Fungi.pdf

FUNGI Nur Dina Amalina, S.Farm., M.Sc., Apt.

Photo’s courtesy of : Sylvia T. Pratiwi

What is a fungus? 

Are diverse and widespread 



Are essential for the well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients

Distinguished from other kingdoms by:  Nutrition  Structural organisation

 Growth  Reproduction

What is a fungus? 

Fungi are eukaryotic protista; differ from bacteria and other prokaryotes. 1. Cell walls containing chitin (rigidity & support), mannan & other polysaccharides 2. Cytoplasmic membrane contains ergosterols 3. Possess true nucleic with nuclear membrane & paired chromosomes. 4. Divide asexually, sexually or by both 5. Unicellular or multicellular 6. heterotrophic organism devoid of chlorophyll that obtains its nutrients by absorption 7. reproduces by spores.

Fungi 

Simplest fungus :- Unicellular budding yeast

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Hypha :- Elongation of apical cell produces a tubular, thread like structure called hypha

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Mycelium :- Tangled mass of hyphae is called mycelium. Fungi producing mycelia are called molds or filamentous fungi.

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Hyphae may be septate or non-septate

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CLASSIFICATION

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Depending on cell morphology 1.

Yeasts

2.

Yeast like fungi

3.

Molds and fleshy fungi

4.

Dimorphic fungi

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1. Yeasts 

On culture - produce smooth, creamy colonies e. g Cryptococcus neoformans (capsulated yeast)

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Unicellular fungi, nonfilamentous, typically oval or spherical cells. Reproduce by mitosis: 

Fission yeasts: Divide evenly to produce two new cells (Schizosaccharomyces).

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Budding yeasts: Divide unevenly by budding (Saccharomyces).

Budding yeasts can form pseudohypha, a short chain of undetached cells. Candida albicans invade tissues through pseudohyphae. 

Yeasts are facultative anaerobes, which allows them to grow in a variety of environments. 

When oxygen is available, they carry out aerobic respiration.

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When oxygen is not available, they ferment carbohydrates to produce ethanol and carbon dioxide.

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2. Yeast like fungi

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

Grow partly as yeasts and partly as elongated cells resembling hyphae which are called pseudohyphae.

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e.g. Candida albicans

3. Molds/ Filamentous fungi

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Form true mycelia & reproduce by formation of different types of spores.

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Vegetative/ aerial hyphae

e.g. Rhizopus, mucor

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Molds and Fleshy Fungi

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Multicellular, filamentous fungi.

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Identified by physical appearance, colony characteristics, and reproductive spores. 

Thallus : Body of a mold or fleshy fungus. Consists of many hyphae.

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Hyphae (Sing : Hypha) : Long filaments of cells joined together.  Septate hyphae :

Cells are divided by cross-walls (septa).

 Coenocytic (Aseptate) hyphae :

Long, continuous cells that are not divided by septa.

Hyphae grow by elongating at the tips. Each part of a hypha is capable of growth.  Vegetative Hypha :

Portion that obtains nutrients.

 Reproductive or Aerial Hypha : 

Portion connected with reproduction.

Mycelium : Large, visible, filamentous mass made up of many hyphae.

4. Dimorphic fungi 

Occur in 2 forms Molds (Filaments) – 25C (soil) Yeasts – 37C (in host tissue) Most fungi causing systemic infections are dimorphic:  Histoplasma capsulatum  Blastomyces dermatidis  Paracoccidioides brasiliensis  Coccidioides immitis  Penicillium marneffei  Sporothrix schenkii

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Body Structure 

The morphology of multicellular fungi enhances their ability to absorb nutrients

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Fungi consist of mycelia, networks of branched hyphae adapted for absorption

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Most fungi have cell walls made of chitin

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Some fungi have hyphae divided into cells by septa, with pores allowing cell-to-cell movement

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Coenocytic fungi lack septa

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Some unique fungi have specialized hyphae that allow them to penetrate the tissues of their host

Fungal hyphae may be septate or aseptate 

Except for yeast, hyphae are organised around and within food source:  Composed of tubular walls containing chitin  Provide enormous surface area: 10cm2 of soil may contain 1km of hyphae with 314cm2 surface area

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Hyphae of septate fungi are divided into cells by crosswalls called septa

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Hyphae of aseptate fungi lack cross walls (coenocytic)

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Parasitic fungi have modified hyphae called haustoria, which penetrate the host tissue but remain outside cell membrane

Hyphae

Nematode

25 µm

Hyphae adapted for trapping and killing prey

Plant cell wall

Fungal hypha

Plant cell

Haustoria

Haustorium

Plant cell plasma membrane

Fungal cell wall composition 

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Structural components: 

chitin microfibrils [ß(1-4)-linked polymer of Nacetylglucosamine]

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ß-linked glucans

Gel-like components: 

