Mycology / 4th Stage 2020 Dr Hero

Tishk International University

Science Faculty

Medical Analysis Department

Autumn Semester 2020-2021

Prepared by

Assistant prof. Dr. Hero M. Ismael

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.

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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

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

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.

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.

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.

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.

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

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 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.

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.

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.

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.

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 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 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.

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 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 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.

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:

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

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.

For example, fungal spores in a group under study may be smooth or ornamented; each condition represents a different state of the same character.

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 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:

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 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.

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.

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.

· 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 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 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).

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3. Cell walls contain chitin and chitosan.

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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 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

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 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

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 periarbuscular space. Arbuscules have a relatively short active life, digested by the host cell.

Phylum: Ascomycota

Class: Ascomycetes (Sac fungi) . The name is derived from the Greek words askos (a leather bottle, bag or bladder) and mykes (a fungus), so ascomycetes are sac fungi. Most fungi which were formerly classified in the artificial group Deuteromycotina or Fungi Imperfecti are conidial forms (anamorphs) of Ascomycota.

Characteristics of Ascomycetes:

6. They are the largest phylum of Fungi, with over 64,000 species.

7. There is a very wide range of lifestyles. Some ascomycetes are saprotrophs, others parasites of plants and animals, including humans.

8. The hyphae with regular septa. Proteinaceous organelles termed Woronin bodies may be closely grouped near the central pore.

9. Cell walls consist of chitin.

10. Asexual reproduction in the ascomycetes may be carried on by fission, budding, fragmentation, arthrospores, chlamydospores, or conidia according to the species and environmental conditions.

11. The characteristic feature of the group is that the sexually produced spores, the ascospores are contained within a sac, the ascus. In most ascomycetes the ascus contains eight ascospores.

12. Most have life cycle with short dikaryophase only in the ascogenous hyphal system that develops after fertilization in the developing fruit body.

Sexual reproduction:

Sexual reproduction in Ascomycetes either homothallic or heterothallic: and sexual reproduction is isogamous (yeasts) or heterogamous as in the higher ascomycetes, the male gamete is called (antheridia) and the female gamete (ascogonium).

1. Gametangial copulation:

In some lower ascomycetes (yeasts). In which two similar gametangia isogamous (morphologically indistinguishable) fuse and forming the ascus.

2. Gametangial contact:

By producing morphologically differentiated gametangia, antheridia and ascogonia precedes sexual reproduction.

3. Spermatization:

Some higher ascomycetes (Neurospora sp.) produce ascogonia but no antheridia. Instead in them the conidia like male sex cell called spermatia are formed in flask shaped cavities called spermagonia.

4. Somatogamy:

In some ascomycetes fusion of somatic hyphae of two compatible mycelia takes place, and the nuclei migrate to the ascogonia through the septal perforation.

The sexual reproduction:

· Occurs on the same mycelium that produces conidia. The formation of multinucleate gametangia: male gametes called (antheridia) and female gametes (ascogonia) precedes sexual reproduction

· Male nuclei pass into the ascogonium via the trichogyne which is an outgrowth of the ascogonium

· Genetically different nuclei pair but do not fuse. Ascogenous hyphae now begin to grow

· Compatible pairs of nuclei migrate and cell division occurs and creates dikaryotic cells- two compatible haploid nuclei

· Crozier- the apical cell of the ascogenous hypha which allows the paired nuclei to divide simultaneously

· Compatible pair of nuclei fuse (karyogamy) to form a zygote. Zygote undergoes meiosis producing ascus with 8 nuclei

· Haploid nuclei cut off to form ascospores. Ascus as it matures becomes turgid, and finally burst to release its ascospores

Ascocarp: With relatively few exception, ascomycetes produce their asci in fruiting bodies called ascocarps (Gr. Askos = sac + Karpos = fruit). In general there are four types of ascocarps:

1. Naked asci: the asci are produce without any fruiting body.

2. Cleistothecium: the asci produce inside a completely closed ascocarp.

3. Perithecium: that is more or less closed, but at maturity is provided with a pore (ostiole) through which the ascospores escape

4. Apothecium: those that produce their asci in an open ascocarp.

Types of asci:

1. Unitunicate-operculate asci:

have a single wall. Some have a lid or operculum at maturity it opens so that the spores can be ejected. . 

