28-1

Fungi

• Overview of fungi– True multicellularity with differentiation– Strict heterotrophs– Release enzymes into environment- digestion is extracellular– Most are saprophytic– Along with bacteria, fungi are important as decomposers

• Biology of fungi– Body - mass of filaments called a mycelium

• Each filament is a hypha- increase surface area for absorption

– Some have crosswalls between cells-septa

– Nonseptate fungi lack crosswalls between cells-multinucleate

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Fungal mycelia and hyphae

• Fig. 28.23

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Fungi cont’d.• Fungal cell structure

– Cell walls contain chitin• Polymer of glucose

– Each glucose has an amino group attached

• Found in exoskeletons of animals

• Energy reserve is glycogen like animal cells

• Move toward food source by growing toward it

– Hyphae can grow as much as a meter per day!

https://www.youtube.com/watch?v=EDkR2HIlEbc

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Fungi cont’d.

• Fungal reproduction– Adapted to dry land - produce wind-blown spores

• Haploid reproductive cell - germinates and develops into new mycelium-asexual

• Sexual reproduction - conjugation of two different mating types

– Designated as + and –

– Dikaryonic state - in some, the + and – nuclei do not fuse for long periods of time

– After fusion of nuclei, a zygote forms - undergoes meiosis

» Produces haploid spores and cycle begins again

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Dispersal of spores

• Fig. 28.24

Bird’s Nest Mushroom

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28-7

Fungi cont’d.

• Diversity of Fungi

- classified by mode of sexual reproduction

1. Zygospore fungi - Phylum Zygomycota• Saprotrophs and parasites

• Rhizopus stolonifer – black bread mold is a familiar zygospore fungus

– life cycle is illustrated on following slide

» Note formation of a zygospore from fusion of + and - hyphae

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Black bread mold Rhizopus stolonifer

• Fig. 28.25

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Fungi cont’d.

2. Sac fungi - Phylum Ascomycota– Sexual reproductive structure called an ascus– Asci are enclosed within an ascocarp

• Ascocarp develops after fusion of + and – hyphae

– Union of + and – nuclei produces and ascus

» Ascus produces spores by meiosis

– In asexual reproduction, the asexual spores are called conidia– Unicellular ascomycetes are often called yeasts

• Unequal binary fission- called budding

• Fermentation by some yeasts produces CO2 and ethanol

– Used to make beer, wine, and bread

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Sexual reproduction in sac fungi

• Fig. 28.26

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Asexual reproduction in sac fungi

• Fig. 28.27

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Fungi cont’d.

3. Club fungi- Phylum Basidiomycota– Characteristic sexual reproductive structure is called a basidium

• Contained within a basidiocarp

– Edible part of a mushroom is the basidiocarp

– Forms after fusion of + and – hyphae

– Sexual reproduction is most prominent in this group• Asexual reproduction can occur by asexual spores called conidia

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Sexual reproduction in club fungi

• Fig. 28.28

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Fungi cont’d.

4. Imperfect fungi - Phylum Deuteromycota– Includes many familiar fungi– Aspergillis- used to make soy sauce from fermenting soy beans– Penicillium- original source of penicillin

• Penicillium roquefortii and camemberti- used in making blue cheeses

– Deuteromycetes always reproduce asexually• Produce conidia on aerial hyphae

– Sexual stage has not been identified and may not exist

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Blue cheese

• Fig. 28.29

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Fungi cont’d.

• Environmental importance of fungi– Fungi and photosynthesizers

• Lichens- associations between fungi and cyanobacteria or green algae

• Efficient at acquiring nutrients and moisture-can colonize poor soil, rocky surfaces

– Produce organic matter and create new soil

• 3 characteristic forms- crustose, foliose, fruticose

• Body of lichen has 3 layers-fungi form top and bottom layers and protect middle layer of photosynthetic cells

– Protects photosynthesizer and delivers water

– Photosynthesized gives the fungus nutrients

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Lichen morphology

• Fig. 28.30

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Fungi cont’d.

• Environmental aspects, cont’d.– Mycorrhizal fungi

• Mutualistic relationships with plant roots

– Helps plants to grow more successfully in poor soils

• Fungi can live on the outside surface of roots, or it can penetrate the root tissues

– Plant provides organic nutrients to the fungus

– Fungus brings water and minerals to the plant

» Hyphae provide lots of surface area for water absorption

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Fungi cont’d.

• Medical aspects of fungi– Fungal diseases of plants

• Many enter through the stomata of the leaves or through a wound

• Smuts and rusts- sac fungi that parasitize cereal crops

– Fungal diseases of humans• Mycoses

– Cutaneous- affect only the skin

– Subcutaneous-deeper skin layers

– Systemic-spread throughout the body

• Many fungal diseases are acquired from the environment

– Ringworm from soil fungi for example

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Smuts and rusts

• Fig. 28.31

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Fungi cont’d.

• Human fungal diseases– Tineas

• Skin infections-can occur anywhere on the skin

– Athlete’s foot- scaling, peeling, and itching between toes

– Ringworm- redness and inflammation due to enzymes released by the fungus; extends outward in a ring-shape

– Histoplasmosis• Caused by Histoplasmosis capsulatum; common in the Midwest

• Carried in bird droppings

• Mild flu-like symptoms, fungus lives in cells of the immune system

• Healed lesions in the lungs calcify

– Candidiasis • Yeast infections resulting from imbalance of normal flora

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Human diseases caused by fungi

• Fig. 28.32

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Fungi cont’d.

• Control of fungi– Fungi more closely resemble animal cells than bacteria– Makes it harder to develop antibiotics that will kill fungi and not

the host– Fungi synthesize steroids differently-fungicides are directed at

steroid biosynthesis