Introduction to Mycology- Structure and Importance of Fungi

Mycology is the branch of biology that deals with the study of fungi, including their structure, classification, and role in nature and human life. Fungi are eukaryotic organisms that can exist as unicellular (yeasts) or multicellular (molds and mushrooms) forms. They are heterotrophic, meaning they obtain nutrients by absorbing organic matter from their surroundings.

1. PRESENTATION FUNGI

2. Introduction to Fungi Fungi – plural of fungus is derived from fungour which means to flourish (as in mushroom which develop overnight) Fungi are eukaryotic, spore-bearing , achlorophyllous organisms that generally reproduce sexually and asexually. They are usually filamentous and their branched somatic structures are surrounded by cell walls containing chitin or cellulose, or both of these substances, together with many other complex organic molecules. Fungi usually obtain food by absorption except a few lower groups where they take in food by ingestion.

3. About 300 species of fungi are presently known to be pathogenic for man. There are 4 types of mycotic diseases which are given as: Hypersensitivity : It is the type of disease which shows the allergy reaction to mold and spores. Mycotoxicosis : It is the type of disease which shows poisoning of man/animals by the contamination of their food & food products by the fungi which produce toxins specially in seeds / grains. Mycetismus : By ingestion of Pre-formed mycotoxin. (Man is directly affected by toxic fungi e.g. poisonous mushroom) Infection : It is a type in which fungi get attached with the host, flourish and reproduce, depending on the host & causing infection. The study of fungi is known as mycology and those who study fungi are known as mycologists .

4. General Properties of Fungi True fungi are defined as: Eukaryotic organisms. Lacking plastids. With absorptive nutrition. Reproducing both sexually and asexually by spores. Hyphae surrounded by cell walls containing chitin and  β -glucans. Mitochondria with flattened cristae and peroxisomes. All fungus are heterotrophic. saprobic = decomposers, nutrient cycle. mutualistic = e.g., mycorrhizae and lichens. parasitic = e.g., athletes foot. Food storage in the form of lipids and glycogen.

5. Importance of studying Fungi Fungi are major component of biodiversity. Essential to the survival of other organisms. Crucial in global ecological process. Source of novel bioactive compounds. Source of biocontrol agents. Source of plant pathogens. Threat to human health. Able to contribute sustainable development. A part of human culture.

6. Characteristics Bacteria Fungi Nature Bacteria can either be producers or decomposers. Most Fungi are decomposers. Cell Wall In Bacteria cell wall is made up of peptidoglycan In Fungi, the cell wall is made up of chitin. Nucleus In Bacteria Nucleus is not present In Fungi Nucleus is present Growth Environment Neutral pH is suitable for the growth of Bacteria Slightly acidic soil is suitable for the growth of fungi. Structure Present in three shapes: Round, Spiral, and Rod They are present in thread-like structures in various shapes. Sterols Sterols are present only in mycoplasma Sterols are present Nutrition Heterotrophs Depend on dead matter. Reproduction They reproduce through Binary fission (asexual) They can be either sexual or asexual Energy Receive energy through proteins and sugars Absorb nutrients from dead matter. Example Escherichia coli Brewer’s yeast

7. Mycosis Fungal Infections (mycosis plural; mycoses) mycosis refers to infections caused by fungi. They maybe caused by yeast, molds and dimorphic fungi in or on the host. A person having weakened immune system is at higher risk of developing fungal infection than someone with a with normal immune system. These infections range from: Superficial(on surface) Cutaneous(skin, hair, nails) Subcutaneous(deeper skin and underlying skin) Systemic/disseminated(involving internal organs)

8. Type Depth / Site Typical Fungi Examples Superficial Very surface (stratum corneum, hair shaft) Malassezia , Piedraia etc. Usually mild, no inflammation Cutaneous Skin, hair, nails (keratinized tissues) Dermatophytes: Trichophyton , Microsporum , Epidermophyton ; Candida (on skin/mucosa) Causes tinea / ringworm, onychomycosis, etc. Subcutaneous Beneath skin, in tissues just under skin Sporothrix , Fonsecaea , Chromoblastomyces , etc. These often enter via traumatic inoculation (e.g. thorn prick) Systemic/ Disseminated Internal organs (lungs, brain, bloodstream, etc.) Opportunistic fungi: Candida , Aspergillus , Cryptococcus , endemic fungi (e.g. Histoplasma ) Most serious; often in immunocompromised hosts

9. Classification of Fungi Phylum Examples Common diseases Zygomycota (Zygomycetes) Rhizopus (black bread mold). Zygomycosis, sinusitis, subcutaneous mycosis. Ascomycota (Ascomycetes or sac fungi) Yeasts, morels, truffles. Oral and vaginal thrush ( Candida albicans ). Basidiomycota (Basidiomycetes or club fungi) Mushrooms, rusts, smuts. Corn smut ( Ustilago maydis ) . Deuteromycota (Deuteromycetes or imperfect fungi) Penicillium, Aspergillus. Aflatoxins production, ringworm.

