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Fungi

The document provides an overview of fungi as a kingdom within the five-kingdom system of life, detailing their characteristics, classifications (yeasts, molds, and macroscopic fungi), and reproductive methods. Fungi are eukaryotic organisms that lack chlorophyll, obtain nutrients through absorption, and play a crucial role in decomposition. It also discusses their structural components, growth requirements, and ecological significance, highlighting their role in human and plant diseases.

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FUNGI
Five-kingdom system  All life on earth is divided into five kingdoms:  Plants  Animals  Fungi  Protozoa  Bacteria
FUNGI  Fungi are eukaryotic microorganisms Two major groups of organisms make up the fungi.  The multicellular filamentous fungi - molds  The unicellular fungi - yeasts.  Study of fungi – mycology  Study of fungal diseases - mycoses
All molds are fungi but all fungi are not molds-- yeasts are fungi but they are unicellular and produce no aerial mycelium molds filamentous fungi that produce aerial mycelium
The Kingdom of the Fungae  Myceteae  Great variety and complexity  Approximately 100,000 species  Majority are unicellular or colonial
The Kingdom of the Fungae Can be divided into three groups:  Yeasts  Molds  Macroscopic Fungi
The Kingdom of the Fungae Can be divided into three groups:  Molds  Long, threadlike cells  Filamentous arrangement (hyphae)  Some are dimorphic (yeast-like and filamentous forms exist)
The Kingdom of the Fungae Macroscopic fungi  Mushrooms, toad stools  Bracket fungi  Stink horns
What is a Fungus? To be considered a fungus, an organism  Must be eukaryotic  Possess cell walls  Grow by extending filamentous cells called hyphae, or by budding  Obtain nutrients by releasing digestive enzymes into the environment to break down organic molecules, which are then absorbed  Have no chlorophyll.  cell walls have chitin.
Different forms of Fungi  mushrooms  rusts  molds  truffles  yeast
GENERAL CHARACTERSTI CS OF FUNGI
General Characterstics  Molds consist –long, branched, thread like filaments of cells called hyphae.  The total hyphal mass of a fungus is called as mycelium.  The hyphae may be septate or aseptate (coenocytic)  Many fungi are dimorphic in nature and change from a yeast form to a mold form.  They consist typical eukaryotic nuclei and membrane bound organelles.  The ribosomes are of 80s type.  Most of the fungi are saprophytes and secure nutrients from dead organic material.  They grow best at optimum pH of 5.5 and optimum temperature of 20-350C.  Fungi are aerobic in nature. Some yeasts are facultatively anaerobic and carry out fermentation.
General Characterstics  Majority of fungi are terrestrial. A few are fresh water or marine.  Some are parasitic and some are symbiotic.  Many are pathogenic and cause several diseases.  They are the important decomposers and breakdown the organic matter.  They lack chlorophyll and cannot carryout photosynthesis.  They range in size from single-celled microscopic yeast to multicellular molds and macroscopic puff balls and mushrooms.  They may be unicellular (yeasts) or multicellular and filamentory ( molds).
General Characterstics  Their primary storage material is glycogen which is a polysaccharide.  They reproduce asexually, sexually or by both methods.  The asexual reproduction occurs by the production of specific types of spores such as arthrospores, chlamydospores, sporangiospores, conidiospores, zoospores and blastospores.  Some fungi exhibit binary fission type of reproduction.  Sexual reproduction involves the union of two compatible nuclei or sex organs or sex cells.  They produce sexual spores such as ascospores, basidio spores, zygospores and oospores.  Some fungi produce useful substances such as penicillin, acetone, butanol sorbitol etc.  Some fungi produce antibiotic substances, eg. Penicillin.  Fungi are usually filamentous.
FUNGI  Fungi play a vital role in the environment  economically important as a food source  Cells of fungi are quite similar to those of plants, protists, and animals.  lack of chlorophyll separates them from plants.  Since they do not ingest their food (by eating) they are not animals.  Most fungi reproduce through the generation of spores (Mycelia sterilia being an exception).  Fungal spores are non-motile (meaning they cannot move of their own accord). This further separates fungi from protists, which also can produce spores, but if they do, they are often motile.
