5.3 Fungi
4 min read•june 18, 2024
are fascinating microorganisms with diverse roles in our world. From used in baking to that produce life-saving antibiotics, these eukaryotes impact our lives in countless ways. Their unique characteristics set them apart from other microbes.
Fungi reproduce through both asexual and sexual methods, allowing for genetic diversity and efficient spread. They're classified into major groups based on their reproductive structures and life cycles. Some fungi can cause infections or produce harmful toxins, while others play crucial ecological roles in and .
Introduction to Fungi
Relevance of fungi in microbiology
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- Fungi are eukaryotic microorganisms studied in microbiology due to their diverse roles and impacts
- are unicellular fungi
- Reproduce by budding or fission, resulting in rapid population growth
- Used in fermentation processes to produce bread, beer, and wine
- Some yeasts, such as , are opportunistic pathogens that cause infections
- are multicellular fungi
- Grow as filamentous that form a network called a
- Produce for reproduction and dispersal, enabling them to spread easily
- Some molds, like , produce antibiotics while others, such as Aspergillus, are used in food production
- are unicellular fungi
Distinguishing characteristics of fungi
- Eukaryotic organisms with membrane-bound organelles and a true nucleus, unlike prokaryotic bacteria
- Cell walls composed of , a tough polysaccharide, which differs from peptidoglycan in bacteria and cellulose in plants
- Heterotrophs that absorb nutrients from their environment rather than producing their own food
- Lack chlorophyll and do not perform photosynthesis, unlike plants and some protists
- Reproduce by producing , both sexually and asexually, allowing for genetic diversity and efficient dispersal
- Some fungi exhibit , the ability to switch between yeast and mold forms depending on environmental conditions
Fungal Reproduction and Classification
Asexual vs sexual fungal reproduction
- Asexual reproduction
- Involves a single parent and produces genetically identical offspring (clones)
- Methods include fragmentation, budding, and spore formation
- Fragmentation occurs when break into smaller pieces, each capable of growing into a new
- Budding involves the formation of a small outgrowth (bud) on the parent cell, which separates and matures into a new individual
- Spore formation occurs when specialized structures produce and release asexual spores, such as or
- Sexual reproduction
- Involves the fusion of two compatible haploid cells to form a diploid zygote
- Meiosis occurs to produce haploid spores, which then germinate to form new haploid individuals
- Allows for genetic recombination and increased genetic diversity within the population
Major groups of fungi
-
- Produce during sexual reproduction, which are thick-walled structures formed by the fusion of two compatible hyphae
- Example: , commonly known as bread mold
-
- Produce within sac-like structures called during sexual reproduction
- Examples: cerevisiae (baker's yeast) and (produces the antibiotic )
-
- Produce on club-shaped structures called during sexual reproduction
- Examples: (button mushrooms) and (a pathogenic yeast)
- (Fungi Imperfecti)
- Fungi with no known sexual stage or those in which sexual reproduction is rare
- Examples: (used in food production) and (causes athlete's foot)
Classification system for fungi
- Kingdom Fungi is divided into four main phyla
- Phylum Zygomycota
- Phylum Ascomycota
- Phylum Basidiomycota
- Phylum Deuteromycota (Fungi Imperfecti)
- Classification is based on morphological characteristics, reproductive structures, and molecular data
Fungal Pathogens and Toxins
Common fungal pathogens and infections
- Candida albicans
- Causes candidiasis, which includes oral thrush and vaginal yeast infections
- Opportunistic pathogen that primarily affects immunocompromised individuals
-
- Causes aspergillosis, a respiratory infection that can lead to invasive infections in immunocompromised patients
- Inhalation of spores can cause allergic reactions or fungal growth in the lungs
- and
- Cause dermatophytoses, such as , athlete's foot, and jock itch
- Infect keratinized tissues, including skin, hair, and nails
- Cryptococcus neoformans
- Causes cryptococcosis, a potentially fatal fungal meningitis that primarily affects immunocompromised individuals
- Infection occurs through inhalation of spores, which can disseminate to the central nervous system
Toxin-producing fungi and health impacts
- are secondary metabolites produced by some fungi that can cause acute or chronic toxicity in humans and animals
- , produced by Aspergillus species, contaminate crops like corn, peanuts, and tree nuts and are potent carcinogens linked to liver cancer
- , produced by , contaminate rye and other cereals, causing ergotism characterized by hallucinations, gangrene, and convulsions
- , produced by Aspergillus and Penicillium species, contaminate grains, coffee, and wine and are nephrotoxic and potentially carcinogenic
- Proper food storage and handling practices are essential to minimize the risk of mycotoxin exposure and associated health problems
Fungal Ecology and Interactions
Ecological roles of fungi
- Decomposition: Fungi play a crucial role in breaking down organic matter, recycling nutrients in ecosystems
- Symbiosis: Many fungi form mutually beneficial relationships with other organisms
- Mycorrhizae: Symbiotic associations between fungi and plant roots, enhancing nutrient uptake for plants
- Lichens: Symbiotic relationships between fungi and algae or cyanobacteria
- : Fungi occupy diverse niches in terrestrial and aquatic environments, influencing ecosystem dynamics
Fungal cell structure and antifungal agents
- includes unique features that can be targeted by
- Cell wall composed of and glucans
- Ergosterol in the cell membrane instead of cholesterol
- Antifungal agents exploit differences between fungal and human cells to selectively target fungi
- Examples include azoles, which inhibit ergosterol synthesis, and echinocandins, which disrupt cell wall formation
Key Terms to Review (83)
Aflatoxin: Aflatoxin is a toxic secondary metabolite produced by certain species of the Aspergillus fungus. It is commonly found in crops like peanuts, maize, and tree nuts and poses significant health risks to humans and animals.
