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Fungi – Definition, Characteristics, Morphology, Importance, Thallus Organization.

What is Fungi?

  • Fungi, a distinct kingdom of eukaryotic organisms, are primarily multicellular entities that do not possess the capability to photosynthesize, distinguishing them from plants.
  • These organisms, instead, are heterotrophic, relying on the absorption of dissolved nutrients from their surroundings, often achieved by excreting digestive enzymes. This method of nutrient acquisition is facilitated by the presence of chitin in their cell walls, a feature that further demarcates fungi from plants, bacteria, and certain protists.
  • The vast realm of fungi encompasses a myriad of microorganisms, from the microscopic yeasts and molds to the more conspicuous mushrooms.
  • These organisms, collectively termed Eumycota or true fungi, share a common evolutionary lineage, a fact corroborated by molecular phylogenetic studies. This classification sets them apart from structurally analogous entities like myxomycetes (slime molds) and oomycetes (water molds).
  • Fungi play a pivotal role in ecological systems, primarily as decomposers, facilitating the breakdown of organic matter and thereby participating in essential nutrient cycling processes. Their ubiquity is often understated due to their minute structures and their propensity to thrive in concealed environments like soil or decaying matter.
  • However, their significance extends beyond decomposition. Symbiotic relationships with plants, animals, and other fungi, as well as parasitic interactions, are common within the fungal kingdom. Moreover, their reproductive capabilities are versatile, encompassing both sexual and asexual modes.
  • From a human-centric perspective, fungi have been indispensable. Historically, they have been utilized as food sources, in the form of mushrooms and truffles, and have been instrumental in food fermentation processes, evident in the production of bread, wine, beer, and soy sauce. The latter half of the 20th century witnessed the harnessing of fungi for antibiotic production.
  • Presently, fungal enzymes find applications in industries and detergents, and certain fungi serve as biological control agents against pests and weeds.
  • However, the relationship between fungi and other organisms is not always symbiotic. Some fungi are pathogenic, causing diseases in plants, animals, and humans. Their ability to produce mycotoxins, compounds detrimental to animal health, underscores their potential harm. Furthermore, certain fungi produce psychotropic compounds, which have been historically used in recreational or spiritual contexts.
  • The vastness of the fungal kingdom is underscored by its estimated biodiversity, ranging from 2.2 to 3.8 million species. Yet, a significant portion of this diversity remains uncharted, with only about 148,000 species described to date. Traditional taxonomic approaches, based on morphology and physiology, have been complemented by molecular genetics, leading to a more nuanced understanding of fungal classification.
  • Etymologically, the term “fungus” traces its origins to Latin and Greek, denoting mushroom-like structures. The study of fungi, termed mycology, similarly derives from Greek roots. The term “mycobiota” encompasses the entirety of fungal species within a specific region, emphasizing the parallelism with terms like “fauna” and “flora.”
  • In conclusion, fungi, with their diverse ecological roles, symbiotic relationships, and economic significance, constitute an integral component of our biosphere. Their study, mycology, continues to unravel the intricacies of this fascinating kingdom, emphasizing their indispensability in maintaining ecological balance and their multifaceted interactions with other organisms.

Definition of Fungi

Fungi are a kingdom of eukaryotic organisms, primarily multicellular, that lack chlorophyll, do not photosynthesize, and obtain nutrients through absorption, often decomposing organic matter in the process. They possess cell walls made of chitin and can reproduce both sexually and asexually. Examples include mushrooms, yeasts, and molds.

Characteristics of Fungi

Fungi, distinct from plants and animals, are eukaryotic organisms with a myriad of unique and shared features that define their biology and ecology. Herein, we delve into the salient characteristics of fungi:

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  1. Cellular Structure and Composition:
    • Fungi are predominantly non-vascular and non-motile.
    • Their cells are eukaryotic, which means they contain membrane-bound organelles and nuclei.
    • Unlike plants, fungi lack chloroplasts and thus, cannot photosynthesize.
    • The fungal cell wall is a complex of chitin and glucan. This is a distinguishing feature as plants have cellulose-based cell walls, and chitin is also found in the exoskeletons of arthropods.
    • Fungi store energy as starch, and their nuclei are typically small.
  2. Growth and Morphology:
    • Fungi can be unicellular (like yeasts) or filamentous. The filamentous structures, known as hyphae, grow by elongation at their tips.
    • Some fungi exhibit dimorphism, transitioning between yeast and hyphal forms based on environmental cues.
    • Structures such as rhizomorphs are formed by certain fungi, akin to plant roots, aiding in nutrient transport.
  3. Reproduction:
    • Fungi reproduce both sexually and asexually, often via spores.
    • They undergo alternation of generations, and interestingly, they lack an embryonic stage, developing directly from spores.
    • Certain fungi produce pheromones, facilitating sexual reproduction.
  4. Nutrition:
    • Being heterotrophic, fungi obtain nutrients by absorption. This is facilitated by their secretion of digestive enzymes into the environment, breaking down complex organic matter.
    • They play a pivotal role in ecosystems as decomposers, recycling nutrients.
  5. Interactions and Ecology:
    • Some fungi establish symbiotic relationships, while others can be parasitic, infecting host organisms.
    • Bioluminescence is exhibited by over a hundred fungal species, a phenomenon where organisms produce and emit light.
  6. Biochemical Pathways:
    • Fungi possess the α-aminoadipate pathway for L-lysine biosynthesis, a feature shared with euglenoids and certain bacteria.
    • They have a unique biosynthetic pathway for terpenes, distinct from plants.
  7. Economic and Ecological Significance:
    • Fungi are paramount in nutrient cycling and have been harnessed by humans for food, medicine, and other industrial applications.
    • However, they can also be pathogenic, causing diseases in plants, animals, and humans.