 Together with bacteria, fungi are the major decomposers of organic materials in the soil.  They degrade complex organic matter into simple organic and inorganic compounds and help recycle carbon, nitrogen, phosphorous, and other elements for reuse by other organisms.  As molds grow by digesting the organic material, they gradually destroy whatever they grow on.  Cause many plant and human diseases.
MOLDS  Molds belong to the fungus family  Molds are multicellular, filamentous fungi  Moulds are microscopic, plant-like org’s,  Growth can be easily recognised by it's cottony appearance.  Very common organisms that grow on food materials to spoil the foods and can be easily be identified
Structure  The thallus (body) of a mold consists of long branching filaments of cells joined together; these filaments are called hyphae (sing:hypha).  Hyphae can grow to immense proportions. The hyphae of a single fungus in Oregon extend across 3.5 miles.
Structure - Hyphae  septate hyphae : Hyphae of most molds contain cross-walls called septa which divide them into distinct, uninucleate (one-nucleus) cell-like units --- septate fungi  coenocytic hypae : Hyphae of few classes of fungi contain no septa and appear as long, continuous cells with many nuclei. Cytoplasm passes through and among cells of the hypha uninterrupted by cross walls - -- coenocytic fungi.  Even in fungi with septate hyphae, there are usually openings in the septa that make the cytoplasm of adjacent “cells” continuous; these fungi are actually
Structure - Hyphae  Hyphae grow by elongating at the tips.  Each part of hyphae is capable of growth, and when a fragment breaks off, it can elongate to form a new hyphae.  In the laboratory, fungi are usually grown from fragments obtained from a fungal thallus.  Portion of a hyphae that obtains nutrients is called the vegetative hyphae  Portion concerned with reproduction is the reproductive or aerial hypha, so named because it projects above the surface of the medium on which the fungus is growing.  Aerial hypae often bear reproductive spores
Structure - Mycelium  When environmental conditions are suitable, the hypae grow to form a filamentous tangled mass called a mycelium, which is visible to the unaided eye .
Characteristics of Fungal Hyphae: Septate versus Coenocytic
Mycelium: Large, Visible Mass of Hyphae
GROWTH  Molds release countless tiny microscopic cells called spores, which spread easily through the air and form new colonies where they find the right conditions.  For molds to grow and reproduce, they need only a food source – any organic material, such as leaves, wood, paper, or dirt – and moisture (relative humidity > 60%).
Growth of mold  Development of fungi cultures usually begins with a spore.  In the presence of moisture, the spore swells with water much like a germinating Plant seed.  Then the spore wall expands through a preformed weak spot [the germ pore] to create a thin, balloon-like protuberance.  This first extension of growth is called a hypha resembling long, worm-like structures.  With continued growth, the hyphae will branch and grow into a visible colony called a "mycelium.“
FUNGI - NUTRITION  All fungi are chemoheterotrophs, requiring organic compounds for energy and carbon.  Mostly saprophytes - obtain their nutrients from dead organic matter.  Play an important role in the environment by decomposing and recycling organic matter.  Few are parasitic on plants causing major losses of crops.  Others find their way into humans or other animals and cause serious infections.
Nutrition of Fungi The nutritional need of a fungus are facilitated by the enzymes cellulase and/or chitinase.  Acquire nutrients by absorption  Most are saprobes  Some trap and kill microscopic soil-dwelling nematodes  Haustoria allow some to derive nutrients from living plants and animals  Most are aerobic; some are anaerobic; many yeasts are facultative anaerobes
NUTRITIONAL ADAPTATIONS  Fungi are generally adapted to environments that would be hostile to bacteria.  Fungi are chemo heterotrophs, and, like bacteria, they absorb nutrients rather than ingesting them as animals do.  Fungi differ from bacteria in certain environmental and nutritional requirements  Fungi usually grow better in an environment with a pH of about 5, which is too acidic for the growth of most common bacteria.  Almost all molds are aerobic. Most yeasts are
NUTRITIONAL ADAPTATIONS  Most fungi are more resistant to osmotic pressure than bacteria; most can therefore grow in relatively high sugar or salt concentrations.  Fungi can grow on substances with a very low moisture content, generally too low to support the growth of bacteria.  Fungi require somewhat less nitrogen than bacteria for an equivalent amount of growth.  Fungi are often capable of metabolizing complex carbohydrates, such as lignin (a component of wood), that most bacteria cannot use for nutrients.
