4th medical analysis mycology / dr hero - lecture notes...used in herbal medicine. the wood rotting...

4th Medical Analysis 2020 Mycology / Dr Hero

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Tishk International University

Science Faculty

Medical Analysis Department

Autumn Semester 2020-2021

Prepared by

Assistant prof. Dr. Hero M. Ismael

MYCOLOGY

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Grading:

Final grade will be based upon the following criteria:

Practical Examination: 7.5

Theory examination: 12.5

Final examination: 10

Final examination: 20

Mycology \ 50 marks

Required books:

1. Alexopouloss, C.J., Mims, C.W.and Blackwell. (1996).Introductory

mycology.

2. Vashishta, B.R., and A.K.Sinha, (2007) Botany for degree students fungi.

3. Solomon, Eldra P., LindaR.Berg, and Diana W.Martin (2008 Biology, eighth

edition.

4. John Webster and Roland Weber, Introduction to Fungi Third Edition, 2007

5. The core material of the course consists of the above book, articles from

media and internet, and lecture’s notes.

……………………………………………………………………………

Syllabus of Mycology (Theory) 2020– 2021

First week

Definition of mycology, how mycology begin in past dim, founder of

mycology, exact definition of fungi

Second week and Third week

Importance of fungi to human

Fourth week

General characteristic of fungi ,type of mycelium, type of septum and their

functions ,fine structure of fungal cell wall.

Fifth week

Tip growth of fungal hypha, fine structure of fungal cell.

Nucleus, pulse field gel electrophoreses, techniques, cell fungal organelles


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Sixth week

Some vegetable structures, stroma, haustorium, appressorium, seclerotium,

biotrops, homothallic fungi, heterothallic fungi

Seventh week

Sexual and asexual reproduction of fungi

Eighth week

First examination

Ninth week /

Fungal systematic, phylogenetic classification, pyretic group, species

concepts, number of fungi, characters, fossil fungi.

Tenth week

Kingdom of Fungi, phyla of Fungi.

General characteristic of chytridiomycota, explanation life cycle of some

genera belong to chytrids.

Eleventh week

General characteristics of zygomycota phylum, explanation of some genera

belong to this phylum

Twelfth week

General characteristic of Ascomycota phylum, some species of

Ascomycetes.

Thirteenth week

General characteristic of basidiomycota phylum, explanation of some

important genera.

Fourteenth week

Second examination

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Mycology

Mycology is the study of fungi (sing. fungus), the word is derived from two

Geek words, mykes, mushroom +logos, discourse or study. A person who

studies fungi is a mycologist.

What are fungi?

Biologists have defined fungi as: eukaryotic, spore – producing,

achlorophyllous organisms with absorptive nutrition that generally

reproduce both sexually and a sexually and whose usually filamentous,

branched somatic structure, known as hyphae, typically is surrounded by cell

walls.

How mycology began in the dim past?

For mushrooms are among the largest fungi and attracted the attention of

naturalists before microscopic or even simple lenses had been thought, with

the invention of the microscopic by Van Leeuwenhoek in the seventeenth

century, the systematic study of fungi began, and the man who deserves the

honor of being called the founder of the science of mycology is Pier Antonio

Micheli, the Italian botanist who, in 1729, published nova plantarum genera,

in which his researches on fungi were included.

Importance of fungi to human:

1. Recycling:

Fungi together with bacteria are responsible for most of the recycling which

returns dead material to the soil by decompose cellulose and lignin, the

primary components of wood, are released back in to ecosystem.

2. Destruction:

Fungi are directly responsible for the destruction of a wide variety of wood

products, including lumber, fabrics, leather goods, and various petroleum

products. dry rot diseases caused by Serpula lacirimans.

3. Mycotoxins:

Certain species of fungi also produce mycotoxins

a. Ochratoxins:

Produced on cereal grains by Aspergillus ochraceus and penicillium

viridicatum.

4th Medical Analysis 2020 Mycology / Dr. Hero


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b. Aflatoxins:

Produced by A. flavus and A. parasiticus on various nuts and grains,

cause liver cancer in humans.

c. Fumonisins

Produced on corn by Fusarium moniliforme.

d. Ergot Alkaloid

Ergotamine, lysergic acid and ergot alkaloid Cause ergotism when

consumed by human or animal, cause burning pain, convulsions,

hallucination, and spontaneous amputation of extremes.

e. Tricothecenes

These are very toxic chemicals produced by Fusarium sp., The most

common symptoms are headache, vertigo, fatigue, tachycardia, salivation

and fever.

4. Food spoilage:

Fungi can cause food spoilage, fungal damage can be responsible for large

losses of stored food, particularly food which contains any moisture?

(Why?). To protect our foods from fungi and bacteria we have using

different methods, including salting, drying, freezing, heating, canning,

irradiation, and the use of chemical additive.

5. Medicines:

a. Penicillin and Cephalosporins

Penicillium chrysogenum, (P. notatum) discovered by the British

microbiologist Alexander Fleming in 1928, Cephalosporins Produced by

Cephalosporium acremonium, like the penicillin, kill bacteria by inhibiting

the enzymes involved in wall biosynthesis.

b. Cyclosporine

This compound an extremely effective immunosuppressant agent. Due

largely to the organ transplants are considered today as almost routine

procedures, is compound was discovered in the early 1970s in

Cylindrocarpon lucidum and Tolypocladium inflatum two fungi that

were isolated from soil samples.

c. Fumagillin

a chemical produced by the ascomycete Aspergillus fumigatus, inhibits the

formation of new blood vessels, because solid tumors need a rich blood

supply, fumagillin shows promise as an anticancer agent.

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6. Historically:

A number of fungi, including fruiting bodies of bracket fungi, have been

used in herbal medicine. The wood rotting fungus Ganoderma lucidum is

cultivated even today for its reputed medical benefits. In North America,

mycelia mats of Fomitopsis officinalis from decayed wood were used to

stop bleeding from ax wounds.

