mycology virology

Mycology-Virology

What are fungi?

• They’re the mushroom that we eat and those found in athlete’s foot

• Eukaryotic, spore-bearing, heterotrophic organisms that produce extracellular enzymes and absorb their nutrition.

Characteristics of Fungi

• Eukaryotic

• Multicellular (except Yeasts)

• Non-vascular organisms (Plants and Animals are vascular)

• Reproduce by means of spores– Both sexual and asexual

• Typically non-motile (except Chytrids which has a mobile phase)

Characteristics of Fungi• Cytoplasmic ultrastructure broadly similar

to plant cells, but differ significantly in kinds of organelles and structures

• Fungi are heterotrophic not autotrophic like plants

• Unlike animals (also heterotrophic), which ingest then digest, fungi digest then ingest (exoenzymes)

Characteristics of Fungi• Most fungi store their food as glycogen

(like animals); plants store food as starch

• Most fungi have very small nuclei, with little repetitive DNA

• Mitosis is generally accomplished without dissolution of the nuclear envelope (produces different type of microtubules during nuclear division

Cell wall containing Chitin

Nutritional Status of Fungi• Saprophytes

– Use non-living organic material– Important scavengers in ecosystems– Along with bacteria, fungi are important in

recycling Carbon, Nitrogen and essential nutrients

• Parasites– Use organic material from living organisms,

harming them in some way– Range of hosts: from single celled diatoms to fungi

to plants to animals to humans


• Mutualists (symbionts)– Fungi that have mutualistically beneficial

relationship with other living organisms– Mycorrhizae: associations of fungi with plant’s

roots– Lichens: associations of fungi with algae or

cyanobacteria


• Fungal cells occurring in branching filaments are called hyphae.– Vegetative hyphae– Aerial hyphae

• A mass of filaments is called a mycelium.

• Cross walls separate the cells in the hypha of many species of fungi (septa)

Fungal Form and Function

AnatomyHyphae and mycelium

HyphaeMycelium

• Coenocytic hyphae – lack cross walls– Also known as non-septate hyphae– Rhizopus stolonifer– Differentiates fungi from other eukaryotic cells,

how?

Septae

Septate hyphaAseptate hypha,a.k.a. coenocytic

Three ploidy types

Haploid – most fungal hyphae and all spores have haploid nuclei

Diploid – diploid nuclei are found transiently during the sexual phase (if present)

Heterokaryon – unfused nuclei from different parents occupying the same unit of hypha

Yeast cells

• Unicellular fungi that do not form hyphae or mycelia

• Oval cells measuring 5 to 10 um in diameter

• Reproduce both sexually and asexually

Yeast and Fungal forms

• Some fungi can form a mycelium under certain environmental conditions and revert to a yeast form under other environmental conditions

• Known as biphasic or dimorphic

• Candida albicans

Are there anaerobic fungi?

• Facultative anaerobes

• Fermentation

• Metabolism

• Glycolysis

• Industrial products: ethyl alcohol, beer, wine, liquor (other products?)

• Saccharomyces cerevisiae

• Aspergillus niger

Reproduction

• Sexual and Asexual means

• Role of spores

• Asexual reproduction– Spores have identical genetic make-up– Does not need to involve union of sex cells– Budding?

Fungal Form and Function

Reproduction

Asexual – default mode under stable

conditions; spores are produced

Sexual – usually only under stressful

conditions; spores are produced;

many mating types possible

(essentially like having many different

sexes or genders)

Sexual Reproduction

• Begin with the production of haploid gametes (produced by parent fungal cells of opposite sexual types)

• Gamete production occurs by meiosis

• Gametes fuse to form diploid cell called zygote

• Gametes are either male (plus) or female (minus)

Sexual reproduction in fungi

zygotes (2n)

fusion of compatible hyphae(plasmogamy)

+

–

hyphae (n)

fused hyphae (n + n)

fusion of nuclei(karyogamy)

meiosis of “zygote-like” structures

dispersal of spores

zygote (2n)

sexual spores (n)

+

–+

–

Sexual reproduction in fungi

Haploid spores may disperse long distances away from the fruiting body

Key

Plasmogamy

Karyogamy

Meiosis

Black Bread Mold

Sexual reproduction

Asexualreproduction

Mating type (+)Mating type (-)

Zygosporangium

Haploid (1n)Heterokaryotic (1n + 1n)Diploid (2n)

Fungal Life Cycles

Key

Haploid (n)

Heterokaryotic

Diploid (2n)

PLASMOGAMY(fusion of cytoplasm)

Heterokaryoticstage

KARYOGAMY(fusion of nuclei)

SEXUALREPRODUCTION

Spore-producingstructures

SporesASEXUALREPRODUCTION

Zygote

Mycelium

GERMINATION GERMINATION

MEIOSIS


Spores

Fusion of compatible hyphae (plasmogamy)

