Microbial World PDF - 2nd Year Natural Sciences

Chapter I. MICROBIAL WORLD 2nd-year Natural Sciences Dr. Fatima-Zohra Kenza LABBANI Natural Sciences Department [email protected] Part 3. EUKARYOTES Microscopic Fungi Microscopic Fungi (Molds...

Chapter I. MICROBIAL WORLD 2nd-year Natural Sciences Dr. Fatima-Zohra Kenza LABBANI Natural Sciences Department [email protected] Part 3. EUKARYOTES Microscopic Fungi Microscopic Fungi (Molds and Yeasts) General Characteristics of Microscopic Fungi Cellular Structure: Eukaryotic microorganisms with membrane- bound nuclei and organelles. The cell walls of fungi are primarily composed of chitin, a complex polysaccharide, which provides structural support and protection. Lack of chloroplast and chlorophyll, making them unable to perform photosynthesis. Cell wall composition General Characteristics of Microscopic Fungi Morphology: Most fungi are filamentous, consisting of hyphae. A network of hyphae forms a mycelium. These hyphae spread over substrates and enable molds to absorb nutrients efficiently General Characteristics of Microscopic Fungi Fungal cell structure Fungal cell structure General Characteristics of Microscopic Fungi Morphology: Yeasts are typically unicellular, though some species can form multicellular pseudohyphae under specific conditions Yeast cells General Characteristics of Microscopic Fungi Dimorphism: Some fungi exhibit dimorphism, meaning they can exist in yeast and hyphal forms depending on environmental conditions, such as temperature and nutrient availability. This is particularly common among pathogenic fungi. For example, Candida albicans exists in a yeast form in normal body conditions but can form hyphal structures under certain stress conditions, contributing to its pathogenicity. General Characteristics of Microscopic Fungi Dimorphism: example Candida albicans General Characteristics of Microscopic Fungi Reproduction: Moulds: They can reproduce both sexually and asexually Asexual reproduction occurs through fragmentation (fungal mycelium separates into pieces, with each component growing into a separate mycelium) Or by spore formation (asexual spores like conidiospores conidia or sporangiospores) Sexual reproduction involves spores formation like zygospores and ascospores General Characteristics of Microscopic Fungi Reproduction: Moulds: Asexual reproduction through fragmentation General Characteristics of Microscopic Fungi Reproduction: Yeasts: They primarily reproduce asexually through budding Some yeasts, like Schizosaccharomyces pombe, reproduce by fission instead of budding, creating two identically sized daughter cells General Characteristics of Microscopic Fungi Reproduction: Yeasts: Asexual reproduction by budding General Characteristics of Microscopic Fungi Reproduction: Yeasts: Asexual reproduction by budding General Characteristics of Microscopic Fungi Reproduction: Yeasts: Asexual reproduction by fission (Schizosaccharomyces pombe) General Characteristics of Microscopic Fungi Reproduction: Yeasts: Some yeasts can also reproduce sexually. Sexual reproduction occurs via specialized structures like asci General Characteristics of Microscopic Fungi Growth conditions: Temperature Most microscopic fungi grow in moderate temperatures, typically between 20-30°C Pathogenic fungi often grow well at body temperature (37°C) Some psychrophilic (cold-loving) fungi can grow at lower temperatures Others are thermophilic, thriving at temperatures up to 50°C General Characteristics of Microscopic Fungi Growth conditions: Moisture High humidity or moisture is essential for most fungal growth Yeasts require a moist environment (water activity (aw) of at least 0.8) Moulds can grow in environments with lower moisture content than yeasts (xerophilic fungi) General Characteristics of Microscopic Fungi Growth conditions: pH Most fungi prefer slightly acidic conditions, with optimal pH ranging from 4-6 Some species can tolerate a wider pH range, from 2-9 General Characteristics of Microscopic Fungi Growth conditions: Oxygen requirements Most fungi are obligate aerobes, requiring oxygen for growth Some yeasts are facultative anaerobes, able to grow with or without oxygen, especially during fermentation Microscopic Fungi ▪ Mode of Nutrition Mode of nutrition Fungi are heterotrophic organisms that obtain nutrients through absorption They secrete enzymes to break down complex organic