Fungi: Structure, Classification, and Replication PDF

# Fungi: Structure, Classification, and Replication ## Features of Fungi and Its Value in Our Life - Fungi are ubiquitous and diverse organisms that degrade organic matter - Fungi have heterotrophic life: they could survive in nature as: - Saprophytic: live on dead or decaying matter - Sym...

# Fungi: Structure, Classification, and Replication ## Features of Fungi and Its Value in Our Life - Fungi are ubiquitous and diverse organisms that degrade organic matter - Fungi have heterotrophic life: they could survive in nature as: - Saprophytic: live on dead or decaying matter - Symbiotic: live together and have mutual advantage - Commensal: one benefits and other neither benefits nor harmed - Parasitic: live on or within a host, they get benefit and harm the other - Fungi mainly infect immunocompromised or hospitalized patients with serious underlying diseases - The incidence of specific invasive mycoses continues to increase with time - The list of opportunistic fungal pathogens likewise increases each year. It seems there are no non-pathogenic fungi anymore! - This increase in fungal infections can be contributed to the ever-growing number of immunocompromised patients ## Fungal Characteristics - Cell wall made of chitin - Heterotrophs and major decomposers - Body is made of long filaments of hyphae which form a mycelium - Reproduce sexually and asexually - Asexually by spores - Sexually by mating of hyphae filaments ## Fungal Morphology and Structure - Eukaryotic organisms. Distinguished by a rigid cell wall composed of chitin and glucan, and a cell membrane in which ergosterol is substituted for cholesterol as the major sterol component - Fungal taxonomy relies heavily on morphology and mode of spore production - Fungi may be unicellular or multicellular - The simplest grouping based on morphology divides fungi into either yeast or mold forms ## Yeast - Yeast can be defined morphologically as a cell that reproduces by budding or by fission. Daughter cells may elongate to form sausage-like pseudohyphae ## Molds - Molds are multicellular organisms consisting of threadlike tubular structures called hyphae that elongate by apical extension - Hyphae are either: - Coenocytic: hollow and multinucleate - Septate: Divided by partitions or cross-walls - Hyphae form together to produce a mat-like structure called a mycelium - Vegetative hyphae grow on or under the surface of a culture medium - Aerial hyphae project above the surface of the medium - Aerial hyphae produce conidia (asexual reproductive elements) - Conidia can easily airborne and disseminate the fungus - Many medical fungi are termed dimorphic because they exist in yeast and mold forms ## Asexual Spores - Asexual spores consist of two general types: - Sporangiospores - Conidia - Sporangiospores are asexual spores produced in a containing structure or sporangium (in class Zygomycetes: as Rhizopus and Mucor spp) - Conidia are asexual spores that are borne naked on specialized structures (Aspergillus, Penicillium, and the dermatophytes) ## Physiology - Most fungi are aerobic, some are facultative anaerobic, or strict anaerobic - Fungi are heterotrophic and biochemically versatile - Primary metabolites: citric acid, ethanol, glycerol - Secondary: antibiotics (as penicillin), and aflatoxins - Fungi are slow growing with cell-doubling times in hours - Fungi reproduce by formation of spores, which may be sexual (teleomorph), or asexual (anamorph) - Fungi in class: Zygomycetes, Ascomycetes, Archiascomycetes, and Basidiomycetes produce both sexual and asexual spores - Histoplasma capsulatum (anamorph) and Ajellomyces capsulatum (teleomorph) are two forms of the same fungus ## Fungal Taxonomy - Kingdom Fungi (Myceteae) - 5 main classes of medically important fungi: - Zygomycetes - Ascomycetes - Archiascomycetes - Basidiomycetes - Deuteromycetes ## The 5 Fungal Classes ### Zygomycetes - Molds with broad, sparsely septate, coenocytic hyphae - Zygomycetes produce sexual zygospores following the fusion of two compatible mating types - The asexual spores of the order Mucor are contained within a sporangium (sporangiospores) - The sporangia are borne at the tips of stalk-like sporangiophores that terminate in a bulbous swelling called the columella - The presence of root-like structures, called rhizoids, is helpful in identifying specific genera within the Mucorales ### Absidia - A Zygomycete, it has been reported to be allergenic - It may cause zygomycosis (an opportunistic fungal infection) and mycotic keratitis (an opportunistic fungal infection of the cornea) - Absidia can cause serious infections in individuals who are malnourished, in diabetic acidosis, or immunocompromised ### Ascomycetes - Ascomycetes include yeasts and molds - The hyphae are septate - Asexual spores are conidiophores - Sexual spores are called "ascospore" and are found within a sac or ascus ### Basidiomycetes - Basidiomycetes are rarely encountered clinically - The only human pathogen is Cryptococcus neoformans - The sexual spore is called basidiospore and is characterized by the extension from a club-shaped structure, the basidium ### Deuteromycetes - Have both yeasts and mold forms - No sexual phase - Many pathogenic fungi are included in this class - They have septate hyphae and produce conidia from conidiophores and conidiogenous cells - The yeasts reproduce by budding, and the molds produce conidia by either a blastic (budding) process or a thallic process, in which hyphal segments fragment into individual cells or arthroconidia The document describes the structure, classification, and replication of fungi. It explains the different types of fungi and their characteristics, including their morphology, physiology, and reproduction. It also discusses the medical importance of fungi and how they can cause infections in humans. It is a comprehensive guide to understanding the world of fungi.