Post on 16-Mar-2018
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BioV 400Mycology
Handout 1
Paper Analysis/project• Some suggested topics…
– Spore dispersa l in f ungi: mode s and mechanisms– Pathogenicity mec hanisms in fung i
– Mycoreme diation: organisms and strateg ies– Modes of actions of anti-f unga l age nts– Ins ights int o the evolutionary pos ition of f ung i– Funga l species as mode l organisms
– Fung i in biotec hnology– Symbiotic a ssociation w ith fung i: getting molecular– Spore for mation during hyphal gr owth– Therape utic approac hes to fungal diseases
References• Deacon, J.W. (1997). Modern Microbiology. Third
Edition, Blackwell Science. ISBN 0-632-03077-1
• Maheshwari, R. (2005). Fungi: Experimental Methods in Biology. Mycology, volume 24, Taylor and Francis, CRC Press. ISBN 1-57444-468-9
• Ulloa, M. and Hanlin, R.T. (2001). Illustrated Dictionary of Mycology. Second Printing, APS Press. ISBN 0-89054-257-0
References• Deacon, J.W. (2006). Fungal Biology. 4th edition,
Blackwell Publishing Ltd. ISBN-13 978-1-4051-3066-0
• Dismukes, W.E., Pappas, P.G., and Sobel, J.D. (2003). Clinical Mycology. Oxford University Press, Inc. ISBN 0-19-514809-6
• Webster, J. and Weber, R.W.S. (2007). Introduction to Fungi. Third Edition, Cambridge University Press. ISBN-13 978-0-521-80739-
References• David M. (2011). 21st Century Guidebook
to Fungi. Cambridge University Press. ISBN13 978-0521186957
• Reiss, E. (2011). Fundamental Medical Mycology. John Wiley & Sons, Inc. ISBN13 978-0470177914
http://yeastwonderfulworld.wordpress.com/
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• As saprotrophs, particularly as decomposers, fungi are essential components of the carbon cycle and are among the few organisms that can break down lignin
Fairy rings
Decomposers • Fungi are important as pathogens of animals and plants – Over 70% of all plant
diseases are caused by fungi
Bioremediation• Oil spills• Cyanide in mining operations• Dioxins and pesticides• Produce organic acids, sugars • Other commercial products
What is a Fungus ?
• Eukaryotic – a true nucleus • Do not contain chlorophyll
• Have cell walls• Produce filamentous structures
• Produce spores
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Estimating the number of fungal species
• Hawksworth, D.L. (2001) The magnitude of fungal diversity: the 1.5 million species estimate revisited. Mycological Research 105 (12): 1422-1432.
• Flowering plants on British Isles described = 2,000 species
• Fungi on British Isles described = 12,000 species• Ratio of 6 fungi to each plant species• Total number of described plant species = 250,000
(most plant species are believed to be described)• 6 x 250,000=1.5 million species of fungi!• Less than 5% of which are described, and at the
current rate of description, it will take >800 years to describe all extant species
Estimating the number of fungal species
LUCA
Eucarya Archaea Bacteria
The Three-Domain System
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Extremophiles (Archea)Thermophiles Halophiles
Methanogens
Cryophiles
The sodium-potassium pump
The Kingdom Fungi• Fungi eukaryotic heterotrophs with cell walls
– Cell walls made of chitin complex carbohydrate found in insects’ exoskeletons
• Structure and Function– Multicellular (except yeasts)– Composed of hyphae thin filaments one cell thick
• Cross w alls cytoplasm and nuclei can move t hrough ope nings
• Wit hout cross walls contain many nuclei
– Secrete en zymes to digest food outside their bodies and absorb the nutrien ts
Fungi – Nutrients• Saprophytic fungi
– Live on dead organic matter = decomposers• Obligate parasites
– Only grow on living hosts (usually plants)• Facultative saprophytes
– Usually parasitic, but can live saprophytically• Facultative parasites
– Usually saprophytic, but can be parasitic when living hosts are available
Taxonomy• Medically important fungi fall in four phyla
– AscomycotaSexual reproduction is ascus ascus
– BasidiomycotaSexual reproduction in basidium basidium
– ZygomycotaSexual reproduction by gametes zygosporesZygomycota
– Mitosporic fungi (Fungi Imperfecti)No recognizable form of sexual reproduction
Hierarchical ClassificationKingdom Fungi
Phylum BasidiomycotaClass Basidiomycetes
Order AgaricalesFamily Agaricaceae
Genus AgaricusSpecies: Agaricus campestris L.
