Topic 7

Study of fungi

Mycology

Out of 100,000 species of fungi, only about 200 are?

pathogenic to humans and animals

important in food chain because they can decompose dead plant matter

Fungi

Fungi are

chemoheterotrophs

Fungi acquired food by?

absorption

Except for ___________, fungi are multicellular

yeasts

Reproduction of fungi

sexual and asexual spores

Eukaryotic, non-photosynthetic heterotrophs which produce exoenzymes and obtain nutrients by absorption

Fungi

Fungi produces

exoenzymes

decomposition of organic matter, causes sporadic opportunistic infections in animals

Saprophytic

Obligatory association with other microorganisms; non-pathogenic

Mutualistic

Fungi can tolerate high?

osmotic pressure

Fungi can tolerate acidic environment as low as

pH 5.0 (optimum pH is about 6)

Fungi’s optimum temp for growth

20-30C

causing systemic mycoses and can tolerate 37C

pathogenic fungi

They are aerobic or facultatively anaerobic; few anaerobic

Fungi

Fungal incubation temp for Dermatophytes

25 °C

Incubation time for Dermatophytes

2–4 weeks

Fungal incubation temp for Aspergillus species;

37 °C

Incubation time for Aspergillus species;

1–4 days

Incubation temp for Yeasts (pathogenic);

37 °C

Incubation time for Yeasts (pathogenic);

1–4 days

Incubation temp for Dimorphic fungi mould phase

25 °C

Incubation time for Dimorphic fungi mould

1 to 4 weeks

Incubation temp for Dimorphic fungi yeast phase

37 °C

Incubation temp for Dimorphic fungi yeast phase;

37 °C

Incubation time for Dimorphic fungi yeast phase

1 to 4 weeks

Incubation temp for Zygomycetes

37 °C

Incubation time for Zygomycetes

1 to 4 days

Growth characteristic of fungi

slow-growing

Reproduction by spore formation may be either

Sexual or asexual

Cell type of fungi

eukaryotic

Cell type of bacteria

prokaryotic

Fungal cell membrane sterol

sterols present

Bacterial cell membrane sterol

sterols absent except Mycoplasma

Fungal cell wall;

glucans, mannans, chitin

Bacterial cell wall

peptidoglycan

Fungal spores

sexual and asexual reproductive spores

Bacterial spores

endospores

Fungal metabolism

heterotrophic, aerobic, facultative anaerobic

Bacterial metabolism

heterotrophic, autotrophic, aerobic, facultative anaerobic, anaerobic

multicellular; vegetative and reproductive phases are two distinct phases;

Molds

Molds can grow as branching filaments called

hyphae

Unicellular; the same cell function in vegetative growth (asexual) as well as in sexual reproduction

Yeast

Yeast appearance

oval or spherical appearance

Two main morphological fungal forms

Yeasts and molds

a mass of threadlike filaments which combine to make up the fungal mycelium

Hyphae

In most molds, the hyphae contain cross-walls called

Septa

the hyphae contain cross-walls called septa, which divide them into uninucleate cell-like units

Septate hyphae

Septa singular

septum

in few class of fungi, the hyphae contain no septa and appear as long, continuous cells with many nuclei

Coenocytic hyphae

Impart rigidity and osmotic stability

Hyphal cell wall

Hyphal cell wall is mainly composed of carbohydrate components including

chitin

Hyphal cell wall in yeasts, contain protein complexed with

polysaccharides

Bilayer cell membrane, the predominant sterol is

ergosterol in contrast to cholesterol

portion of hypha that obtains nutrients

Vegetative hypha

portion concerned with reproduction; projects above the surface of the medium on which the fungus is growing; often bear reproductive spores

Reproductive/aerial hypha

Nonfilamentous, unicellular fungi

Yeasts

Yeast appearance

Spherical or oval

Frequently found as a white powdery coating on fruits and leaves

Yeasts

Some yeasts produce buds that fail to detach themselves. These buds form a short chain of cells called a

pseudohypha

Yeasts are capable of 

facultative anaerobic growth

If oxygen is present, yeasts perform ______________ to metabolize carbohydrates into carbon dioxide and water

aerobic respiration

If oxygen is absent, they ____________ and produce ethanol and carbon dioxide.

ferment carbohydrates

This fermentation is used in the brewing, wine-making and baking

ferment carbohydrates

species produce ethanol in brewed beverages and carbon dioxide for leavening bread dough

Saccharomyces

Some pathogenic species of fungi can exhibit ______

dimorphism (two forms)

produce vegetative and aerial hyphae

Moldlike form

reproduce by budding

Yeastlike form

Dimorphism is temperature dependent:

• At 37C, the fungus is yeastlike

• At 25C, it is moldlike

Growth of a Hypha

1. Elongation at tips

2. When a fragment breaks off, it can elongate to form a new hypha

In some species, mature elements at the center of colonies produce aerial hyphae that facilitates dispersal of

Mature spores

Large colonies with growth and extension of hyphae at their peripheries

Colony formation of Molds

Sporangiospores are formed only by fungi in the phylum

Zygomycota

In dermatophytes, multicellular structures called ________ are produced

microconidia

are formed from the disintegration of hyphae within keratinized structures

Arthroconidia

Yeasts asexual division

budding

are soft, smooth and round

Colonies

Multicellular, filamentous (hyphae)

Mold

Growth pattern of yeast

Smooth, moist colonies

Growth pattern of mold

Fuzzy, cottony colonies

Example of yeast

Candida albicans, Saccharomyces

Example of mold

Aspergillus, Penicillium, Rhizopus

produce both sexual and asexual forms

Teleomorphs

Three phyla

• Ascomycota

• Basidiomycota

• Zygomycota

Although most of veterinary importance are __________, some fungi in each of the three phyla can also produce disease in animals.

deuteromycetes

Zygomycota is also known as

“conjugation fungi”

Saprophytic molds that have coenocytic hyphae

Zygomycota

asexual spores of zygomycota

sporangiospores

sexual spores of zygomycota

zygospores

Ascomycetes also called

sac fungi

Septate hyphae mostly but unicellular yeast may form pseudomycelium

Ascomycetes

the septa possess central pores called

septal pores

Spores are produced in

Asci

Ascomycetes reproduction

asexually by budding or by spores

Fertilization occurs in two steps:

plasmogamy and karyogamy

Basidiomycetes also called as

club fungi

Most advanced and most commonly seen

Basidiomycetes

Basidiomycetes reproduce asexually by

basidium

Basidiomycetes is the most common decomposers of

wood