PHARMACEUTICAL MICROBIOLOGY - V. A. Galynkin - 2015

PART I. MICROBIAL BIOLOGY

CHAPTER 2. FUNGI

2.1 Taxonomic Position of Fungi in the Living World

Fungi represent a large and widespread group of organisms in nature, comprising about 100,000 species. They inhabit soil, Water, and plant or animal debris [9].

Fungi constitute a distinct kingdom, Fungi (Mycota), possessing characteristics of both plants and animals. Fungi (Fig. 19) are achlorophyllous, lower eukaryotic organisms that utilize exclusively organic matter for Nutrition. The vegetative body of fungi, known as the thallus or mycelium, consists of branching filaments called hyphae. In lower unicellular fungi, hyphae lack transverse septa dividing them into separate compartments. In higher fungi, the mycelium is septate. The mycelium may develop On the surface of the substrate or penetrate deep into its bulk. The thickness (diameter) of hyphae ranges from 5 to 50 µm or more. The uniqueness of fungi is manifested not only in the combination of plant- and animal-like traits, but also in the presence of specific features and properties characteristic exclusively of members of the kingdom Mycota: a mycelial vegetative body Structure; complex nuclear cycles and pleomorphism; multinucleation and heterokaryosis (the presence of genetically different nuclei within a single Cell); and dikaryosis (the prolonged coexistence of two nuclei within a single cell that divide synchronously, mimicking a diploid nucleus).

Class="center">Fig. 19. Morphology of fungi. Vegetative structures: stolons (1) and rhizoids (2) of Mucor nigricans; oidia (3) and chlamydospores (4) of Mucor chibinensis; pseudomycelium (5) and blastoconidia (6) of Candida spp.; budding Cells (7) of Saccharomyces cerevisiae. Anamorphs: sporangium with spores (8), sporangiophore (9), conidiophore (10), sterigmata (11), conidia (12) of Aspergillus spp. (A) and Penicillium spp. (B). Teleomorphs: asci with ascospores (13) of S. cerevisiae (Endomycetes), perithecium containing asci with ascospores (14) of Sordaria sp. (Ascomycetes), zygospore (15) of Mucor spp. (Zygomycetes).

Plant characteristics: holophytic mode of nutrition (absorption of nutrients through The Cell wall), ability to synthesize Vitamins, presence of a rigid cell wall, vacuoles, transverse septa in the mycelium, cell polarity, capacity for indeterminate growth, and reproduction via spores. Animal characteristics: absence of chlorophyll, heterotrophic nutrition, formation of urea during Nitrogen METABOLISM and Glycogen during Carbohydrate Metabolism, presence of Chitin in The Cell wall, formation of Lysosomes in the Cytoplasm, and specific primary structures of Cytochromes and tRNAs. The Classification of fungi, based on structural-chemical and morphological criteria, is presented in Table 3. True fungi are subdivided into six classes: Chytridiomycetes, Oomycetes, Zygomycetes, Ascomycetes (or sac fungi), Basidiomycetes, and Deuteromycetes (or fungi imperfecti).

Chytridiomycetes. Primitive lower unicellular organisms. The mycelium is either absent or rudimentary. The cell wall contains chitin and lacks Cellulose. Both Selection/8.html">Asexual and sexual reproduction occur. They are predominantly aquatic. Certain species cause diseases in agricultural crops.

Oomycetes. Unicellular (lower) mycelial fungi. Cellulose and glucan serve as the Structural components of the cell wall. Asexual reproduction occurs. They inhabit aquatic environments, whereas terrestrial forms are parasites of higher plants.

Zygomycetes. The mycelium is well-developed, multinucleate, and non-septate (lower fungi). The cell wall contains chitin and occasionally glucan. They reproduce via sporangiospores, less commonly through conidia or sexually. Widely distributed in the topsoil, they develop on organic plant debris. They are utilized in the microbiological industry to produce soybean curd (tofu), alcohol from potatoes, the antibiotic ramycin, among other products.

Table 3. Classes of Fungi [10].

Typical representatives of this class include fungi of the genus Mucor (pin Molds). In Mucor (Fig. 19), colorless sporangiophores emerge from the unicellular mycelium, each bearing a single sporangium at its apex. In the presence of moisture, the wall of the mature sporangium easily dissolves, releasing several thousand sporangiospores that subsequently germinate. These fungi can cause mucormycosis in animals and humans.

Ascomycetes, or sac fungi. Higher fungi characterized by a branched, multicellular mycelium. Reproduction is vegetative, asexual (via conidia), and sexual (the ascigerous stage). The sexual process results in The formation of asci, or sacs, inside which—following the fusion of sex cell nuclei (Gametes)—ascospores are formed, typically numbering eight per ascus. Ascomycetes are widely distributed in nature, with approximately 30,000 known species. They inhabit soil, organic substrates, animal feed, and food products, causing their spoilage. They parasitize plants and animals and degrade cellulose. Toxic species are capable of causing mycotoxicoses. They are utilized as producers of Antibiotics, Alkaloids, growth factors (Gibberellins), and Enzymes. Edible fungi such as morels and truffles belong to Ascomycetes.