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Yeasts reproduce asexually by budding
Morphology• Pathogenic fungi exist as yeasts or as
hyphae– Yeast is a unicellular organism– Hyphae are multicellular filamentous
structures
• Some fungi occur in both yeast and mycelialforms (dimorphic fungi)– Yeast (parasitic or pathogenic form)– Mycelium (saprophytic form)
Hyphae Without Cross Walls
Nuclei
Cell wall
Nuclei
Cytoplasm
Cross wall
Cell wall
Cytoplasm
Hyphae With Cross Walls
Hyphae StructureDimorphic Fungi
• Yeast Form• Parasitic form• Tissue form
• Cultured at 37ºC• Mycelial Form
• Saprophytic form• Cultured at 25ºC
The Kingdom Fungi• Reproduction
– Sexually• Two different mating typ es + (plus) and – (minus)• + and – fuse together, grow, form a diploid zygote
nucleus produce haploid spores– Asexually
• Cells or hyphae break off from a fungus and begin to grow on thei r own
• Some produce spores in sporangia which are found at the tips of speciali zed hyphae called sporangiophores
Tips fuse
Dikaryon
2 nucleiper cell
Nucleifuse
Meiosis
Dikaryoticstage(nn)
Diploidstage(2n)
Haploidstage(n)
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Spores• Sexual
• Asexual– Arthrospore– Blastospore
– Chlamydospore– Conidia• Microconidia• Macroconidia
Chlamydospores• Nuclear ploidy same as parent cell• Formed from a vegetative cell or cells• Shape may reflect cell shape• Wall may become thickened and dark
in color• Are resistant to unfavorable
environmental conditions
Intercalary hyphal chlamydospores in Mucor plumbeus vs. Terminal
chlamydospore in Pythium undulatumThe Kingdom Fungi
• How Fungi Spread– Fungal spores
• Scatter easily in the wind• Must land in favorable environment
– Temperature– Moistu re– Food
• Some are specialized to lure animals, flies– Disperse spores over long distances
The same sequence of events is common to most fungal life cycle Mitospores
Result from mitosis and cell division
No change in nuclear ploidy
Usually produced in great quantities
Resistance to unfavorable environmental conditions varies
Are important in dispersal
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Mitosporesmotile zoosporesnon-motile produced from hyphae conidianon-motile produced from
sporangia sporangiospores
Representative asexual spores of molds-overview
Conidiospores MeiosporesResult from meiosisAre haploid
Are genetically different from parent hyphae
May serve as a resistant stage
Are important in dispersal
Spore characteristicsLow water contentLarge quantities of storage compoundsWall structure different from parent
hyphaeWall differentiation
All cellular organelles are present except a vacuole
Germination factors
Water Temperature Nutrition pH (4.5-6.5) Oxygen
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Germination process Water content increases spore swells
enzymes go into solution Vacuolation increases Endoplasmic reticulum and other organelles
increase Respiration increases and mitochondria
enlarge and form more cristae
Vesicles involved in wall synthesis appearLipids disappear as they are used up as an
energy sourceAn opening on the spore wall appears or the
plug in a germ pore is removedA hyphal tube, called the germ tube, emerges
from the opening or pore
Germination process
Growth of a hypha from a spore Dimorphic fungus• Candida albicans (yeast
and hyphal stages• The yeast form produces
hyphae and pseudohyphae• Pseudohyphae give rise to
yeast cells by apical and lateral budding
• Causes candidiasis
Dimorphic fungus C. albicans
• C. albicans grows as unicellular yeast under some environmental conditions and as a filamentous fungus under other conditions
• Growth at 37°C in YPD medium
Dimorphic fungus C. albicans
• Budding yeast with septum
• Mother cell and daughter bud
• Growth at 37°C in YPD medium
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Dimorphic fungus C. albicans
• Mother and daughter cells
• Hypha-inducing conditions• Mother cell forms a germ
tube
• A septum will later form between the mother cell and the germ tube to become hypha
Dimorphic fungus C. albicans
• 3 hours after the appearance of the germ tube
• Hypha with septa• A new germ tube
form at the distal pole of the cell