Historically, due to certain morphological similarities with plants, fungi were erroneously classified under the plant kingdom. However, advancements in molecular biology and phylogenetics have firmly established fungi as a separate kingdom, highlighting their unique evolutionary trajectory. Their diverse roles, from decomposers to pathogens, underscore their ecological significance and the importance of understanding their biology.

Dimorphism of fungi

Dimorphism, a distinctive trait observed in certain fungi, refers to their ability to exist in two distinct morphological forms. This phenomenon is particularly prevalent among some pathogenic fungi, allowing them to adapt and thrive in varied environments.

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  1. Nature of Dimorphism:
    • Certain fungi that are pathogenic to animals and humans predominantly manifest as unicellular yeasts within the host. However, when cultured in laboratory conditions or present in soil, they adopt a filamentous mold form.
    • Conversely, some plant-pathogenic fungi exhibit the opposite behavior. Within the host cell, they present as multicellular or filamentous molds, but when cultured in laboratory media, they assume a yeast-like form.
  2. Examples of Dimorphic Fungi:
    • Human Pathogens: Notable human pathogenic fungi displaying dimorphism include Histoplasma, Sporothrix, and Blastomyces.
    • Plant Pathogens: On the plant side, fungi such as those from the Taphrinales and Ustilaginales orders are exemplary of this dimorphic behavior.
  3. Factors Influencing Dimorphism:
    • The transition between the two morphological states in dimorphic fungi is not arbitrary but is influenced by specific environmental or physiological cues.
    • For instance, temperature plays a pivotal role in determining the morphological state of certain fungi. A shift in temperature from 20-25°C to 37°C can induce yeast-like growth in fungi like Paracoccidioids brasiliensis and Blastomyces dermatitidis.

In essence, dimorphism in fungi is an adaptive mechanism, allowing them to navigate and colonize diverse environments, from host organisms to external surroundings. This inherent flexibility underscores the evolutionary advantage it confers, especially for pathogenic fungi, facilitating their survival and propagation in varied conditions. Understanding this phenomenon is crucial, especially in the context of medical and agricultural research, as it sheds light on fungal pathogenicity and potential intervention strategies.

Structure of Fungi

Fungi, distinct from other eukaryotic organisms, exhibit a unique structural composition that underpins their ecological roles and biological functions. Herein, we elucidate the fundamental structural attributes of fungi:

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  1. Cellular Organization:
    • Fungi can manifest as single-celled organisms, exemplified by yeasts, or as multicellular entities.
    • Unlike many eukaryotes, a significant proportion of fungi adopt a filamentous configuration.
  2. Hyphal Structure:
    • The primary structural unit of most fungi is the hypha, a long, slender, thread-like structure.
    • Collectively, an intricate network of these hyphae constitutes the mycelium, which is the vegetative part of the fungus. This mycelial network serves as the primary mode of growth and nutrient absorption.
  3. Cell Wall Composition:
    • A defining feature of fungi is their robust cell wall, which provides structural integrity and protection.
    • This wall is predominantly composed of chitin, a complex polysaccharide, setting fungi apart from plants, which have cellulose-based cell walls.
  4. Protoplast Components:
    • Beneath the cell wall lies the protoplast, encompassing the vital cellular components.
    • The protoplast houses the cell membrane, a semi-permeable barrier regulating the ingress and egress of substances.
    • The cytoplasm, a gel-like matrix, contains various cell organelles essential for metabolic processes and cellular functions.
  5. Nuclear Characteristics:
    • Central to the fungal cell is the nucleus, a repository of genetic information.
    • This nucleus is characterized by its clarity and dense chromatin threads, which contain the organism’s DNA.
    • Encasing the nucleus is the nuclear membrane, safeguarding the genetic material and maintaining the nucleus’s distinct environment.

In summary, the structural framework of fungi, from their filamentous hyphae to their chitin-rich cell walls, is tailored to their ecological niches and biological roles. This unique architecture facilitates their growth, reproduction, and interactions with the environment, underscoring the importance of understanding fungal morphology in the broader context of biology and ecology.

Thallus organization of fungi

The structural organization of fungi is intricate, with the thallus playing a central role in defining their morphology and function. The thallus, essentially the body of the fungus, exhibits varied organizational patterns that are pivotal for the growth, nutrition, and reproduction of these organisms.