Basidiomycetes. Higher fungi with a multicellular mycelium. The basidium serves as the specialized fruiting structure. Basidia produce external spores at the tips of hyphae As a result of sexual reproduction. They are Saprophytes and facultative parasites of cereal grains (causing smuts and rusts). Edible and poisonous cap fungi also belong to Basidiomycetes.

Deuteromycetes, or fungi imperfecti. Higher fungi with a multicellular, extensively branched mycelium. Their entire life cycle occurs in the haploid stage, without alternating nuclear phases. They reproduce vegetatively and asexually via conidia. Conidia vary in shape and coloration and are produced on specialized Branches of the mycelium known as conidiophores or within pycnidia (dense conidiomatal fruiting structures).

This is the most numerous class, encompassing fungi of the genera Aspergillus, Penicillium, Stachybotrys, Fusarium, etc. (see Fig. 19). In Aspergillus, or HEAD mold, the mycelium is septate and conidiophores are unicellular; their apex expands into a vesicle from which outgrowths called sterigmata extend, bearing abjointing conidia. Conidia may exhibit various colors, most frequently black, and are arranged radially, resembling streams of water flowing from a watering can.

In fungi of the genus Penicillium (blue-green mold), the mycelium and conidiophores are multicellular. The upper portions of the conidiophores branch in a manner resembling a hand, with their terminal segments—the sterigmata—terminating in conidia. They produce green, white, and other pigments. They inhabit soil, damp indoor environments, feedstuffs, and food products.

Fungi imperfecti also include dermatophytes—the causative agents of microsporia, trichophytosis, and favus in animals—as well as Yeast-like fungi of the genera Candida and Cryptococcus, which cause candidiasis and cryptococcosis.

Yeasts. Achlorophyllous, unicellular fungi lacking a true mycelium (15). They constitute a phylogenetically heterogeneous group of organisms, some of which are typical Ascomycetes, others Basidiomycetes, and yet others Deuteromycetes.

These are large spherical or rod-shaped cells measuring 3 to 7 µm, while elongated forms may exceed 20 µm.

In specialized literature, the collective term "molds" ("mold fungi") is frequently encountered. These are filamentous, microscopic fungi belonging to various classes that are capable of forming substrate and aerial mycelia, such as Mucor, Aspergillus, Penicillium, and others.

The cells of microscopic fungi vary in shape and size but share common structural elements. The fungal cell consists of a cell wall, cytoplasm with a Plasma Membrane and Endoplasmic reticulum, Mitochondria, Ribosomes, inclusions, vacuoles, and one or more nuclei (Fig. 2).

2.2 Morphology and Ultrastructure of Fungi

The life cycle of fungi involves the formation of vegetative and reproductive structures. The vegetative structure is represented by the mycelium and its modifications. Under favorable conditions, any part of the mycelium can give rise to a new individual.

Structures specifically intended for reproduction are referred to as reproductive structures.

Fungi exhibit Three types of reproduction: vegetative, asexual, and sexual. In many species, these types succeed one another sequentially during the developmental cycle.

Vegetative Reproduction is usually accomplished by unspecialized PARTS OF THE mycelium that give rise to a new mycelium. The mycelium of most fungi possesses a high capacity for regeneration, which underlies this mode of reproduction and is widely applied, for example, in preparing spawn for the artificial cultivation of edible mushrooms such as the button mushroom (Agaricus bisporus), oyster mushroom (Pleurotus ostreatus), and others, as well as in producing fungal biomass for food and feed purposes.

Specialized structures of vegetative reproduction include oidia, which are thin-walled cells, and chlamydospores, thick-walled cells formed by the fragmentation of the mycelium, which give rise to a new mycelium. Chlamydospores also function to survive unfavorable conditions (Fig. 19, 20). In most yeasts, vegetative reproduction occurs via cell budding.

Fig. 20. Fungal chlamydospores in pure culture: chlamydospores of Mycogone perniciosa, the CAUSATIVE AGENT OF wet bubble disease in cultivated mushrooms [9].

Asexual reproduction is accomplished through various specialized cells or multicellular structures called spores. Fungi produce

endogenous and exogenous asexual spores. Endogenous motile spores, or zoospores, develop in zoosporangia of various shapes. These are naked cells equipped with flagella, the number, arrangement, and structure of which vary across different systematic groups of fungi. Zoospores of diverse structures are characteristic of Representatives of the phyla Oomycota, Hyphochytriomycota, and Chytridiomycota—that is, primarily aquatic and, less frequently, terrestrial fungi. Reproduction via zoospores requires water, at least in the form of discrete droplets on The surface of soil or plants, through which zoospores can move using their flagella. Endogenous non-motile spores, or sporangiospores, are enclosed in a wall and formed inside sporangia, which develop on specialized hyphae known as sporangiophores that typically rise above the substrate. Sporangiospores mediate asexual reproduction in zygomycetes.

Exogenous asexual fungal spores, or conidia, are non-motile and form on specialized, differentiated spore-bearing structures called conidiophores, which are usually morphologically distinct from the vegetative mycelium. Typical conidia are characteristic of ascomycetes, basidiomycetes, and anamorphic fungi. Like zygomycetes, these are predominantly terrestrial fungi, and the dispersal of non-motile asexual spores (sporangiospores and conidia) in such fungi is carried out mainly in a passive manner by air or water currents. Occasionally, spore dispersal can be mediated by animals, for example, when the fruiting bodies of agaric mushrooms are consumed. Specialized structures associated with vegetative and asexual reproduction in fungi are termed anamorphs.

