Fungi
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FUNGI. Fungus Fungi MYCOLOGY. Eukaryotic spore-bearing protists, lacking chlorophyll Fungi Molds: Filamentous and multicellular Yeasts: Mostly, unicellular. Fungi are heterotrophic: Chemoorganotrophic Require organic compounds for nutrition. Saprophytic:

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Fungi

FUNGI


Fungi

  • Fungus

  • Fungi

  • MYCOLOGY


Fungi

  • Eukaryotic spore-bearing protists, lacking chlorophyll

  • Fungi

    • Molds: Filamentous and multicellular

    • Yeasts: Mostly, unicellular


Fungi

  • Fungi are heterotrophic:

    • Chemoorganotrophic

    • Require organic compounds for nutrition.

  • Saprophytic:

    • If they feed on dead organic matter.

    • Important in industrial fermentations – for brewing of beer, wine making & production of antibiotics as penicillin.

  • Parasitic:


Fungi

  • Dimorphic Fungi:

    • Exist in 2 forms.

    • Human/animal pathogenic fungi:

      • Have unicellular & yeastlike form in host

      • Under saprophytic conditions, have a filamentous mold form

    • Plant pathogens

      • In Taphrina, smuts

      • Mycelial form occurs in host

      • Unicellular yeastlike form occurs in lab culture.


Morphology

MORPHOLOGY

  • Size range:

    • 1 to 5 μm in width;

    • 5 to 30 μm or more in length.

  • Shape:

    • Egg-shaped or spherical.

    • Depends on age and environment

  • No organelles of locomotion.


Fungi

  • Thallus (pl. thalli)

    • Body of a fungus

    • Consists of a single cell as in yeasts

    • Consists of branched filaments, as in molds, 5 to 10 μm across

    • Surrounded by a true cell wall

    • Exception: In slime molds.

      • Thallus has a naked mass of protoplasm.


Fungi

  • Thallus of a mold has 2 parts:

    • Mycelium (pl, mycelia) and

    • Spores (resistant, resting, or dormant cells).


Fungi

  • A complex of several filaments - Hypha (pl, hyphae)

  • A spore, on germination, puts out a germ tube(s)

  • Germ tubes elongate and branch to form hyphae.

  • A complex of several hyphae - Mycelium


Hypha

HYPHA

  • Composed of an outer tubelike wall surrounding a cavity, the LUMEN, which is filled / lined by protoplasm.

  • Between the protoplasm and the wall is the PLASMALEMMA, a double-layered membrane

  • Hyphal wall consists of microfibrils composed for the most part of hemicelluloses or chitin

  • True cellulose - Only in the walls of lower fungi.


Fungi

  • Growth of a hypha is distal, near the tip.

  • New hypha is divided into cells by crosswalls which are formed by centripetal invagination from the existing cell wall.

  • Crosswalls constrict the plasmalemma

  • Grow inward to form an incomplete septum (pl, septa)

  • Septum has a central pore to allow protoplasmic streaming.


Fungi

  • Hyphae occur in three forms

    • Nonseptate / Coenocytic: No septa.

    • Septate with uninucleate cells.

    • Septate with multinucleate cells

      • Each cell has > 1 nucleus.


Fungi

Types of hyphae:(A) Nonseptate (coenocytic), (B) septatewith uninucleate cells, (C) septate with multinucleate cells.


Reproduction

REPRODUCTION

  • Asexual / Somatic / Vegetative

  • Sexual


Asexual reproduction

Asexual Reproduction

  • Fission of somatic cells yielding 2 similar daughter cells;

  • Budding of somatic cells or spores

    • Each bud, a small outgrowth of parent cell

  • Fragmentation of the hyphal cells

    • Each fragment becomes a new organism

  • Spore formation.

    • Many types.


Types of spores

Types of Spores

  • Sporangiospores: Single-celled spores, formed within sacs called sporangia at the end of hyphae – sporangiophore

    • Aplanospores: Nonmotile sporangiospores

    • Zoospores: Motile sporangiospores, motility due to flagella.

  • Conidiospores or conidia: Formed at the tip or side of a hypha

    • Microconidia: Small, single-celled

    • Macroconidia: Large, multicelled


Fungi

  • Arthrospores or Oidia: Single-celled spores, formed by disjointing of hyphal cells

  • ChIamydospores: Thick-walled, single-celled, highly resistant.

  • Blastospores: Spores formed by budding.


Sexual reproduction

Sexual Reproduction

  • Joining of two cells

  • Fusion of protoplasts (Plasmogamy)

  • Fusion of haploid nuclei of 2 mating types (Karyogamy)

  • Formation of a diploid nucleus

  • Meiosis to reduce the number of chromosomes to haploid no.

  • Gametangia:

    • Sex organelles of fungi

    • Forms differentiated sex cells (gametes)

    • May have one or more gamete nuclei.

    • Male gametangium – Antheridium

    • Female gametangium – Oogonium


Fungi

Methods of sexual reproduction in fungi


Fungi

  • Gametic copulation:

    • Fusion of gametes.

  • Gamete-gametangial copulation:

    • 2 gametangia come into contact without fusion;

    • Male nucleus migrates through pore or fertilization tube into female gametangium.

  • Gametangial copulation:

    • 2 gametangia or their protoplasts fuse

    • A zygote forms & develops into a resting spore.

  • Somatic copulation:

    • Fusion of somatic or vegetative cells.

  • Spermatization:

    • Spermatia uniting with receptive hyphae of compatible female strain.

    • Spermatium empties its contents into the latter during plasmogamy.


Fungi

  • Sexual spores:

    • Produced by the fusion of 2 nuclei

    • Occur in smaller numbers than asexual spores.

  • These single-celled spores are produced in a sac called ASCUS

  • Usually has 8 ascospores in each ascus.


Fungi

  • Ascospores.

    • Nuclear fusion occurs in the ascus.

    • Diploid zygote nucleus divides by meiosis

    • 4 haploid nuclei are produced

    • Haploid nuclei divide by mitosis

    • Forms 8 ascospores, typically in each ascus.


Fungi

  • Basidiospores

    • Single-celled spores, borne on a club-shaped structure called a basidium

    • A basidium begins with one nucleus from each parent.

    • Nuclear fusion & meiosis occurs in basidium

    • Basidium assumes a species-specific shape & produces tapering projections: Sterigmata.

    • Basidiospores are formed in Sterigmata

    • The nuclei produced after nuclear fission from meiosis move towards sterigmata


Fungi

  • Zygospores

    • Large, thick-walled spores

    • Formed when the tips of two sexually compatible hyphae or gametangia of certain fungi fuse together


Fungi

  • Oospores

    • Formed within a special female structure: Oogonium.

    • Male gametes formed in an antheridium

    • Fertilization of the eggs (Oospheres) results in Oospores.


Cultivation of fungi

Cultivation of Fungi

  • Almost all of them grow aerobically

  • At temperatures from 20 to 30°C

  • Good to use a medium that favors their growth but is not optimal for the growth of bacteria.

  • Acidic (pH 5.6) media that incorporates a relatively high conc. of sugar are tolerated by molds but are inhibitory to many bacteria.


Fungi

  • Sabouraud Media

    • contains maltose and peptone as important components

    • Glucose

    • For the isolation of molds and certain yeasts

    • Selective action is due to the high sugar conc and low pH.


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