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  1. Hyphal Structure:
    • The primary structural component of the fungal thallus is the hypha (plural: hyphae). These are slender, tubular filaments that collectively form the foundational architecture of most fungi.
    • Derived from the Greek word “hyphe,” meaning web, hyphae aptly describe the web-like appearance of the fungal mycelium.
  2. Mycelium:
    • The entirety of the hyphal network is termed the mycelium. This intricate meshwork permeates the substrate, facilitating nutrient absorption and growth.
    • Each hypha is a transparent filament filled with cytoplasm, encapsulated by a thin cell wall.
  3. Differentiation of the Thallus:
    • In many fungi, the thallus is bifurcated into two primary segments: the vegetative and the reproductive parts.
      • Vegetative Part: This segment is instrumental in nutrient absorption, ensuring the sustenance of the fungus.
      • Reproductive Part: Dedicated to the formation of reproductive structures, this part is pivotal for the propagation of the species.
    • Fungi with such a clear demarcation between vegetative and reproductive structures are termed eucarpic.
  4. Holocarpic Thallus:
    • Contrasting the eucarpic organization, some fungi possess a holocarpic thallus. In these fungi, there’s an absence of clear differentiation between vegetative and reproductive structures.
    • Following a phase of vegetative growth, the entire thallus transitions into reproductive structures. The term “holocarpic” is derived from the Greek words “holos” (entirely) and “karpos” (fruit), aptly describing the all-encompassing nature of the reproductive phase in these fungi.

In summation, the thallus organization in fungi is a testament to their adaptive capabilities, allowing them to thrive in diverse environments. Whether it’s the intricate network of hyphae or the specialized reproductive structures, the thallus is central to the life cycle and ecological roles of fungi. Understanding this organization provides insights into fungal biology, ecology, and their interactions with the environment.

Morphology of Fungi

The morphology of fungi is diverse and intricate, encompassing both microscopic and macroscopic structures that define their growth, reproduction, and interactions with the environment.

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  1. Microscopic Structures:
    • Hyphae: The foundational units of most fungi are hyphae, which are slender, cylindrical, thread-like entities measuring between 2–10 µm in diameter. These structures grow at their tips, known as apices, and can extend to several centimeters in length. New hyphae emerge either by branching from existing ones or through the forking of growing hyphal tips.
    • Mycelium: As hyphae grow and branch, they form an interconnected network termed the mycelium.
    • Septate vs. Coenocytic Hyphae: Hyphae can be categorized as either septate, having internal cross walls (septa) that compartmentalize the structure, or coenocytic, which lack these divisions and essentially function as multinucleate supercells.
    • Specialized Hyphal Structures: Some fungi evolve specialized hyphal structures for nutrient acquisition from hosts. Examples include haustoria in plant-parasitic fungi and arbuscules in mycorrhizal fungi.
    • Cell Wall Composition: Unique to fungi among eukaryotes, their cell walls contain chitin, a biopolymer, in addition to glucans and other components.
  2. Macroscopic Structures:
    • Visible Mycelia: In certain conditions, fungal mycelia become visible to the naked eye, manifesting as molds on surfaces like damp walls or spoiled food. When cultivated on solid agar in laboratory settings, these mycelia form colonies, which can be characterized by their growth patterns, colors, and other diagnostic features.
    • Fruit Bodies: In some fungi, particularly the basidiomycetes and certain ascomycetes, the mycelium can differentiate into large structures known as fruit bodies. These can be macroscopic and are often recognized as mushrooms. They play a pivotal role in sexual reproduction.
    • Apothecium: Specific to ascomycetes, the apothecium is a cup-shaped macroscopic structure housing the hymenium, a tissue layer responsible for spore production.
    • Colony Dimensions: Some fungal colonies can achieve remarkable sizes and ages. For instance, a clonal colony of Armillaria solidipes spans over 900 hectares and is estimated to be nearly 9,000 years old.

In summary, the morphology of fungi is a testament to their adaptability and evolutionary success. From the microscopic intricacies of their hyphal networks to the macroscopic grandeur of their fruit bodies, fungi exhibit a range of structures that facilitate their survival, growth, and reproduction across diverse habitats.

Types of Fungi

The Kingdom Fungi, with its vast diversity and adaptability, has been systematically classified based on various criteria. This classification provides a structured understanding of the relationships and characteristics of different fungal groups. Here’s a detailed breakdown:

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  1. Based on Nutritional Modes:
    • Saprophytic Fungi: These fungi derive their nutrients from decaying organic matter. They play a crucial role in decomposition and nutrient cycling. Notable examples include Rhizopus, Penicillium, and Aspergillus.
    • Parasitic Fungi: These fungi establish a relationship with living organisms, either plants or animals, from which they extract nutrients, often to the detriment of the host. Taphrina and Puccinia are classic examples.
    • Symbiotic Fungi: Engaging in mutualistic interactions, these fungi coexist with other species, benefiting both parties. Lichens, a partnership between fungi and algae, and mycorrhiza, an association between fungi and plant roots, exemplify this category.
  2. Based On Spore Formation:
    • Zygomycetes: Characterized by the formation of zygospores through the fusion of two distinct cells, these fungi possess non-septate hyphae. Asexual reproduction is facilitated by sporangiospores. Mucor is a representative example.
    • Ascomycetes: Often referred to as “sac fungi”, these can exist in various lifestyles, from decomposers to parasites. Ascospores are the sexual spores, while conidiospores facilitate asexual reproduction. Saccharomyces serves as a model organism in this group.
    • Basidiomycetes: Commonly recognized as mushrooms, many of these fungi are parasitic. They reproduce sexually via basidiospores. Asexual reproduction mechanisms include conidia, budding, and fragmentation. Agaricus is a prominent member of this class.
    • Deuteromycetes: Dubbed as “imperfect fungi”, they exhibit an irregular reproductive cycle, lacking a sexual phase. Their primary mode of asexual reproduction is through conidia. Trichoderma is an illustrative example.

In conclusion, the classification of fungi provides a systematic approach to understanding the vast diversity within this kingdom. By categorizing fungi based on their nutritional modes and spore formation, researchers and mycologists can better comprehend their ecological roles, evolutionary relationships, and potential applications in various fields.

Reproduction of Fungi

Fungi exhibit a multifaceted reproductive system, encompassing both asexual and sexual mechanisms. This versatility in reproduction underscores their adaptability and evolutionary success across diverse habitats.

  1. Asexual Reproduction:
    • Mechanisms: Asexual reproduction in fungi predominantly occurs through vegetative spores known as conidia or by the fragmentation of mycelium. In the latter, the mycelium breaks into individual segments, each of which can grow into a new mycelium.
    • Significance: Asexual reproduction allows for rapid dispersal and colonization of new niches. It also ensures the propagation of genetically identical offspring, optimized for specific environmental conditions.
    • Fungi Imperfecti: This term refers to fungi that lack an observable sexual stage, emphasizing their reliance on asexual reproduction. However, it’s worth noting that “Fungi imperfecti” or Deuteromycota is not a taxonomically recognized group but rather denotes fungi with an unobserved sexual phase.
  2. Sexual Reproduction:
    • Mechanisms: Sexual reproduction in fungi is intricate. It often involves the fusion of specialized structures or hyphae from two compatible individuals. This fusion, termed anastomosis, initiates the sexual cycle. Depending on the fungal group, specialized structures like asci (in ascomycetes) or basidia (in basidiomycetes) are formed for spore production.
    • Dikaryotic Phase: Many fungi, especially ascomycetes and basidiomycetes, exhibit a dikaryotic phase where two genetically distinct nuclei coexist within a single hyphal cell. This phase can be extensive and is crucial for sexual reproduction.
    • Spore Dispersal: Fungi employ various strategies for spore dispersal. Some utilize wind, while others rely on water droplets or attract insects with vivid colors and odors. Mechanisms like forcible ejection ensure that spores are released efficiently and can travel considerable distances.
    • Homothallism: This is a unique form of sexual reproduction where a single individual can produce offspring by fusing two of its own haploid nuclei. This self-fertile mode of reproduction is believed to be one of the earliest forms of sexual reproduction among eukaryotes.
    • Other Processes: Parasexual processes, though less common, also play a role in genetic exchange among certain fungi. This involves the fusion of hyphae and the exchange of genetic material without the typical meiotic cycle.
  3. Significance of Sexual Reproduction:
    • Sexual reproduction provides genetic diversity, which is crucial for adaptation and evolution. It allows fungi to generate offspring with varied genetic compositions, enhancing their ability to survive in changing environments.

In summary, the reproductive strategies of fungi are diverse and sophisticated, reflecting their evolutionary adaptability and their ability to colonize a myriad of ecological niches. Whether through simple asexual spore production or complex sexual mechanisms, fungi ensure their continued survival and proliferation across ecosystems.

Mycotoxins

Mycotoxins are a group of potent secondary metabolites produced by certain fungi. These compounds, while serving various ecological functions for the fungi, can be harmful or even lethal to animals and plants upon exposure.

  1. Origins and Types:
    • Mycotoxins are synthesized by various fungi, especially those responsible for the spoilage of food. Notable examples include certain species of the Aspergillus genus, which can contaminate grains and nuts.
    • Some of the most recognized mycotoxins include aflatoxins, potent carcinogens that can severely affect the liver; ergot alkaloids from the fungus Claviceps purpurea, historically linked to the ergotism epidemics; and amatoxins found in some Amanita mushrooms, which are deadly if ingested.
    • Other significant mycotoxins encompass ochratoxins, patulin, trichothecenes, fumonisins, and T-2 mycotoxin. These compounds can have a profound impact on human health and the well-being of livestock.
  2. Biological Role:
    • Mycotoxins are considered secondary metabolites, meaning they are not essential for the basic growth, development, or reproduction of the fungus. However, they play crucial roles in the survival and competitiveness of the producing fungi in their environment.
    • These compounds may confer advantages in terms of physiological adaptation, allowing the fungus to thrive in various conditions. They can also provide a competitive edge against other microbes and deter predators or herbivores from consuming the fungi.
  3. Impact on Humans:
    • Mycotoxins can have severe health implications for humans, especially when they contaminate food sources. Chronic exposure can lead to various diseases and conditions, including liver damage, carcinogenesis, and acute poisoning.
    • The historical significance of mycotoxins is evident in events like the ergotism epidemics, caused by the consumption of cereals tainted with ergot alkaloids.
  4. Biochemical Pathways:
    • Research has illuminated specific biochemical pathways in fungi dedicated to the synthesis of mycotoxins. These pathways underscore the evolutionary importance of these compounds to the fungi, even if they are not essential for basic life processes.