7. Fungi as food:

Various types of mushrooms can be grown on inexpensive substrate

commonly regarded as waste material, that is, manure, tobacco stems, rice

and wheat straw, and sawdust.

All edible mushroom fungi make good food, because they,

a. Have a good content of protein (20 – 30 % of dry matter) that contains all

essential amino acids.

b. Contain B –vitamins

c. Are low in fat

d. Are free of cholesterol.

e. In addition to tasting good.

f. Various mushrooms also have been reported to have medicinal properties

ranging from anti tumor to hypercholesterolemia effects.

Morels and truffles, two forms that are highly prized for their tastes. Some

of the wildest poisonous mushroom (toadstool) belongs to the genera

Amanita and Helvella.

8. Industrial fungi:

Species of Penicillium are responsible for the highly prized flavors of

cheeses such as Danish blue, Roquefort, and Camembert.

Rhizopus, Mucor, and Actinomucor are example of fungi that are used to

increase the digestibility of vegetable materials such as rice, wheat, and

soybean and to impart meatlike flavors to the end products.

Fungi also have been used commercially to produce a variety of chemical

compound, including ergosterol, cortisone, various enzymes such as

catalase, lactase and lipase, acids such as lactic citric, and oxalic .and plant

growth regulators known as gibberellins. Baking and brewing industries:

Sacchromyces cerevisiae.


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9. Plant diseases:

Most species of plants are subject to attack by a number of different types of

fungal pathogens. Example of plant diseases such as rust, smut, powdery

mildew, downy mildew, spot root and seed rot… (etc.).

How protect our important plants from attack by fungi?

Including agricultural practices such as crop rotation, genetic engineering

for the production of plants that are genetically resistant to certain fungal

pathogens, the use of quarantines that prevent the spread of pathogen

chemical control by using fungicide

10. Fungi caused diseases to human and animals:

Fungal infection or as they called mycoses (sing. Mycosis), according to

type of infection, we can classify them as following:

A-Superficial Dandruff caused by Malassezia sp.

B- (cutaneous) or dermatophytic infection:

Ringworm, infection of hair, nails, and skin caused by Trichophyton sp.

C- Subcutaneous mycoses or intermediate infection:

The infection will occur below the skin, (e.g. Candida albicans.)

D- Systematic infection Disease that occur deep within the tissue and

organs, which may be fatal (e.g. Histoplasma sp.).

E- Opportunistic infection (Aspergillus sp.)

Q1/ Fungi caused ringworm can be ecologically divided in to three

groups. Explain.

Q2/ The successful treatment of fungal diseases is more difficult than

those by caused by bacteria. Give reasons?

11. Mycorrhiza:

The hyphae of some fungi form specialized organs with the roots of plants,

known as mycorrhizae. (Symbiotic associations) The fungi hyphae act as

additional roots and greatly increase the the absorption of water and uptake

of phosphorus and other mineral. The root plant supply fungus with sugars,

amino acids, and other organic substances, such as Glomus.

12. Fungi as experimental and genetic tools:

Different fungi have become popular experimental organisms for studies of

fundamental biological processes.

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Why certain species of fungi are especially valuable as genetic tools?

Because they grow rapidly, have short generation times and small

genomes for eukaryotes. One of the most famous fungi used in genetic

studies is, of course, the red bread mold Neurospora.

13. Biological control:

The parasitic interactions of fungi with insects and other arthropods are

important for their biological control potential as well as their general

biological information. Host specificity is important in biological control

because of the large number of beneficial insects need protection from

harm. In fact, this is one of the distinct advantages of specific biological,

rather, than chemical, control such as Beauveria sp. and Metarhizium sp.

14. Fungi form symbiotic relationships with some animals:

Cattle and other grazing animals do not have the enzymes necessary to

digest cellulose and lignin. Their survival depended on fungi that inhabit

their guts, that secretes enzymes that break down these organic compounds.

15. Endophytes:

Diversity of fungi known as endophytes, also has been shown to present in

the leaves and stems of healthy plants rang from conifers to grasses, many of

these fungi appear to protect their hosts from pathogenic fungi as well as

from insects grazing mammals


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Characteristics of fungi

The fungus or thallus (thalli) typically consists of microscopic, tubular,

thread like hyphae (sing hypha) that branch in all direction, spreading over

or within whatever substrate the fungus uses for food. collectively, these

structures make up the body of the fungus, which is termed mycelium,

whoever not all fungi produce mycelia composed of hyphae. Many forms,

commonly referred to as yeasts, exist as single cells that are capable of

reproducing quickly by budding or fission.

Dimorphic fungi:

Some species of fungi can exist as either hyphae outside their hosts, but

assume yeast like appearance inside the host, for example, common in form

that causes diseases of humans and other animals.

Increased temperature, reduced oxygen, and suboptimal nutrients are the

most important factors that caused to converted mycelium of dimorphic

fungi to yeast form, and vice –versa

Types of mycelia:

A. Aseptate mycelium:

A Fungal hypha is composed of a thin, usually transparent, tubular wall filled

or lined with layer of protoplasm varying in thickness, when examined with

the aid of the light microscope the aseptate, multinucleate mycelium is called

coenocytic, the septa in the aseptate, are formed only to:

a- cut off reproductive structures

b- to seal off a damage portion

c- At old hyphae

This type of mycelium present in lower fungi (include two phyla

Chytridiomcota and Zygomycota).

B. Septate mycelium:

The hypha of higher fungi that belong to (phyla Ascomycota and

Basidiomycota) develop internal cross walls called septa which divide the

hyphae into segments or cell, the septa appear at regular intervals behind the

hyphal tip, each cell that may contain one, two, or many nuclei. the presence

of septa gives mechanical support to the hyphae. Complete partition do not

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occur in the vegetative phase of fungi ,in some cases, the septa possess more

than one pore and rarely none at all.( a fully developed septum )

Ultrastructural studies of a variety of different types of fungi have shown that

septa vary in their construction .while some are simple and others complexes,

all types appear to form by the centripetally, means the septum originates at

the periphery on the inside of tubular hyphal wall as a ring of wall material,

the ring growth grows slowly inwards towards the centre.( the aseptate

Rhizopus takes 20 – 25 minutes to completely seal off a damaged portion. the

complex dolipore septum in Rhizoctonia is completed in 10 minutes,Cibora

takes only 6 minutes ) Possesses a single central pore through which

cytoplasm, cytoplasm organelles and even nuclei can regularly pass from one

cell to other.

