Fungi

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9/27/2010

KINGDOM FUNGI
By Anna liza E. Casil, M.D.

Introduction to Fungi


A large and diverse group ranging from a single-celled yeast or filamentous mold to a fleshy mushroom Include some of the most important organisms, in terms of ecological and economic roles Their ability to breakdown dead organic material allow continuation of the cycle of nutrients through ecosystem





Introduction to Fungi


Symbiotic fungi, which inhabit plant roots, supply essential nutrients to most vascular plants

 Mycology

◦ The branch of microbiology that studies fungi

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General Characteristics of Fungi


Heterotrophic
◦ Use organic compounds as carbon source



Nonphototrophic
◦ Do not use light as energy source



Absorptive
◦ Take up nutrients in solution



Saprophytic
◦ Obtain nutrients by decomposing deal organic matter

Morphology of Fungi


Yeasts
◦ Single-celled form of fungus ◦ Do not have chlorophyll ◦ Able to reproduce by budding  Sometimes, the bud remains with the mother cell and produces a pseudohypha

◦ Form round, pasty or mucoid colonies with a pleasant odor, when on solid media

Morphology of Fungi


Molds
◦ Highly branched and loosely intertwined hyphae that form a mycelium ◦ Mycelia form woolly growth on damp and decaying material in nature and fuzzy spreading colonies on solid culture media

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Morphology of Fungi


Mycelium
◦ A mass of hyphae ◦ coenocytic--undivided ◦ septa--incomplete divisions



Thallus
◦ body of the fungus ◦ Consists of long interconnected filaments



Hyphae
◦ individual filaments

FUNGAL HYPHAE Coenocytic (undivided) hypha

THALLUS

Septate hypha

septum

Morphology of Fungi


Dimorphism
◦ Fungi are able to grow either as a mold or as a yeast ◦ In pathogenic fungi, it is temperature-dependent  Yeastlike at 37°C  Moldlike at 25°C

Mucor sp.

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Morphology of Fungi


Fleshy fungi
◦ Form the fruiting structures ◦ Consist of tightly intertwines hyphae ◦ Ex: mushrooms, truffles or shelf fungi

Reproduction of Fungi


Asexual
◦ elongation and fragmentation ◦ budding ◦ asexual spores  Formed by the hyphae of one organism  Genetically identical to the parent



Sexual
◦ spores
 Result from the fusion of nuclei from two opposite mating strains of the same species of fungus

Types of Asexual Spores


Conidia
◦ Uni- or multicellular spores that are not enclosed in a sac ◦ Ex. Aspergillus



Arthrospores
◦ Formed by the fragmentation of a septate hypha into single, slighlty thickened cells ◦ Ex. Coccidioides immitis



Blastoconidia
◦ Consists of buds coming off the parent cell ◦ Ex. Candida albicans and Cryptococcus

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Types of Asexual Spores


Chlamydospores
◦ Thick-walled spores formed by rounding and enlargement within a hyphal segment ◦ Ex.Yeast form of C. albicans



Sporangiospores
◦ Formed within a sac (sporangium) ◦ Each sporangium can contain hundred of sporangiospores ◦ Ex. Rhizopus

Sexual reproduction
Sexual spores results from sexual reproduction, consisting of three phases: 

Plasmogamy

Haploid donor cell nucleus (+) penetrates cytoplasm of recipient cell (–) + and – nuclei fuse Diploid nucleus produces haploid nuclei (sexual spores)



Karyogamy Meiosis



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Sexual Spores


Zygospore
◦ Fusion of haploid cells produces one zygospore



Ascospore
◦ Formed in a sac (ascus)



Basidiospore
◦ Formed externally on a pedestal (basidium)

Divisions of Fungi


The Lower Fungi
◦ All are coenocytic and lack septa ◦ Chytridiomycetes and Zygomycetes



The Higher Fungi
◦ All are septated, terrestrial, and have nonmotile conidia and gametes ◦ Ascomycetes, Basidiomycetes and Deuteromycetes

Basis for Classification
 

Sexual reproduction Shape and internal structure of the sporangia ◦ The structure which...
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