FUNGI - Genome  Fungi have relatively very small nuclei, containing very few nucleotides in their genomes.  Example: the amount of nucleotides in mushrooms is eight times that in E. coli (a prokaryote) but is only 1% of that in humans .
Cultural Characteristics  Some molds look velvety on the upper surface  some look dry and powdery  some wet or gelatinous.  Some molds are loose and fluffy  some are compact.  some are hard.  Some possess pigments in their mycelium (red,yellow, blue- green, brown, black, pink, orange etc)  Mold growth on surfaces can often be seen in the form of discoloration  The appearance of the molds indicates its genus.
Physiological Characteristics Temperature requirement –Most molds grow well at ordinary temperature Mesophilic and psychrotrophic range. Optimum temperature = 25 to 30 c but few grow well at 35 to 37c or above(Aspergillus)  A number of molds grow well at refrigeration and freezing temperatures : -5 to -10c  Few are thermophilic - can grow at a high temperature.
Physiological Requirements Moisture requirement – Aw of 0.6 -0.65  Molds require less moisture to grow than yeast and bacteria.  If dried food has a moisture content below 14 to 15%, it will prevent or delay mold growth.  Xerophilic molds use the humidity in the air as their only water source; other molds need more moisture
Physiological Requirements  Oxygen Requirement –  Molds are aerobic require oxygen for their growth.  Fungi are aerobic or facultatively anaerobic, anaerobic.  pH :Grow over a wide range of pH(2-8.5) Majority are favored by an acid pH.
Media  In general can utilize many foods, ranging from simple to complex.  Most molds possess a variety of hydrolytic enzymes and some are grown for their amylases, pectinases, lipases and proteinases.
Identification  Yeast identification, like bacterial identification, involves biochemical tests. However, multicellular fungi are identified on the basis of physical appearance, including colony characteristics and reproductive spores.
Where are molds found?  Found in virtually every environment and can be detected, both indoors and outdoors, year round.  Mold growth is encouraged by warm and humid conditions.  Outdoors - they can be found in shady, damp areas or places where leaves or other vegetation is decomposing.  Indoors - they can be found where humidity levels are high, such as basements or showers
REPRODUCTION  Fungi reproduce by the production of spores  Fungal spores can be either asexual or sexual .  Filamentous fungi can reproduce asexually by fragmentation of their hyphae.  Mold reproduce using both sexual and asexual reproduction methods.  Molds reproduce through producing very large numbers of small spores, which may contain a single nucleus or be multinucleate.  Spores are formed from aerial hyphae  Mold spores can be asexual (the products of mitosis) or sexual (the products of meiosis)  Many species can produce both types.  Spores are of considerable importance in the identification of fungi  At the end of the hyphae are the reproductive structures that produce spores.  Spores are produced on different structures depending on species.
Asexual and Sexual Reproduction in fungi  Telemorphs : The sexual fungi (perfect, meiotic).  They produce sexual spores.  Anamorph: The asexual fungi (imperfect, mitotic)  Ex: Penicillium is an anamorph that arose from a mutation in a telemorph.  Holomorph: the whole fungus, including anamorphs and teleomorph.  many fungi can have both, especially Ascomycota-- most have either one or the other
Asexual Spores  Asexual Spores are called conidia (sing: conidium)  When these spores germinate, they become organism that are genetically identical to the parent cell.  Asexual spores are produced by the hypae of an individual fungus through mitosis and subsequent cell division  There is no fusion of the nuclei of cells.
Asexual Spores  Conidiospore/conidium (plural: conidia): Unicellular or multicellular spores that are produced in a chain at the end of a conidiophores.  Such spores are produced by Aspergillus.  Conidia are not enclosed in a sac.  Blastospores : blastoconidia are produced in a cluster by budding from a parent cell (conidium).  consists of buds coming off the parent cell.  Such spores are found in yeasts, such as candidia albicans and Cryptococcus.  Sporangiospores: Spores formed within a sporangium, or sac, at the end of an aerial hypha called a sporangiophore.  The sporangium can contain hundreds of sporangiospores.  Such spores are produced by Rhizopus.