2.3 Organization OF THE Yeast Cell Cycle

The cell cycle has been most thoroughly investigated in the yeast Saccharomyces cerevisiae, although many principles are universal for all Eukaryotic cells (Fig. 21).

The Introduction/5.html">Eukaryotic Cell cycle is divided into four phases: G₁, S, G₂, and M. Nuclear DNA Synthesis occupies only a fraction of interphase—a period designated as the S phase of the cell cycle. Between the end of the M phase and the onset of DNA synthesis lies an interval known as the G₁ phase (from the English "gap"). Another interval, termed the G₂ phase, separates the end of DNA synthesis from THE START OF the M phase. Thus, interphase consists of a sequence of phases: G₁, S, and G₂, and typically accounts for at least 90% of the total cell cycle duration. The cell cycle features three distinct critical checkpoints: in the G₁ phase, in the S phase, and at the G₂+M transition (the G₂/M checkpoint), which are regulated by intracellular processes. The duration of cell cycle phases varies; on average, the G₁ phase accounts for 30–40% of the total cell cycle duration, the S phase for 30–50%, the G₂ phase for 10–20%, and the M phase for 5–10%. These parameters can vary considerably depending on the biological species, but remain relatively constant for a specific cell type. There is a specific critical point within the G₁ phase designated as the Start point (Start). Upon passing this checkpoint (referred to as the restriction point in higher eukaryotes), the cell undergoes irreversible changes committing it to complete all subsequent Stages of the cell cycle. Such Determination of the cell cycle implies intracellular control over the completion of each cell cycle phase (Hartwell L.H., 1974). In other words, past the Start point, the cell is committed to completing the cycle, and exit from it is impossible (though arrest is not) in any other phase (S, G₂, M). This cell cycle commitment entails intracellular control over the completion of each phase. Events occurring in the G₂ phase, for example, cannot unfold during the S phase, and vice versa.

If, upon completion of the cell cycle, conditions are unfavorable for entering a new cycle, cells transition into the G₀ state. By definition, this state simply characterizes cells that are quiescent and not engaged in the cell cycle. Cells preparing to enter the cell cycle may reside in this state (for example, growing to the critical size required to pass the Start point), in which case there is a temporary extension of the G₁ phase. Sometimes, such additional conditions for entering the cell cycle involve the synthesis of non-constitutive enzyme systems required for a specific substrate (for instance, yeast growth on n-alkanes requires the Induction of the P-450 system (Galynkin V.A. et al., 1990)). On the other hand, cells engaged in the synthesis of a target product (e.g., antibiotic biosynthesis) also reside in the G₀ state; in this case, we are dealing with physiological differentiation. Cells undergoing morphological differentiation (e.g., spore formation) are likewise found in the G₀ state. In some instances, morphological and physiological differentiation coincide (the synthesis of certain antibiotics coincides temporally with the transition to sporulation). Finally, morphologically differentiated cells may enter the cell cycle while maintaining this status. Under such conditions, growth occurs not as individual cells but as a mycelium, which also leads to an average increase in Cell Division time. Essentially, cells either return from the G₀ state to the cell cycle (sometimes in a new morphological status) or undergo programmed cell death (the autolytic program).

In the yeast Saccharomyces cerevisiae (Fig. 21), one of the genes controlling passage through the Start point was identified and named cdc28 (the analog of cdc2). The CDC28 protein encoded by this Gene Functions as a protein kinase, but its activity requires the presence of another protein called a cyclin. It is this cyclin that is periodically synthesized during the CELL CYCLE AND degraded by its completion (E.W. Murray, 1991).

Further research demonstrated that it is appropriate to speak not of a single cyclin, but of an entire family of cyclins. Three groups of cyclins were discovered: G₁ cyclins, which control entry into the cycle (the Start point); S-phase cyclins, which control the progression through the S phase; and M-phase cyclins, which control the completion of the cycle. Furthermore, cyclins responsible for each phase of the cycle are synthesized during their respective phases and subsequently degraded enzymatically (Dirick L. 1995, Nasmyth K., 1996). It was shown that cycle phases are initiated by soluble cytoplasmic factors. The M-phase activator was designated as the M-phase-promoting factor (MPF), and the S-phase activator was termed the S-phase-promoting factor. MPF is universally significant for eukaryotic cells and highly conserved throughout evolution.

Fig. 21. Four phases are illustrated: G₁, S, G₂, M, along with the exit from the cell cycle into the G₀ state. The respective phase-promoting factors are shown, represented as a complex of a cyclin (depicted as a circle) and a cyclin-dependent kinase (CDK, depicted as a square). The degradation of cyclins following the passage of cell cycle phases is indicated. The diagram also illustrates the anaphase-promoting complex (APC), which is required for the progression of anaphase, a stage of mitosis involving chromosome segregation.

The cycle regulation mechanism based on the activation of cyclin-dependent Kinases (CDKs) is operational across all eukaryotes, although its specific details vary significantly among particular types of eukaryotic cells.

Figure 22 illustrates the asexual reproduction of the yeast Saccharomyces cerevisiae accompanied by concurrent biochemical processes and Changes in the cellular genetic status.