2. Unitunicate-inoperculateasci:

the asci have no operculum, but have a special elastic ring mechanism built into their tip.

3. Prototunicate asci:

have no active spore-shooting mechanism. These asci are usually more or less spherical.

4-Bitunicate asci (Jack-in-a-box):

have a double wall a thin inextensible outer wall covers a thick, elastic inner wall. At maturity the thin outer wall splits, and the thick inner wall absorbs water and expands upward, carrying the ascospores with it.

Classification: Major groups of ascomycetes

· Hemiascomycetes: nonascocarpic ascomycetes (Naked asci)

· Plectomycetes: Cleistothecia (closed) unitunicate asci

· Pyrenomycetes: Perithecia (flasks) unitunicate asci

· Discomycetes: Apothecia (cups) unitunicate asci: operculate or inoperculate

· Loculoascomycetes: Pseudothecia (flask-like) bitunicate asci

Hemiascomycetes:

Order: Saccharomycetales (ascomycetous yeasts, mostly)

Order: Eurotiales:

Family: Trichocomaceae

1. The class Plectomycetes originally contained all ascomycetes which produce their asci within a cleistothecium.

2. Asci are scattered throughout the cleistothecium, not produced by a fertile layer (hymenium).

3. Asci are mostly globose and thin-walled, and the ascospores are released passively after disintegration of the ascus wall, not by active discharge.

4. This order contains a number of cleistothecial fungi whose anamorphs are usually phialidically formed conidia.

5. The most important family is the Trichocomaceae, which includes the teleomorphs of Aspergillus and Penicillium. There are other important opportunistic pathogens of Eurotialean affinity known only in their anamorphic forms.

6. Eurotium teleomorphic genera of some Aspergillus

7. Talaromyces, teleomorphic genus of some Penicillium

Clavicipitales:

Clavicipitaceae

This group contains fungi with several distinguishing characteristics. Perithecia develop on a fleshy stroma. Thick apical cap perforated by a narrow pore through which the ascospores are discharged.

The best known ergot fungus is Claviceps purpurea. Most members are pathogens or endophytes of grasses. Claviceps sclerotia are the source of toxic alkaloids, the ergot of rye. In past centuries the contamination of rye bread with ergot was responsible for horrifying outbreaks of ergotism involving gangrene, loss of limbs and death. Ergot contains a wide variety of alkaloids that stimulate the central and sympathetic nervous systems in various ways producing a range of secondary effects

Ergot preparations have been used for centuries for hastening childbirth and controlling subsequent bleeding

Cordyceps parasitizes insects. The conidia of certain species of Cordyceps show promise as agents of biological control of insects.

Discomycetes

Order Pezizales (operculate discomycetes)

· Cup-shaped fruiting bodies (apothecia)

· Unitunicate asci those are either operculate or inoperculate

Pezizales commonly produce their ascocarps, which are often quite large, on the surface of forest soil, dead wood or dung. The ascocarp is generally an apothecium which can range in diameter from less than one millimetre to several centimetres. It is often cup-shaped or disc-like, fleshy, sometimes stalked, and frequently brightly coloured.

The asci are, in most cases, cylindrical with a well-defined lid called operculum which is the characteristic feature of the Pezizales. The asci are interspersed by filamentous paraphyses, the tips of which often contain carotenoids giving the apothecia their striking yellow, orange or red colours.

Pezizaceae

Peziza sp.

Peziza is a large genus containing around 100 species. They are commonly encountered in a very wide range of habitats including soil, manure heaps, dung, rotting wood or straw, burnt ground and sand dunes.

Family: Orbiliaceae

Predatory fungi belonging to Ascomycota

All known trap-forming ascomycetes are belong to the family Orbiliaceae, that produce an apothecium.

Arthrobotrys:

The predatory fungi (nematophagous fungi) are present in the soil; they develop structures for trapping nematodes:

· adhesive knobs

· Lateral branches.

Adhesive knobs are Single-celled globose knobs, covered by a sticky secretion and spaced at intervals along a hypha, form the morphologically simplest trapping organs. These knobs are borne directly on the hypha or on short lateral branches in such a way that a nematode may become attached to several knobs.

