residential buildings, can provoke asthma attacks. Indoor residential air is typically dominated by spores of Aspergillus and mucoraceous Molds.

Therefore, the composition and concentration of airborne spores are of direct relevance to medical mycology.

Aquatic fungi. Water bodies occupy a substantial portion of the planet's surface. The surface of seas and oceans alone accounts for 3/4 of this area. The science of hydrobiology investigates the composition, Abundance, biology, and developmental patterns of aquatic organisms.

Fungi inhabiting freshwater and marine water bodies primarily belong to lower fungi, which, according to modern concepts, have been excluded from the kingdom Fungi, though many mycologists still consider them as true fungal representatives.

Aquatic fungi participate in the cycling of matter in water bodies, as well as in the decomposition and Mineralization of organic compounds. Many fungi parasitize fish, animals, and Algae, causing various diseases and even epidemics that disrupt aquatic trophic chains. Aquatic fungi are also aggressive agents of biological deterioration in aquatic structures, equipment, and Materials. They are the subject of study in aquatic mycology.

Fungi of freshwaters. The Qualitative and quantitative composition of freshwater fungi varies depending on temperature, season, organic matter content, and other factors. As a rule, fungi are more abundant in littoral zones and standing water than in flowing rivers and streams.

Phycomycetes that produce zoospores (motile spores) are typical Representatives of the microflora in freshwaters. Alongside phycomycetes, species of deuteromycetes that decompose plant residues are also found. Additionally, there are species that parasitize algae, insects, and other representatives of zooplankton and phytoplankton.

Marine fungi. Most fungi widespread in marine waters are ascomycetes and deuteromycetes. Among them, one finds saprophytic forms developing on wood and fishing gear, as well as parasitic forms living on marine fauna (Sponges, shrimp, crabs, Mollusks, fish) and flora (micro- and macroalgae).

Representatives of the genera Cladosporium, Chaetomium, and Trichoderma have been found on wood debris submerged in sea water. In marine environments, especially in coastal zones, fungi of the genera Alternaria, Cladosporium, Trichoderma, Fusarium, Aspergillus, and Penicillium are widespread. These species can be found even at depths of up to 4,000 m. The flora of marine environments is characterized by the presence of Yeasts, which are also found at depths of up to 4,000 m.

The ability of aquatic fungi to utilize a specific substrate is, as with other ecological groups of fungi, one of the regulating Factors Determining the colonization by various species. For marine saprophytic fungi, such specific substrates include cellulose, pectin, and Chitin. Aquatic phycomycetes predominantly utilize organic nitrogen sources, whereas many hyphomycete species utilize nitrate and ammonium nitrogen.

Phytopathogenic fungi. Phytopathogenic fungi infect plants. This group comprises over 10,000 species of fungi. Based on their degree of parasitism, phytopathogenic fungi are divided into obligate and facultative. In obligate parasites, The life cycle takes place within a living plant. Facultative parasites are capable of parasitizing a living plant, but can also lead a saprophytic lifestyle.

Phytopathogenic fungi parasitize agricultural crops, infecting and causing diseases in various Organs of the aerial parts and ROOT systems of plants during their vegetation period, as well as during the storage of grain, vegetables, and fruits. Phytopathogenic fungi cause the following diseases: wilting — damage to the vascular and root systems. The fungus localizes and develops within the vascular vessels, causing their mechanical blockage, which leads to plant wilting;

rotting — under the action of fungal Enzymes, softening and destruction of tissues occurs as a primary symptom;

spotting, or necrosis — the death of isolated tissue areas at the sites of fungal infection;

ulcers (anthracnose) — spots characterized by tissue softening and The formation of depressions where fungal sporulation takes place;

fungal coating — the development of mycelium and sporulation On the surface of infected plant organs;

pustules — formations on affected tissue resulting from the rupture of its epidermis by convex fungal fruiting bodies;

mummification — an affected plant organ, penetrated by fungal mycelium, often taking the shape of a dark-colored sclerotium.