Fig. 22. Asexual reproduction of yeast

Sexual reproduction in fungi, the associated process of nuclear phase alternation, and The structure of reproductive Organs all vary among different fungal groups. The most critical milestones of the Sexual process in fungi are plasmogamy, karyogamy, and Meiosis. Consequently, a fungus may exist in haploid or diploid stages. In ascomycetes and basidiomycetes, plasmogamy and karyogamy are separated in time, resulting in a distinct stage of dikaryotic mycelium following plasmogamy, where haploid nuclei are paired and closely associated—yet unmerged—forming a dikaryon. The nuclei of the dikaryon typically divide synchronously with parallel orientations of the mitotic spindle axes. At a certain point in the developmental cycle, they fuse to form a diploid nucleus, which subsequently undergoes reductional division. The alternation of nuclear phases will be examined in detail in the descriptions of fungal phyla and classes.

The sexual process results in the formation of haploid, genetically heterogeneous spores, which fundamentally distinguishes them from asexual fungal spores. These haploid spores are located either on the mycelium or, more frequently, on the surface or inside structured fruiting bodies known as teleomorphs. Thus, reproduction via sexually derived spores gives rise to forms with novel combinations of genetic material, providing the basis for further evolutionary diversification, whereas reproduction via asexually derived spores promotes the dissemination and preservation of the given form.

Types of sexual process in fungi. Sexual reproduction in fungi is known in all groups except for anamorphic, or imperfect, fungi. The sexual process in fungi is diverse, and its features form the basis for class classification. Three MAIN TYPES OF the sexual process are known in fungi: gametogamy, gametangiogamy, and somatogamy (Fig. 23).

Fig. 23. Types of the sexual process in fungi [9].

Gametogamy — the fusion of gametes produced within gametangia. A distinction is made between isogamy — the fusion of motile, morphologically identical gametes, and heterogamy — the fusion of motile gametes that differ in size and often in the degree of motility. These Two Types of gametogamy are characteristic of Chytridiomycetes and Hyphochytriomycetes. In oogamy, large, non-motile egg cells (oospheres) formed within specialized oogonia are fertilized by small, motile spermatozoa developing in specialized antheridia. In many fungi with this type of sexual process, distinct spermatozoa are not formed; instead, the egg cell is fertilized by the content of the multinucleate antheridial outgrowths, which is not differentiated into separate spermatozoa. This type of oogamy is characteristic of all representatives of the phylum Oomycota.

The second type of sexual process, gametangiogamy, consists in the fusion of two usually multinucleate specialized structures whose contents are not differentiated into gametes. Gametangiogamy is characteristic of Zygomycota and Ascomycota. Gametangiogamy in Zygomycota is termed zygogamy. It involves the fusion of primarily multinucleate cells—gametangia—that are well-distinguished from the vegetative mycelium on which they are formed, but are not morphologically differentiated into male and female sexual types. From the zygote formed as a result of their fusion, a thick-walled, pigmented zygospore develops, which germinates after a dormant period into a specialized germ sporangium (Figs. 23, 24).

Fig. 24 (1). Life cycle and zygote of Rhizopus nigricans: a — sporangium, b — sporangiophore, c — rhizoids, d — zygospore, e — suspensors, f — stolon.

Fig. 24 (2). Life Cycle of Mucor mucedo. 1 — haploid sporangiospores; 2 — vegetative mycelium; 3 — sporangia developing on a homothallic vegetative mycelium; 4 — formation of zygophores through the interaction of (+) and (-) mycelial strands; 5 — fusion of zygophores; 6 — Formation of the paragametangium; 7 — formation of a delimited gametangium with suspensors; 8 — young zygospore; 9 — mature zygospore; 10 — germination of the zygospore [11].

In Ascomycota, gametangiogamy also involves the fusion of two multinucleate gametangia, but unlike Zygomycota, their sex organs are differentiated into female — the ascogonium, and male — the antheridium. The ascogonium consists of two cells: a large multinucleate cell (the ascogonium proper) and a slender, thread-like trichogyne located at its apex, through which the Contents of the multinucleate antheridium flow into the ascogonium. This process involves only plasmogamy, and the nuclei pair up to form a dikaryon. From the fertilized ascogonium, without any period of dormancy, ascogenous dikaryotic hyphae grow. Within their cells, the nuclei of the dikaryon fuse to form a diploid nucleus, which subsequently undergoes meiotic division. As a result of this process, specialized structures—asci (or asci sacs)—are formed on the ascogenous hyphae via a rather complex pathway, inside which, following post-meiotic mitotic nuclear divisions, eight endogenous haploid ascospores are formed (Fig. 25).

Fig. 25. Sexual process and development of asci in Pyronema omphaloides: 1 — cluster of sex organs, 2a — antheridium, b, c — ascogonium with trichogyne, 3 — development of binucleate (dikaryotic) ascogenous hyphae from the fertilized ascogonium, 4 — diagram of ascus formation from ascogenous hyphae via a crozier, 5 — young and mature ascus with ascospores [9].