Aflatoxins: Aflatoxins are a group of highly toxic and carcinogenic compounds produced by certain strains of the Aspergillus fungus, particularly Aspergillus flavus and Aspergillus parasiticus. These naturally occurring mycotoxins can contaminate a variety of agricultural commodities and pose significant health risks to humans and animals if consumed in high amounts.
Agaricus bisporus: Agaricus bisporus, commonly known as the white button mushroom, is a species of edible fungus that belongs to the Basidiomycota phylum. It is one of the most widely cultivated and consumed mushrooms in the world, prized for its culinary versatility and nutritional value.
Antifungal Agents: Antifungal agents are a class of medications used to treat fungal infections by inhibiting or killing fungal cells. These agents play a crucial role in the management of various mycotic diseases affecting humans, animals, and plants.
Antifungal medications: Antifungal medications are pharmaceutical agents used to treat and prevent mycoses, which are fungal infections. They work by targeting various components of fungal cells, such as cell membranes or enzymes.
Asci: Asci are the specialized reproductive structures found in the phylum Ascomycota, a major group of fungi. These structures are responsible for the production and release of sexual spores called ascospores, which are a key feature of the fungal life cycle.
Ascocarps: Ascocarps are the fruiting bodies of ascomycete fungi, responsible for producing and releasing spores. They come in various shapes and sizes, including apothecia, perithecia, and cleistothecia.
Ascomycota: Ascomycota is a phylum of fungi known for their sac-like structures called asci, where spores are produced. This group includes yeasts, molds, and morels.
Ascospores: Ascospores are specialized spores produced within an ascus, a sac-like structure, during the sexual reproduction of ascomycete fungi. They play a crucial role in the dissemination and genetic diversity of these fungi.
Ascospores: Ascospores are a type of spore produced within a specialized structure called an ascus by certain fungi, particularly those in the phylum Ascomycota. These spores serve as a means of asexual reproduction and dispersal for the fungal organism.
Ascus: An ascus is a specialized cell in which spores of ascomycete fungi are formed. It typically contains eight ascospores arranged in a sac-like structure.
Aspergillus fumigatus: Aspergillus fumigatus is a ubiquitous fungus that can cause a range of respiratory infections, from mild allergic responses to life-threatening invasive disease. It is a key topic in the study of fungi, the anatomy and microbiota of the respiratory tract, as well as respiratory mycoses.
Aspergillus oryzae: Aspergillus oryzae is a filamentous fungus that has been widely used in the production of traditional Japanese foods and fermented beverages. It is a key microorganism in the fermentation processes that create products like soy sauce, miso, and sake.
Basidia: Basidia are specialized reproductive structures found in Basidiomycota fungi, responsible for producing basidiospores. They typically develop on the gills of mushrooms and other basidiomycete fruiting bodies.
Basidia: Basidia are club-shaped structures found in the fruiting bodies of basidiomycete fungi, such as mushrooms and puffballs. They are the spore-bearing structures that produce and release the fungal spores, enabling the dispersal and reproduction of these organisms.
Basidiocarps: Basidiocarps are the fruiting bodies of basidiomycete fungi, responsible for producing and dispersing spores. They often appear as mushrooms, brackets, or puffballs.