In conclusion, mycotoxins, while serving pivotal roles for fungi in their ecological niches, pose significant health risks to animals and plants. Their presence in food sources necessitates rigorous monitoring and management to ensure the safety of human and animal consumption.

Pathogenic mechanisms of Fungi

Fungi have evolved sophisticated mechanisms to infect and thrive within their hosts, often overcoming the host’s defense systems. Two exemplary fungi, Ustilago maydis and Cryptococcus neoformans, demonstrate the intricate strategies fungi employ to establish infections.

  1. Ustilago maydis and Plant Defense:
    • Ustilago maydis is a notorious plant pathogen responsible for smut disease in maize and teosinte.
    • Plants, in their defense against such pathogens, initiate an oxidative burst, producing reactive oxygen species at the invasion site. This is a primary defense mechanism to counteract microbial attacks.
    • U. maydis, however, has evolved a counter-defense mechanism. It activates an oxidative stress response, governed by the YAP1 gene, to neutralize the plant’s oxidative burst. This response not only shields U. maydis from the plant’s defense but is also pivotal for its virulence.
    • Additionally, U. maydis possesses a robust recombinational DNA repair system, functional during both mitosis and meiosis. This system might aid the fungus in mitigating DNA damage inflicted by the plant’s oxidative defenses.
  2. Cryptococcus neoformans and Host Immunity:
    • Cryptococcus neoformans is a versatile encapsulated yeast capable of infecting both plants and animals. In animals, it primarily targets the lungs and is engulfed by alveolar macrophages.
    • Remarkably, certain C. neoformans strains can endure and even proliferate within these macrophages. This intracellular survival underpins the fungus’s latency, its ability to disseminate within the host, and its resistance to antifungal treatments.
    • To counteract the hostile environment within the macrophage, C. neoformans amplifies the expression of genes linked to the oxidative stress response.
    • Another intriguing survival mechanism involves its reproductive strategy. Most C. neoformans are of mating “type a”. Their filaments can become diploid, either through endoduplication or stimulated nuclear fusion, leading to the formation of blastospores. These diploid nuclei can undergo meiosis, resulting in haploid basidiospores that disperse. This process, termed monokaryotic fruiting, necessitates the DMC1 gene, which facilitates chromosome pairing during meiosis and mends DNA double-strand breaks. The ability of C. neoformans to undergo this unique form of meiosis in the oxidative environment of the host macrophage, coupled with its DNA repair capability, might significantly contribute to its virulence.

In summary, fungi have evolved intricate mechanisms to counteract host defenses, ensuring their survival and propagation. Understanding these mechanisms is crucial for devising effective strategies to combat fungal infections.

Examples of Fungi

There are different types of fungi which are range from the smallest unicellular fungi e.g. yeast to larger multicellular which has the ability to form hyphal threads or false roots. That’s why fungi are divided into different groups according to their morphologies.

Yeast Cell

  • These are larger than most bacteria. The size of yeast is ranged from 1 to 5 um in width and from 5 to 30 um or more in length.
  • Yeast can be found in egg-shaped, elongated shapes and some of them are also found in spherical shapes.
  • They lack flagella, which means they are nonmotile.
  • These are single celled fungi and can be found in soil, plants, animals, and in aquatic environments. 
  • Yeast is eukaryotic, which means they contain organelles that are usually found in the cells of higher animals.
  • An example of yeast is Saccharomyces cerevisiae, It contains membrane-bound nucleus, a vacuole, mitochondria, Golgi apparatus as well as the E.R (endoplasmic reticulum).
  • The cell wall of Saccharomyces cerevisiae is consists of glucan (a polysaccharide compound) and mannoproteins.
  • Yeast has a single, linear double-stranded DNA which is made up of several repeated sequences. 
  • Yeast mainly reproduces by budding, where an outgrowth/bud occurs on the surface of the mother cell that eventually breaks off with its genetic material and grows to develop a new cell.

