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Molds, mildews, & mushroomsAn introduction to fungi
Fungi• Large monophyletic Kingdom –
– Ca. 98,000 species described– Estimated to be 1.5 million species
• Significant group of organisms – both basic and applied biology
• Fungi play variety of roles – can be either destructive or beneficial
A number are plant pathogens• Fungi are major pathogens of
plants – cause great deal of damage to crops (losses of 20-50% of yield)
• Example: Wheat rust– Major losses in yields of wheat– Romans had a god of rust - Robigus– In Southeastern US
• Wheat rust severe, can’t grow wheat
• Corn replaced wheat – cornbread, bourbon
Coffee rust epidemic in Ceylon
Irish potato famine
• Potato imported to Europe in 1500’s, became a staple
• Several years of favorable weather lead to epidemic of late blight of potatoes
• Caused the Irish potato famine – mid 1800’s
Late blight of potato• Caused by
Phytophthora infestans
• No longer considered a true fungus
Fungal diseases of animals & humans
• Generally less widespread than diseases caused by bacteria and viruses (exception – athletes foot), but can be severe
• Certain diseases endemic to geographic areas – e.g. valley fever caused by Coccidioides sp. in the desert SW
• Incidence of human mycoses is on the increase with use of immunosuppresant drugs and AIDS
Fungi as symbionts• Mycorrhizal
association is very common among plants
• Lichens
Fungi as decomposers
• Important agents in the flow of energy and cycling of nutrients in biosphere
• Decomposition particularly of plant litter
• Food for higher trophic levels
Fungi as agents of deterioration
• Cause deterioration of organics –food, wood, clothing, leather
• Variety of antifungal products developed
Food and food supplements
• Yeast – bread and alcohol• Mushrooms• Fermentation of plant
products (soybeans) – soya sauce, tempeh, miso tofu,etc.
• Biotechnology – enzymes, antibiotics, statins, organic acid production
Mycotoxins• Produced by microfungal species on
different stored food products• Aflatoxin produced by Aspergillus flavus
Allergens
• Spores present in outdoor & indoor air
• Sick building syndrome• Stachybotrys
Myths & Religions
• Hallucigenic mushrooms
Used as model systems in biology
• Neurospora crassa – 1 gene – 1 enzyme
• Saccharomyces• Aspergillus
Major characteristics of fungi
• Eukaryotic• Heterotrophic• Osmotrophs• Modular organisms – indeterminate growth• Multinucleate• Generally surrounded by cell wall• Generally nonmotile (some produce motile cells)• Most form spores as reproductive units
Fungal biology
• Fungal body = thallus
• Vegetative (somatic) phase – absorbs and assimilates nutrients, grows
• Reproductive phase - all or part of thallus may differentiate to form reproductive structures – spores
• Asexual (mitosis) or sexual reproduction (meiosis, fertilization)
Vegetative thallus
• Variable – but most fungi form a branching network of multinucleate filaments
• Filament = hypha (pl. hyphae)
• Exceptions – yeasts, some lower fungi
Mycelium = filamentous fungal thallus
• All hyphae in a thallus form the mycelium
Largest mycelia • Armillaria gallica – fungus humongous
• 30 acres, 10 tons, 1500 years old – now larger Armillaria species have been found
Hyphae• Walled tubes that contain cytoplasm• Eukaryotic – nuclei, mitochondria, ER, etc• Grow at tip• Form lateral branches that grow at tip
Basic types of hyphae
• Aseptate hyphae – lack crosswalls, found in lower fungi
• Septate hyphae – crosswalls divide hyphae into compartments, are incomplete, found in higher fungi
For filamentous fungi• What is a cell?
– Not typical with one nucleus controlling a defined volume of cytoplasm, many nuclei occur together
– Have age transitions – tip is young with senescent cytoplasm away from the tip
• What is an individual?