10. Fungal Reproduction and Sporulation 1. Reproduction means forming new individuals similar to the parent species. 2. It ensures the survival and spread of fungi under changing environments. 3. Types of reproduction in fungi: • Asexual reproduction – without fusion of nuclei. • Sexual reproduction – involves nuclear fusion and meiosis. • Some fungi can reproduce by both methods depending on conditions.

11. Asexual Reproduction Asexual reproduction forms new individuals without gamete fusion. It includes both vegetative and spore-based methods. Main types include: Fragmentation, Fission, Budding, and Sclerotia and Rhizomorphs. Each type helps fungi survive and spread under favorable conditions.

12. Asexual Reproduction Methods Fragmentation : A part of somatic body is detached Body consist of fragments. Each fragment can grow into new individual. Commonly used in labs to maintain fungal cultures. Types: Arthrospores and Chlamydospores: Arthrospores: The hyphae may break up into component cells. Each component behaves as spore that on germination give rise to a new hyphae. Chlamydospores: Some cells become enveloped in a thick wall before they separate from each other. Fission : The somatic cell split into two daughter cells i.e. by formation of constriction or transverse wall.e.g. Yeast. Budding : Formation of small outgrowth. One of the daughter nuclei migrate into bud. Sclerotia and Rhizomorphs : These are modifications of hypha which resistant to unfavourable conditions and many remain dormant for long period and germinate on return of favourable conditions.

13. Fungal Spores – Features and Importance Spores are tiny reproductive and survival bodies formed by fungi. They can be asexual or sexual depending on how they are produced. Features of fungal spores: Microscopic, light, and varied in color and shape. May be unicellular or multicellular with thick or ornamented walls. Contain stored food materials like lipids and glycogen. Can stay dormant under unfavorable conditions.

14. Asexual Spores and Their Types Two major kinds of asexual spores: a) Sporangiospores – formed inside a sac (sporangium). b) Conidia – formed externally on conidiophores. a) Sporangiospores : Endogenous - formed and contained within a sporangium • Found in Chytridiomycota and Oomycota. • Types: Zoospores (motile) and Aplanospores (non-motile). b) Conidia : Conidia are Exogenous - often formed at the tip of supporting hyphae called conidiospores. • Found in Ascomycota and Basidiomycota. • Types: Thallic (from hypha breakage) and Blastic (from budding).

15. Sexual Reproduction 1. Sexual reproduction involves fusion of nuclei and meiosis. 2 . Stages: • Plasmogamy – fusion of cytoplasm. • Karyogamy – fusion of nuclei. • Meiosis – produces haploid spores. 3 . Types of sexual spores: • Oospores – in Mastigomycota. • Zygospores – in Zygomycota (e.g., Rhizopus). • Ascospores – in Ascomycota (sac fungi). • Basidiospores – in Basidiomycota (club fungi). • Deuteromycota – no sexual spores.

16. Major Sexual Spores and Formation 1. Ascospores: • Formed in ascus after karyogamy and meiosis (8 per ascus). • Found in fruiting bodies called ascocarps. 2. Basidiospores: • Form on basidium (club-shaped), usually four per basidium. • Produced in mushrooms and other Basidiomycota. 3. Zygospores: • Formed by fusion of mating hyphae (e.g., in Rhizopus). • Thick-walled and serve as resting spores during unfavorable times.

17. Sexual Compatibility and Variations Homothallic fungi: self-fertile; same mycelium can reproduce sexually. Heterothallic fungi: require opposite mating types (+ and -). Types of Heterothallism : • Bipolar – two mating types (A and a). • Tetrapolar – four mating types (A, a, B, b). Importance : promotes genetic diversity and prevents inbreeding.

18. Heterokaryosis and Parasexuality Heterokaryosis: • Presence of genetically different nuclei in a single cell. • Occurs through mutation, fusion of hyphae, or diploidization. • Adds variation in imperfect fungi without sexual reproduction. Parasexuality: • Found in Aspergillus nidulans and similar fungi. • Involves nucleus fusion, diploid formation, mitotic crossing over, and haploidization. • Genetic recombination occurs without meiosis.

19. Importance and Summary Significance of Parasexuality: • Used to produce new fungal strains for industrial use. • Helps improve fermentation, enzyme, and antibiotic production. • Used in studying fungal genetics and pathogenicity. Summary : • Fungi reproduce sexually and asexually for survival and diversity. • Spores ensure spreading and adaptation. • Heterokaryosis and parasexuality introduce genetic variation. • These processes help fungi evolve and thrive in different environments.

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