Mycology

Yeast, molds, mushrooms, mildews and the
other fungi pervade our World. They work great
good and terrible evil. Upon them, indeed,
hangs the balance of life; for without their
presence in the cycle of decay and
regeneration, neither man nor/or any other
living things could survive.
-Lucy Kavaler.

 The living world is divided into the five kingdoms of Planta,
Animalia, Fungi, Protista and Monera. It is important to
recognize that the fungi are not related to bacteria (Monera).

 Fungi are eukaryotica, heterotrophic, unicellular to
filamentous, rigid cell walled, sporebearing, organisms that
usually reproduce by both sexual and asexual means.
Further they are insensitive
to antibacterial antibiotics.

 Eukaryotic cells also exhibit mitosis. But not prokaryotic
cells.

 Heterotrophic - that are either saprophytes (living on dead
organic matter) or parasites (utilizing living tissue).
 Like plants, fungi have rigid cell walls and are therefore non-
motile, a feature which separates them from animals.

FUNGI (Mycology)

 Diverse group of heterotrophs.
 Many are ecologically important saprophytes (consume dead and decaying matter)
 Others are parasites.
 Most are multicellular, but yeasts are unicellular.
 Most are aerobes or facultative anaerobes.
 Cell walls are made up of chitin & glycan & a cell membrane
ergosterol.
 Over 80,000 to 100,000 fungal species identified. 1.5 million
may exist. Only about 50 - 100 are human or animal
pathogens.
 Most human fungal infections are nosocomial and/or occur in immunocompromised
individuals (opportunistic infections).
 Fungal diseases in plants cause over 1 billion dollars/year in
losses.

 Harmful fungi:
 Human, Animal and Plant Diseases.
25-50% of harvested fruits and vegetables are damaged by fungi.
Fungal infections of plants are commonly called rots, rusts, blights, wilts, and smuts. eg
Phytophthora infestans:

 Beneficial fungi:
 Decomposers- separates carbon, nitrogen, phosphorous & other critical constituents.
 Industrial process
 Making bread , wine and beer.
 In preparation of some cheese, soy sauces & sufu.
 In production of many organic acids ( Citric, galic acids etc.)
 In Production of Alcohol/ethanol
 In antibiotics (Penicillin, griseofulvin)
 In certain drugs (Ergometine, cortisone)
 In Immunosuppressive drug cyclosporine
 Biopesticides
 As a Research tools in study of the fundamental biological process.
 As model system

 Candida oleophila: Prevents fungal growth on harvested fruits.
 Saccharomyces cerevisiae: Used to make bread and wine.
 Genetically engineered yeast strains are used to make proteins (Hepatitis B vaccine).
 Taxomyces: Produces anticancer drug taxol.
 Trichoderma: Produces cellulase. Used to make fruit juice.

 Widely distributed.
 Primarily terrestrial organisms few freshwater
or marine.
 Some pathogenic.
 Beneficial relationship.

 Multicellular, filamentous fungi.
 Identify by physical appearance, colony
characteristics, and reproductive spores.
 THALLUS: varies in complexity & size ranging
from the single cell yeast, multicellular molds to
macroscopic puff balls & mushrooms.
(rudimentary plant).
 Pseudomycetes: Schizomycetes,
Myxomycetes (Slime molds).
 Eumycetes: Phycomycetes, Ascomycetes,
Basidiomycetes & Fungi imperfecti.

 Associated with nutrition and reproduction.
 Hyphae- has thin rigid cell wall
Hyphae are composed of an outercell wall and inner
lumen, which contains the cytosol and organells. A
plasma membrane surrounds the cytoplasm and lies next
to the cell walls.

Hyphae (Sing: Hypha): Long filaments of cells joined together
by Apical extention.

 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. Apical extention.
 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.
 Vegetative Mycelium
 Aerial Mycelium

 Unicellular, spherical or ellipsoidal cells, unconnected.
 Eucaryotic, lack mycelia, Blastospores/blastoconidia
 Reproduce by mitosis.
Reproduce by mitosis:
 Fission yeasts: Divide evenly to produce two new cells
(Schizosaccharomyces).
 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.
 When oxygen is not available, they ferment carbohydrates to produce ethanol and
carbon dioxide.

YEAST LIKE FUNGI: Thick walled spore like structure -
Chlamydospores/chlamydoconidia.

 Can exist as both multicellular fungi (molds) and
yeasts.
 Many pathogenic species.
 Mold form produces aerial and vegetative hyphae.
 Yeast form reproduces by budding.

