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FUNGI

Chapter 12

Mycology

Study of fungi

Yeasts, Molds, Fleshy fungi

Yeasts = unicellular organisms

Molds = multi-cellular and filamentous

Over 100,000 species known

~100 = animal pathogens

Most are plant pathogens

FUNGI ARE……..

Eukaryotic, chemoheterotrophs

Require organic compounds

Aerobic or facultative anaerobes

Most are saphrophytes - decomposers

Secrete many extracellular enzymes

Absorb nutrients rather than ingest them

Can metabolize large, complex CHOs

MOST FUNGI ..…...

Are found in soil & water

Can grow in low moisture

Optimal growth in pH = 5

Resistant to high osmotic pressure

Can grow in high sugar or high salt

Require less N than bacteria

Contain ergosterols in cell membranes, glucans, mannans and chitin in cell wall

IDENTIFICATION of FUNGI

Physical appearance, vegetative & reproductive structures are used to identify

MOLDS - multicellular, filamentous

Rusts, molds, smuts, mildew

FLESHY FUNGI - multicellular, filamentous

Mushrooms, puffballs, coral fungi

Biochemical tests to identify

YEASTS - unicellular

YEASTS

Unicellular, nonfilamentous, spherical or oval

FOUND: widely distributed

Form colonies

REPRODUCE:

Asexually

Budding

Fission

BUDDING YEAST

Parent cells forms a bud(s)

Bud elongates

Parent cell’s nucleus divides by mitosis

One nuclei migrates to bud

Bud enlarges

Cell wall synthesis

Bud breaks off

Saccharomyces cerevisiae

Bakers’ yeast = Brewers’ yeast

Can use O2 or organic compound as final electron acceptor

Aerobic: produce CO2

Anaerobic: fermentation of CHOs --> ethanol

CHARACTERISTICS OF

MOLDS & FLESHY FUNGI

Multicellular, filamentous & macroscopic

BODY = THALLUS

THALLUS = entire vegetative structure / body

May be a single cell or long filaments of cells joined together

These filaments are called HYPHAE (hypha = singular)

Often are branched

HYPHAE

Hyphae are classified based on presence or absence of crosswalls separating nuclei

SEPTATE HYPHAE

Divides the hyphae into uninucleate units

Chains of distinct cells

Pores to allow movement of cytoplasm between hyphae

COENOCYTIC HYPHAE or NON-SEPTATE

If there are no crosswalls or do not have complete cross walls

Incomplete septa ∴ cytoplasmic streaming

Hyphae grow by elongating at their tips

Each fragment is capable of growing on it’s own

MYCELIUM

MYCELIUM = several hyphae grow & intertwine together that form a filamentous mass

Intertwined hyphae Macroscopic (can see with the naked eye)

VEGETATIVE MYCELLIUM: obtains nutrients

Grows on substrate

AERIAL MYCELLIUM or REPRODUCTIVE MYCELLIUM

Grow in the air, above substrate

Often bears reproductive spores

DIMORPHIC FUNGI

DIMORPHISM = “TWO SHAPES”

Exist as a yeast or a mold

Shape may be dependent upon:

Temperature: 37°C = yeast & at 25°C = mold

Environment: food availability, Oxygen etc.

Many of the pathogenic fungi are dimorphic

Candida albicans

LIFE CYCLE of MOLDS

Increase in number by mitosis

Numerous ways to reproduce

ASEXUALLY - fragmentation of hyphae

SPORULATION - sexual and/or asexual spores

Depends on the species

Spores are formed from the aerial mycelia

Fungal spores are not as resistant as bacterial spores

ASEXUAL SPORES: formed from one organism & can grow to become a new identical organism

SEXUAL SPORES: formed from the fusion of nuclei of 2 different types of strains from the same species of fungi

ASEXUAL SPORE FORMATION

Formed on aerial hyphae

Produced by mitosis & cell division

More common than sexual spores

Classified by morphology of asexual spores

Five types of asexual spores

ASEXUAL SPORE TYPES #1

Arthrospore

Formed by fragmentation of septate hyphae into single cells

Chlamydospores

Thick walled spores formed by rounding & enlargement of a hyphal segment

Candida albicans

Sporangiospores

Formed within sacs called a sporangium

Formed at the end of a sporangiophore

Rhizopus

ASEXUAL SPORE TYPES #2

Conidiospores

Unicellular or multicellular not enclosed in a sac

Produced at the end of a conidiophore

Aspergillus

Blastospores

Consists of a bud coming off a parent cell

Cryptococcus

SEXUAL SPORE FORMATION

Two haploid nuclei fuse --> diploid nucleus

Diploid nucleus = DIPLOID ZYGOTE NUCLEUS

Meiosis of diploid nucleus ---> haploid sexual spores

May be genetic recombinants

Used to identify & classify fungi

CLASSIFICATION OF FUNGI

According to type of sexual spores produced and morphogy are place in one of FOUR PHYLA

ZYGOMYCOTA

Produce zygospores

Coenocytic hyphae

Saprophytic molds

Rhizopus

ASCOMYCOTA

Produce ascospores

From 2 similar or dissimilar cells

Septate hyphae

“Sac fungi”

Penicillium notatum

BASIDIOMYCOTA

Produce basidiospores

Septate hyphae

“Club fungi”

Mushrooms

DEUTEROMYCOTA

No sexual spores identified

Septate hyphae

FUNGAL DISEASES

MYCOSES or MYCOTIC DISEASES

Usually chronic infections/diseases

Usually grow slowly

Five groups based on tissue involvement & mode of entry

Systemic

Subcutaneous

Cutaneous

Superficial

Opportunistic

MYCOSES #1

Systemic - found deep in the body

Can affect a number of tissues & organs

Caused by inhalation of spores of saprophytic fungi into the lungs

Histoplasmosis & Coccidiomycosis

Subcutaneous – found beneath the skin

Caused by direct implantation of spores or mycelia of saprophytic fungi through puncture wounds

MYCOSES #2

Cutaneous – infect epidermis, hair and nails

Caused by Dermatophytes, “ringworm”

Secrete keratinase ( degrades the keratin

Transmitted from human to human by direct contact or by contact with infected hair & contaminated fomites, only contagious mycoses.

Superficial – found on hair shafts and superficial epidermal cells

Opportunistic – usually harmless in normal, healthy people

Can be pathogenic in immunocompromised individuals

Candidiasis – Candida albicans - thrush, vulvovaginitis

Aspergillosis – Aspergillus - lung disease

PCP: Pneumocystis carinii pneumonia

OPPORTUNISTIC pneumonia of immune compromised individuals

Especially of AIDS patients

All people are exposed to the organism but do not get the disease

Discovered in 1908 - misclassified as a protozoan

1970s = HUMAN PATHOGEN

Recently rRNA ---> FUNGI?

If fungi ---> Deuteromycota until sexual spores identified

ECONOMIC USES

Food production

S. cerevisiae - bread, beer & wine

Torulopis - cellulase = enzyme that breaks down cellulose

Clears fruit juice

Medicine

TAXOL - anticancer drug produced by Taxomyces

Agricultural

Decomposers of organic material & plant debris

PROBLEMS

MYCOSES

Food spoilage

Fruit, grain, vegetables

Plant pathogens

Diseases of trees: Dutch elm, spreading chestnut

Ireland 1800s - potato blight

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