In the most complex fungi the septum wall near the central pore is swollen or

inflated to from a barrel –shaped structure. This type of septum is referred to

as a dolipore septum surrounded by membrane called the septal pore cap or

parenthosome is present in the cytoplasm on either side of a dolipore septum.

Depending upon the species involved, the sepal pore cap may be perforate or

imperforate. Spate with multiple, small microspores or plasmodesmata –like

channels as already noted.

Function of septum is movement of cytoplasm, cytoplasm organelles and

even nuclei can regularly pass from one cell to other.

Fungi belong to ascomycetes have the spherical structure called Woronin

body they block the septal pore and prevent loss of cytoplasm, if the hyphae

damage ,so septa (simple or complex ) are the first line of defence against

mechanical damage.


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Fungal cell wall:

Fungal is surrounded by a definite cell wall, this wall is the structure that

gives fungi most of their unique features, the cell wall have important

functions:

1. The wall's ability to safely contain tugor pressure appears to be primordial

reason for the survival and evolution of fungi.

2. Plays several other important roles in the life of a fungus. for example ,

the wall confers shape to the hypha .

3. It acts as a filter controlling to some extent what enters the fungal

protoplast.

4. It protects the protoplast against environmental hazards.

5. It functions in the recognition of events associated not only with sexual

reproduction but also with various interactions of fungi with potential

plant and animal symbionts.

Fungal walls and hyphal tip growth:

The fungal cell wall is a dynamic structure that is subject to change and

modification at different stages in the life of fungus, it is composed basically

of a skeletal microfibrillar component located to the inner side of the wall

and usually embedded in an amorphous matrix material that extends to the

outer surface of the wall.

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The skeletal component consists of highly crystalline, water-insoluble

materials that include β-linked glucans and chitin, while the matrix

consists mainly of polysaccharides that are mostly water soluble. These

latter polysaccharides include β-glucans and glycoprotein.

Miscellaneous components that may be present in the cell walls of fungi

include lipids, melanins, D- galactosamine polymers, and polyuronide.

On the other hand, cellulose is a characteristic component of the walls of the

stramenopiles. (Oomycota)

Mechanism of fungal tip growth:

Most ideas on the mechanism of apical growth are based on the

accumulation of vesicles at apex, transmission electron microscopic studies

have shown that the apex of growing hypha is packed with vesicles that fall

into two sizes these include macro vesicles with diameter greater than 100

nm and microvesicales smaller than 100 nm in diameter.

In most of the true fungi these vesicles are tightly clustered with some other

structure to form a unique and dynamic structure called the spitzenkorper it

acts as a supply center for vesicles involved in hyphal tip growth. Vesicles

arise from a Golgi bodies or from specialized areas of the endoplasmic

reticulum and release their contents into the wall when they fuse with the

plasma membrane, these contents include enzymes responsible for wall lyses

and wall synthesis

We can summarize their role of vesicles as following:

1. To transport enzymes that breaks the bonds between the existing wall

components and insert new one.

2. To transport new wall components, either as precursors or as preformed

units for incorporation into the wall.

3. The membranes of fused vesicles are contributed to extensions (or

increase the surface area) of plasma membrane.

The exact role that micro vesicles play in hyphal tip growth is less clear,

some workers believe that at least some of these tiny vesicle are involve d in

the movement of the enzyme chitin synthase through the cytoplasm to the

plasma membrane at the hyphal apex where it catalyzes the formation of the

microfibrils of the chitin skeleton of the fungal wall. If this is true, then these

vesicles may so – called chitosomes.


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Somatic structure of fungi:

Stroma

Is a compact, somatic structure much like miniature mattress or a cushion on

which or in which fruiting bodies usually are formed.

Sclerotium:

Is a hard resting bodies, compact mass of hyphae with or without host tissue,

usually with a darkened rind, and capable of surviving under unfavorable

environmental conditions they come in various sizes and shapes and may

remain dormant for long periods of time and then germinate on the return of

favorable conditions such as ergot fungus Claviceps purpurea .

Rhizomorph or mycelial cord:

A thick strand of somatic hyphae in which the hyphae have lost their

individuality and form complex tissues, with the whole mass behaving as an

organized unit, the structure of the growing tip of the rhizomorph somewhat

resembles that of a root tip, it is resistant to adverse conditions and remain

dormant until favorable condition return.

The rhizomorphs may attaint great length, so it translocated nutrients for

long distances.

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Hyphae of plant pathogenic fungi growing within the tissues of their hosts

exhibit various patterns of growth depending upon the type of pathogen

involved as following:

i. Perthotrophs or necrotrophs, use enzymes and toxins to kill host cells in

advance of their hyphae and then grow between and into dead and dying

cells.

ii. Biotrophs: are ecologically obligate parasites and in vivo obtain nutrients

only from living host cells, the hyphae of most biotrophs grow primarily

between host cells and given rise to specialized hyphal branches that

penetrate the host cell plasma membrane without killing the cell. These

branches are known as haustoria and are thought to be involved in the

uptake of nutrients from the host cell.

iii. Hemibiotrophs: initially require living host cells but soon cause the death

of the host cells in advance of their hyphae like the perthotrophs noted

above. (e.g. Colletotrichium sp.)

Appressoria:

These are specialized infection structures formed at the tips of germ tubes or

hyphae on the outside of host appressoria adhere to host surfaces and form

penetrati0n pegs that enter the host either by growing into stomatal opening

or by directly penetrating the host epidermis, appressorium produced by rust

fungi.