Mannoproteins (form matrix throughout wall)

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Antigenic glycoproteins, agglutinans, adhesions—on cell wall surface

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Melanins—dark brown to black pigments (confer resistance to enzyme lysis, confer mechanical strength and protect cells from UV light, solar radiation and desiccation)

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Plasma membrane—semi-permeable

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Ergosterol is the major lipid component of the underlying plasma

Common wall constituents found in each division of fungi Division

Fibrous

Gel-like Polymer

Basidiomycota

Chitin β -(1-3), β-(1-6) Glucan

Xylomannoproteins α (1-3) Glucan

Ascomycota

chitin β -(1-3), β-(1-6) Glucan

Galactomannoproteins α (1-3) Glucan

Zygomycota

Chitin Chitosan

Polyglucuronic acid Glucuronomannoproteins Polyphosphate

Chytridiomycota

Chitin Glucan

Glucan

Taken from : http://bugs.bio.usyd.edu.au/learning/resources/Mycology/StructureFunction/wallComposition.sht ml

Reproduction in fungi 

Sexual (by meiosis) - formation of zygospores, ascospores or basidiospores

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Asexual reproduction (by mitosis) – budding or fission

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Asexual spores are formed on or in specialized structures.

Vary in size, shape & colour but these characteristics are constant for a particular species.  Spores are the agent of dispersal responsible for geographic distribution of fungi:  Carried by wind or water  Germinate in moist places with appropriate substrata 

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Reproduction in fungi 

Micro conidia - Small, single celled

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Macro conidia – Large, single or many celled

konidia

2 2

Generalised life cycle of fungi

Asexual Sexual

Sexual Reproduction 

Fungal nuclei are normally haploid, with the exception of transient diploid stages formed during the sexual life cycles

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Sexual reproduction requires the fusion of hyphae from different mating types

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Fungi use sexual signaling molecules called pheromones to communicate their mating type

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Plasmogamy is the union of cytoplasm from two parent mycelia

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In most fungi, the haploid nuclei from each parent do not fuse right away; they coexist in the mycelium, called a heterokaryon

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In some fungi, the haploid nuclei pair off two to a cell; such a mycelium is said to be dikaryotic

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Hours, days, or even centuries may pass before the occurrence of karyogamy, nuclear fusion

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During karyogamy, the haploid nuclei fuse, producing diploid cells

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The diploid phase is short-lived and undergoes meiosis, producing haploid spores

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The paired processes of karyogamy and meiosis produce genetic variation

Asexual Reproduction 

In addition to sexual reproduction, many fungi can reproduce asexually

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Molds produce haploid spores by mitosis and form visible mycelia

Asexual Reproduction  

Other fungi that can reproduce asexually are yeasts, which are single cells

10 m

Instead of producing spores, yeasts reproduce asexually by simple cell division and the pinching of “bud cells” from a parent cell Parent cell

Bud

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A sporangium is a sac or case in which spores

are produced.

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This is a Rhizopus sporangium.

Sac fungi

Club fungi

Basidiomycota

Arbuscular mycorrhizal fungi

Ascomycota

 Fungi have radiated

Zygote fungi

Glomeromycota

Chytrids

Zygomycota

Phylogeny/Classification

 The four phyla of

fungi are identified by the shape and presence of their sporangium

Chytridiomycota

into a diverse set of lineages

Phylogeny/Cl assification

Five Phyla of Fungi

Chytrids 

The most primitive fungi

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Fungi classified in the phylum Chytridiomycota, or chytrids

Hyphae

25 m

 Are found in freshwater and

terrestrial habitats, but mainly aquatic  Can be saprobic or parasitic

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Chytrids are unique among fungi  In having flagellated spores,

called zoospores

Flagellum 4 m

Zygomycetes 

Lower fungi;

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Broad, nonseptate hyphae

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Asexual spores - Sporangiospores: present within a swollen saclike structure called Sporangium

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They include fast-growing molds, parasites, and commensal symbionts

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The zygomycetes are named for their sexually produced zygosporangia

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Zygosporangia resistant to freezing and drying

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Are capable of persisting through unfavorable conditions

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Can undergo meiosis when conditions improve

The life cycle of black bread mold (Rhizopus stolonifer) is fairly typical of the phylum

Bread Mold – a Zygomycete Fungi

Two views of a Zygomycota’s sporangium

Zygomycota – common molds

The fungal mass of hyphae, known as the MYCELIUM penetrates the bread and produces the fruiting bodies on top of the stalks.