Asexual Reproduction
sexual reproduction  During sexual reproduction, compatible nuclei unite within the mycelium and form sexual spores.  Sexually opposite cells may unite within a single mycelium, or different mycelia.  When the cells unite, the nuclei fuse and form a diploid nucleus.  Several divisions follow, and the haploid state is reestablished.
Sexual spores  Sexual spores result from the fusion of nuclei from two opposite mating strains of the same species of fungus.  Fungi produce sexual spores less frequently than asexual spores.  Organism that grow from sexual spores will have genetic characteristics of both parental strains.
Sexual Spores  Fungal sexual spores results from sexual reproduction which consists of three phases:  Plasmogamy (Cell fusion): A haploid nucleus of a donor cell (+) penetrates the cytoplasm of a recipient cell (-).  Karyogamy(Nuclear fusion): The (+) and (-) nuclei fuse to form a diploid zygote nucleus.  Meiosis. The diploid nucleus gives rise to haploid nuclei (sexual spores), some of which may be genetic recombinants.
 Oospores are produced when male gametes (reproductive nuclei)enter a large spherical cell (oogonium) and fertilize the eggs within.  Ascospores are produced within spherical cells called asci  most often in groups of 4 or 8  Usually the asci are produced within some kind of enclosing structure and thus are not found exposed on the hyphae.
 Zygospores :  Do not occur inside any kind of enclosing structure  produced by the direct fusion of two hyphal protrusions from neighbouring filaments.  Usually zygospores are recognized as large, nearly spherical, often dark brown or black, rough-walled spores with two connecting hyphae, representing the two mating gametangia
 Basidiospores : produced externally on a structure called a basidium. Basidia come in a variety of forms, but those commonly encountered on moulds will be club-shaped and bear four or eight spores on sharp projections at the apex.
Common Molds  Absidia  Alternaria  Ascomycetes  Aspergillus  Basidiomycetes  Cladosporium  Curvularia  Fusarium  Mucor  Penicillium  Pithomyces  Stachybotrys  Trichoderma  Ulocladium
Fungal spores - Bacterial endospores  Fungal spores are quite different from bacterial endospores.  Bacterial endospores allows a bacterial cell to survive adverse environmental conditions.  A single vegetative bacterial cell forms one endospore, which eventually germinates to produce a single vegetative bacterial cell. This process is not reproduction because it does not increase the total number of bacterial cells.  But after a mold forms a spore, the spore detaches from the parent and germinates into a new mold. Unlike the bacterial endospore, this is a true reproductive spore; a second organism grows from the spore.  Although fungal spores can survive for extended periods in dry or hot environment, most do not exhibit the extreme tolerance and longevity of bacterial endospores.
YEAST
Yeasts  Yeasts are single-celled eukaryotic microorganisms.  Size: yeasts are 5 to 10 µm in diameter.  They are larger than bacteria.  Yeasts are non filamentous unicellular fungi.  Typically spherical or oval in shape  Yeasts consists single nucleus and eukaryotic organelles.  classified in the kingdom Fungi, with 1,500 species currently described.  estimated to be 1% of all fungal species.
Yeast Yeasts are very important economically: - Yeasts are responsible for fermentation of beer and bread. (Saccharomyces cerevisiae) - Ethanol production - Wastewater treatment: a mixed culture of yeasts Candida lipolytic Candida tropicalis, and Yarrowia lipolytica grown on hydrocarbons or gas oil.
Cytological methods  Unstained yeast cells can hardly be visualized by light microscopy. At 1000 fold magnification, it may be possible to see the yeast vacuole and cytosolic inclusion bodies.  By phase contrast microscopy together with an appropriate staining technique, several cellular structures can be distinguished.  A very convenient tool to localize and even to follow the movement of particular proteins within yeasts cells is the use of the green fluorescent protein (GFP) from the jelly fish (Acquorea Victoria) as a reporter molecule.  Organelle ultrastructure and macromolecular architecture can only be obtained with the aid of EM.
Structure of Yeast Cell  Yeast cells share most of the structural and functional features of higher Eukaryotes — which has rendered yeast an ideal model for Eukaryotic cell biology.  Ultrastructural features observed: Cell wall, periplasm, Plasma membrane, bud scar, cytoplasm, nucleus, mitochondria, Endoplasmic reticulum, Golgi Apparatus, Secretory vesicles, vacuole, peroxisomes.
Structure of Yeast Cell  In contrast to mammalian cells, peculiarities of yeast cells are that they are surrounded by a rigid cell wall and develop birth scars during cell division, the vacuole corresponds to lysosomes is higher cells.  Bud scars are specialized, ring –shaped convex protrusions at the cell surface which remain on the mother cells (of budding yeasts) after cell division and birth of daughter cells. The concave indentations remaining on the surface of the daughter cell after budding are called birth scars. 
Structure of Yeast Cell  Yeast cytoplasm is an acidic (pH 5.25) colloidal fluid.  Cytoskeleton comprises the microtubules and the microfilament.  Freely suspended 80s ribosomes  Yeast nucleus is a round lobate organelle 1.5 μm in diameter.  yeast nuclear DNA can be isolated as linear molecules ranging in size from 10 μm - 50 μm.  Endoplasmic Reticulum is the site of bio synthesis and modifications of proteins that are to be exported.
Structure of Yeast Cell  From ER, proteins are directed to the Golgi Apparatus by vesicles, which fuse at the Cis side and are exported from the Golgi Apparatus at the trans side. In Golgi further modifications of the protein by carbohydrate side chains may take place.  Proteins delivered from the Golgi are directed to different destination within the cell or to the exterior via different secretory vesicles to the vacuole, the bud region during mitosis, the plasma membrane , the periplasm.  Peroxisomes (membrane-enclosed organelles that contain enzymes involved in a variety of metabolic reactions, including several aspects of energy metabolism) perform a variety of metabolic functions in Eukaryotic cells.  Mitochondria – under aerobic conditions, yeast mitochondria are involved in ATP synthesis coupled to oxidative phosphorylation
Yeasts  Like molds, yeasts are widely distributed in nature; they are frequently found as a white powdery coating on fruits and leaves.
Reproduction  Most yeasts reproduce asexually.  Yeasts grow as single cells producing daughter cells either by an asymmetric division process called Budding - the budding yeasts or by  Binary fission (splitting in two) - the fission yeasts.  Budding: a small bud cell forms on the cell, which gradually enlarge and separate from the mother cells.  Most of the yeasts reproduce by budding.
Budding  In budding the parent cell forms a protuberance (bud) on its outer surface. As the bud elongates, the parent cell’s nucleus divides, and one nucleus migrates into the bud. Cell wall material is then laid down between the bud and parent cell, and the bud eventually breaks away.  Yeasts reproduce rapidly. One yeast cell can in time produce up to 24 daughter cells by budding.  Budding yeasts divide unevenly (Saccharomyces)
Budding
Bud Scar
Bud Scar
Pseudohypha  Some yeasts produce buds that fail to detach themselves; these buds form a short chain of cell called a pseudohypha.  Candida albicana attaches to human epithelial cells as a yeasts but usually requires pseudohypha to invade deeper tissues
Fission: similar to budding During this parent cells elongates, grow to certain size its nucleus divides, and two equal daughter cells are produced. Only a few yeast species reproduce by fission. e.g. Schizosaccharomyces  divide evenly to produce two new cells.
Yeast respiration  Yeasts are facultative anaerobes, which allows them to grow in a variety of environments.  When oxygen is available, they carry out aerobic respiration.  When oxygen is not available, they ferment carbohydrates to produce ethanol and carbon dioxide.  Yeasts can use oxygen or an organic compound as the final electron acceptor; this is valuable attribute because it allows these fungi to survive in various environments.  If given access to oxygen, yeasts perform aerobic respiration to metabolize carbohydrate to carbon dioxide and water  Denied oxygen, they ferment carbohydrates and produce ethanol and carbon dioxide.  This fermentation is used in the brewing, wine-making, and baking industries. Saccharomyces species produce ethanol in brewed beverages and Co2 for leavening bread dough .