Mycology class notes 2013

7/29/2019 Mycology class notes 2013

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Introduction

General characteristics of fungi

o Either autotrophic or heterotrophico Primitive plants lacking chlorophyllo Mainly Eukaryotic and multicellularo Few species of Fungi are unicellular. Best exemple: Yeasto 70,000 species identified (>1.5 million to be discovered, 1700 discovered each year)

Importance of Fungi

o Heterotrophic bacteria are the principle decomposer of the biosphere.o Necessary to the plant existence of the world.o As decomposition releases carbon dioxide into the atmosphere, nitrogenous compound goes to the soil so the

organisms can make use of it.

o 20 cm of fertile soil contains nearly 5 metric tons of Fungio 500 known species of Fungi in harmony breaking down organic material in the sea as their relative on land.o Fungi can live in any type of environment. As the decomposers, Fungi often come into dire conflict with the

human interests. Equipped with a powerful arsenal of enzymes that break down organic substances including

lignin and cellulose of wood. Fungi attack clove, paint, leather, waxes, jet fuel, petroleum compounds and also

insolation on cables and wires.

o Fungi are important medically and economically as pests, pathogens, valuable for crops and garden plants.o 150 species fungi that cause diseases to humans and animals.o All fungi infection of humans are most common in tropical regions, however an alarming increase of number of

individuals infected with fungi in all regions of the world. This increase is due in part to the growing number of

population of individuals with compromised immune system such as AIDS patients.o 40% of all deaths from hospital acquired infection (mid 1980s where found known to be bacteria nor virus but

to fungi).

o 80% of deaths are due to pneumonia caused by the organism Pneumocystis Carinio Another serious pathologic infection is Candida which causes a rash and other infections of the mucus

membrane

o Other fungi are commercially valuable: Yeast (Saccharomyces Cerevisiae) useful because they produce ethanoland carbon dioxide which plays a center role in baking, growing, and wine making.

o Other fungi provide a distinctive flavor and aroma of specific cheese which produced by certain kind ofpenicillium

o Commercial use of Fungi is growing and many antibiotics including the one frompenicillium. Mushrooms eatenregularly by humans, and some of them are cultivated commercially.

o Fungi can break down substances leading in the investigation of toxic waste cleanup program. White rot fungus(Phanerochaete chrysosporium) survive by digesting wood materials has been very effective in the degradation

of toxic organic compounds.

Symbiotic relationship of Fungi

o Atleast 80% of all vascular plants form a mutually beneficial association between their roots and the fungi.


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o Lichens: Important for irrigation of the soil. THeyre a combination of algae and fungi. Lichens many of whichoccupy extreme hostile habitats. Algal/cyanobacterial (Blue/green algae) cells

o Symbiotic relationship exists between fungi and insects. One relationship in which the fungi produce the enzymecellulase and other enzymes for the digestion of plant material are cultivated by ants known as Fungus Garden.

Ants supply the fungus with the leaf cuttings and also ant droppings? Ants eat nothing but fungus. Neither the

ant or the fungus can exist without each other.

Biology and Characteristics of Fungi

o Most fungi are composed ofhyphae.o Most fungi are heterotrophic absorbers.o Fungi have unique variations of mitosis and meiosis.o Fungi reproduce both asexually and sexuallyo Mostly terrestrial, but some are aquatic.o Some unicellular (yeast) but most are filamentouso Some structures like mushrooms are very compact hyphae. Many hyphae = filaments.o Growth of the hyphae occur at their tips but the proteins are synthesized throughout the mycelium.o Individual fungi can produce more than 1km of new hyphae within 24 hours.o The hyphae are divided by partitions or cross-wall called septum. In other species, septum grows at the base of

the reproductive structure.

o Aseptate = coenocytic (multinucleate) = non separated by septums. Most septums are perforated by a center,so that the protoplaste of an adjacent cell are continuous from cell to cell.

o All fungi have cell walls. The cell wall of plants are built from cellulose microfibrils, but in fungi the cell wall iscomposed primarily of another type of polysaccharide known as chitin, is more resistant than cellulose from

biodegradation. The same material of hard shells like the exoskeleton of arthropods.

o Protoplaste vs cytoplasme = protoplasm without organelleso The surface to volume ratio of fungi is very high so they are in intimate contact with the environment such as

bacteria.

Sporangium (ball), Sporagiophore (neck), septum (base), sporangia (the ensemble)

Conidium (little balls), conidiophore (neck) and conidia (the ensemble)


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Septate Hyphae vs. Coenocytic Hyphae

Mycellium

Collection of hyphae

Rhizoid

Small and short filament from fungi. A specialized hyphae.

Haustorium

Hyphe enters cell to absorb nutrients for parasitic fungi.

Fungi are heterotrophic absorbers

Because of their rigid cell wall, fungi are unable to engulf small microorganisms or small particles. Typically thefungus will secrete enzymes into a food source and they absorb the small molecules that are released.

Fungi absorb food mostly at or near the growing tips of the hyphae. Fungi are heterotrophic : Saprophytes (food from dead organism) or parasites (food from living organism,

disease or relationship = mutualistic symbionts.)

Some fungi like yeast, they maintain their energy by fermentation by producing alcohol from glucose. Glycogen is the primary storage of polysaccharide and in some fungi, as it is in animals and bacteria, lipid have

an important storage function.

A specialized hyphae known as rhizoids, which anchor to substrate. The parasitic fungi often have a similarspecialized hyphae known as Haustorium which absorbs nourishment directly from cells of other organisms.

Fungi have unique variations of mitosis and meiosis

In fungi the process of mitosis and meiosis are different from those that of plants and many protistas. In most fungi, the nuclear envelope does not disintegrate (like in normal cell prophase). But it is constricted nea

the midpoint between the two daughter nuclei. In other species, it breaks down near the mid region. In most fungi, the spindle fiber forms within the nuclei envelope (instead of in the cytoplasm like in normal

cells). But in some groups of fungi such as (Basidiomycetes) it appears the spindle form within the cytoplasm

and move into the nucleus.

Except Chytrides (Aquatic fungi), all fungi lack centrioles (organelle that produces the fibers), but they form aunique structure called spindle pole bodies. Both spindle pole bodies and centrioles function at a microtubule

organizing center during mitosis/meiosis.


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Fungi reproduce both asexually and sexually

Fungi are produced through formation of spores that are produced either asexually or sexually. Except for theChytrids (aquatic fungi),none-motile spores are the characteristic means of reproduction of fungi.

Some spores are dry and very small, which explains the distance of species, other spores and slimy and stickyand are carried on the bodies of insects and arthropods which are carried place to place.

The bright colors and other features of many types of molds are due to the spores. However, there are fungithat never produce spores.

The most common method of asexual reproduction of fungi by mean of spores, which either produce sporangia(or sporangium)

Hyphae that support formation ofconidia is known as conidiophore. Sexual reproduction in fungi happen in 3 distinct phases: Plasmogamy, Karyogamy and meosis. In some species

karyogamy follows plasmogamy almost immediately while other species, the two nuclei do not fuse for some

time in heterokaryotic stage. Karyogamy may not take place for several months or years.

1. Plasmogamy: Unification of two of protoplastes and two nuclei come together.2. Heterokaryotic stage (Dikaryotic stage): two nuclei beside each other in one cell3. Karyogamy: Unification of two nuclei become a zygote.4. Zygote stage5. Meiosis: Zygote produces spores.6. Spore stage7. GerminationMycelium

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Mycology class notes 2013