Fungal organelles:

1. Nucleus:

In septate forms, nuclei generally appear to be distributed randomly

throughout the cytoplasm of any an actively growing hypha. In septate forms

individual hyphal compartments may, depending upon the species involved


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and the phase of the life cycle examined, routinely contain one, two, or

many nuclei.

The nuclei of most fungi are quite small although generally spherical to

ovoid in shape, they are extremely plastic structures that are capable of

squeezing through tiny septal pores as wall as through narrow structure at

the tips of which various types of spores are produced. Nuclei also have a

tendency to become thin and elongated or tear –drop shaped while moving

into germ tubes arising from germinating spores.

Until the last few years, most light microscopic studies of fungal nuclei have

involved the use of killed and fixed samples stained with dyes such as,

giemsa, iron- hematoxylin, and acetocarmine. More recently, fluorescent

stains including and mitramycin have proved to be of great value in the

study of fungal nuclei. Transmission electron microscopy has, of course,

also contributed greatly to our knowledge of fungal nuclei.

2. Spindle pole bodies (SPBs):

is nucleus associated organelles, is a small, electron dense cytoplasmic

structure that lies adjacent to the nuclear envelope in most true fungi

,evidence indicates that these structures function as microtubule organizing

centers during mitosis and meiosis. SPBs appear as flat, bar shaped

structures, multilayered disks, or globular masses. During prophase the SPB

duplicated itself and in some species may appear as large, spectacular

structure. The duplicated SPD then separates into identical halves that

eventually become positioned at opposite poles of the dividing nucleus. The

behavior of SPBs during mitosis and meiosis, of course, reminiscent of that

of centrioles. Species of fungi that produce flagellate cells lack SPBs

(phylum chytridiomycota), possessing in stead a pair of centrioles that are

associated with the nuclear envelope.

Nuclear divisions: in the fungi are basically intranuclear. By means that

the bulk of the nuclear envelope remains intact until late telophase when it

breaks in the interzonal region and then re – forms around the daughter

nuclei .the typical fungal nucleus usually contains prominent nucleolus that

is often centrally positioned.

Fungal chromosomes: are usually quite small and difficult to visualize in

squashed and stained preparations as a result, direct chromosome counts

are difficult to make, however, a new methods to karyotype analysis called

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pulsed field gel electrophoresis (PFGE) has proved to be extremely

valuable for determining chromosome numbers in fungi. In this technique,

chromosomes in an agarose gel are exposed to a pulsed electrical field that

causes them to move at different velocities independent upon their sizes and

shapes. After staining with ethidium bromide and exposure to ultraviolet

light, the chromosome can be resolved as the distinct that can be counted.

3. Mitochondrion:

Mitochondria are numerous in hyphae and, when viewed with light

microscopy, are barely visible as tiny thread or rod like structures, oriented

more or less parallel to the long axis of a hypha; branched or lobed

mitochondria are common in fungi.

4. Other cytoplasmic components of fungi include:

ribosomes, strande of endoplasmic reticulum, vacuoles, lipid bodies,

glycogen storage particles, microbodies, Golgi bodies, filasomes,

multivesicular bodies, and the microtubules and microfilaments that

comprise the fungal cytoskeleton. Spherical structures known as woronin

bodies also are present in certain types of fungi and typically are associated

with septal pores. Also are present in certain type of fungi and typically are

associated with septal pores.

5. Vacuoles:

the cytoplasm of young hyphae or fungal cells hyphal tips vacuoles are

mostly small, variously shaped structures with finely to moderately granular

contents, there is evidence to suggest that these types of vacuoles are part of

the lysosomal system. Older parts of hyphae may, however, contain

centrally located vacuoles that almost completely fill the hyphae in this case

the nuclei and other organelles are found in a thin layer of protoplasm

immediately adjacent to the plasma membrane around the periphery of the

hypha.


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Reproduction of fungi

Reproduction is the formation of new individuals having all the

characteristics typical of the species. Two general types of reproduction are

recognized: sexual and asexual. Asexual reproduction sometimes called

somatic reproduction, does not involve karyogamy, the fusion of nuclei,

and meiosis. Likewise, specialized sex cells or sex organs are not involved.

Asexual methods of reproduction commonly found in fungi may be

summarized as follows:

1. Fragmentation of the soma:

Each fragment growing into a new individual. Some fungi employ

fragmentation of hyphae as normal means of propagation (e.g. sterile fungi

such as Rhizoctonia). Fragmentation may occur by the tearing off of parts of

the mycelium through external force. Under favorable conditions such bits

of mycelium will start a new individual. Often in the laboratory we employ

mycelial fragmentation to keep fungal cultures growing on artificial media

by transferring a bit of mycelium to fresh media and this starting a new

colony.

2. Fission of somatic cells into daughter cells:

It is the simple splitting of a cell into two daughter cells by constriction and

the formation of a cell wall is a characteristic of a number of forms including

some yeasts. (e.g. Schizosaccharomyces)

3. Budding of somatic cells or spores:

Each bud producing a new individual. Budding, on the other hand, involves

the production of a small outgrowth form apparent cell .as the bud is formed,

the nucleus of the parent cell divides mitotically and one daughter nucleus

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migrates into the bud. the bud increases in size while still attached to the

parent cell and eventually breaks off and forms a new individual chain of

buds, forming a short mycelium, referred to as pseudomycelium are

sometimes produced. Budding take place in the majority of yeasts, but it also

occurs in many other fungi. (e.g. Saccharomyces cerevisiae)

4. Production of mitotic spores:

The most common method of asexual reproduction in fungi is by means of

spores, asexual spores vary greatly in morphology.

A -they may be thin or thick walled

B- Vary in color from hyaline, transparent, through green, yellow,

orange, red and brown to black.

C- In size from minute to large

D-in shape from globose through oval, oblong, and needle shape to

helical to even insect like appearance.

E- In number of cells from one to many.

F- In the arrangement of cells and in the way in which the spores

themselves are borne. Spores may be borne in or on microscopic to those

exceeding several feet in diameter and sometimes weighting many

pounds.

Although some fungi produce only one type of spore such as (Alternaria

sp), other produce as many as four types such as (Puccinia graminis).