Basidiomycota: Basidiomycota is a phylum of fungi characterized by the production of sexual spores on a structure called a basidium. They include mushrooms, puffballs, and shelf fungi.
Basidiospores: Basidiospores are reproductive spores produced by Basidiomycete fungi. They are typically formed on specialized cells called basidia during the sexual reproduction phase.
Basidiospores: Basidiospores are the reproductive spores produced by fungi in the phylum Basidiomycota. These spores are formed on club-shaped structures called basidia and are the primary means of dispersal and propagation for many fungal species.
Blastomycosis: Blastomycosis is a fungal infection caused by the dimorphic fungus Blastomyces dermatitidis. It primarily affects the lungs but can disseminate to other body parts such as skin and bones.
Budding yeasts: Budding yeasts are a type of unicellular fungi that reproduce asexually through a process called budding. During budding, a new cell forms as a small protrusion on the parent cell and eventually detaches to become an independent organism.
Candida albicans: Candida albicans is a dimorphic fungus that can exist in both yeast and hyphal forms. It is a common opportunistic pathogen in humans, causing infections primarily when the immune system is compromised.
Chitin: Chitin is a long-chain polymer of N-acetylglucosamine, a derivative of glucose, which forms the structural component in the exoskeletons of arthropods and the cell walls of fungi. It provides rigidity and structural integrity to these organisms.
Chitin: Chitin is a long-chain polymer of N-acetylglucosamine, a derivative of glucose. It is a structural polysaccharide that is a major component of the cell walls of fungi and the exoskeletons of arthropods, such as crustaceans and insects.
Chytrids: Chytrids are a group of fungi characterized by their production of zoospores, which have a single flagellum. They are primarily aquatic and can be found in freshwater and soil environments.
Claviceps purpurea: Claviceps purpurea is a fungus that infects rye and other cereal grains, producing a dark, elongated fruiting body known as an ergot. This fungus is a significant agricultural pest and has also been historically important in the development of certain pharmaceuticals.
Conidia: Conidia are asexual, non-motile spores of fungi that are produced externally on specialized structures called conidiophores. They play a crucial role in the reproduction and dispersion of various fungal species.
Conidia: Conidia are asexual spores produced by fungi that serve as a means of dispersal and reproduction. They are formed through a process called conidiation and play a crucial role in the life cycle and ecology of many fungal species.
Cryptococcus neoformans: Cryptococcus neoformans is an encapsulated yeast that primarily causes infections in immunocompromised individuals. It is notable for causing severe respiratory and central nervous system infections.
Decomposition: Decomposition is the process by which organic matter, such as plant and animal remains, is broken down into simpler substances through the action of microorganisms, enzymes, and physical forces. This process is a crucial part of nutrient cycling and energy flow in ecosystems.
Dermatophytes: Dermatophytes are a group of fungi that cause infections in keratinized tissues such as skin, hair, and nails. They are responsible for common fungal infections like athlete's foot and ringworm.
Deuteromycota: Deuteromycota, also known as Fungi Imperfecti, are a group of fungi that lack a known sexual stage in their life cycle. They are classified based on their asexual reproductive structures and other morphological characteristics.
Dikaryotic: Dikaryotic refers to a fungal cell state where two genetically distinct nuclei coexist within a single cell. This stage is common in the life cycle of many fungi, particularly in the phylum Basidiomycota and Ascomycota.
Dimorphic fungi: Dimorphic fungi are fungi that can exist in two different morphological forms: as molds at lower temperatures and as yeasts at higher temperatures. This ability allows them to adapt to varying environmental conditions.
Dimorphism: Dimorphism refers to the ability of certain organisms, such as fungi and some pathogens, to exist in two distinct forms or phases. This versatility allows these organisms to adapt to different environmental conditions and host interactions, often contributing to their virulence and pathogenicity.
Enterocystozoan bieneusi: Enterocystozoan bieneusi is a microsporidian fungus that primarily infects the intestinal cells of humans and other animals, causing microsporidiosis. It is an obligate intracellular parasite known for its zoonotic potential.
Ergosterols: Ergosterols are a group of sterol compounds that form an essential component of fungal cell membranes, similar to cholesterol in animal cells. They play a crucial role in maintaining cell membrane integrity and fluidity.
Ergot Alkaloids: Ergot alkaloids are a group of naturally occurring toxins produced by the fungus Claviceps purpurea, which infects grains such as rye, wheat, and barley. These alkaloids have potent physiological effects on the human body and have been historically used for both medicinal and recreational purposes.
