Lecture (1) mycology, Dr. kareema Amine Alkhafaji, Assistant professor.
Definition: mycology is the study of fungi .
Fungi are not plants.
Living things are organized for study into large, basic groups called kingdoms. Fungi were listed in the Plant Kingdom for many years. Then scientists learned that fungi show a closer relation to animals, but are unique and separate life forms. Now, Fungi are placed in their own Kingdom.
Systemic fungi: Fungi are usually classified in four divisions: the Chytridiomycota (chytrids), Zygomycota (bread molds), Ascomycota (yeasts and sac fungi), and the Basidiomycota (club fungi). Placement into a division is based on the way in which the fungus reproduces sexually. The shape and internal structure of the sporangia, which produce the spores, are the most useful character for identifying these various major groups.
There are also two conventional groups which are not recognized as formal taxonomic groups (i.e. they are polyphyletic); these are the Deuteromycota (fungi imperfecti), and the lichens. The Deuteromycota includes all fungi which have lost the ability to reproduce sexually. As a result, it is not known for certain into which group they should be placed, and thus the Deuteromycota becomes a convenient place to dump them until someone gets around to working out their biology.
Unlike other fungi, the lichens are not a single organism, but rather a symbiotic association between a fungus and an alga. The fungal member of the lichen is usually an ascomycete or basidiomycete, and the alga is usually a cyanobacterium or a chlorophyte (green alga). Often the fungal partner is unable to grow without the algal symbiont, making it difficult to classify these organisms. They will be treated here as a separate group, but it should be realized that they are neither single organisms, nor a monophyletic group.
It should also be noted that some organisms carry the name of mold or fungus, but are NOT classified in the Kingdom Fungi. These include the slime molds and water molds (Oomycota). The slime molds are now known to be a mixture of three or four unrelated groups, and the oomycetes are now classified in the Chromista, with the diatoms and brown algae.
The benefit and disadvantages of fungi
Abundant worldwide, most fungi are inconspicuous because of the small size of their structures, and their cryptic lifestyles in soil, on dead matter, and as symbionts of plants, animals, or other fungi. They may become noticeable when fruiting, either as mushrooms or molds. Fungi perform an essential role in the decomposition of organic matter and have fundamental roles in nutrient cycling and exchange. They have long been used as a direct source of food, such as mushrooms and truffles, as a leavening agent for bread, and in fermentation of various food products, such as viniger,wine, beer, and soy sauceFungi are also grown in large vats to produce flavorings for cooking, vitamins and enzymes for removing stains. Since the 1940s, fungi have been used for the production of antibiotics In addition to their role in food production, Fungi also play an important role in the production of natural antibiotics.The first natural antibiotic (penicillin) discovered was produced by the fungus, Penicillium, Drugs made from fungi cure diseases and stop the rejection of transplanted hearts and other organs.and, more recently, various enzymes produced by fungi are used industrially and in detergents Some species of yeasts and mycelial fungi are used in processes aimed at reducing the concentrations and toxicities of waste materials, particularly from industrial processes, before those wastes are released into the environment - a process known as bioremediation.. Fungi are also used as biological pesticides to control weeds, plant diseases and insect pests. Many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, that are toxic and carcinogenic to animals and humans. The fruiting structures of a few species contain psychotropic compounds and are consumed recreationally or in traditional spiritual ceremonies. Fungi can break down manufactured materials and buildings, and become significant pathogens of humans and other animals. Losses of crops due to fungal diseases (e.g. rice blast disease) or food spoilage can have a large impact on human food supplies and local economies.
General Characteristics of True Fungi (Mycota or Eumycota)
1. All are eukaryotic fungi have a nucleus that surrounds and protects its DNA. Unlike animal cells, fungi have a rigid cell wall that is made of chitin. The fungal cell wall provides protection and support for the cell. Inside the fungal cell wall is the cell or plasma membrane, which regulates the flow of substances into and out of the fungal cell. Fungi also have the following internal structures: nucleus, nucleolus, ribosomes (60S/40S), smooth and rough ER, Golgi, mitochondria, and a cytoskeleton.