matter into simpler compounds that can be absorbed through their cell walls Based on their mode of nutrition, microscopic fungi can be classified into three main categories: saprophytic fungi, parasitic fungi, and symbiotic fungi Mode of nutrition Saprophytic fungi: They are essential decomposers in the ecosystem They play a crucial role in decomposition and nutrient cycling in ecosystems. They obtain their nutrients from dead and decaying organic matter, playing a vital role in the recycling of nutrients. They feed on decaying animal and plant tissues, such as rotten fruits, vegetables, and wood. Mode of nutrition Parasitic fungi: Parasitic fungi obtain nutrition from living organisms, often causing harm or diseases to their hosts. Parasitic fungi infect living plants, animals, and humans, causing diseases Parasitic fungi can be divided into plant pathogens and animal and human pathogens Mode of nutrition Parasitic fungi: 1) Plant pathogens - Obligate parasites, e.g.: Rust Fungi (Puccinia species): they produce specialised structures called haustoria, which penetrate plant cells to absorb nutrients. They cause rust diseases in plants Powdery Mildew (Blumeria species): form a white powdery coating on plant leaves. This mildew inhibits photosynthesis and weakens the plant by consuming its nutrients. Mode of nutrition Parasitic fungi: 1) Plant pathogens - Facultative parasites: They can survive on dead organic material but can also infect living hosts when conditions are favorable. Alternaria: infects a variety of plants and causes leaf spots, blights, and rots. It often occurs in plants already weakened by other stressors. Fusarium: a soil-borne pathogen that affects plants, especially root crops. It can cause wilting by blocking water transport in the plant's vascular system. Mode of nutrition Parasitic fungi: 2) Animal and human pathogens: Candida: a yeast that can be part of the normal human microbiota but becomes pathogenic in cases of immunosuppression, causing infections such as thrush and candidiasis. Aspergillus: known to infect animals and humans, particularly those with compromised immune systems. It can cause respiratory infections like aspergillosis, particularly in the lungs Mode of nutrition Symbiotic fungi: They form mutually beneficial relationships with other organisms. This category includes: Mycorrhizae and Lichens Mode of nutrition Symbiotic fungi: 1) Mycorrhizae (Mycorrhizal fungi): Form associations with plant roots. Fungi improve nutrient uptake (phosphorus, nitrogen) and water absorption for plants, while plants provide carbohydrates to the fungi. Enhanced plant growth and development Increased resistance to diseases and stress Mode of nutrition Symbiotic fungi: 2) Lichens: Symbiotic association or a mutualistic relationship between a fungus and an alga or cyanobacterium. Fungi receive carbohydrates from Algae or cyanobacteria (photosynthesis). Algae or cyanobacteria receive a protected environment, water, and minerals from the fungus Microscopic Fungi ▪ Classification of Fungi Classification of Fungi Based on their morphological characteristics and modes of reproduction, which include both sexual and asexual methods, microscopic fungi can be classified into: 1) Ascomycetes (Ascomycota) 2) Zygomycetes (Zygomycota) 3) Basidiomycetes (Basidiomycota) 4) Deuteromycetes or Imperfect Fungi (Deuteromycota) 5) Chytridiomycetes (Chytridiomycota) Classification of Fungi 1) Ascomycetes: The largest and the most diverse group of fungi. The defining feature of Ascomycetes is the ascus (plural: asci) Ascus is a sac-like structure where ascospores are formed during sexual reproduction Ascomycetes are characterised by the production of ascospores within Asci Classification of Fungi 1) Ascomycetes: Their cell walls contain chitin and β-glucans Ascomycetes typically have septate hyphae, meaning they are divided into cells by cross-walls (septa) with pores that allow cytoplasmic exchange Most are multicellular, though some (like yeasts) are unicellular. They exhibit a wide range of morphological forms They can reproduce both sexually and asexually Classification of Fungi 1) Ascomycetes: Asexual Reproduction: Ascomycetes can reproduce asexually through the production of conidia (asexual spores) on specialised hyphae called conidiophores. These conidia are easily dispersed by air or water and allow the fungi to colonise new substrates