topic 7: Comprehensive Mycology: Fungi Types, Structures, and Reproduction (pt1)

What is mycology?

The study of fungi.

How many species of fungi are estimated to exist worldwide?

Approximately 100,000 species.

What is the ecological role of fungi?

They decompose dead plant matter and recycle nutrients in the environment.

What type of organisms are fungi classified as?

Eukaryotic and non-photosynthetic organisms.

How do fungi obtain nutrients?

By secreting exoenzymes into their surroundings and absorbing the digested materials.

What is the primary reproductive method of fungi?

They reproduce by sexual and asexual spores.

What are yeasts and how do they typically live?

Are unicellular fungi that often live as commensals on body surfaces.

What are parasitic fungi?

Fungi that live on living hosts and can cause diseases, such as dermatophytes that cause ringworm.

What are saprophytic fungi?

Fungi that live on decaying organic matter and play a major role in decomposition.

What are mutualistic fungi?

Fungi that form obligatory, non-pathogenic associations with other organisms.

What is ergosterol?

The main sterol in fungal cell membranes and a primary target of many antifungal drugs.

How do fungi differ from bacteria in terms of cell structure?

Fungi are eukaryotic with sterols in their membranes, while bacteria are prokaryotic and generally lack sterols.

What are the major morphological types of fungi?

Molds, yeasts, and dimorphic fungi.

What are molds?

Multicellular fungi that grow as branching filaments called hyphae.

How do yeasts reproduce asexually?

By budding, where a protrusion forms on the parent cell and eventually separates.

What is dimorphism in fungi?

The ability of some fungi to exist in two distinct morphological forms depending on temperature.

What are septate hyphae?

Hyphae that contain cross walls called septa, dividing the hypha into cell-like units.

What is the function of vegetative hyphae?

They grow into the substrate and absorb nutrients.

What is the composition of the fungal cell wall?

Composed of chitin with cellulose cross linkages and other carbohydrate components.

What are the typical incubation conditions for dermatophytes?

Incubation temperature of 25°C for 2 to 4 weeks.

What distinguishes teleomorphs in fungi?

They produce both sexual and asexual forms in their life cycle.

What is the optimal pH for fungal growth?

Around 6, although they can tolerate acidic environments with pH as low as about 5.

How do fungi grow in laboratory conditions compared to bacteria?

Fungi are comparatively slow-growing on laboratory media compared to bacteria.

What is the significance of yeast fermentation?

produces ethanol and carbon dioxide, used in brewing, wine-making, and baking.

What are coenocytic hyphae?

Hyphae that lack septa and consist of long, continuous multinucleated cells.

What is the role of reproductive or aerial hyphae?

They project above the surface of the medium and bear reproductive spores.

Mold colonies

• expand at the periphery due to hyphal extension.

• usually appear fuzzy or cottony.

Yeast colonies

• expand at the periphery due to hyphal extension.

• are typically soft, smooth, creamy, and round.

What are Zygomycota commonly known as?

• Conjugation fungi

What type of hyphae do Zygomycota have?

Coenocytic hyphae (no septa)

What is the asexual reproductive structure in Zygomycota?

Sporangiospores inside sporangia

What is formed during sexual reproduction in Zygomycota?

Thick-walled zygospores

Give an example of a Zygomycota.

Rhizopus stolonifer (common black bread mold)

What are Ascomycota commonly referred to as?

• sac fungi

• Have separate hyphae with septal spores

What type of hyphae do Ascomycota possess?

Separate hyphae and Septate spore

What are the sexual spores produced by Ascomycota called?

Ascospores

What is a common method of asexual reproduction in Ascomycota?

Budding (yeasts)

What are some examples of Ascomycota?

Saccharomyces, Aspergillus, Penicillium, Candida

What are Basidiomycota commonly known as?

• Club fungi

• Considered most advanced fungi

• Commonly seen as mushroom

• Major wood decomposers because they digest cellulose and lignin

What are the sexual spores produced by Basidiomycota called?

Basidiospores

What is a significant role of Basidiomycota in the ecosystem?

Major wood decomposers

Give an example of a pathogenic Basidiomycota.

Cryptococcus neoformans

What are Deuteromycota also known as?

Fungi Imperfecti

What type of reproduction do Deuteromycota primarily exhibit?

Asexual reproduction only, mainly conidia

What are dermatophytes known for?

Infecting skin, hair, and nails

What are dimorphic fungi?

● Important systemic pathogens such as Histoplasma, Blastomyces, and Coccidioides.