2. Fungi exist in both large (macroscopic) and small (microscopic) forms. Macroscopic fungi include mushrooms and puffballs. One of the largest fungi ever found was 3.5 miles long and covered 2200 acres in Oregon. Another large fungi, discovered in Washington, covered 1500 acres and weighed 100 tons!
Microscopic fungi are dimorphic, which means that they exist in either of the two forms: multicellular mold or unicellular yeast.
Most of fungi are filamentous Composed of individual microscopic long, hair-like filaments called hyphae(Mold), which exhibit apical growth and which branch to form a network of a visible mass of hyphae called a mycelium. Hyphae are used for absorbing nutrients and for sexual reproduction!
Unlike yeast, molds grow primarily OUTSIDE the human body and prefer temperatures below 30°C and can be found growing both at room temperature and inside the refrigerator. Molds also prefer acidic environments, which is why they can often be found growing on citrus fruit, cheese, and bread. Molds can reproduce either asexually or sexually using reproductive spores. During asexual reproduction, the bread mold (Rhizopus) releases spores that germinate (grow) to produce vegetative (feeding) hyphae. During sexual reproduction, the reproductive hyphae "mate" and produce a zygospore.
3. Some are unicellular e.g. yeasts. Yeasts are small, round, and unicellular. Yeast reproduce asexually by a process called budding. During budding, the cell s genetic information is duplicated, creating an identical copy or clone of the original cell. As the new cell pinches off or buds from the surface, a bud scar is produced.
Yeast prefer temperatures of 35-40°C and can grow INSIDE the human body. An example of this is the yeast, Candida albicans, which grows on the mucosal membranes of humans and other animals. Yeast also play an important role in the food industry, where they are used bread- and cheese-making , as well as in beer and wine production . This type of yeast is called Brewer s yeast (Saccharomyces cerevisiae).
4. Protoplasm of a hypha or cell is surrounded by a rigid wall Composed primarily of chitin and glucans, although the walls of some species contain cellulose.
5. Many reproduce both sexually and asexually. Both sexual and asexual reproduction often result in the production of spores.
6. Their nuclei are typically haploid and hyphal compartments are often multinucleate Although the Oomycota and some yeasts possess diploid nuclei.
7. All are achlorophyllous. They lack chlorophyll pigments and are incapable of photosynthesis.
8. All are chemoheterotrophic (chemo-organotrophic)They utilise pre-existing organic sources of carbon in their environment and the energy from chemical reactions to synthesize the organic compounds they require for growth and energy.
9. Possess characteristic range of storage compounds e.g. trehalose, glycogen, sugar alcohols and lipids.
10. May be free-living or may form intimate relationships with other organisms i.e. may be free-living, parasitic or mutualistic (symbiotic).
Fungal Nutrition
ALL fungi are CHEMOHETEROTROPHIC (chemo-organotrophic) - synthesizing the organic compounds they need for growth and energy from pre-existing organic sources in their environment, using the energy from chemical reactions. Since their protoplasm is protected by a rigid wall, fungi must obtain their nutrients by the process of ABSORPTION.SMALL MOLECULES (e.g. simple sugars, amino acids) in solution can be absorbed directly across the fungal wall and plasma membrane.
§ LARGER, MORE COMPLEX MOLECULES (e.g. polymers such as polysaccharides and proteins) must be first broken down into smaller molecules, which can then be absorbed. This degradation takes place outside the fungal cell or hypha and is achieved by enzymes which are either released through or are bound to the fungal wall. Because these enzymes act outside the cell they are called EXTRACELLULAR ENZYMES.