rapidly Other methods can be present like budding (in yeasts), fragmentation, chlamydospores Classification of Fungi 1) Ascomycetes: Classification of Fungi 1) Ascomycetes: Aspergillus sp. Classification of Fungi 1) Ascomycetes: Sexual Reproduction: involves the fusion of compatible hyphae (plasmogamy), leading to the formation of asci and ascospores within fruiting bodies as follows: ✓ Formation of dikaryotic cells (two haploid nuclei per cell) ✓ Development of ascogenous hyphae ✓ Formation of asci within an ascocarp (fruiting body) ✓ Karyogamy (nuclear fusion) within asci ✓ Meiosis followed by mitosis to produce typically 8 haploid ascospores This cycle enhances genetic diversity and allows for greater adaptability. Classification of Fungi 1) Ascomycetes: Sexual Reproduction: can also involve the fusion of two haploid nuclei to form a diploid zygote, which then undergoes meiosis to produce haploid ascospores. Classification of Fungi 1) Ascomycetes: Classification of Fungi 1) Ascomycetes: Classification of Fungi 1) Ascomycetes: Asexual Reproduction of Aspergillus - Conidiospores Formation: The asexual cycle begins with the production of conidiospores formed on conidiophores. - Dispersal and Germination: Conidiospores are released into the environment and can disperse long distances. - Under favorable conditions, they germinate to form new haploid mycelium, which can then produce more conidiophores, continuing the asexual cycle. Sexual Reproduction of Aspergillus - Ascospore Formation: The sexual cycle involves the formation of ascospores within a structure called ascus. - Plasmogamy and Karyogamy: two compatible mating types undergo plasmogamy to form a dikaryotic stage - Cleistothecium Development: The dikaryotic cells develop into a closed fruiting body called a cleistothecium. - Karyogamy and Meiosis: within the cleistothecium, karyogamy (fusion of nuclei) occurs, followed by meiosis, leading to the formation of ascospores - Ascospore Release: the mature cleistothecium releases ascospores into the environment. These ascospores can germinate under suitable conditions to form new mycelium, completing the sexual cycle. Classification of Fungi 1) Ascomycetes: Asexual Reproduction Haploid Phase: S. cerevisiae can exist as haploid cells of two mating types (a, α). These haploid cells reproduce asexually through budding. Sexual Reproduction - Mating: Haploid cells of opposite mating types (a and α) can mate when they encounter each other. This process involves the fusion of their membranes and nuclei, forming a diploid cell (a/α). - Diploid Phase: The diploid cells can also reproduce asexually by budding, similar to the haploid phase. - Under nutrient-rich conditions, diploid cells continue to reproduce asexually. - Sporulation: In response to nutrient deprivation, diploid cells undergo meiosis to form an ascus containing four haploid spores (two "a" and two "α"). These spores are released when conditions become favorable, germinating into new active haploid cells, thus completing the cycle. - This dual-mode life cycle allows S. cerevisiae to adapt to various environmental conditions, ensuring survival and genetic diversity. Classification of Fungi 1) Ascomycetes: Diversity: Ascomycetes include a broad range of lifestyles, morphologies, and ecological roles, such as ✓ Yeasts: unicellular Ascomycetes, like Saccharomyces cerevisiae. They reproduce asexually through budding and are valuable in industries involving fermentation. Classification of Fungi 1) Ascomycetes: ✓ Moulds: Filamentous Ascomycetes, like Penicillium and Aspergillus, grow on various substrates. ✓ Lichens: Some Ascomycetes form symbiotic relationships with photosynthetic organisms, like algae or cyanobacteria, resulting in lichens. Classification of Fungi 2) Zygomycetes: A class of microscopic fungi within the phylum Zygomycota They have coenocytic hyphae, meaning they lack septa (cross-walls), resulting in a continuous cytoplasmic mass with many nuclei Classification of Fungi 2) Zygomycetes: The cell walls contain chitin, similar to other fungi, but they also have chitosan, which provides added structural strength and rigidity. Many Zygomycetes are saprotrophic, like Rhizopus, known for causing bread mould Some are parasitic on insects and other animals Certain zygomycetes form symbiotic relationships with plants, assisting in nutrient uptake. Classification of Fungi 2) Zygomycetes: Asexual reproduction is the most common form of reproduction in Zygomycetes and occurs through sporangiospores. Classification of Fungi 2) Zygomycetes: Asexual reproduction: specialized structures called sporangia form at the tips of upright hyphae, known as sporangiophores. Within each sporangium, numerous sporangiospores develop and are released to disperse and germinate in favorable conditions. Classification of Fungi 2) Zygomycetes: Sexual reproduction: is characterized by forming a thick-walled, resistant spore called a zygospore. When two compatible hyphae meet, they produce specialized cells called gametangia that fuse (plasmogamy), followed by nuclear fusion (karyogamy) to form a diploid zygospore Classification of Fungi 2) Zygomycetes: Sexual reproduction: Zygospores can withstand adverse environmental conditions and remain dormant for extended periods until conditions improve, at which point they germinate and undergo meiosis to produce haploid spores Classification of Fungi 3) Basidiomycetes: Basidiomycetes is a class within the phylum Basidiomycota They are characterized by their unique reproductive structures called basidium (plural: basidia) where sexual spores, called basidiospores, are produced Basidiomycota possess septate hyphae, with septa containing specialized pores (known as dolipore septa) that facilitate nutrient and cytoplasmic exchange between cells Classification of Fungi 3) Basidiomycetes: Classification of Fungi 3) Basidiomycetes: Asexual reproduction: while less common in Basidiomycetes, some species reproduce asexually through conidia (asexual spores) or fragmentation of hyphae, allowing rapid colonization of substrates Classification of Fungi 3) Basidiomycetes: Sexual reproduction: Plasmogamy and dikaryotic cells : two compatible hyphae fuse, resulting in a dikaryotic mycelium (two different nuclei in one cell without immediately fusing them) Basidiocarp Formation: Under suitable conditions, the dikaryotic mycelium forms a basidiocarp. Karyogamy and Meiosis: In the basidia on the basidiocarp, karyogamy occurs, followed by meiosis, producing haploid basidiospores. Spore Release and Germination: Basidiospores are released and germinate into new haploid mycelia Classification of Fungi 3) Basidiomycetes Basidiomycota includes a wide variety of forms and ecological roles, such as Yeasts like Cryptococcus, and moulds like Puccinia graminis, and Ustilago maydis Classification of Fungi 4) Deuteromycetes: The class Deuteromycetes, also known as imperfect fungi, are a group of microscopic fungi characterised by their asexual reproduction and lack of a known sexual reproduction in their life cycle. Most Deuteromycetes exist in a filamentous form. They possess well- developed, branched, and septate hyphae with multinucleate cells and simple pore septa Some species can also exist in yeast form, especially those that exhibit dimorphism. The cell wall of these fungi primarily contains chitin-glucan Classification of Fungi 4) Deuteromycetes: Asexual reproduction: Deuteromycetes are called "imperfect fungi" because they lack an observed sexual reproductive stage (the "perfect" stage in fungal terminology). They reproduce asexually through conidia, which are asexual spores formed on structures called conidiophores. These conidia are produced externally and are dispersed to propagate the fungi Classification of Fungi 4) Deuteromycetes: Some species may also reproduce through hyphal fragments, budding, arthrospores, or chlamydospores Classification of Fungi 4) Deuteromycetes: Classification of Fungi 4) Deuteromycetes: Classification of Fungi 4) Deuteromycetes: Diversity: Deuteromycetes include several medically, economically, and ecologically important fungi, such as Candida albicans (a common human pathogen causing candidiasis). Economic and Industrial Importance of Microscopic Fungi Yeasts like Saccharomyces cerevisiae are vital in industrial fermentation, being used in bread, beer, and wine production due to their ability to convert sugars into alcohol and carbon dioxide. Moulds are essential in the production of antibiotics, such as Penicillium species that produce penicillin. Additionally, moulds are used in the production of certain cheeses (e.g., blue cheese) and in biotechnological applications for enzyme and metabolite production.  THE END Dr. Fatima-Zohra Kenza LABBANI [email protected] Natural Sciences Department