Mycelia = a mass of hyphae or filaments

Rhizoids = root-like hyphae The Rhizoids meet underground and mating occurs between hyphae of different molds (SEXUAL REPRODUCTION)

Zygomycetes 

Some zygomycetes, such as Pilobolus can actually “aim” their sporangia toward conditions associated with good food sources

This decomposer of animal dung bends toward bright light and shoots its sporangia up to 2 meters 0.5 mm

Ascomycetes 

Fungi in the phylum Ascomycota  Include unicellular yeasts and

complex multicellular (filamentous) cup fungi  Are found in a variety of marine,

freshwater, and terrestrial habitats Morchella esculenta

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Sexual spores called ascospores are present within a sac like structure called Ascus.

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Several asci may be seen within a fruiting body as seen in Penicillium, Aspergillus

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Each ascus has 4 to 8 ascospores

In sexual reproduction, haploid mycelia of opposite mating strains fuse Asexual spores are called conidia borne on conidiophore Hyphae are septate

Aspergillus flavus conidiophore

Yeast is an Ascomycete Fungus

Division Basidiomycota: club fungi It is characterized by basidia – club shaped hyphae that produce basidiaspores during sexual reproduction.  Important decomposers of wood / plant material  Include: 

 Mycorrhiza-forming mutualists

 Mushroom-forming fungi  Plant parasites e.g. rusts and smuts

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Characterised by dikaryotic mycelium that reproduces sexually via basidiocarps

Basidiomycete or Club Fungi

PHYLUM DEUTEROMYCOTA

No Longer Exist!!

• • • • • • •

22,000 species. No known sexual stage. Saprophytic, parasitic and predatory. Many produce conidia. Most classified as Ascomycota. Fusarium wilt of tomato, potato and cotton. Athletes foot, ring worm

Division Deuteromycota - No Longer Exist!! “Imperfect fungi” (penicillin) Unrelated group Asexual No info on sexual cycle

25,000 species

Penicillin

Woops… now Ascomycota

Candida albicans “yeast infection”

Botrytis: “Noble Rot”

Kingdom Fungi Uses: • medicine • Food Ecological value: • major decomposers • symbiotic relationships (N2 fixers) Problems: • some strains are deadly • athletes foot • destroy library books • destroy crops

About 100,000 species

Fungi in Industry

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Fungi produce many products used in the medical field such as penicillin, cephalosporin antibotics, cortisone

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Fungi are used in genetic engineering – vaccine for hepatitis B was developed using the yeast plasmid as the vector.

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Yeast is used to make ethanol.

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Yeast are known for making breads rise.

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Mushrooms, morels and truffles are widely consumed by humans.

Useful Properties of Fungi

Source of food e.g. mushrooms

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Antibiotic production e.g. Penicillin from Penicillium notatum Fermentation - Production of alcohol, bread, cheese e.g. Sacchromyces spps

Useful Properties of Fungi

Ergot from Claviceps purpurea, used to induce uterine contractions

Vaccines for Hepatitis B – Sacchromyces cerevisiae

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Absorptive nutrition enables fungi to live as decomposers and symbionts 

Fungi are heterotrophs that acquire nutrients by absorption

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Secrete hydrolytic enzymes and acids to decompose complex molecules into simpler ones that can be absorbed

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Specialised into three main types:  Saprobes - absorb nutrients from dead organic material  Parasitic fungi - absorb nutrients from cells of living hosts; some are pathogenic  Mutualistic fungi - absorb nutrients from a host, but reciprocate to benefit the host

Fungi decompose dead plant and animal matter 

Called saprophytes, they act as recyclers of dead organic matter, obtaining food from this material.

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Hyphal tips release enzymes that eventually decompose and release organic materials into the surrounding environment.

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Saprophytic fungi appear on dead trees, logs, plant litter such as leaves, and even dead insects and animals. Examples: "Gem-studded Puffball" (Lycoperdon perlatum) and "Turkey Tail"(Trametes versicolor).

Fungi form beneficial partnerships (symbiosis) with other organisms such as plants:

Algae

hyphae

Lichen – symbiotic relationship between algae and fungi

Fungus-Animal Symbioses 

Some fungi share their digestive services with animals

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These fungi help break down plant material in the guts of cows and other grazing mammals

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Many species of ants use the digestive power of fungi by raising them in “farms”

Fungus-Algae Symbioses

Some fungi are pathogens 

About 30% of the 100,000 known species of fungi are parasites, mostly on or in plants.

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Many people have allergies triggered by mold.

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Fungal skin infections – skin, nails and hair 

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Ringworm, athlete’s foot

Internal organs – Histoplasmosis

Fungal Infections/ Mycoses 

Superficial mycoses:  2 types: surface and cutaneous mycoses  Skin, hair & nails.  Mild but chronic disease

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Deep mycoses: 2

types: subcutaneous & systemic mycoses  Caused by soil saprophytes  Infection

is accidental  Range from a symptomatic infection to fatal disease

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Opportunistic infections 

Mainly caused by fungi which are common lab contaminant on culture media  Aspergillus  Pencillium  Mucor

 Rhizopus  Candida

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Produce serious & fatal infections

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