Fungal spores produced asexually are either borne in sporangia and are

then called sporangiospores, while the spores which are produced at the

tip or side of hyphae in various ways and are then called conidia.

Sporangium is a saclike structure whose entire contents are converted

through cleavage into one or more, usually many, spores. The

sporangiospores of nearly all the true fungi are nonmotile and are called

aplanospores. However, motile sporangiospores called zoospores are

produced in one phylum of true fungi, namely Chytridiomycota.

These spores usually are equipped with a single flagellum. The flagellum

is attached to the posterior end of the spore and divided into two parts the

proximal portion is much longer then the distal or terminal portion, which

is usually very short and flexible. The microtubules forming the familiar 2+

9 axoneme of the flagellum are atached to a modified centriole referred to


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as the kinetosome or basal body which is in turn anchored in the zoospore

cytoplasm by various filaments and microtubules.

On the other hand, hyphae of some spices routinely break up into their

component cells that then behave as spores, these spores are known as

arthrospores. If the cells become enveloped in a thick wall before they

separated from each other or from other hyphal cells adjoining them, they

often are called chlamydospores.

Sexual reproduction in fungi

Sexual reproduction in fungi, as in other living organisms, involves the

union of two compatible nuclei. The process of sexual reproduction consists

of three distinct phases.

1. Plasmogamy: a union of two protoplasts brings the nuclei close together

within the same cell. Plasmogamy resulting in a binucleate cell

containing one nucleus from each parent. Such pair of nuclei we call a

dikaryon .

2. Karyogamy: karyogamy follows plasmogamy almost immediately in

some species, while in others these two events are separated in time and

space; it is the fusion of the two nuclei brought together by plasmogamy.

3. Meiosis: This again reduces the number of chromosomes to the haploid.

Sexual reproduction is characterized by the union of two nuclei followed

by meiosis.

Sporangium Conidia Arthrospore Chlamydospore

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The significance of sexual reproduction is that it results in a very high

incidence of recombination and formation of new genotypes; this enables

fungi to adapt readily to a multitude of environmental conditions.

In the true fungi it may or may not involve specialized sex cells and sex

organs.

Holocarpic:

The entire thallus may be converted into one or more reproductive

structures, so that somatic and reproductive phases do not occur together in

the same individual.

Eucarpic:

The reproductive organs arise from only a portion of the thallus, while the

remainder continues normal somatic activities.

What is the importance of asexually reproduction in fungi?

a- Is more important for the colonization of the species because it results in

the production of large numbers of individuals.

b- Asexual cycle is usually repeated several times during the season.

Whereas the most of the fungi involves the formation of specialized

spores; four types of sex spores that have been given special names are

Oospores, zygospores, ascospores and basidiospores.

The sex organs of fungi are generally called gametangia, these may form

different sex cells called gametes or simply may contain nuclei that are the

functional gametes. We use the terms isogametangia and isogametes,

respectively, to designate gametangia and gametes that are morphologically

indistinguishable, we use heterogametangia and heterogametes to

designate male and female gametangia and gametes that are morphologically

different. In the latter case, the male gametangium is called the antheridium

and the female gametangium is called either an oogonium or an

ascogonium depending on the fungal group .it should be noted that a large

number of fungi lack differentiated sex organs, and hyphae and nuclei are

functionally the gametangia and gametes.

Fungal systematics

The last few decades have brought a number of changes to the study of

fungal systematics and evolution. The major advances include:


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1- Recognition of the artificial nature of three or even fine kingdom

classification systems and the polyphyly of organisms traditionally

known as fungi.

2- Acceptance of the theory and data analysis techniques of phylogenetic

systematics.

3- Development and application of molecular techniques in mycology.

4- Additional discoveries of new taxa, including fossils.

Kingdoms:

Whittaker (1969) broke the tradition of a three – kingdom system of

classification. In doing so, he recognized that the classification of all living

organisms as prokaryotes, animals, or plants (including fungi) did not reflect

their relationships. Whittaker’s addition of the kingdoms: Fungi and Protista

attempted to place organisms in kingdoms that more nearly reflected their

presumed evolutionary relationships. This was an important beginning in the

attempt to establish monophyletic groups (group that contain an ancestor

and all its descendants) and to develop a hierarchical classification to reflect

the relationships of these groups.

A classification based on evolutionary relationships is known as a

phylogenetic classification, and taxa (sing. taxon) the names of groups of

organisms, all correspond to monophyletic lineages, although organisms can

be classified on the basis of arbitrary criteria.

phylogenetic classification is an aid to understanding evolutionary changes

and allow one to make predictions about the organisms based on what is

known about their close relatives. In an attempt to recognize monophyletic

groups, the organisms once classified as fungi, now are considered in three

different groups, the monophyletic kingdoms Fungi and Stramenopila and

four protest phyla.

The kingdom Fungi includes four phyla:

1. Chytridiomycota

2. Zygomycota

3. Ascomycota

4. Basidiomycota

Stramenopila includes the phyla:

1. Oomycota

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2. Hyphochytriomycota

3. Labyrinthulomycota

Four other phyla are considered as protests:

1. Myxomycota

2. Dictyosteliomycota

3. Acrasiomycota

4. Plasmodiophoromycota

As we mention, a monophyletic group consists of an ancestor and all its

descendants. Because Chytridiomycota, Zygomycota, Ascomycota, and

Basidiomycota form an inclusive group with the ancestor represented by the

node that joins them, they are a monophyletic group included here as Fungi.

Groups that are not monophyletic may be polyphyletic, groups do not share

a close common ancestor. The old concept of "fungi "including Oomycota

and slime molds is clearly polyphyletic.

Q/ Fungi are more closely related to animals than the plants? Explain.

1. Neither fungi nor animals are producers as plants are. Both must use

external food sources for energy.

2. Fungi and animals share a molecule called chitin that is not found in

plants. Fungi and many invertebrate animals use this complex

carbohydrate for structural purposes. In fungi, chitin is the structural

component of the cell walls. In animals, it appears in hard structures such

as the exoskeletons of insects and the beaks of octopuses and other

mollusks.