The third type, somatogamy, is a sexual process in which ordinary somatic or vegetative Cells of the mycelium fuse. Sex organs and gametes are absent. Somatogamy is characteristic of certain representatives of the phyla Chytridiomycota and Hyphochytriomycota that possess a unicellular thallus. In this case, two unicellular individuals fuse entirely. This type of somatogamy is called hologamy. Somatogamy in Basidiomycota involves the fusion of two vegetative cells of the haploid mycelium. As in Ascomycota, only plasmogamy initially takes place, resulting in the formation of dikaryons and a dikaryotic mycelium (consisting of binucleate cells). This is the longest stage in the life cycle of basidiomycetous fungi. Subsequently, specialized cells called basidia develop on this dikaryotic mycelium; within these basidia, the nuclei of the dikaryon fuse and the diploid nucleus undergoes meiosis, after which exogenous haploid basidiospores are formed on the basidium (Fig. 26).

Fig. 26. Types of basidia. 1 — holobasidium; 2-4 — heterobasidia; 5 — telio- (phragmo-) basidium [9].

Endogenous ascospores of ascomycetes and exogenous basidiospores of basidiomycetes are formed as a result of the sexual process, meaning their appearance is associated with the Sexual reproduction of these groups. The sexual process in ascomycetes and basidiomycetes shares two characteristic general features: first, a Separation between plasmogamy and karyogamy leading to the appearance of a dikaryotic phase; and second, the absence of a dormant state in the zygote, as the meiotic division of the diploid nucleus occurs immediately after the fusion of the haploid nuclei of the dikaryon.

Based on The Nature of sexual differentiation, fungi are divided into homothallic (bisexual) and heterothallic (unisexual/dioecious) forms. In homothallic fungi, cells of the same mycelium are capable of fusing. Both male and female sex organs are formed on the same mycelium (for example, oogonia and antheridia in oomycetes). In heterothallic fungi, sex organs are not initiated on a mycelium grown from a single spore, and consequently, zygotes are not formed. They develop only when two mycelia of different mating types (+ and -, or male and female) encounter one another. THE CONCEPT OF heterothallism pertains to the haploid stage, since Sex Determination in fungi is primarily genotypic. Heterothallism in fungi can be of two types: bipolar, when sex is determined by a single pair of alleles, and tetrapolar, when sex is determined by two pairs of alleles located on different Chromosomes and combining independently. In the case of bipolar sex determination, all hyphae grown from the spores of a single fruiting body fall into two groups, and the sexual process occurs upon the combination of mycelia from these two different groups. In the case of tetrapolar sex determination, hyphae grown from the spores of a single fruiting body fall into four mating groups. Here, group I fuses exclusively with group II, and group III exclusively with group IV. The numerical ratios of these groups for agarics (basidiomycetes), in which tetrapolar heterothallism is extremely widespread, correspond to a 1:1:1:1 ratio (Fig. 27).

Fig. 27. Diagram of sex distribution in fungi.

In imperfect (anamorphic) fungi, the sexual process is absent, and these fungi spend their life cycle entirely in the haploid state. To a certain extent, the absence of a sexual process in this group is compensated for by heterokaryosis and the parasexual process based upon it. Heterokaryosis (the presence of genetically different nuclei within the cells of a mycelium) is characteristic of many groups of fungi and ensures fungal adaptation to changing environmental conditions. In such a mycelium, nuclei may occasionally fuse to form a diploid heterozygous nucleus. This nucleus divides mitotically, accompanied by mitotic recombination and subsequent vegetative haploidization of these diploid nuclei through the loss of a portion of their chromosomes. This complex process, which includes mitotic recombination as its most essential feature, is termed the parasexual process. It is known in various groups of fungi and is of particular importance for imperfect fungi that lack a true sexual process.

2.4 Features of Nuclear Division

Mitosis and Meiosis in fungi exhibit A number of specific features. In the majority of fungal species, nuclear division is closed, meaning the nuclear envelope remains intact throughout the process. Centrioles are present only in pseudofungi and certain fungi with flagellated stages; in all other species, the mitotic spindle is formed by simpler protein structures known as spindle pole bodies (SPBs). The phases of mitosis alternate rapidly, and chromosomes are small in size; combined, these factors complicate microscopic examination, which is why nuclear division in fungi was previously thought to occur amitotically. Telophase of mitosis is asynchronous, which can result in the formation of heteroploid daughter nuclei containing unequal numbers of chromosomes. Most frequently, heteroploidy involves varying numbers of B-chromosomes. Mitosis and new Cell Formation (cytokinesis) in mycelial (non-yeast) fungi occur independently of each other—nuclei migrate into the daughter cell only after it has been separated from the mother cell by a septum (in fungi with coenocytic mycelium, cytokinesis is generally rare, occurring only during the regeneration of damaged areas and the formation of reproductive organs).

Asexual reproductive propagation occurs via specialized cells—spores (Figs. 22, 28)—formed without a sexual act. Sexual reproduction involves the EXCHANGE OF GENETIC material through nuclear fusion (karyogamy) and reductional division (meiosis), associated with the formation of specific morphological structures.

Fig. 28. Illustration of two basidia (shown in red) with basidiospores (shown in green).

Asexual reproductive structures are referred to as anamorphs, whereas sexual ones are known as teleomorphs. Fungi possessing a sexual stage of development are called perfect fungi. Conversely, fungi that lack a sexual stage in their life cycle are termed imperfect fungi, deuteromycetes, or mitosporic fungi.