Phytopathology is the science that studies phytopathogenic fungi.

Phytopathogenic fungi are found among representatives of all fungal classes, both lower and higher. Among micromycetes, these include representatives of the genera Fusarium, Alternaria, Cladosporium, and Penicillium.

Wood-destroying fungi. These fungi break down wood at all stages: from damage to living forest trees to the decomposition of wood during storage, and subsequently in structures and finished products. Wood Cell walls consist primarily of cellulose (the main component), hemicelluloses, lignin, Pectins, as well as small amounts of resins, Proteins, and Other Compounds. Wood-destroying fungi are predominantly basidiomycetes, along with certain species of ascomycetes, and deuteromycetes during the later stages of decomposition. They include both saprotrophs and parasites.

The specific term "dry rot fungi" refers to a group of fungi that damage wooden parts of buildings (Serpula lacrymans).

Fungi pathogenic to humans and animals. These fungi are studied by medical and veterinary mycology. They cause diseases known as mycoses. Most pathogens belong to deuteromycetes (about 150 known species), phycomycetes (26 species), and ascomycetes (28 species). Based on their localization site, mycosis-causing fungi can be divided into those causing systemic (generalized) mycoses and localized mycoses.

Generalized mycoses. Candidiasis is a disease caused by Yeast-like fungi of the genus Candida (most commonly Candida albicans). These saprophytic organisms are very widespread on many plants, fruits, vegetables, soil, and dairy products. They are typical representatives of the saprophytic flora of the Human and Animal digestive tract and oral mucosa. The disease develops when the body is weakened by unfavorable factors or during antibiotic therapy, which leads to dysbiosis (an imbalance in The ratio of

microorganisms). In this case, Antibiotics eliminate the bacterial microflora sensitive to them, allowing the more resistant yeast flora to overgrow. To prevent this, antifungal agents such as nystatin and antifungin are prescribed alongside antibiotic therapy.

Pneumonomycoses are diseases caused by fungi that parasitize the Tissues of the Bronchi and Lungs. A typical pathogen is Aspergillus fumigatus. This disease is very common in birds (especially waterfowl) and cattle, and much less frequently in humans. The source of infection is typically contaminated feed or various plant raw materials. In addition to Aspergillus fumigatus, human and animal mycoses are caused by certain species of Penicillium and mucoraceous fungi.

Mycoses of the Integumentary System are caused by dermatophytes and keratinophilic fungi. The most dangerous disease is ringworm. The primary pathogens are species of the genera Microsporum, Trichophyton, and Epidermophiton. These fungi are capable of developing in both yeast and mycelial (hyphal) forms, exhibiting dimorphism. Pathogenic properties are inherent to both forms.

Entomopathogenic fungi. This ecological group of fungi is diverse both in the Nature of the relationship between the fungi and insects and in the degree of obligate or facultative parasitism on insects. The term "entomophilic" implies a specific trophic relationship between fungi and insects; they are also referred to as "insect-parasitic fungi". Such fungi include representatives of asco-, zygo-, and basidiomycetes. They are divided into ectoparasites and endoparasites. Ectoparasites are located on the surface of the insect's body (with the mycelium developing externally). Besides ascomycetes, some deuteromycetes are also ectoparasites. The mycelium of endoparasites develops inside the insect's body.

Predatory fungi. This is an extremely fascinating ecological group of fungi whose representatives are capable of capturing, killing, and digesting nematodes and Protozoa. The most typical representative of nematode-trapping predators is Arthrobotrys oligospora. The predator captures the nematode using so-called traps—special rings formed in its mycelium that are covered with sticky mucus.

Mycophilic fungi are organisms capable of living on other fungi as a nutrient substrate. They parasitize phytopathogenic fungi as well as higher edible species. Among obligate

parasites, both intracellular and extracellular forms exist. Mycophilic fungi have been identified among Ascomycota, Basidiomycota, and Deuteromycota. For instance, the widespread soil deuteromycete Trichoderma can parasitize numerous species of soil hyphomycetes. Many species of Aspergillus and Penicillium are capable of penetrating the sporangiophores of mucoralean fungi.