3. Both animals and fungi have spores or gametes with a single smooth,

posterior inserted flagellum.

4. The branch uniting the fungi and animals is well-supported based on a

number of molecular phylogenetic datasets, including:

Characters:

A character is any attribute or feature of an organism that can serve as a

basis for comparison with other organisms. The different expressions of a

character are known as character states.

http://www.brighthub.com/guides/insects.aspx


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For example, fungal spores in a group under study may be smooth or

ornamented; each condition represents a different state of the same

character.

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Mycologists use many types of characters to contribute to their evolutionary

studies, including morphology, anatomy, ultrastructural features,

biochemistry, nucleic acid sequences, and various other attributes

.characters are the basis for building trees, and all types can and should be

used in phylogenetic analysis. Gross morphological features are easily

discernible at low magnifications. Examples of these characters include the

basic shape of the fungal thallus and the form, color, and size of spore –

producing structures. By 1887 the basics of fungal life cycles and

morphology were already wall established and used for classification. Gross

morphological features served to establish many higher level taxa such as

those within Ascomycota and Basidiomycota .Gross cultural morphology

also may be used in groups such as Ascomycota wood-decaying members of

Basidiomycota.

a. Anatomical characters of fungi can be observed with a compound

microscope in squash mounts, hand cut sections, or microtome sections of

embedded material. A freezing microtome may offer an alternative to the

more time- consuming process of embedding fungus tissue in plastic or

paraffin.

b. Electron microscopy and ever- improving techniques in specimen

preparation. Although the characters derived from ultrastructural studies

are basically morphological or anatomical, they offer a much greater

magnitude of resolution and magnification.

c. Transmission electron microscopy was of paramount importance in

providing new characters for a reassessment of evolutionary hypotheses,

especially the structures associated with flagella and nuclei division, ascus


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wall structure, new organelles and organelle spatial relationships,

conidium, ontogeny, and the internal structure of mitochondria.

d. Scanning electron microscopy requires less specimen preparation and

allows high – resolution observation of external or exposed inner surface

structures. This technique has been used extensively to resolve minute

spore ornamentations and, in some cases, details of conidium ontogeny.

e. Chemical techniques such as chromatography and protein electrophoresis

have been useful in the comparison of fungal pigments and isozymes.

f. Geographical distribution also has been used as a character, often for

fungi with restricted distributions.

g. Most recently, molecular techniques have come to mycology and provide

a wealth of potential characters. The DNA sequence characters readily

lend themselves to polygenetic analysis and can be polarized to provide

information on the direction of evolution.

Furthermore, these characters can extend across all taxa and all forms to

provide a large number of independent data sets.

Species concepts:

There are three basic concepts are important to discuss:

1. Morphological species concept:

Is based on morphological characters alone ,the systematist groups

individuals on the basis of observed similarities and distinguishes them from

others on the basis of observed similarities and distinguishes them from

others on the basis of discontinuities in the characters .most fungal species

have been defined using this concept.

2. Biological species concept:

Defines a species as a natural population or population of individuals that are

actually or potentially interbreeding and are isolated reproductively from other

such populations. This concept obviously cannot be applied to asexually –

reproducing fungi, but it has been used with Basidiomycota, Ascomycota and

Zygomycota. Cultures established from single spores are combined in culture and

examined for evidence of sexual reproduction after a suitable period of time

.Neurospora sitophila was define in this way.

3. Polygenetic species concept:

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Has become more common in mycology due to the increased use of

phylogenic methods. The application of DNA complementarily studies to

yeasts, a group with few morphological characters, is an example of one of

the first uses of this method in fungi. The application of concept is difficult

when hyperdization (reticulate evolution) has occurred between lineages.

Because there are many ways to define a species.

Numbers of fungi:

Vast numbers of fungi inhabit the earth. Hawksworth (1991) compared

fungal species numbers with those of other groups from several geographical

regions that had been explored extensively for their biodiversity. He

obtained comparison ratios that led him to extrapolate a conservative figure

of 1.5 million species of fungi worldwide. This staggering number means

that only about 5% (less than 120000) of the world’s species are known, and

there are some even higher estimates of the number of fungi if this estimate

is accurate, this makes fungi the least well- known of any group of

organisms.

Phylum: Chytridiomycota

Biology and general characteristics:

Phylum Chytridiomycota contains the single class Chytridiomycetes. The name

is derived from the Greek chytridion, meaning "little pot", describing the

structure containing unreleased spores. The chytrids are the most primitive of

the fungi. Many members are saprotrophs, utilizing cellulose, chitin, keratin,

etc., from decaying plant and animal debris in soil and mud, whilst species

of Caulochytrium grow as mycoparasites on the mycelium and conidia of

terrestrial fungi. The thalli are coenocytic and usually form no true mycelium

(having rhizoids instead). These are the only members of the Kingdom Fungi

that produce motile cells at some stage in their life history.

1. The motile cells (both zoospores and gametes) of these organisms each

possess a single, posteriorly directed, whiplash flagellum. Zoospores of


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chytrids each contain a single nucleus, the shape and location of which

may vary from species to species.

2. The coenocytic structure of the thallus, whether a globose or ovoid

structure, an elongated simple hypha, or a well- developed mycelium. Cell

walls of these fungi are known to contain chitin and glucan; nuclear

divisions in the group are intranuclear and centric.

3. The members of this phylum are present in both aquatic habitats (usually

fresh water) and soils. There are a few anaerobic species, some of which

have been shown to exist in the guts of herbivores belonging to a variety

of mammalian families.

4. Because of their extremely small sizes, most chytrids can be detected only

by microscopic examination either of the cells and tissues of the animals

and plants that some of them parasitize or the dead organic materials they

colonize. Many of the saprobe species can be isolated from water and soil

samples by baiting with substrates such as pollen, leaves, fruit, snake skin,

exoskeletons of insects and other arthropods.