Fungal Life Cycles

Key

Haploid (n)

Heterokaryotic

Diploid (2n)


Heterokaryoticstage


SEXUALREPRODUCTION



Zygote

Mycelium


MEIOSIS


Spores

Fusion of compatible hyphae (plasmogamy)

…initiates a heterokaryotic phase

Fungal Life Cycles

Key

Haploid (n)

Heterokaryotic

Diploid (2n)


Heterokaryoticstage


SEXUALREPRODUCTION



Zygote

Mycelium


MEIOSIS


Spores

Fusion of nuclei (karyogamy)

Fungal Life Cycles

Key

Haploid (n)

Heterokaryotic

Diploid (2n)


Heterokaryoticstage


SEXUALREPRODUCTION



Zygote

Mycelium


MEIOSIS


Spores


…initiates a zygotic phase

Fungal Life Cycles

Key

Haploid (n)

Heterokaryotic

Diploid (2n)


Heterokaryoticstage


SEXUALREPRODUCTION



Zygote

Mycelium


MEIOSIS


Spores


…initiates a zygotic phase

…which is perhaps best described as “zygote like”

Fungal Life Cycles

Key

Haploid (n)

Heterokaryotic

Diploid (2n)


Heterokaryoticstage


SEXUALREPRODUCTION



Zygote

Mycelium


MEIOSIS


Spores

Meiosis in “zygote-like” cells produces spores or cells that will produce spores

Fungal Life Cycles

Key

Haploid (n)

Heterokaryotic

Diploid (2n)


Heterokaryoticstage


SEXUALREPRODUCTION



Zygote

Mycelium


MEIOSIS


Spores

Both asexual & sexual reproduction produce

haploid spores

Kind of Asexual Spores• Arthrospore – spore formed by

fragmentation of the tip of the hyphae

• Blastospore – produced as an outgrowth along a septate hypha.

• Conidiospores – unprotected spores formed by mitosis at the tips of the hyphae

• Sporangiospores – spores produced within a sac called sporangium

Sexual reproduction in a chytrid:flagellated spores

spores

Other forms of Reproduction

• Budding

• Occurs in yeasts when it undergoes mitosis and forms a tiny cell at its border

• The cell produced increases in size and eventually separates from the parent cell

Budding Yeast

http://upload.wikimedia.org/wikipedia/commons/c/c3/Budding_yeast_Lifecycle.png

Body Plan• unicellular (yeast), filamentous, or both (=dimorphic)

• Hypha (pl. hyphae) is the basic “cellular” unit in filamentous fungi; they may be septate or coenocytic (aseptate); collectively a mycelium

• limited tissue differentiation and division of labor

• somatic & reproductive structures

• plectenchyma: all organized fungal tissue, somatic & reproductive

Nuclear Status• Eukaryotic; uni, bi- or multinucleate• Haploid, diploid (less frequent)• Monokaryon (1 nucleus per hyphal compartment)

• Dikaryon (2 nuclei per hyphal compartment) • Homokaryotic

• Heterokaryotic

• Mitosis– intranuclear: nuclear membrane doesn't

breakdown during mitosis– centric in flagellated forms; typical centrioles

of eukaryotes– noncentric in nonflagellated forms; possess

spindle pole bodies (SPBs); differ from centrioles in lacking microtubular component

Organelles• typical eukaryote assemblage of organelles

+ fungal specific ones• mitochondria • endoplasmic reticulum • Golgi equivalents

single cisternal elements • vacuoles • microbodies

function in fatty acid degradation, Nitrogen metabolism

Cell Wall• well defined

• chitin

1-4 n-acetyal glucosamine -glucans

polymers of glucose

1-3 glucose

• cellulose in some

1-4 glucose

chitin -glucans

Chitin

Cellulose

1-3 glucan

•fungal specific organelles involved in cell wall growth

Spitzenkorper

associated with growing hyphal tips in septate fungi

chitosome

microvesicles transporting chitin synthases to growing cell wall

Uses of Fungi

As Biotic control agents

The first antibiotic used by humans

Staphylococcus

Penicillium

Zone of inhibited growth

Uses/Functions of Fungi

Biotic control agents

Used against termites, rice weevils, etc.


Interesting example…

of agriculture in insects

Leaf-cutter ants cut and carry leaf fragments to their nests where the fragments are used to farm fungi


Interesting example… of fungal cowboys

Some soil fungisnare nematodeworms in hyphalnooses and thendigest them

unlucky nematode

fungal hypha

Functions/Uses of Fungi

Interesting example… of fungi & conservation

The golden toad became extinct within the past 20 years, owing to anthropogenicenvironmental deterioration,which also facilitated pathogenic chytrid fungi

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