 Dimorphism in pathogenic fungi typically depends on
temperature:
 At 37oC: Yeast form.
 At 25oC: Mold form.

 Histoplasma capsulatum, sportrichum, blastomyces &
coccidiodesimnitis.
 Dimorphism in nonpathogenic fungi may depend on
other factors: Carbon dioxide concentration.

NUTRITIONAL ADAPTATIONS OF FUNGI
Absorptive mode.
Fungi absorb their food, rather than ingesting it.
 Fungi grow better at a pH of 5, which is too acidic for most bacteria.
 Almost all molds are aerobic. Most yeasts are facultative anaerobes.
 Fungi are more resistant to high osmotic pressure than bacteria.
 Fungi can grow on substances with very low moisture.
 Fungi require less nitrogen than bacteria to grow.
 Fungi can break down complex carbohydrates (wood, paper), that
most bacteria cannot.
 EXTRACELLULAR DIGESTION
 Primary storage - Glycogen
 Saprophytes, Parasites & Symbiotic.

 ASEXUAL REPRODUCTION
 BUDDING : Somatic vegetative cell may bud to produce new
organisms.
 SPORES : Asexually or after sexual reproduction, in individual
fungus through mitosis & subsequent cell division.
 Types of spores:
 Arthroconidia/Arthrospores
 Chlamydospores: Thick-walled spore formed within a hyphal
segment.
 Sporangiospores: Asexual spore formed within a sac
(sporangium).
 Conidiospores : Unicellular or multicellular spore that is not
enclosed in a sac.
 Blastospores.

Sexual spores: Formed by the fusion of nuclei from two
opposite mating strains of the same species. New
organisms are different from both parents.

Two basic types of reproductive propagules are found in the
fungi:

(a) Sexual propagules are produced by the fusion of two nuclei that
then generally undergo meiosis.
Sexual methods of reproduction involve plasmogamy (cytoplasmic
fusion of two cells), karyogamy fusion of two nuclei), genetic
recombination and meiosis. The resulting haploid spore is said to
be asexual spore, e.g. zygospores, ascospores and
basidiospores. If a sexual spore is produced only by fusion of a
nucleus of one mating type with a nucleus of another mating type
(+ and - strains), the fungus is said to be heterothallic. In contrast,
homothallic moulds produce sexual spores following the fusion of
two nuclei from the same strain.

(b) Asexual propagules are termed either spores or conidia depending
on their mode of production, and which arise following mitosis of a
parent nucleus. Conidia arise either by budding off conidiogenous
hyphae or by differentiation of preformed hyphae. Asexual spores
are commonly formed by consecutive cleavages of a sporangium.
Asexual forms of reproduction represent the major method for the
maintenance and dissemination of many fungi.

 SEXUAL REPRODUCTION:
 Union of compatible nuclei
 Homothallic
 Heterothallic
 Gamatangia or hyphae.
 Dikaryotic stage
 Eg; zygomycetes the zygote develop into zygospore
 Ascomycetes - ascospore
 Basidiomycetes - basidiospore

 Zygomycota (Bread Mold) The conjugation
fungi
 Ascomycota - The sac fungi.
 Basidiomycetes – The club fungi.
 Deuteromycota

 The bread mold/The conjugation fungi/pin moulds.
 Zygomycetes eg: Rhizopus stolonifier.
 Aseptate hyphae – haploid and thick walled resting spore.
Generally not pathogens.
Rhizopus nigricans: Common black bread mold. May cause opportunistic infections in
diabetes patients.
Rhizopus – produce food – tempeh from soybean
Mucor spp – in making cheese – sufu.
Anesthetics, birth control agent , etc.

 Asexual Reproduction: Used most of the time.
Sporangiospore: Asexual spore enclosed within a
sporangium or sac at the end on an aerial hypha.
- columella, hyphae, stolon, rhizoids.

 Sexual Reproduction: Occurs through conjugation, the
joining of hypha of two different strains (plus and minus).
 Includes projection Progametangia, multi nucleated gamatangia.
Zygospores: Sexual spores which are enclosed in a thick,
resistant wall.

Medically important orders and genera include:

1. Entomophthorales subcutaneous zygomycosis
(Entomophthoromycosis) - Conidiobolus and
Basidiobolus.

2. Mucorales - subcutaneous and systemic
zygomycosis (Mucormycosis) - Rhizopus, Mucor,
Rhizomucor, Absidia, Cunninghamella, Mortierella,
Saksenaea and Apophysomyces.