Anamorphs and teleomorphs are strictly confined to specific Phases of the fungal life cycle, develop under particular environmental conditions, and perform distinct, differentiated functions (Table 5).

Table 5. Functional and morphological Differentiation of the thallus

2.5 ULTRASTRUCTURE OF THE Fungal Cell

Cell Wall

The cell wall (Figs. 2, 29) provides the cell with mechanical strength and a constant shape, acts as a permeability barrier, and protects the cell from external influences. A characteristic feature of the cell wall is its capacity for growth and intensive remodeling throughout The Development of fungi (during their ontogeny).

Fig. 29. Model of the yeast cell Cytoskeleton [12].

Cell wall components can be divided into two groups: structural components (a microfibrillar network) and compounds filling the space between them (the matrix). The former are represented by Polysaccharides, including aminosaccharides (chitin and chitosan) and glucans containing β-(1,3), β-(1,4), and β-(1,6) linkages. The latter comprise mannoproteins, galactomannoproteins, glucuronomannoproteins, xylomannoproteins, and α-(1,3) glucans. Filamentous and yeast fungi exhibit significant differences in the chemical Composition and Structure of their cell walls. For instance, the chitin content ranges from 0.2–26.2% of the dry mass of cell walls in filamentous fungi, and 1–4% in yeasts. In addition to polysaccharides, Proteins and Lipids are present in the cell wall. Some of these proteins function as enzymes. Cell wall lipids determine its Hydrophobicity and participate in the Synthesis of cell wall components by activating chitin synthetase.

In many fungi, particularly yeasts, the outer layer of the cell wall forms a capsule—a highly hydrated mucilaginous polysaccharide layer. Many enzymes are localized within the capsule; it takes part in the uptake of nutrients from the substrate, mediates cell-to-cell and cell-substrate adhesion, and protects the cell against external stressors (such as desiccation and radiation).

Variations in capsule size within the same culture are related to the age and physiological state of the cells.

Fungal Cell Organelles

Fungal cell organelles are typical of most eukaryotes. The cell contains a nucleus holding hereditary information in the form of DNA organized into chromosomes. The Nucleus is filled with nucleoplasm, contains a nucleolus (the site of preribosome synthesis), and is enclosed by a double envelope (the nuclear membrane). The nuclear membrane features pores that connect the nucleoplasm with the cytoplasm.

Mitochondria contain the Enzymes of the Respiratory Chain, Oxidative Phosphorylation, and The Tricarboxylic Acid Cycle, thereby meeting the cell's energy demands.

80S ribosomes are the organelles responsible for Protein Synthesis. Some ribosomes are distributed randomly throughout the cytoplasm, whereas the majority are attached to the membranes of The endoplasmic reticulum, mitochondria, and other organelles.

Membranes represent one of the primary components of cellular organelles. Most metabolic processes are associated with them, and they account for 40 to 90% of the total cell mass.

The cytoplasmic membrane functions as an osmotic barrier, houses The Active Transport system, and is capable of pinocytosis and phagocytosis.

The endoplasmic reticulum (ER) is located in the cytoplasm as a network of unoriented tubules, cisternae, and channels; it performs a transport function, links the cytoplasmic membrane to the nuclear membrane, forms partition surfaces within the cytoplasm, and may bear ribosomes on its membranes.

The Golgi apparatus is a system of vacuoles that facilitates excretion via reverse pinocytosis using vesicles that accumulate secretory products, and transports substances synthesized in the ER to other organelles. Furthermore, the Golgi apparatus serves as the site for the synthesis of new membranes and the formation of lysosomes.

Lysosomes contain about a hundred enzymes, predominantly Hydrolases, which carry out digestive functions.

Vacuoles originate from the ER and perform diverse functions. They can accumulate toxic Metabolic waste products, participate in the compartmentalization (segregation and concentration) of substances within the cell, and store essential metabolites such as polyphosphates, Amino Acids, and purine and pyrimidine bases. Vacuoles also maintain cellular turgor.

The de novo formation of ER and Golgi membranes occurs using the nuclear membrane as a template. The cytoplasm contains inclusions that serve as nutrient reserves: glycogen, volutin (polyphosphate), and lipids.

The cytoskeleton, alongside membrane structures, ensures intracellular organization and a high degree of biological order in all metabolic processes occurring within the cell. The cytoskeleton is a well-developed network of protein filaments, among which microfilaments and microtubules play the most prominent role. Both are composed of globular protein subunits that can easily assemble and disassemble within the cell. In addition, accessory proteins exist that either link filaments to one another or to other cellular structures, or regulate the rate and extent of filament polymerization. The cytoskeleton is involved in the movement of cell organelles and the amoeboid movement characteristic of certain fungi.

Other motile fungal cells (zoospores, planogametes) move by means of flagella. Fungal flagella differ in structure from bacterial flagella, yet they closely resemble similar organelles found in Protozoa and many motile PLANT AND ANIMAL gametes.

2.6 Ecological Groups of Fungi

Fungi are widespread in nature across a vast variety of substrates. While they primarily favor aquatic or humid habitats, they can also be found in relatively dry environments. As heterotrophs, fungi feed on organic carbon compounds. Nitrogen, phosphorus, sulfur, and Metal Ions can be absorbed in inorganic forms. Fungi acquire nutrients by participating in the decomposition of organic matter or by parasitizing animals and plants.