● Coccidioides immitis produces highly infectious arthroconidia.

• Fungi that grow as yeasts at 37°C and as molds at 25°C

What is the process of asexual reproduction in fungi?

• Spore formation

• Mitosis: asexual

• Meiosis: sexual

What is the significance of plasmogamy in fungal reproduction?

Fusion of cytoplasm of two cells without nuclear fusion

What occurs during karyogamy?

Fusion of nuclei to form a diploid nucleus

What are the three main phases of meiosis in fungi?

Plasmogamy, karyogamy, and meiosis

What is an antheridium?

Male gametangium in fungi

What is an oogonium?

Female gametangium in fungi

What is the difference between isogamy and anisogamy?

Isogamy involves morphologically similar gametes, while anisogamy involves gametes of different sizes.

What is the role of spermatization in fungal reproduction?

Transfer of male cells (spermatia) to a receptive hypha

What are the main types of sexual spores?

Ascospores, basidiospores, zygospores, and oospores

What is a characteristic of coenocytic hyphae?

They have no septa.

What is a common feature of dimorphic fungi?

They can grow in two different forms depending on temperature.

Hyphae

collectively form a mycelium

Yeast form

At approximately 37 C

Mold-form like with hyphae

At approximately 25 C

Coenocytic hyphae

• lack septa

• Consist of long, continuous multinucleated cells

Reproductive or aerial hyphae

project above the surface of the medium and bear reproductive spores.

Plasma membrane

A bilayer in which ergosterol is the predominant sterol, in contrast to cholesterol in mammalian cell membranes.

Mold colonies

● Mold colonies expand at the periphery due to hyphal extension.

● In some species, mature parts at the center of the colony produce aerial hyphae that

bear spores such as

conidia or sporangiospores for dispersal.

● Mold colonies usually appear fuzzy or cottony.

Sporangia

Are borne on sporangiophores (specializes hyphae)

Pathogenic yeasts

Include fungi that cause infections in humans and animals.

Opportunistic molds

Infect mainly immunocompromised hosts.

Planogametic copulation

● Also called gametic copulation

● Fusion of motile gametes (planogametes)

● Occurs in water or moist environments

Isogamy (type of planogametic copulation)

● Gametes are morphologically similar but compatible

● Fusion forms a motile zygote

Synchytrium Anisogamy (example of planogametic copulation)

● Gametes differ in size

● Larger gamete fuses with smaller one to form a zygote

Isogametangial copulation

● Gametangia are similar in size and morphology

● Walls dissolve at contact point and contents fuse

Ascospores

● Sexual spores formed inside asci in ascomycota

Basidiospores

● Sexual spores formed on basidia in Basidiomycota.

Zygospores

● Large, thick-walled spores formed at the tips of two compatible

What are the types of asexual spores?

Zoospores, sporangiospores, chlamydospores, blastoconidia, arthroconidia, macroconidia, and microconidia

Sporangiospores

● Asexual spores formed within sac-like structures called sporangia.

● Sporangia are borne on specialized hyphae called sporangiophores.

● Characteristic of Zygomycota such as Rhizopus and Mucor.

Chlamydospores

● Thick-walled, resistant spores formed from cells of vegetative hyphae.

● Contain storage materials and allow survival in adverse conditions.

● Produced by Candida albicans and considered a diagnostic clue.

Blastoconidia or blastospores

● Asexual spores produced by budding from a parent cell.

● Common in yeasts such as Candida and Cryptococcus. Conidospores attach as chains of phialoconidia.

● Also seen in Aspergillus and Fusarium.

Arthroconidia

● Asexual spores formed by fragmentation of septate hyphae into rectangular or barrel-shaped cells.

● Produced by some dermatophytes and by Coccidioides immitis.

● Arthroconidia of Coccidioides

Macroconidia and microconidia

● Large and small multicelled

conidia produced by dermatophytes in culture.

● They reportedly lack mitochondria. Sexual reproduction (Meiosis)

● Involves the fusion of nuclei from two compatible parent cells.

It proceeds through three main phases: OCD

Oidia

● Thin-walled spores formed when hyphae fragment into individual cells under adverse

conditions.

● These fragments resemble small yeast-like cells.

Conidia

● Asexual spores formed externally at the tips or sides of specialized hyphae called conidiophores.

● They are not enclosed in a sac.

● Typical of Penicillium and Aspergillus species

Phialocondia

● Conidia that are produced from flask-shaped cells called phialides.

● Penicillium has an extra branch called a phialide where

Mycelium

formed by a mass of hyphae.