 Sac fungi., / Common Moulds.
 Ascomycetes
 Yeast, blue and green moulds of blue cheese and citrus fruits, cup fungi & edible morels.
 Saprophytes or parasites. (hypomycetes)
 Septate, porous, haploid hyphae.

 Asexual Reproduction: Conidiospores not enclosed in a sac. Become
airborne easily. Form chains (broom-like structures). By Conidia.
 Sexual Reproduction: Ascospores enclosed in a sac-like structure
(ascus). Requires Antheridium and Ascogonium – bulbous sexual
bodies containing many nuclei (Haploid). Sexual reproduction is by the
formation of endogenous ascospores, typically eight, in an ascus. Asci are
often housed in a fruiting body or ascocarp e.g. cleistothecia or perithecia.
Process include – dikaryogamy , plasmogamy, Synkaryogamy.

Include common antibiotic producing fungi and yeasts, and several human pathogens.
Penicillium notatum (Produces penicillin)
Saccharomyces (Brewer’s yeast)
Trychophyton (Athlete’s foot)
Aspergillus (Carcinogenic aflatoxin in peanuts),
Blastomyces (Respiratory infections)
Histoplasma capsulatum (Respiratory and systemic infections)
Ergotis – toxic condition in human and animals – accompanied by gangrene, psychotic
delusions, nervous spasm, absorption and convulsions.

No classes are now recognized; although in the past they have often been
grouped on how the asci were arranged (Hemiascomycetes, Plectomycetes,
Pyrenomycetes, Discomycetes, Laboulbeniomycetes and Loculoascomycetes).

Medically important genera include the teleomorphs of known pathogenic
fungi
e.g. Arthroderma,Nannizzia, Ajellomyces, Pseudallescheria, Eurotium etc.,
agents of mycetoma, like Leptosphaeria and Neotestudina, and of black piedra,
like Piedraia hortae.

Severe nail infection with Trichophyton Disseminated Histoplasma
rubrum in a 37-year-old male AIDS patient. capsulatum, skin infection.
Source: Intern. J. Dermatol. 31(1992): 453. Source: Microbiology Perspectives,
1999.

YEAST – THE ONE CELLED ASCOMYCETES:
Yeast – unicellular
Forms ascus
Oval/spherical, cellwall,Vacuole in the cytoplasm &
nucleus.
Asexually Reproduction: Budding
Sexual Reproduction: 2 nuclear division resulting in 4
nuclei. – Ascospores.

 The club fungi
Have septate hyphae.
 Include mushrooms, toadstools, rusts, and smuts. Four classes
may be distinguished: Hymenomycetes (mushrooms),
Gasteromycetes (puff balls), Urediniomycetes (rusts) and
Ustilaginomycetes (smuts).

Sexual Reproduction: Produce basidiospores: Spores formed
externally on a club shaped sexual structure or base called
basidium.
Asexual Reproduction: Through hyphae.

Genera of medical importance include:
1. Teleomorphs of known pathogenic fungi, e.g. Filobasidiella.
2. Coprinus and Schizophyllium agents of basidiomycosis.
3. Mushroom poisoning by Aminita, Lepiota, Coprinus and Psilocybe etc.
 Cryptococcus: Causes opportunistic respiratory and CNS infections in
AIDS patients.
 Amanita: Mushroom produces lethal toxins to humans.
 Claviceps purpurea: Produces ergot toxin in wheat and rye.

Deuteromycetes ( secondary fungi)
 Not known to produce sexual spores.
 Reproduce asexually.
 Catch-all category for unclassified fungi:
 Pneumocystis carinii: Causes pneumonia in AIDS
patients. Leading cause of death in AIDS patients.
Originally classified as a protozoan.
 Candida albicans: Causes yeast infections of vagina
in women. Opportunistic infections of mucous
membranes in AIDS patients.

Source: Atlas of Clinical Oral Pathology, 1999

 1 Chytridiomycetes (chytrids)
 Terrestrial & aquatic fungi.
 Asexually – motile zoospores with single,
posterior, whiplash flagella.
 Single cell, multinucleate mass/true mycelium.
 Sexually – zygote formation.
 Eg: Allomyces.

 DIVISION MYXOMYCOTA (Acellular Slime
Molds)
 DIVISION ACRASIOMYCOTA (Cellular Slime
Molds)
 DIVISION OOMYCOTA (Water Molds)

Mycology

More Related Content

What's hot

Viewers also liked

Similar to Mycology

More from Dr. Majid Mohiuddin (Hashmi)

Recently uploaded

Mycology