Fungal Diversity

Reading: Chap. 31

I. IntroductionA. What is a fungus?

B. What does a fungus do?

C. Basic fungal life cycle

D. Who cares about fungi?

II. Fungal PhylaA. Overview

B-E. Life cycles of the phyla

III. Fungal mutualismsA. Lichens

B. Mycorrhizae

Characteristics of Fungi

Non-motile eukaryotes lacking chlorophyllContain nucleus, mitochondria, 80S ribosomesPlasma membrane contains ergosterol instead of

cholesterol.Cell wall is composed of chitin and various glucans,

mannans, and complex polysaccharidesLarger than bacteriaRelatively simple nutritional requirements, wide range of

growth ratesForm visible colonies in days to weeks

Unicellular or multicellular depending on the species

Molds

Multicellular, tubular structures (hyphae)

Hyphae can be septate (regular crosswalls) or nonseptate (coenocytic) depending on the species (grow by apical extension)Vegetative hyphae grow on or in media (absorb

nutrients); form seen in tissue, few distinguishing features

Aerial hyphae contain structures for production of spores (asexual propagules); usually only seen in culture

Fungi

The parts:

Fig. 31.1

Cell walls - made of chitin. Same material that is in the external skeletons of arthropods - insects, arachnids, and crustaceans.

Molds - identificationIdentification based on colony morphology (pigment,

texture) and morphology of reproductive structuresConidia - spores formed by budding (blastoconidia) or

disarticulation of existing hypha (arthroconidia)

Sporangiospores - produced by free-cell formation within sporangium in nonseptate molds

1. sporangium2. sporangiophore3. Endospores4. Nonseptate hyphae5. rhizoids

1

2

3

4

5

1. Conidiopspores2. Phialides3. Vesicle4. Conidiophore5. Septate hyphae

5

1

2 34

YEASTSAlso yeasts - single-celled

e.g., Saccharomyces cerevisiaeCandida albicans

31.15

YeastsUnicellular, 3-5 µm, reproduce by budding

(blastoconidia formation) or fissionIdentified by microscopic morphology (grow on

cornmeal agar) and biochemical tests (sugar assimilation, enzymatic activity).

Molds and yeast are not exclusive forms, some species may exist in both yeast and mold forms (dimorphism).

Colonial Morphology of Fungi

Cryptococcus neoformans

Candida albicans

Wangiella dermatitidis

Aspergillus fumigatus

T. menta-grophytes

Trichophyton tonsurans

FUNGAL LIFE CYCLE

Asexual - budding or cell division

Sexual - fusion of 2 mating types spore formation

FUNGAL NUTRITION & ENVIRONMENT

Organic compounds needed for growthsaprophytes as feed on dead organic matter

Adapted to: growth at pH 5 growth on surfaces growth under high osmotic conditions growth at low water levels growth in low nitrogen environments growth on unusual nutrient sources

B. What does a fungus do?Absorptive heterotroph

Such as:

Parasite/pathogen

Mutualist

Detritivore

Also eat:- wood in houses, boats, fences; - food; - other materials - cloth, paint, leather, waxes, jet fuel, petroleum, paper, wire insulation, photographic film,- to name a few.

What do all of these materials have in common?

They are all C-based.

C. Basic fungal life cycle

fig. 31.2

2. Fertilization doesn’t happen all at once

Plasmogamy - fusion of cytoplasmKaryogamy - fusion of nuclei (gametes)

heterokaryoticdikaryotic

Classification of Fungi

Taxonomy is based on structural features of the teleomorph (sexual phase). Zygomycota - includes all fungi with nonseptate hyphae

Ascomycota - includes most human pathogens

Basidiomycota - mainly saprobes or plant pathogens

Deuteromycota (fungi imperfecti)Sexual phase unknown or doesn’t exist. Some can be

assigned to above groups based on phylogenetic analysis.

B. Zygomycota 1. No dikaryotic growth

2. Both sexual and asexual sporangia

C. Ascomycota - Life cycle

1. Dikaryotic growth2. Fruiting body: ascocarp3. Fertile layer with asci4. Eight ascospores per ascus (sac)5. Asexual reproduction via conidia

D. Basidiomycota - Life cycle1. Dikaryotic growth2. Fruiting body: basidiocarp3. Fertile layer on gills with basidia (“clubs”)4. Four spores per basidium5. Asexual reproduction is rare

E. Deuteromycota - “fungi imperfecti”

1. Not a true phylum (not a natural group): polyphyletic

2. Fungi with no known sexual reproduction

3. Asexual reproduction by conidia

III. Fungal mutualisms

Definitions:Symbiosis - 2 organisms living together in

intimate physical contactMutualism - both organisms benefit from the

relationshipParasitism - one benefits, one losesCommensalism - one benefits, other not

affected

A. Lichens

1. Partnersa. Fungal partner

- gives protection- mostly Ascomycetes (~25,000 spp.)- only found in lichens (not free-living)

b. Photosynthetic partner - gives fixed carbon (sugars)- green alga or cyanobacterium- can be free-living

A. Lichens2. Anatomy

medulla

a. most of lichen body is fungal hyphaeb. photosynthetic partner in a distinct layerc. sexual reproduction of fungal partner onlyd. asexual reproduction: soredia, fragmentation

Ectomycorrhizal fungi (EMF)

Rootcells

EMF

Figure 29.9a

A. Lichens3. Morphology

fruticose

foliose crustose

A. Lichens4. Importance

a. rock weathering, soil formation in primary succession

- acid secretion

- trapping particulates

- nitrogen fixation (cyanobacteria)

b. Indicators: susceptible to pollutants