Order: Lecanorales

Lichens

1. Lichens are usually Discomycetes in the order Lecanorales

2. Lichens are symbiotic relationships between a fungus and algae or a cyanobacterium housed by the fungus in a thallus.

3. As the algae or cyanos can live independent of the fungi but not the reverse in nature, it is thought that the fungus is parasitizing the photosynthetic partner.

4. There are 20,000 species of lichens.

5. They grow very slowly, (0.1 – 1 mm) a year.

6. They can grow in the most extreme environments: in the arctic, the deserts, on trees.

7. They are now used as indicators of pollution or biomarkers

8. The thallus consists of layers of hyphae of Ascomycetes. The top layer is made up of tightly knit hyphae forming a protective barrier, below which the photosynthetic organisms live. Below them the hyphae are loosely knit, demarcated by a substrate layer which again can be made up of more compacted hyphae.

Lichens

Fungal infections in Human (mycoses):

Mycosis (pl. mycoses) is a fungal infection of animals, including humans. Mycoses are common and a variety of environmental and physiological conditions can contribute to the development of fungal diseases. Inhalation of fungal spores or localized colonization of the skin may initiate persistent infections; therefore, mycoses often start in the lungs or on the skin

Clinical Groupings for Fungal Infections

Fungal infections is classified by the location on or in the body where the infection occurs

1. Superficial Mycoses

2. Cutaneous Mycoses

3. Subcutaneous Mycoses

4. Dimorphic Systemic Mycoses

5. Opportunistic Systemic Mycoses

1. Superficial Mycoses

These are superficial cosmetic fungal infections of the skin or hair shaft. No living tissue is invaded and there is no cellular response from the host. Essentially no pathological changes are elicited. These infections are often harmless that patients are often unaware of their condition.

Malassezia furfur 

is the causative agent of Pityriasis versicolor, seborrhoeic dermatitis and dandruff. M. furfur is a lipophilic yeast living on the skin as part of the normal flora.

Seborrhoeic dermatitis and dandruff: Clinical manifestations are characterised by erythema and scaling in areas with a rich supply of sebaceous glands ie the scalp, face, eyebrows, ears and upper trunk. Lesions are red and covered with greasy scales and itching is common in the scalp.

2. Cutaneous Mycoses

Have particular affinity for the keratin of the skin, nails, and hair. Most cutaneous infections are caused by the dermatophytes and Candida spp.

Dermatophytes: are a group of morphologically and physiologically related molds some of which cause well defined infections: dermatophytoses (tineas or ringworm).

The causative agents are: Microsporum, Trichophyton and Epidermophyton (Darmatophyte).

Dermatomycoses are cutaneous infections due to other fungi, the most common of which are Candida spp.

Dermatophytes require keratin and they are restricted to hair, nails, and skin. Predisposing factors for the dermatophytoses are skin trauma, hydration state of macerated skin, occlusion, and elevated temperature, humidity and the host’s defenses. These infections are more severe in people with diabetes mellitus, lymphoid malignancies and immunosuppression.

Pathogenesis:

The infections caused by dermatophytes (ringworm) have been named according to the Latin term of the body site after the word tinea. The clinical manifestations are as follows:

1. Tinea barbae (ringworm of the beard and mustache)

2. Tinea capitis (scalp, eyebrows, and eyelashes)

3. Tinea corporis (glabrous skin)

4. Tinea cruris (groin)

5. Tinea manuum (hand)

6. Tinea pedis (feet)

7. Tinea unguium (nails).

3. Subcutaneous Mycoses

These are chronic, localized infections of the skin and subcutaneous tissue following the traumatic implantation of the etiologic agent.  The causative fungi are all soil saprophytes of regional epidemiology whose ability to adapt to the tissue environment and elicit disease is extremely variable.