Fungal Cell Structure: Fungal cell structure refers to the unique features and components that make up the cells of fungi, a diverse group of eukaryotic organisms. Understanding the structure of fungal cells is crucial in the study of fungi, their biology, and their interactions with other organisms.
Fungal Ecology: Fungal ecology is the study of the interactions and relationships between fungi and their surrounding environment, including other organisms, abiotic factors, and the roles they play in various ecosystems. It explores the diverse ways in which fungi influence and are influenced by the natural world.
Fungi: Fungi are a kingdom of eukaryotic organisms that include microorganisms such as yeasts, molds, and mushrooms. They play crucial roles in nutrient cycling and decomposition.
Fungicides: Fungicides are chemical or biological agents specifically designed to inhibit or eliminate fungal pathogens that can cause diseases in plants and other organisms. They play a crucial role in agriculture, medicine, and various industries by controlling harmful fungi.
Hyphae: Hyphae are the long, thread-like structures that make up the mycelium of a fungus. They are important for nutrient absorption and growth.
Hyphae: Hyphae are the long, branching filamentous structures that make up the body of a fungus. They are the fundamental units of fungal growth and are responsible for the characteristic appearance and function of fungi.
Karyogamy: Karyogamy is the process in which two haploid nuclei fuse to form a diploid nucleus during sexual reproduction in fungi. This is a critical step in the fungal life cycle, leading to genetic recombination.
Microsporidia: Microsporidia are a group of spore-forming unicellular parasites primarily affecting insects and other arthropods, but also causing disease in humans. They are known for their unique infection mechanism involving a polar tube.
Microsporidiosis: Microsporidiosis is an infection caused by microsporidia, a group of spore-forming unicellular parasites. It primarily affects immunocompromised individuals, leading to various clinical manifestations.
Microsporum: Microsporum is a genus of fungi known for causing dermatophytosis in humans and animals, primarily affecting the skin, hair, and nails. It is one of the main pathogens responsible for ringworm infections.
Molds: Molds are filamentous fungi that grow in the form of multicellular thread-like structures called hyphae. They play significant roles in decomposition and can reproduce both sexually and asexually.
Molds: Molds are a type of fungi that grow in the form of multicellular filaments called hyphae. They are ubiquitous in the environment and play a crucial role in the decomposition of organic matter as well as in various industrial and medical applications.
Mucor: Mucor is a genus of fungi commonly found in soil, decaying organic matter, and sometimes in human respiratory systems. It can cause mucormycosis, a serious infection particularly affecting immunocompromised individuals.
Mycelium: Mycelium is the vegetative part of a fungus, consisting of a network of fine white filaments (hyphae). It plays a crucial role in nutrient absorption and decomposition.
Mycelium: Mycelium is the vegetative part of a fungus, consisting of a network of fine, tubular filaments called hyphae. It is the primary structure responsible for the growth, reproduction, and nutrient absorption of fungi, playing a crucial role in their biology and ecological functions.
Mycology: Mycology is the scientific study of fungi, which are a diverse group of eukaryotic organisms that include yeasts, molds, and mushrooms. As a branch of microbiology, mycology focuses on the identification, classification, and understanding of the biology, ecology, and pathogenic potential of these fascinating microbes.
Mycorrhizal fungi: Mycorrhizal fungi are symbiotic associations between fungi and plant roots that enhance nutrient uptake for the plant and provide carbohydrates to the fungi. They are crucial for plant health and soil ecology.
Mycoses: Mycoses are fungal infections that can affect various parts of the body, including the skin. They can range from superficial infections to more serious systemic conditions.
Mycotoxins: Mycotoxins are toxic secondary metabolites produced by certain fungi that can contaminate food and animal feed. They pose a significant threat to human and animal health due to their ability to cause a wide range of adverse effects, including carcinogenic, mutagenic, teratogenic, and immunosuppressive properties.
Neurospora crassa: Neurospora crassa is a type of filamentous fungus often used as a model organism in molecular and cellular biology. It is known for its role in genetic and biochemical research.
Ochratoxins: Ochratoxins are a group of toxic secondary metabolites produced by certain species of Aspergillus and Penicillium fungi. These mycotoxins are known for their nephrotoxic, carcinogenic, and immunosuppressive properties, making them a significant concern in food and agricultural safety.
Penicillin: Penicillin is a group of antibiotics derived from Penicillium fungi. It is widely used to treat bacterial infections by inhibiting cell wall synthesis.
Penicillium: Penicillium is a genus of fungi known for its role in natural environments, food production, and antibiotic discovery. It is commonly found in soil, decaying vegetation, and indoor environments.