Molds

  • These are the types of fungi that grown well in warmth and moist environment. They can be found on the surface of different food, from where it can get nutrients.
  • Molds are multicellular organisms and can be seen by naked eyes.
  • When they are observed under the microscope a numerous filaments (hyphae) are founds which are known as Mycelium.
  • The thallus of molds is made up of two important parts known as the mycelium or mycelia and the spores. The spores are resistant, resting or dormant cell.
  • Mycelium is referred to as a complex of several filaments which are known as hyphae (singular, hypha). New hyphae generally rise from a spore which on germination puts out a germ tube or tubes. These germ tubes elongate and the branch to form hyphae.
  • The hyphae are about 5 to 10 um wide.
  • The hyphae are made up of an outer tubelike wall which is enclosing a cavity, the lumen, which is loaded wilth protoplasm. 
  • A double-layered membrane is present between the protoplasm and the wall known as plasmalemma, which surrounds the protoplasm. 
  • The hyphal wall is made up of microfibrils which is consist of hemicelluloses or chitin: true cellulose found only in the walls of lower fungi. 
  • Wall matrix material in which the microfibrils are embedded consists of proteins, lipids, and other substances.
  • The microfibrils are embedded within the Wall matrix which is compoed of proteins, lipids, and other substances.
  • The growth of a hypha mainly occurs near the tip. The main region of elongation occurs in the region just after the tip. 
  • The young hypha separated into cells by a cross-wall which is developed by centripetal invagination (inward growth) from the existing cell wall. These cross-walls constrict the plasmalemma and grow inward to form generally an incomplete septum (plural, septa) that has a central pore which allows for protoplasmic streaming. Even nuclei may migrate from cell to cell in the hypha.
Structure of hypha
Structure of hypha

There are three forms of hyphae such as 

  • Nonseptate, or coenocytic, these types of hyphae have no septa. 
  • Septate with uninucleate cells
  • Septate with multinucleate cells, Each cell contains more than one nucleus in each compartment.
types of hypha
types of hypha

There are two types of mycelia such as 

  1. Vegetative: This type of mycelium enters within the medium to get nutrients; soluble nutrients are received through the walls. (Insoluble nutrients are first digested externally by secreted enzymes.) 
  2. Reproductive: This type of mycelia is involved in spore production and usually extend from the medium into the air. The mycelium of a mold may be a loosely woven network or it may be an organized, compact structure, as in mushrooms.

Yeast-like Fungi

  • These are a types of yeast that grow like normal yeast. The individual cells of Yeast-like fungi aggregates and forms a structure is known as pseudo hyphae (not a true hyphae).
  • One example of this type of fungi is Candida. When it observed under a microscope, it shows the organism contain several layers which make up the cell wall.
  • The  C. albicans wall made up of layers of mannoproteins, lipids, and a beta glucan, a chitin inner layer also present that strengthen the cell wall. 
  • C. albicans appears in spherical or ovoid shape and size ranges between 4 to 8 micrometers.
  • They also reproduced by the budding process. They create an elongated chain of cells as they continue dividing to form the pseudohyphae. 
  • C. albicans is a type of polymorphic fungus that can be found in four types of morphology such as the yeast cell, pseudohyphae, hyphae as well as chlamydospores.
  • They have varying appearances when they are viewed under the microscope. This depends on different conditions such as the availability of nutrition, pH, and temperature among others.

Uses of Fungi

Fungi, with their diverse metabolic capabilities and adaptability, have been harnessed by humans for a myriad of applications ranging from culinary to medicinal and industrial.

  1. Culinary and Nutritional Uses:
    • Fungi, especially mushrooms, have been integral to human diets for millennia. Mushroom cultivation, both commercial and wild-harvested, is a significant industry. Examples include the commonly consumed Agaricus bisporus, known as button or Portobello mushrooms, and Asian varieties like shiitakes and oyster mushrooms.
    • Fungi also play a pivotal role in food processing. Saccharomyces cerevisiae, a unicellular fungus, is indispensable for bread-making and alcoholic fermentation. Other fungi, like Aspergillus oryzae, are crucial for brewing soy sauce and sake, and for preparing miso.
    • Certain cheeses owe their unique flavors and textures to fungal inoculation, such as the blue veins in Stilton or Roquefort cheeses, attributed to Penicillium roqueforti.
  2. Medicinal and Therapeutic Uses:
    • Fungi are treasure troves of pharmacologically active compounds. The mold Penicillium rubens gave us the life-saving antibiotic penicillin G. Other antibiotics, immunosuppressants, and cholesterol-lowering drugs have also been derived from fungi.
    • Traditional medicine practices, particularly in Asia, have long utilized certain mushrooms for their supposed therapeutic properties, including Ganoderma lucidum and Ophiocordyceps sinensis.
  3. Industrial and Biotechnological Applications:
    • Fungi are prolific producers of secondary metabolites, many of which find applications in industries. They are employed to produce vitamins, enzymes, and organic acids.
    • Genetic engineering techniques have been developed for fungi, enabling their use in metabolic engineering. Genetically modified yeast species offer potential avenues for efficient pharmaceutical production.
    • Fungi are also being explored for their potential in textile production, meat substitution, and other biotechnological applications.
  4. Environmental and Agricultural Applications:
    • Fungi can be allies in pest control. Entomopathogenic fungi, which parasitize insects, are being used as biopesticides.
    • Certain fungi can degrade pollutants, offering solutions for bioremediation of contaminated sites.
    • In agriculture, fungi can outcompete or parasitize harmful pathogens, providing a natural means of crop protection.
  5. Research and Model Organisms:
    • Fungi have been instrumental in advancing biological research. Organisms like Neurospora crassa, Saccharomyces cerevisiae, and Aspergillus nidulans have been used to unravel fundamental biological processes, from genetics to cell biology.
  6. Safety and Precautions:
    • While many fungi are beneficial, some are toxic and can cause harm when consumed. Notable toxic species include certain Amanita mushrooms. It’s imperative to exercise caution and ensure proper identification before consuming wild mushrooms.