Dimorphic fungus C. albicans
• 5 hours growth under hypha-inducing conditions
• Hyphae form a mycelium
• Beginning of the formation of blastospores from hyphae
Dimorphic fungus: on 37ºC Dimorphic fungus: on 25ºC
Mycotic diseases• Hypersensitivity
Allergic reaction to molds or spores
• MycotoxicosesPoisoning by food products contaminated by
fungi
• Mushroom poisoningThe ingestion of toxin
• Infection
Hypersensitivity• FARMER’S LUNG Moldy hay
• MALT WORKER’S DISEASE Moldy barley
• CHEESE WASHER’S LUNG Moldy cheese
• WOOD TRIMMER’S DISEASE Moldy wood
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Infection caused by pathogenic fungi
• Most pathogenic fungi do not produce toxins
• But show physiologic modifications during a parasitic infection
– Increased metabolic state– Modified metabolic pathways– Modified cell wall structure
• Carbohydrate content• Lipid structure• RNA aggregates
Pathogenicity of fungi
1. Thermotolerance
2. Ability to survive in tissue environment
3. Ability to withstand host defenses
Pathogenic fungi• Normal host
– Systemic pathogens 25 species– Cutaneous pathogens 33 species– Subcutaneous pathogens 10 species
• Immunocompromised host– Opportunistic fungi 300 species
A clinician must distinguish between
• Colonization• Transient fungemia
Dissemination of fungi through the blood stream
• True infection
EYE
SKIN
UROGENITAL TRACT
ANUS
MOUTHRESPIRA TORY
TRAC T
Multiplication of an organism at a given site without harm to the host
Colonization
EYE
SKIN
UROGENITAL TRACT
ANUS
MOUTHRESPIRA TORY
TRAC T
Infection
Invasion and multiplicationof organisms in body tissue resulting inlocal cellular injury
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Revived interest in mycology
1. Increased frequency of mycotic diseases
2. Increased awareness by physicians
3. Better trained laboratory personnel
4. More invasive procedures used on patients
5. Increased use of immunosuppressive drugs
6. Increase in immunosuppressive diseases
Diagnosis• 1. Wet Mount• 2. Skin test• 3. Serology• 4. Fluorescent antibody• 5. Biopsy and histopathology• 6. Culture
Treatment Since they are eu karyoti c, fungi are biochemically similar
to the human host Thus it is difficult to develop chemotherapeuti c agents that
will destroy th e pathogenic fungus and not harm the patient
Fungal therapy Try to induce cell injury by causing the cel l me mbrane of t he
fungus to become per meable
Challenge Find an age nt that will selectively injure f unga l cells wit hout
damaging host cells
All eukaryotic cells contain sterols
•Mammalian cells cholesterol•Fungal cells ergosterol
Primary anti-fungal agents
1. Polyene derivatives– Amphotericin B– Nystatin
2. Azoles– Ketoconazole– Fluconazole– Itraconazole– Voriconazole
Amphotericin B• Mode of action Amphotericin B binds to sterols Ergosterol cell walls of fungi
Greater avidity for ergosterol Binding alters the permeability of the cell wall
and results in the leakage of the intracellular of the fungus
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AMPHOTERICIN B generates pores in the membrane Amphotericin B
• Intravenous administration• Thrombo-phlebitis
• Nephrotoxic• Fever• Chills
• Anemia• Extended administration
Acetyl-CoAAcetoacetyl-CoA
HMG-CoAMevalonic Acid
Squalene
Squalene-2,3-Epoxide
Lanosterol
ErgosterolPolyenes
Azoles
Morpholines
Allylamines
JB 5/00
Ergosterol Synthesis
3. Griseofulvin4. 5-fluorocytosine
5. Allylamines– Terbinafine (Lamisil)6. Echinocandins
– Caspofungin
Primary anti-fungal agents
Medical Mycology:The Last 50 Years
02468
101214
1950 1960 1970 1980 1990 2000
Nysta
tinAm
phot
erici
n B (1
958)
Gris
eofu
lvin
5-FC MiconazoleKetoconazole
Fluc onazoleItraconazole
L-A mBABCDABLC Terbinafine
Vorico nPosacon
XMP
Sordarins
Cas
pof u
ngin
MicafunRav ucon
Ani
dula
fung
in
# of drugsClinical Classification
•Cutaneous•Subcutaneous
•Systemic•Opportunistic
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Opportunistic fungiUbiquitous saprophytes and
occasional pathogens that invade the tissues of those who have:
• Predisposing diseases:Diabetes, cancer, leukemia, etc.
• Predisposing conditions:Agammaglobulinemia, steroid or
antibiotic therapy