Hyphae from two individuals may fuse • two or more one
Hyphal pieces may be separated from thallus • one two or more
Basic structure of hyphae
• Size – 2 μm to 1 mm in diameter, – 5-10 μm most common
• Surrounded by cell wall – gives hypha shape and prevents it from bursting from osmotic pressure– Cell walls composed primarily of polysaccharides
with less than 10% proteins and lipids– Microfibrillar polysaccharides embedded in an
amorphous matrix
Cell walls• Microfibrillar polysaccharides – in most fungi is
chitin – polymer of N-acetyl glucosamine ( 1,4) • Chitin accounts for 5-60% of cell wall• Amorphous matrix contains a variety of
polysaccharides – glucans, mannans
Fine structure of hyphae• Apical region of hyphal tip – typically 150-
500 μm long.• Dense cytoplasm, rich in organelles, few
vacuoles• Extreme tip (1-5 μm) contains many small
vesicles (the apical vesicle cluster, AVC) – with light microscope = spitzenkörper (in sepatate hyphae only); no other organelles
• Behind the apical region, vacuoles increase in number and size, lipid granules accumulate
Fungal hypha
Hyphal tip
Nuclei• Small (1-2 μm)• Nuclear envelope does not break down during
division, chromosomes not distinct• In apical region there are 1-50 nuclei• Fungal DNA less complex than other
eukaryotes - fewer repeated DNA segments compared to other eukaryotes (less than 10% compared to 35% in mammals)
Nuclei
Organelles
• Mitochondria – elongate with platelike cristae
• Endoplasmic reticulum – narrow membrane bound channels
• Golgi – ringed cisternae not flattened stacks
Hyphal growth
• Growth occurs at the tip
• Grow in pulse of radiolabelled wall precusor
• Vesicles also concentrated at tip – few other organelles in tip
Hyphal growth• Not the same as cellular growth • Filamentous fungi do not undergo cell division
after cell has doubled in size• Duplication cycle (analogous to cell cycle)• Apical compartment grows to a particular length,
nuclear division followed by formation of 1 to several septa
Hyphal branching
Hyphal branching
Carbon nutrition of fungi• All fungi are heterotrophic – obtain C from
organic sources
• In this regard, they are like animals, but
• Absorb nutrients from environment, do not ingest food
Three modes of heterotrophy• Saprotrophs (saprophytes)– obtain C from
non-living organic matter
• Biotrophs – obtain C from living organic matter– Parasites– Symbionts
• Necrotrophs – kill organisms and use C of dead bodies – Parasites
• Facultative or obligate
Fungi and Plants
• Originally fungi were classified with plants – nonmotile, have cell wall
• Are also similar to plants in that they are modular organisms not unitary like animals
• Modules in plants – buds and branch; in fungi – hyphal tips
• Comparison of characteristics of modular with unitary organisms
Unitary vs modular organismsCharacteristic Unitary Modular
Growth pattern determinate Indeterminate, iterative
Size Adults vary little Varies greatly
Mobility mobile immobile
Acquisition of resources
Use mobility Grow to resources
Reproductive capability
Increases with age, decreases
Can increase indefinitely
Unitary vs modular organisms
Clonal reproduction
Unusual Common
Internal age structure
Absent Present
Longevity Definite life span
Indefinite life span
Local damage Serious Unimportant
Vegetative phase Reproductive phase
• After period of growth, differentiation may occur
• Reproduction can be sexual or asexual
• Functions of reproduction
– Recombination of genetic information
– Propagation and dispersal of fungus
– Dormancy – dispersal through time
Asexual reproduction• Fragmentation of thallus
• Production of asexual spores (two main types)
– Sporangiospores – develop within a sporangium
• Lower fungi
– Conidium (pl. conidia) – formed externally at the tips of specialized hyphae
• Higher fungi
Sporangiospores
Conidia
Sexual reproduction
• Three events occur in sexual life cycle– Plasmogamy – union of two cytoplasms– Karyogamy – union of two nuclei– Meiosis – reduction division
• (In most organisms plasmogamy and karyogamy occur close together – called syngamy or fertilization
Sexual life cycle
• The three events lead to three phases based on nuclear condition
– Haploid (1n) – one set of chromosomes per nucleus
– Diploid (2n) – two sets of chromosomes per nucleus
– Dikaryotic (n+n) – two sets of chromosomes in separate nuclei
• Vegetative phase may be any of the above
Sexual life cycle
Sexual reproduction
• Spores are typically produced
• May be produced after plasmogamy & karyogamy – diploid (zygospores)
• May be produced after meiosis – haploid (meiospores)
Reproductive phases• Fungi may carry out sexual reproduction,
asexual reproduction or both types
• The sexual reproductive phase is the teleomorph (perfect phase)
• The teleomorph is used in phylogenetic classification system
• No problem for those species that reproduce sexually or both sexually and asexually – can identify and classify based on teleomorph
Reproductive phases• Asexual reproductive phase = anamorph
(imperfect phase)• For those fungi that only produce
anamorph, there is a problem – can’t classify in the phylogenetic classification system for fungi
• Sometimes difficult to connect anamorph and teleomorph - holomorph
• Separate artificial classification scheme set up for anamorphs
Phylogeny of fungi
• Traditionally fungi were classified with plants
• Theories that fungi evolved from algae
• Today, considered that fungi did not evolve from algae and are not very closely related to plants – more closely related to animals
Evidence for phylogeny of fungi
• A number of lines of evidence that fungi are not closely related to plants
• Most compelling evidence comes from recent work comparing base sequences of rDNA and other genes among organisms
Kindom Fungi• “lower fungi”
– Zoosporic fungi –• Chytridiomycota -706 spp,
Blastocladiomycota –179 spp, Neocallimastigomycota -20 spp
– “Zygomycota” – four subphyla– Glomeromycota – 169 spp.
• “higher fungi”– Ascomycota – 64,163
spp.– Basidiomycota – 31,515
spp.
Fungal phyla – lower fungi
• Zoosporic fungi• Chytridiomycota • Blastocladiomycota• Neocallimastigomycota
• “Zygomycota”
Fungal phyla – higher fungi
• Ascomycota • Basidiomycota
Classification
• Endings for major taxa of fungi
– -mycota = phylum (division)
– -mycotina = subphylum
– -mycetes = class
– -ales = order
– -aceae = family