In conclusion, fungi, with their multifaceted roles, have significantly impacted human civilization, from food and medicine to industry and environment. Their continued study promises further innovations and solutions to contemporary challenges.

Advantages of Fungi

Fungi play a crucial role in various ecological, industrial, and medical contexts. Here’s a comprehensive overview of the advantages associated with fungi:

  1. Decomposition and Nutrient Cycling:
    • Fungi are primary decomposers in many ecosystems, breaking down organic matter, including dead plants and animals. This decomposition releases essential nutrients back into the soil, facilitating nutrient cycling.
  2. Mycorrhizal Associations:
    • Many fungi form symbiotic relationships with plants called mycorrhizae. These associations enhance nutrient and water uptake for plants, while the fungi receive sugars and other organic compounds in return.
  3. Food Source:
    • Several fungi, like mushrooms, are edible and provide a source of nutrition for humans. Examples include Agaricus bisporus (button mushrooms) and Lentinula edodes (shiitake mushrooms).
  4. Medicinal Uses:
    • Penicillin, the first antibiotic discovered, was derived from the fungus Penicillium. Other fungi produce compounds with therapeutic properties, such as statins for cholesterol management and immunosuppressants like cyclosporine.
  5. Biotechnological Applications:
    • Fungi are used in various industrial processes, including the production of enzymes, organic acids, and biofuels. Yeasts, like Saccharomyces cerevisiae, play a vital role in baking and brewing.
  6. Bioremediation:
    • Certain fungi can degrade pollutants and contaminants, making them valuable in bioremediation efforts to clean up polluted environments.
  7. Research and Model Organisms:
    • Fungi, such as Saccharomyces cerevisiae (baker’s yeast) and Neurospora crassa, serve as model organisms in scientific research, aiding in understanding cellular and molecular processes.
  8. Agricultural Benefits:
    • Some fungi act as biopesticides, targeting and killing pests. Examples include Beauveria bassiana and Metarhizium anisopliae, which infect and kill insects.
  9. Traditional and Alternative Medicine:
    • Certain mushrooms, like Ganoderma lucidum (reishi) and Inonotus obliquus (chaga), have been used in traditional medicine for their purported health benefits.
  10. Cultured Foods:
    • Fungi play a role in the fermentation of various foods and beverages, including cheese, soy sauce, tempeh, and kombucha.
  1. Biochemical Production:
    • Fungi are employed in the production of chemicals like citric acid, ethanol, and other valuable compounds.
  1. Natural Pest Control:
    • Fungi can act as natural antagonists to certain pests and pathogens, reducing the need for chemical pesticides.
  1. Genetic Engineering:
    • Fungi can be genetically modified for the production of proteins, vaccines, and other compounds, offering a potential alternative to traditional manufacturing methods.

In summary, fungi offer a myriad of benefits, from ecological roles to vast applications in industries and medicine. Their versatility and importance underscore the need for continued research and understanding of these organisms.

Disadvantages of Fungi

Fungi, while offering numerous benefits to ecosystems and humans, also present several disadvantages. Here’s a comprehensive overview of the drawbacks associated with fungi:

  1. Disease Agents:
    • Human Pathogens: Certain fungi can cause diseases in humans, known as mycoses. Examples include Candida (causing thrush and systemic infections), Aspergillus (leading to aspergillosis), and Cryptococcus (resulting in meningitis).
    • Plant Pathogens: Many fungi are responsible for significant crop losses worldwide. Rusts, smuts, and mildews can devastate agricultural produce, leading to economic repercussions.
    • Animal Pathogens: Fungi can also afflict animals, including livestock, leading to diseases like ringworm.
  2. Food Spoilage:
    • Fungi, especially molds, are primary agents of food spoilage. They can degrade stored food, making it unfit for consumption and leading to economic losses.
  3. Mycotoxin Production:
    • Certain fungi produce toxic compounds called mycotoxins. These toxins can contaminate food and feed, posing severe health risks when ingested. Aflatoxins produced by Aspergillus species and ergot alkaloids from Claviceps purpurea are notable examples.
  4. Allergies:
    • Fungal spores can act as allergens, triggering allergic reactions in sensitive individuals. Conditions like allergic rhinitis, asthma, and hypersensitivity pneumonitis can be exacerbated by fungal spores.
  5. Structural Damage:
    • Fungi, particularly molds and wood-decay fungi, can cause damage to buildings and infrastructure. They can degrade wood, paints, and other materials, leading to structural weaknesses.
  6. Economic Impact:
    • Fungal infections in agriculture can lead to reduced yields, affecting the economy. Additionally, the cost of fungicides, treatments, and preventive measures can be substantial.
  7. Biodeterioration:
    • Fungi can degrade various materials, including textiles, paper, leather, and petroleum products, leading to their deterioration over time.
  8. Ecological Impact:
    • Invasive fungal species can disrupt native ecosystems, outcompeting and displacing native species, and altering habitat structures.
  9. Aesthetic Concerns:
    • Fungal growth, especially molds, can cause discoloration and unsightly appearances on walls, ceilings, fabrics, and other surfaces.
  10. Resistant Strains:
    • Over-reliance on fungicides in agriculture has led to the emergence of resistant fungal strains, making disease management more challenging.