5. There is considerable variation within Chytridiomycota in thallus

structure. The most morphologically simple forms are endobiotic, living

entirely within the cells of their host. The mature thallus is surrounded by

a cell wall. Other species are epibiotic, producing their reproductive

organs on the surface of either a living host or some species of dead

organic matter with their nutrient-absorbing structures sunken into the

living or dead tissues.

6. They may be holocarpic forms that the entire thallus may be converted

into one or more reproductive structures, or they are eucarpic chytrids.

7. A system of rhizoids is an integral part of the thallium. Rhizoids are short,

delicate filaments that contain protoplasm but no nuclei and eventually

may be separated from the remainder of the thallus by the septa. They

serve to anchor the thallus to its substratum and nourish it by digesting

and absorbing food.

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8. There is considerable variation within Chytridiomycota in the nature of

the asexual or sexual reproductive structures. Sexual reproduction in the

chytrids has been reported to be accomplished by a variety of different

methods, outline below:

a) Planogametic copulation

b) Gametangial copulation

c) Somatogamy

A. Planogametic copulation:

i. Conjugation of isogamous planogametes:

The two swimming gametes that are morphologically similar but

physiologically different unite in water to form a motile zygote. In some

species, gametes originating in the same gametangium will not fuse.

ii. Conjugation of anisogamous planogametes:

One planogamete is considerably larger than the other, fusion take place

in water, and a motile zygote is formed.

iii. Fertilization of a non-motile female (egg) by a motile male gamete:

The two nuclei approach one another and fuse in the incipient resting

spore. The resting spore develops a thick wall and, eventually

germinates in the manner of a sporangium. It is very likely that meiosis

occurs during germination of the resting body.


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B. Gametangial copulation:

Transfer of the entire protoplast of one gametangium into the other.

C. Somatogamy:

It is simply the fusion of somatic structures, in some chytrids; fusion

between rhizoidal filaments precedes the formation of a resting spore.

The Chytridiomycota, of which about 800 species are known, are classified

into five orders. Three of these orders:

Order: Blastocladiales

Order: Chytridiales (chytrids)

Order: Neocallimastigales (anaerobic rumen fungi)

Order: Chytridiales

Synchytrium sp.

This is the largest order, comprising more than 50% of the total number of

chytrids. The classification of the Chytridiales has traditionally been based

on thallus morphology, Future systems of classification will be based on

zoospore ultrastructure and the comparison of several different types of

DNA sequences.

In this genus the thallus is endobiotic and holocarpic, and at reproduction it

may become to a prosorus which later gives rise to a sorus of sporangia.

Alternatively the thallus may turn into a resting spore which can function

either directly as a sporangium and give rise to zoospores. Sexual

reproduction is by copulation of isogametes, resulting in the formation of

thalli which develop into thick walled resting spores.

Order: Blastocladiales .

Genus: Allomyces macrogynus . The thallus consists of a group of well-developed, branched rhizoids by

means of which the fungus attaches itself to the substrate, usually

dichotomously branched, on which the reproductive organs are formed.

The gametangia are cut off the tips of the somatic hyphae by the successive

formation of two septa.

• The female gametangia and gametes of Allomyces produce a pheromone

called sirenine, to which male gametes are attracted.

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• Male gametes also produce a female attracting pheromone by the name of

parisin. Shortly after their release from the gametangia, the gametes of

Allomyces fuse in pairs. Once the gametes contact one another form a

binucleate fusion cell.

• Nuclear fusion is initiated quickly by multiple contacts between the

membranes of two nuclei and karyogamy is accomplished.

• The mature zygote is initially biflagellate. The zygote eventually loss its

flagella encyst, and soon germinate, first germ tube is produced that

develops into rhizoid. Then the main body of the zygote enlarges and gives

rise to the first hyphal tube, which elongates, branches dichotomously, and

develops into a diploid sporothallus.

• At maturity, the sporothalli form two types of sporangia: thin walled,

elongate, colorless zoosporangium (mitosporangia) and oval, thick walled,

resistant sporangium (meiosporangia) that contain melanin pigments and

appear reddish brown.

• Coelomomyces sp. consists of obligate parasites of insects, usually

mosquito larvae. This genus is unusual in that the vegetative thallus lacking


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rhizoids. The life cycle is completed in unrelated alternate animal hosts,

sporothalli occurring in mosquito larvae (Insecta) and gametothalli in a

copepod (Crustacea). Attempts are being made to use Coelomomyces in the

biological control of mosquitoes.

• Catenaria sp. a facultative parasite of nematodes and their eggs, liver fluke

eggs and some other invertebrates, can be grown in culture.

Neocallimastigales (rumen fungi)

A very interesting and unusual group of zoosporic fungi inhabits the

rumens (foreguts) of ruminants like cows and sheep. They have also been

found in some non-ruminants such as horses and many large herbivores.

These fungi are obligate anaerobes which can flourish in the rumen

because oxygen is depleted there, some of which are facultative anaerobes

capable of scavenging free oxygen. The zoospores attach themselves in

large numbers to the herbage fragments, and germinate to form rhizoidal or

rhizomycelial thalli with sporangia capable of releasing further zoospores

within about 30 h. Anaeromyces with polycentric thalli, and Neocallimastix

which are monocentric. The zoospores of Anaeromyces are uniflagellate

whilst those of Neocallimastix are multiflagellate.

In the posterior portion of the zoospore of N. hurleyensis near the point of

insertion of the flagella, an irregularly shaped complex structure interpreted

as a hydrogenosome has been reported in place of a mitochondrion. In

zoospores of N. patriciarum there are many presumed hydrogenosomes

concentrated around the region of flagellar insertion. Hydrogenosomes are

organelles capable of the anaerobic metabolism of hexoses to acetic and

Neocallimastix sp.

(a)Rhizoidal thallus with

zoosporangium.

(b) Release of zoospores.

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formic acids. Protons (H) act as electron acceptors, so that gaseous H2 is

released by the activity of the enzyme hydrogenase.

Phylum: Zygomycota

This phylum contains two classes: .

