Transcript Document

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:
– If they feed on dead organic matter.
– Important in industrial fermentations – for
brewing of beer, wine making & production of
antibiotics as penicillin.
• Parasitic:
• 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
• 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.
• 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.
• Thallus of a mold has 2 parts:
– Mycelium (pl, mycelia) and
– Spores (resistant, resting, or dormant cells).
• 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
• 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.
• 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.
• Hyphae occur in three forms
– Nonseptate / Coenocytic: No septa.
– Septate with uninucleate cells.
– Septate with multinucleate cells
• Each cell has > 1 nucleus.
Types of hyphae:
(A) Nonseptate (coenocytic), (B) septate
with uninucleate cells, (C) septate with multinucleate cells.
REPRODUCTION
• Asexual / Somatic / Vegetative
• Sexual
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
• 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
• Arthrospores or Oidia: Single-celled
spores, formed by disjointing of hyphal
cells
• ChIamydospores: Thick-walled, singlecelled, highly resistant.
• Blastospores: Spores formed by budding.
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:
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Sex organelles of fungi
Forms differentiated sex cells (gametes)
May have one or more gamete nuclei.
Male gametangium – Antheridium
Female gametangium – Oogonium
Methods of sexual reproduction in 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.
• 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.
• 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.
• 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
• Zygospores
– Large, thick-walled spores
– Formed when the tips of two sexually
compatible hyphae or gametangia of certain
fungi fuse together
• 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
• 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.
• 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.