In summary, while fungi play essential roles in various ecological and industrial processes, their negative impacts cannot be overlooked. Effective management and understanding of fungi are crucial to mitigate their adverse effects.

Quiz

Which of the following is NOT a characteristic of fungi?

A) Eukaryotic cells
B) Photosynthetic
C) Decomposers
D) Cell walls made of chitin

Which type of fungi forms a mutualistic relationship with the roots of most plants?

A) Yeasts
B) Molds
C) Mycorrhizae
D) Lichens

Which fungus is known for producing the first antibiotic, penicillin?

A) Aspergillus niger
B) Saccharomyces cerevisiae
C) Penicillium chrysogenum
D) Candida albicans

Which group of fungi reproduces using spores called conidia?

A) Zygomycetes
B) Ascomycetes
C) Basidiomycetes
D) Deuteromycetes

Which of the following fungi is commonly used in baking to make bread rise?

A) Rhizopus
B) Agaricus
C) Saccharomyces cerevisiae
D) Penicillium

Which type of fungi is responsible for athlete’s foot in humans?

A) Yeasts
B) Dermatophytes
C) Mushrooms
D) Lichens

Lichens are a symbiotic relationship between fungi and which of the following?

A) Bacteria
B) Algae
C) Protozoa
D) Viruses

Which of the following is NOT a method of asexual reproduction in fungi?

A) Budding
B) Sporangia
C) Binary fission
D) Ascospores

The primary role of fungi in an ecosystem is as:

A) Predators
B) Decomposers
C) Herbivores
D) Producers

Which of the following fungi is known for its hallucinogenic properties?

A) Agaricus bisporus
B) Candida albicans
C) Amanita muscaria
D) Aspergillus niger

FAQ

What are fungi?

Fungi are a group of eukaryotic organisms that include yeasts, molds, and mushrooms. Unlike plants, they do not perform photosynthesis and obtain their nutrients through absorption.

How do fungi reproduce?

Fungi can reproduce both sexually and asexually. Common methods of asexual reproduction include budding, sporulation, and fragmentation. Sexual reproduction involves the fusion of specialized sexual structures.

Are all fungi harmful?

No, while some fungi can cause diseases in plants, animals, and humans, many fungi play beneficial roles such as decomposers in ecosystems, symbiotic partners with plants, and sources of food and medicine for humans.

What is the difference between fungi and plants?

Fungi and plants are both eukaryotic, but they differ in many ways. For instance, fungi have cell walls made of chitin, while plants have cell walls made of cellulose. Additionally, fungi do not perform photosynthesis like plants.

Why are fungi important in the environment?

Fungi play a crucial role as decomposers, breaking down organic matter and recycling nutrients in ecosystems. They also form symbiotic relationships with plants, enhancing nutrient uptake.

Can fungi be used as medicine?

Yes, certain fungi produce compounds that have medicinal properties. For example, the mold Penicillium chrysogenum is the source of the antibiotic penicillin.

What are mycorrhizae?

Mycorrhizae are symbiotic associations between fungi and plant roots. The fungi assist the plant with nutrient absorption, while the plant provides the fungi with carbohydrates.

Are mushrooms a type of fungi?

Yes, mushrooms are the fruiting bodies of certain fungi. They play a role in reproduction, producing spores that can spread and grow into new fungal organisms.

How can I identify if a mushroom is edible or poisonous?

Proper identification is crucial as many edible mushrooms have poisonous look-alikes. It’s essential to consult with experts or use reliable field guides. It’s always advised to err on the side of caution and avoid consumption if unsure.

Do fungi have a role in biotechnology?

Yes, fungi are used in various biotechnological applications, from the production of enzymes, antibiotics, and biofuels to the fermentation of foods and beverages.

  1. McGinnis MR, Tyring SK. Introduction to Mycology. In: Baron S, editor. Medical Microbiology. 4th edition. Galveston (TX): University of Texas Medical Branch at Galveston; 1996. Available from: https://www.ncbi.nlm.nih.gov/books/NBK8125/
  2. Microbiology 5th Edition by Michael Joseph Pelczar 
  3. https://www.biology-pages.info/F/Fungi.html#Characteristics_of_Fungi
  4. https://microbenotes.com/characteristics-of-fungi/
  5. https://www.microscopemaster.com/fungi.html

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