1- Class: Zygomycetes .

2- Class: Trichomycetes (parasites or commensals inside the guts of living

arthropods e.g. millipedes and the larvae of aquatic insects)

Characteristics of Zygomycetes:

1. The more than 1000 species are primarily terrestrial. They feed on decaying

plant and animal matter (substrates of starch and sugar), though this group

does contain symbiotic members as well as parasitic forms.

2. Hyphae are mostly coenocytic (i.e., non-septate - no cross-walls).

.

3. Cell walls contain chitin and chitosan.

.

4. They lack any motile stage. Asexual reproduction is by non-motile spores

which are called aplanospores, and sporangiospores because they are

typically contained within sporangia. They are dispersed passively by wind,

insects and rain splash.

5. Sexual reproduction is by gametangial copulation which is typically

isogamous and results in the formation of a zygospore. The gametangia

arise from hyphae of a single mycelium in homothallic species, or from

different but sexually compatible mycelia in heterothallic species.

Zygosporangia usually develop thick walls, and act as resting spores.

The most prominent orders of the Zygomycetes are:

• Order: Mucorales

• Order: Entomophthorales

• Order: Glomales

Order: Mucorales:

Most members of the Mucorales are saprotrophs, and are common in soil

and on the droppings of rodents and large herbivores. Others cause rots of

fruits and some occur on the decaying fruiting bodies of mushrooms and


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toadstools. In most members of the Mucorales, numerous spores are

contained in globose sporangia borne at the tips of aerial sporangiophores.

Within the sporangium the spores may surround a central core or columella,

although it is absent in some species (e.g. Mortierella spp.). Some species

possess few spored sporangia, termed sporangiola, and in some groups the

spores are arranged as a single row inside a cylindrical sac termed a

merosporangium.

Rhizopus sp. a very common zygomycete (bread mold). There are about

10 species which grow in soil and on fruits, other foods and all kinds of

decaying materials. Rhizopus spp. grows rapidly also occurs frequently as

laboratory contaminants. An aerial hypha grows out, and where it touches on

the substratum it bears rhizoids and sporangiophores.

When compatible Zygophores contact one another, their tips swell to form

progametangia that fuse apically to form a fusion septum. Septa then form

to wall off a gametangium at the tip of each progametangium, the remainder

of which becomes the suspensor the fusion septum dissolves and the

protoplasts of the two gametangia mix (plasmogamy) and eventually

karyogamy take place. The cell formed initially by the fusion of two

gametangia enlarges, develops a thick, multilayered wall, and becomes the

zygosporangium

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Life cycle of Rhizopus sp.

A number of investigators have suggested that the pheromones initiating

sexual development in Mucorales are mating type specific and function as

precursors of compound known as trisporic acids, once formed, trisporic

acid stimulates the formation carotenoids, which in turn results bin the

formation of more trisporic acid. The accumulation of trisporic acid tend to

suppress the formation of asexual reproductive structures and induces the

formation of zygomorphes. Species producing zygospores only in certain

mating called heterothallic since the two compatible strains could not be

distinguish morphologically) labeled one (+) and the other negative (‒).

Family: Pilobolaceae

The generic name Pilobolus means literally the ‘hat thrower’, referring to

the sporangial discharge mechanism. Pilobolus which grow on the dung of

herbivores. All species produce phototropic, mostly unbranched

sporangiophores that arise directly from the substrate in dark columellate


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sporangia with persistent, cutinized walls that covered with crystals,

probably composed of calcium oxalate. Inflated structures with bright

yellow carotenoid pigments called trophocysts give rise to the sporophores

in Pilobolus produce sub sporangial vesicles, immediately below the

sporangium in Pilobolus.

Family: Thamnidiaceae

In this family two kinds of asexual reproductive structure are found, namely

columellate sporangia and smaller, few-spored, usually non-columellate

sporangia termed sporangiola, which are often borne in whorls or at the tips

of branches. The example is Thamnidium sp.

Rhizopus sp. Pilobolus sp. Thamnidium sp.

Mucormycosis or Zygomycosis:

The class Zygomycetes includes a variety of filamentous fungi that may

cause life threatening human disease and, over the past decade.

R. oryzae the most common underlying condition for development of

zygomycosis is diabetes (ketoacidosis), leukaemia, cancer, solid organ or

bone marrow transplantation and injection drug use. The human infection

caused by the Mucorales can be classified as sinus disease, localized or

extended to the orbit and/or brain, pulmonary, cutaneous, gastrointestinal,

disseminated and miscellaneous infection.

Order: Entomophthorales

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Mostly parasites on insects, some parasites on nematodes, algae, etc. or

saprobic, can be use as agent for biological control; some species have

septate mycelium that can break up into “hyphal bodies” that can germinate

to produce asexual spores. Sexual reproduction zygote known in many

species as (Azygospore) all species studied is homothallic

Pathogenesis: in immunocompetent hosts in tropical and subtropical areas

of developing countries. Entomophthorales characterized by slowly

enlarging subcutaneous nodules that eventually ulcerate, is typically caused

by Basidiobolus ranarum Conidiobolus coronatus infections commonly

present as chronic sinusitis that usually does not extend to the central

nervous system.

Entomophthora sp. Conidiobolus sp. Basidiobolus sp.

Order: Glomales

Glomales

The roots of most terrestrial plants grow in a mutualistic symbiosis with

fungi, i.e. an association in which both partners benefit. Such symbiotic

associations are termed mycorrhiza (Gr. ‘fungus root’).

General features of VAM and AM

A coarse, intercellular, aseptate coenocytic mycelium within the root tissues

may develop large, balloon-shaped intercalary or terminal thick walled

vesicles which are multinucleate and contain large amounts of lipid. Hyphae

penetrating host cells to form richly branched arbuscules which is a type of

haustorium, and there is an interchange of nutrients and water across the


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periarbuscular space. Arbuscules have a relatively short active life, digested

by the host cell.

4th medical analysis mycology / dr hero - lecture notes...used in herbal medicine. the wood rotting...

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