Many fungi tolerate significant Temperature fluctuations; mesophilic fungi typically develop best within 24–30 °C, thermophiles range from 33–55 °C, and psychrophiles thrive from -2 °C to +20 °C. Light, particularly in the short-wave region, can influence fungal sporulation.

Ecological groups of fungi evolved over the course of evolution. Saprotrophic fungi contribute to the Mineralization of organic matter and Humus formation, xylotrophic fungi break down wood, and keratinophiles are capable of living on the Hair, feathers, and horns of deceased animals. Symbiotrophic fungi form mycorrhizae, which are of vital importance to the life of many plants. Lichens represent stable symbiotic associations between a fungus and Algae or cyanobacteria. Plant- and animal-parasitic fungi are described below.

Like other organisms, fungi tend to exist within relatively narrow ranges of temperature, humidity, soil conditions, and other environmental factors, which ultimately dictate their geographic distribution. Population dispersal is hindered by geographic barriers (such as oceans, deserts, and mountain ranges) and facilitated by dispersal agents such as air, water, animals, and humans.

Certain fungi exhibit The ability to persist for extended periods within restricted, unchanging zones known as endemic areas (foci). Examples include the deep mycosis agents Coccidioides immitis and Paracoccidioides brasiliensis, which occur in regions with specific climatic conditions (Central America for the former and South America for the latter). The dermatophytes Trichophyton soudanense is found exclusively in Africa, whereas T. concentricum is localized to Southern Oceania. Many fungi, including various agents of human mycoses and phytopathogenic species, are cosmopolitan and can be discovered in any locality where conditions prove favorable.

2.7 Industrial Applications of Fungi

Since ancient times, humans have utilized the yeast Saccharomyces cerevisiae to produce bread, beer, and wine. Modern industrial microbiology employs fungi to manufacture a diverse array of products: antibiotics, alkaloids, proteins, vitamins, herbicides, enzymes, Coenzymes, Enzyme Inhibitors, polysaccharides, lipids, organic acids, and more. Table 6 lists industrial antibiotics and other bioactive substances produced for medicine and agriculture; Table 7 provides data on the Practical Applications OF fungal enzymes; and Table 8 details organic acids obtained via fungal Fermentation. Certain yeast strains are used to produce Single-Cell Protein (fodder protein) from non-food raw Materials. Many basidiomycetous fungi (macromycetes that form large fruiting bodies) possess medicinal properties and are cultivated using surface or submerged (fermenter) Methods for use as Pharmaceuticals and dietary supplements (Table 9).

Table 6. Industrially Produced BIOLOGICALLY ACTIVE SUBSTANCES from Fungi

Table 7. Industrially Produced Fungal Enzymes

Table 8. Organic Acids Obtained via Fungal Fermentation

Table 9. Medicinal Properties of Basidiomycetes [13]

Note: * - commercial product (pharmaceutical or dietary Supplement), + - non-commercial product

Biologically active substances:

1 - antifungal

2 - anti-inflammatory

3 - antitumor

4 - antiviral

5 - antibacterial and antiprotozoal

6 - Blood pressure-regulating

7 - Cardiovascular system-potentiating

8 - anticholesterolemic, antilipidemic

9 - antidiabetic

10 - immunomodulating

11 - Kidney-tonifying

12 - hepatoprotective

13 - Nervous system-tonifying

14 - sexual function-potentiating

15 - used for Chronic Bronchitis

2.8 Fungi as Pathogens of Humans and Animals

Fungi can harm humans and animals by poisoning them with their metabolites, causing hypersensitivity to various substances that make up their cells or are produced by them (mycogenic allergy), and causing infectious diseases (mycoses).

Poisoning can occur through the ingestion of poisonous or spoiled mushrooms, or due to improper preparation and storage of cap mushrooms. Their toxins affect the digestive and nervous systems, as well as other body Tissues.

Another group of diseases caused by poisoning with fungal metabolites (mycotoxicoses) is associated with toxin-producing fungi colonizing plants and producing toxic substances—either during growth or during crop storage—which remain active even after plant products are processed into feed or food.

Mycogenic allergies occur in sensitive individuals in response to fungal antigenic substances. They manifest as Skin rashes, rhinitis, Conjunctivitis, diarrhea, asthmatic symptoms, etc. Allergens can include mycelial cells, fungal spores, and their metabolic or breakdown products. These diseases can occur and develop among personnel at biotechnology enterprises that use fungi as producers of biologically active substances, as well as among residents of surrounding areas due to air pollution caused by poor industrial emission Treatment. Preventive measures include strict compliance with the sanitary zone size around the enterprise, adherence to safety protocols (protective clothing, masks, respirators, equipment sealing), and thorough purification of air that has come into contact with microorganisms.

Working in storage facilities is also hazardous, as molds can develop there due to improper storage of raw materials under conditions of high humidity, surface Condensation, etc. Such facilities must be equipped with supply and exhaust ventilation, and a constant temperature must be maintained to prevent condensation.