Symbiotic fungi. Symbiosis is a mutually beneficial, close association (coexistence) of two different organisms.

Symbiosis with plants. Lichens are organisms formed as a result of the symbiosis between fungi (primarily ascomycetes) and algae. These two organisms differ in their type of nutrition: fungi are heterotrophs, whereas algae are autotrophs. During symbiosis, the fungal component obtains essential carbon sources from the alga, while the alga receives mineral nutrients, Vitamins, organic nitrogen, moisture, and other compounds from the fungus.

Mycorrhizal fungi. Mycorrhizae of woody plants are formed by basidiomycetous fungi. Certain fungi consistently appear beneath specific trees; evidently, their mycelium penetrates the roots and supplies the plants with nutrients. In turn, the plant provides oxygen to the fungus (especially in oxygen-depleted soils). A physiological characteristic of mycorrhizal fungi is their requirement for B-group vitamins—thiamine, pantothenic acid, nicotinic acid, and biotin.

Symbiosis with animals. A classic example is the symbiosis between fungi and various insects, where large cells known as mycetomes develop within the gut and body of the insect. Ants and termites utilize fungal mycelium as a primary food source.

Edible fungi. This group predominantly comprises fungi with juicy, fleshy fruit bodies. They are represented by basidiomycetes that form cap-and-stem structures, as well as ascomycetes with succulent fruit bodies. Edible fungi are frequently mycorrhizal, though many are saprophytic soil fungi that fruit on decomposing forest litter and other organic substrates (such as compost or manure).

There are several hundred known species of edible fungi, yet only a few dozen are utilized by humans for consumption.

In recent years, the industrial-scale cultivation of edible fungi (such as button mushrooms and oyster mushrooms) has developed intensively. The yield of such crops ranges from 15–40 kg/m² of surface area, with multiple harvests collected from the same area throughout the year.

Fungi damaging industrial products, materials, and structures. The deterioration of materials, industrial raw stocks, and manufactured goods is viewed as a specific ecological niche for fungi. The species composition and the degree of damage depend on the nature of the substrate and its accessibility to the fungus. The rate of corrosion in metallic and non-metallic products is influenced by physicochemical factors such as pH, temperature, humidity, and the concentrations of oxygen and carbon dioxide. Many saprophytic fungi can utilize recalcitrant substrates (including optical Glass, paraffins, fuels, oils, and lubricants).

For instance, Bacteria, yeasts, and fungi—chiefly of the genera Aspergillus, Trichoderma, and Penicillium—have been detected in rolling oils, cooling systems, and rinse waters of steel-rolling enterprises. The fungus Cladosporium resinae is frequently found in aviation fuel storage tanks. The spores of this fungus remain viable in kerosene vapors for over three months. Fungal proliferation in aircraft fuel systems can trigger emergencies due to the corrosion of fuel pumps or tank walls. To prevent this, biocides (growth inhibitors of destructive microorganisms) are applied, along with anticorrosive coatings.

Fungi are capable of degrading plastics. Approximately one hundred fungal species have been isolated from such materials, with Aspergillus, Penicillium, and Fusarium being the most prevalent. Many aquatic fungi can induce plastic corrosion. Certain fungi are known to destroy optical glass (Aspergillus niger). Mica components in various devices are also susceptible to fungal damage, with Aspergillus species acting as the most aggressive agents of mica degradation.

Synthetic rubbers can be decomposed by species of the genera Cephalosporium and Penicillium. Fungi also break down bituminous and polymeric materials, and under conditions of high humidity, they are capable of destroying paintings and works of fine art. Cladosporium elatum, Cephalosporium acremonium, and Aspergillus versicolor have been isolated from damaged areas of paintings.