Chromoblastomycosis caused by Fonsecaea pedrosoi, Cladosporium sp. is a subcutaneous mycosis characterized by verrucoid lesions of the skin (usually of the lower extremities)

4. Dimorphic Systemic Mycoses

These are fungal infections of the body caused by dimorphic fungal pathogens which can overcome the physiological and cellular defences of the normal human host by changing their morphological form.  Attack the deep tissues and organ systems; often create symptoms. They are geographically restricted and the primary site of infection is usually pulmonary, following the inhalation of conidia. .The causative fungi are:

Histoplasma capsulatum Blastomyces dermatitidis Coccidioides immitis Paracoccidioides brasiliensis

Histoplasma capsulatum

The fungus produces two types of conidia in culture. Macroconidia are spherical and tuberculate, i.e. they have finger-like projections and sessil microconidia. Histoplasma capsulatum grows as a mycelium at room temperature, but at 37oC it develops small budding yeast cells.

Pathogenicity: Histoplasmosis

An intracellular mycotic infection caused by the inhalation of the fungus. Approximately 95% of cases of histoplasmosis are benign. Pulmonary infections may take the form of influenza-like symptoms in the majority of immunocompetent patients but sometimes develop into more severe tuberculosis-like illnesses. Following initial infection, yeast cells can be disseminated, causing systemic mycoses in other organs. World-wide Distribution especially U.S.A. more prevalent in men than in women, often by a ratio of 10: 1

5. Opportunistic Systemic Mycoses

These are fungal infections of the body which occur almost exclusively in debilitated patients whose normal defence mechanisms are impaired. The organisms involved are cosmopolitan fungi which have a very low inherent virulence. The increased incidence of these infections and the diversity of fungi causing them, has parallelled the emergence of AIDS, more aggressive cancer and post-transplantation chemotherapy and the use of antibiotics, cytotoxins, immunosuppressives, corticosteroids and other macro disruptive procedures that result in lowered resistance of the host.

Candida spp. . The name ‘candida’ refers to the white colour of the organisms in culture. Candidal infection is known as ‘candidiasis’ or ‘moniliasis’. C. albicans is a member of the normal flora of humans (mouth, gut and genitourinary tract) and any reduction in colonization resistance by antibiotics will permit a swift increase in numbers of Candida. However, if the host's defenses are lowered, the organism can cause infection of the mucosa (the lining of the mouth, anus and genitals).

Candida infections:

· Oral

HYPERLINK "http://dermnetnz.org/fungal/oral-candidiasis.html" candidiasis (oral thrush)

· Vulvovaginal

HYPERLINK "http://dermnetnz.org/fungal/vaginal-candidiasis.html"

HYPERLINK "http://dermnetnz.org/fungal/vaginal-candidiasis.html" candidiasis (genital infection in women) and Balanitis (penile infection)

· Intertrigo (skin fold infections)

· Napkin dermatitis (nappy or diaper rash)

· Paronychia (nail fold infection) and Onychomycosis (nail plate infection)

Zygomycosis

An especially life-threatening form of zygomycosis (also known as mucormycosis), is known as the Rhinocerebral mycosis, spores enter through sinuses. Grows rapidly outward to the eyes and inward towards the brain, which occurs in diabetics with ketoacidosis. In addition to diabetic ketoacidosis, neutropenia and corticosteroids are other major risk factors for zygomycosis. The causative agents are: Rhizopus, Mucor and Rhizomucor

Aspergillosis

Almost any organ or system in the human body may be involved

Spores inhaled → lung infection in susceptible patient → spread to other parts of the body via the bloodstream → potentially fatal abscesses in various organs

A. flavus and A. fumigates have essentially caused every known variant of aspergillosis, in particular: pulmonary, disseminated, and other systemic infections in immunocompromised patients, chronic colonizing infections, mainly of predisposed hosts (e.g., allergic bronchopulmonary aspergillosis), mostly in long-term asthmatic and cystic fibrosis patients. Pulmonary aspergilloma (fungus ball) in lungs of persons with pre-existing cavitation. chronic mycotic sinusitis, and otomycosis.

MYCOLOGY

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Mycology / 3rd Stage 2020 Dr. Hero

Sporangium Conidia Arthrospore Chlamydospore

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Neocallimastix sp.

(a)Rhizoidal thallus with zoosporangium.

(b) Release of zoospores.

Neurospora crassa Claviceps purpurea Perithecial stroma Perithecium

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Arthrobotrys: (a) conidiophores with conidia (b) Traped namatod showing infection knobe and assimilative hyphae

(c) Adhesive trapping networks.

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Trichophyton sp. Microsporum sp. Epidermophyton sp.

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Candida spp.

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