Human mycoses. In recent decades, opportunistic mycoses have become the most common; they occur against the Background of weakened Immunity and are caused by opportunistic fungi found among representatives of the genera Penicillium, Aspergillus, Mucor, Alernaria, Cladosporium, Fusarium, Candida, Geotrichum, Saccharomyces, Rhodotorula, Sporobomyces, Trichosporon (Table 10). They can be part of the normal Human and Animal microbiota and activate their parasitic properties under The Influence of irrational antibiotic and corticosteroid therapy, The Use of immunosuppressants, and weakened body reactivity due to a prior illness.

Table 10. Main causative agents of human mycoses

Along with these, There are also mycoses caused by pathogenic fungi. These include dermatomycoses and deep mycoses (coccidioidomycosis, paracoccidioidomycosis, blastomycosis, histoplasmosis). In total, there are about 100 species of pathogenic fungi, whereas opportunistic fungi number several hundred species.

Table 10 lists the most important causative agents (etiological agents) of human mycoses. An etiological agent is either a single parasitic species or a group of closely related microorganisms. The Clinical presentation of a mycosis varies widely depending on the underlying disease, the Location OF THE lesion, or the severity of the infection. For example, Aspergilli can cause lesions in the skin, subcutaneous tissues, and Lungs; fungi of the genus Candida can affect the mucous membranes of the Mouth and genitals, skin, Nails, Bronchi, lungs, and other organs.

Most agents of mycoses are cosmopolites. Infection can occur through contact, via clothing or footwear (dermatomycoses), or from infected animals (microsporia, trichophytosis). FOOT mycoses, which affect approximately one-fifth of the world's population, are transmitted by walking barefoot in bathhouses, swimming pools, etc. Some mycoses are wound infections (mycetomas, sporotrichosis, chromomycosis, lobomycosis). Most deep mycoses are respiratory infections (histoplasmosis, blastomycosis, coccidioidomycosis, "mold" mycoses).

Prevention and Therapy

Fungi, including pathogenic ones, surround us constantly. Therefore, the most reliable method of prevention is a healthy lifestyle that helps strengthen The Immune System, which protects the body against foreign agents. This includes proper nutrition, regular exercise, outdoor walks, and quitting bad habits (smoking, alcohol).

Foot mycoses can be prevented by observing personal hygiene. When working in dusty rooms, a respirator should be worn.

A predisposing factor for the development of candidiasis is dysbiosis and hypovitaminosis. Therefore, eubiotic preparations containing beneficial lactic acid Bacteria and vitamins are used for its prevention.

Therapeutic methods depend on the Nature of the disease. For superficial mycoses, topical agents are used (imidazole derivatives, undecylenic acid, nitrophenol, etc.). For disseminated and generalized forms, antibiotics such as griseofulvin, nystatin, amphotericin B, etc., are administered.

Imidazole derivatives (amicazole, isoconazole, ketoconazole, clotrimazole, miconazole, sulconazole, tioconazole, econazole) and triazoles (itraconazole, fluconazole) are active against filamentous fungi and yeasts. They are frequently used to treat candidiasis.

In treating mycoses caused by Candida and Cryptococcus species, 5-flucytosine is used, which was originally developed as an antineoplastic agent.

Allylamine derivatives (batrafen, lamisil) are effective against dermatophytes and Candida albicans, but are primarily used in the treatment of onychomycosis (fungal nail infections).

For disseminated and generalized forms, antifungal antibiotics are administered, among which polyenes (amphotericin B, nystatin, pimaricin, levorin, fungizone, etc.) and griseofulvin are the most widely used.

Amphotericin B is effective in treating Infections caused by Candida, Aspergillus, Blastomyces, Coccidioides, and Histoplasma species. Other polyene antibiotics (nystatin, pimaricin) share a spectrum of activity similar to amphotericin B, but they are more toxic to mammals.

Griseofulvin is a narrow-spectrum antibiotic; it is effective against dermatophytes, but not against yeasts, particularly those of the genus Candida. Griseofulvin interferes with the mitotic process during fungal Replication by disrupting the synthesis of microtubule spindle proteins.

All of these agents are used under medical supervision after establishing a definitive Diagnosis. Diagnosing the disease requires confirming its mycotic nature through Microscopy, or, whenever possible, isolating a pure culture of the causative agent. Immunological methods (serodiagnosis, skin tests) also prove helpful. Laboratory findings must align with the clinical presentation of the disease, although the symptoms of mycoses are often non-specific.

Animal Mycoses

Domestic animals frequently suffer from dermatophytosis caused by fungi of the genera Trichophyton and Microsporum, which can be transmitted to humans. Among the causative agents of generalized mycoses, Candida albicans is the most widespread, causing significant economic losses in livestock and poultry farming, particularly among young animals. The development of candidiasis is facilitated by the use of antibiotics as a preventive measure against bacterial infections.

Systemic infections such as coccidioidomycosis, cryptococcosis, histoplasmosis, and sporotrichosis have been identified in rodents.

Certain fungi affect only animals and are not known to infect humans. For instance, Histoplasma farciminosum causes deep-seated mycosis in horses, mules, and donkeys, while Pityrosporum pachydermatis causes dermatomycosis in dogs, cattle, horses, pigs, and rhinoceroses. Fungi of the genus Saprolegnia (Oomycetes) parasitize fish.