§ Since water is essential for the diffusion of extracellular enzymes and nutrients across the fungal wall and plasma membrane, actively growing fungi are usually restricted to relatively moist (or humid) environments.Empty
Hyphal Ultrastructure
Diagram illustrating the ultra structure of a septate hypha
§ Each HYPHA is: essentially a tube - consisting of a rigid wall and containing protoplasm .tapered at its tip - this is the region of active growth (i.e. the extension zone). SEPTA (cross-walls), if present, can usually be observed down a light microscope .some fungi possess septa at regular intervals along the lengths of their hyphae in others, cross-walls form only to isolate old or damaged regions of a hypha or to isolate reproductive structures. some septa possess one of more PORES - such septa divide up the hyphae into a series of interconnected HYPHAL COMPARTMENTS, rather than separate, discrete cells. The PLASMA MEMBRANE is closely associated with the hyphal wall and in some regions may even be firmly attached to it - making it difficult to plasmolyse hyphae.Each hyphal cell or compartment normally contains one or more NUCLEI. In species whose septa possess a large central pore, the number of nuclei within a hyphal compartment won t remain static because the nuclei are able to pass between adjacent compartments, via the central septal pore. Other CYTOPLASMIC ORGANELLES are those commonly found in all eukaryotic cells. The GROWING TIP is structurally and functionally very different from the rest of the hypha .its cytoplasm appears more dense .there are no major organelles at the extreme tip at the extreme tip there is an accumulation of membrane-bound vesicles - the APICAL VESICULAR CLUSTER (COMPLEX) (AVC) - which plays an important role in apical growth. VACUOLES may be visible in sub-apical hyphal compartments - although small at first, they grow larger and merge with one another; they store and recycle cellular metabolites, e.g. enzymes and nutrients. In the oldest parts of the hypha the protoplasm may breakdown completely, due either to AUTOLYSIS (self-digestion) or in natural environments HETEROLYSIS (degradation due to the activities of other microorganisms).
The Fungal Wall
Functions :1-PROTECTS the underlying protoplasm; 2-determines and MAINTAINS THE SHAPE of the fungal cell or hypha; if you remove the wall the resulting protoplast will always assume a spherical shape; 3-acts as an INTERFACE between the fungus and its environment; 4-acts as a BINDING SITE for some enzymes; 5-possesses ANTIGENIC properties - which allow interactions with other organisms.
Chemical composition of the wall: it consists of -POLYMERIC FIBRILS ( –chitin -cellulose (in the Oomycota) )-AMORPHOUS MATRIX COMPONENTS (glucans, proteins ,lipids ,heteropolymers (mixed polymers) of mannose, galactose, fucose and xylose ).The types and amounts of these various components vary amongst different groups of fungi and may even vary during the life cycle of a single species. Arrangement of the wall components:
§ The diagram above represents a section through the mature lateral wall of hyphae of Neurospora crassa.
§ In general, the inner part of the wall consists of POLYMERIC FIBRILS embedded in an AMORPHOUS MATRIX and this is covered by further layers of matrix material.
§ At the HYPHAL TIP the wall is thinner and simpler in structure, consisting of only TWO LAYERS - an inner layer of fibrils embedded in protein and outer layer of mainly protein.
§ EXTRA LAYERS of wall material are deposited in the lateral walls behind the extending apex - strengthening the wall as the hypha matures.
§ In the oldest parts of the hyphae (and in many fungal spores) LIPIDS and PIGMENTS may be deposited in the wall:
o LIPIDS serve as a nutrient reserve and help prevent desiccation
o PIGMENTS, such as MELANIN, help protect the protoplast against the damaging effects of UV radiation.
§ N.B. Although represented as distinct layers in the diagram above, these four zones merge into one another.
Septa: Septa (cross-walls) can be seen by light microscopy, as illustrated in this series of images. . But electron microscopy has revealed that several different types of septa exist among the major taxonomic groups of fungi. Oomycota and Zygomycota:
§ In general, the hyphae of fungi belonging to these groups are not regularly septate (although there are some exceptions).
§ But septa in the form of COMPLETE CROSS-WALLS are formed to isolate old or damaged regions of the mycelium or to separate reproductive structures from somatic hyphae.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .