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Pteridophytes gymnosperm angiosperms
Bsc botony (Botony)
University of Calicut
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MODULE Morphology and General Properties of Fungi
Microbiology
Notes
51
MORPHOLOGY AND GENERAL
PROPERTIES OF FUNGI
51 INTRODUCTION
Fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds (British English: moulds), as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, protists and bacteria. One major difference is that fungal cells have cell walls that contain chitin, unlike the cell walls of plants and some protists, which contain cellulose, and unlike the cell walls of bacteria. These and other differences show that the fungi form a single group of related organisms, named the Eumycota (true fungi or Eumycetes), that share a common ancestor (is a monophyletic group). This fungal group is distinct from the structurally similar myxomycetes (slime molds) and oomycetes (water molds). The discipline of biology devoted to the study of fungi is known as mycology. Mycology has often been regarded as a branch of botany, even though it is a separate kingdom in biological taxonomy. Genetic studies have shown that fungi are more closely related to animals than to plants. Fungi are not able to ingest their food like animals do, nor can they manufacture their own food the way plants do. Instead, fungi feed by absorption of nutrients from the environment around them. They accomplish this by growing through and within the substrate on which they are feeding. Numerous hyphae network through the wood, cheese, soil, or flesh from which they are growing. The hyphae secrete digestive enzymes which break down the substrate, making it easier for the fungus to absorb the nutrients which the substrate contains. This filamentous growth means that the fungus is in intimate contact with its surroundings; it has a very large surface area compared to its volume. While this makes diffusion of nutrients into the hyphae easier, it also makes the fungus susceptible to dehydration and ion imbalance. But usually this is not a problem, since the fungus is growing within a moist substrate.
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Morphology and General Properties of Fungi
MODULE
Microbiology
Notes
Most fungi are saprophytes , feeding on dead or decaying material. This helps to remove leaf litter and other debris that would otherwise accumulate on the ground. Nutrients absorbed by the fungus then become available for other organisms which may eat fungi. A very few fungi actively capture prey, such as Arthrobotrys which snares nematodes on which it feeds. Many fungi are parastitic , feeding on living organisms without killing them. Ergot, corn smut, Dutch elm disease, and ringworm are all diseases caused by parasitic fungi.
OBJECTIVES
After reading this lesson, you will be able to:
z describe the morphology of fungi
z explain the physiology of fungi
z classify fungi
z describe the colony morphology
z describe the pathogenecity of fungi
51 MORPHOLOGY OF FUNGI
(a) General. Fungi vary widely in size and shape, from unicellular, microscopic organisms to multicellular forms easily seen with the naked eye. Individual cells range from 1 μ to 30 μ. Microscopic fungi exist as either molds or yeasts or both. Internally, fungal cells are fairly typical eucaryotic cells.
(b) Molds. The molds form large multicellular aggregates of long branching filaments, called hyphae. There are vegetative hyphae and reproductive hyphae. Spores are borne on the reproductive hyphae. (Fungal spores should not be confused with bacterial spores that are resistant bodies formed for bacterial survival rather than reproductive purposes.) Spore size, shape and structure are used in the classification and identification of fungi. The tube-like hyphae are responsible for the fluffy appearance of the macroscopic mold colony. The hyphae and other structures combine to form an elaborate network called a mycelium.
(c) Yeasts. These are large (5 to 8 μ), single-celled organisms that rarely form filaments. Most yeasts reproduce by the asexual process of budding. Yeast colonies are usually characterized by a smooth surface similar to that of many bacteria.
443
Morphology and General Properties of Fungi
MODULE
Microbiology
Notes
bronchial mucosa, and lungs. It occurs largely as a complication of a chronic, debilitating disease, such as uncontrolled diabetes.
(b) Class Ascomycetes. The sac fungi: yeasts, mildews, and cheese molds. Fungi of this class are implicated in only three fungus diseases, all of which are rare. (c) Class Basidiomycetes. Mushrooms, toadstools, rusts, and smuts. The only pathogens in this class are the mushrooms of the genus Amanita, which cause severe systemic poisoning (sometimes death) when eaten.
(d) Class Deuteromyceters. Fungi imperfecti: a heterogeneous collection of fungi without sexual reproduction. Most of the pathogens encountered in medical mycology belong to this class.
INTEXT QUESTION 51.
- Study of fungi is ................
- Fungi are fed by ................ of nutrients from the environment around them
- ................ of fungi secrete enzymes which helps in absorption of nutrients
- Fungi that produce asexual spores are known as ................
- ................ morphology is used to describe the characteristics of fungal colony Table 51 Characteristics of Fungi Taxonomic Hypha Type of Characteristic Origin of Examples Pathogenicity class of Fungi Reproduction spore Spore of Fungi Phycomycetes Asptate Asexually Sporangio- Sporangio Nuisance Very rare spore phore fungi Mucormycosis Sexually Zygospore Fussion of including or oospore nuclei general Absidia, Muclor, and Rhizopus Ascomycetes Septate Asexually Blastospore Budding Allescheria Rare Conidium Conidio- Aspergillus Maduromcosis phore Piedraia Aspergillosis Sexually Ascospore Ascus Saccharomyces Black Piedra (perfect yeast) Basidiomycetes Septate Sexually Basidio-spore Basidium Mushrooms, Rare smuts and Mushroom rusts poisoning Deutero- Septate Asexually Thallospore Thallus Most Most Mycoses mycetes (hypha) saprophytes encountered {fungi and pathogens in medical imperfecti) Conidium Conidio- encountered mycology phore in medical mycology (Imperfect mold and yeast)
MODULE Morphology and General Properties of Fungi
Microbiology
Notes
Fig. 51.
Colony Morphology Colony morphology is a method that scientists use to describe the characteristics of an individual colony of fungi growing on agar in a Petri dish. It can be used to help to identify them.
MODULE Morphology and General Properties of Fungi
Microbiology
Notes
more common, the latter generally have more serious consequences. Table 51 lists the more common fungus diseases and the important etiological agents in each. Note that frequently more than one species of organism may cause identical symptoms. Table 51.
Disease Synonym or Brief Important Etiological Description Agents Cutaneous and Superficial Mycoses Tinea capitis’ Ringworm of the scalp Microsporum spp Trichophyton spp Tinea corporis Ringworm of the body Same as Tinea capitis Tinia barbae Infection of bearded area of Trichophyton spp face and neck Tinea cruris Ringworm of the groin Trichophyton spp (jock itch) Candida albicans Epidermophyton floccosum Tinea pedis Ringworm of the feet Same as Tinea cruris (athlete’s foot) Tinea versicolor Depigmented, scaly patches Malassezia furfur of skin Otomycosis Fungus infection of the Aspergillus spp (aspergillosis) ear canal Cutaneous Yeast infection of nails, skin Candida albicans and other Candidiasis mouth,Vagina species (moniliasis, thrush) Mycetoma Tumor-like swelling, draining Pseudallescheria boydii and abscess other Actinomycosis Chronic, suppurative or Actinomyces israelii granulomatous disease of [actuallyclassified asbacteria, jaw,thorax, or abdomen but causefungus-like infections] Subcutaneous and Systemic Fungus Infections Nocardiosis Infection of lungs, otherorgans, NocardIa asteroids[actually and lowerextremities (Madura classified asbacteria, but cause foot) fungus-like infections] Chromoblastomycosis Warty nodules or vegetations N. brasIlIensIs of skinand subcutaneous tissues Cladosporium carrionii Sporotrichosis Ulcers of skin and underlying Fonsecaea pedrosoi tissues and gumma-likeswelling of regional lymph nodes. Blastomycosis Inflamatory lesions of the skin, Phialophora verrucosa lungs,or bones. Sporot schenkii
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Morphology and General Properties of Fungi
MODULE
Microbiology
Notes
Coccidioidomycosis Self-limited respiratory disease Blastomyces dermatltidis orchronic progresssive infection of various organs Histoplasmosis Fungus infection of the lungs, Coccidioides immitis with fever; anemia; loss of Histoplasma capsulatum weight,enlargement of lymph nodes, liver,spleen Cryptococcosis Systemic fungus infection of Cryptococcus noeformans lungs or meninges
(b) Diseases caused by fungi are collectively called mycoses (singular, mycosis). They are divided into four general categories on the basis of the primary tissue affected by the pathogen: 1. Superficial mycoses are infections limited to the hair and dead layers of the skin. 2. Cutaneous mycoses (dermatophytoses or ringworm) affect only the skin, hair, and nails. 3. Subcutaneous mycoses affect the subcutaneous tissue below the skin and occasionally bone. 4. Systemic (“deep”) mycoses infect the internal organs and may spread throughout the host
(c) Those fungi infecting the outer layers of the skin are rarely severe and are usually transmitted by contact with infected animals or humans. The agents of subcutaneous and systemic mycoses, however, are normally saprophytic fungi growing in the soil. Humans generally acquire these mycoses only when the spores of these organisms are either inhaled or introduced into the body through a break in the skin.
(d) Some fungi incapable of causing infectious diseases produce toxic substances that poison the person who ingests them. These substances are collectively called mycotoxins. The most commonly known mycotoxin poisoning is from certain mushrooms; however, mycotoxins may be produced by fungi growing on grain, nuts, and other agricultural products.
Medically Important Fungi
An accurate taxonomic scheme of the major fungal pathogens and contaminants encountered in medicine is not presented here; instead, a simpler but perhaps more useful organization will be applied. Morphology is particularly helpful in speciating filamentous fungi and Pneumocystis carinii (see Other fungi, below), but may also play a role in identifying certain yeasts.
449
Morphology and General Properties of Fungi
MODULE
Microbiology
Notes
Dermatophytes
Fungi infecting stratum corneum, hair, and nails. Grossly, colonies often display fluffy or fine texture and are pale colored or white. Grow moderately rapidly to slowly and have narrow, septate hyphae.
Dimorphic fungi
Fungi that characteristically grow as a mold under certain environmental conditions (usually 25-30°C) and as a yeast under other conditions (usually at 35-37°C). Medically important dimorphic fungi can be highly pathogenic; special caution is warranted when handling fungal cultures largely because of the risk of culturing one of these organisms.
Yeasts
Yeasts are unicellular fungi that reproduce by budding (with rare exceptions). Unlike many of the other fungi presented here, biochemical tests and carbohydrate or nitrate assimilation are disproportionately important for identification.
MODULE Morphology and General Properties of Fungi
Microbiology
Notes
INTEXT QUESTIONS 51.
- Disease caused by fungi are collectively called ....................
- Localised fungal infections are called as ....................
- Unicellular fungi that reproduce by budding are ....................
- Involvement of nasal cavity, paranasal sinuses with invasion to brain is called ....................
WHAT HAVE YOU LEARNT
z Fungus is a member of eukaryotic organisms which includes yeasts and molds z Scientific study of fungi is known as mycology z Fungi feed by absorption of nutrients from environment z Hyphae secrets digestive enzymes which breaks down the substrate and makes it easier for fungus to absorb the nutrients z Fungi vary widely in size & shape from unicellular microscopic organism to multicellular organism z Spore size, shape & structure are used in the classification & identification of fungi z Hypae and other structures form mycelium z Fungi reproduces sexually and asexually z Fungi that produce asexual spore are Deuteromycetes fungi imperfecti z Fungi are classified based upon hypae, spore and reproduction z Colony morphology are used to describe individual colony of fungi z Fungal infections are localised skin infections and systemic infections z Mycoses are diseases caused by fungi
TERMINAL QUESTIONS
- Describe the morphology of fungi
- Explain the physiology of fungi
- Classify fungi
Pteridophytes gymnosperm angiosperms
Course: Bsc botony (Botony)
University: University of Calicut
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