Penicillium chrysogenum: Penicillium chrysogenum is a species of fungus that is best known for its ability to produce the antibiotic penicillin, one of the most important and widely used medications in modern medicine. As a member of the Fungi kingdom, it plays a significant role in the context of the 5.3 Fungi topic.
Polar tubule: A polar tubule is a specialized structure used by microsporidia, a group of spore-forming unicellular parasites, to invade host cells. It acts like a harpoon to pierce the host cell membrane and inject infectious material.
Pseudohypha: Pseudohyphae are chains of elongated yeast cells that remain attached to one another, resembling the filaments of true hyphae but with constrictions at the septa. They are typically observed in certain species of fungi during specific growth conditions.
Rhizopus stolonifer: Rhizopus stolonifer is a species of filamentous fungi commonly known as black bread mold. It primarily grows on bread and other carbohydrate-rich substrates.
Ringworm: Ringworm is a common fungal infection of the skin caused by dermatophytes. It presents as a red, circular rash with clearer skin in the middle.
Rusts: Rusts are a group of fungal pathogens that primarily affect plants, causing disease and significant agricultural damage. They belong to the phylum Basidiomycota and are known for their complex life cycles involving multiple hosts.
Saccharomyces: Saccharomyces is a genus of fungi known for its role in fermentation and baking. It includes species like Saccharomyces cerevisiae, commonly used in the production of bread, beer, and wine.
Septate hyphae: Septate hyphae are fungal filaments characterized by their segmented structure with cross-walls called septa. These septa divide the hyphae into distinct, individual cells.
Smuts: Smuts are a group of fungi that primarily affect cereal crops and grasses, causing diseases characterized by black, powdery spores. These pathogens belong to the order Ustilaginales.
Sporangiospores: Sporangiospores are asexual spores produced within specialized reproductive structures called sporangia by certain fungi. These spores are an important part of the fungal life cycle and play a crucial role in the dispersal and propagation of fungal species.
Spores: Spores are reproductive cells produced by fungi, capable of developing into a new individual without sexual fusion. They are adapted to survive in adverse environmental conditions.
Spores: Spores are specialized reproductive structures produced by various microorganisms, including fungi, bacteria, and some protists. They are designed to withstand harsh environmental conditions and serve as a means of dispersal and survival for the parent organism.
Symbiosis: Symbiosis refers to the close and often long-term interaction between two or more different organisms, where at least one organism benefits from the relationship. This term is central to understanding the complex relationships that exist among various microorganisms, as well as between microbes and their host organisms, in the context of the topics 1.3 Types of Microorganisms, 4.1 Prokaryote Habitats, Relationships, and Microbiomes, 5.3 Fungi, and 5.5 Lichens.
Thallus: Thallus is the vegetative body of fungi, algae, and some non-vascular plants. It lacks true roots, stems, and leaves.
Trichophyton: Trichophyton is a genus of fungi primarily responsible for dermatophytic infections in humans, such as athlete's foot and ringworm. These fungi invade keratinized tissues including skin, hair, and nails.
Trichophyton rubrum: Trichophyton rubrum is a dermatophytic fungus that causes common skin infections such as athlete's foot, jock itch, and ringworm. It thrives in warm, moist environments and primarily affects keratinized tissues like skin, nails, and hair.
Valley fever: Valley fever, also known as coccidioidomycosis, is a fungal infection caused by Coccidioides species. It primarily affects the lungs but can spread to other parts of the body.
Yeasts: Yeasts are unicellular fungi that reproduce asexually by budding or binary fission. They are used in various industries and play a crucial role in fermentation processes.
Yeasts: Yeasts are a diverse group of single-celled fungi that play a vital role in various biological and industrial processes. They are eukaryotic microorganisms that reproduce asexually through budding or binary fission, and they are found in a wide range of environments, from the human gut to the fermentation of alcoholic beverages.
Zygomycota: Zygomycota is a phylum of fungi characterized by the formation of zygospores during sexual reproduction. They include fast-growing molds commonly found on decaying plant and animal matter.
Zygospores: Zygospores are thick-walled resting spores formed by the fusion of two similar gametangia in fungi. They are a key characteristic of the phylum Zygomycota, providing a means for survival in adverse conditions.
Zygospores: Zygospores are a specialized type of spore formed during sexual reproduction in certain fungi, particularly in the phylum Glomeromycota and the order Mucorales. They serve as a resting, resistant stage in the fungal life cycle, allowing the organism to survive unfavorable environmental conditions.