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Sexual Reproduction in Fungi

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Sexual Reproduction in Fungi MYCOPLASMA OR PPLO’S • Genus of bacteria, smallest, wall-less free living prokayotes belonging to class-Mollicutes. • lacks cell wall, so resistant to antibiotics which target the cell wall. • They cause various diseases in humans like various respiratory diseases and pelvic inflammatory disorders • first discovered by Pasteur in 1843 when he was studying the causal organisms of pleuropneumonia in catties. • He named it as Pleuropneumonia like organisms (PPLO • first isolated by two French bacteriologists E. Nocard and E.R. Roux in 1898 from pleural fluids of catties affected with pleuropneumonia and these organisms were named as Mycoplasma in 1929 by Nowar. Mycoplasma • highly pleomorphic, • reproduce by budding and/or by fission and by producing small bodies. • They lack sterols but are capable of incorporating exogenous sterols obtained from growth medium. Habit and Habitat of Mycoplasma: • Mycoplasmas are parasitic as well as saprophytic. • More than 200 mycoplasma like bodies are found to be associated with sewage, plants, animals, insects, humus, hot water springs and other high temperature environment. • They have been found in phloem tissues of diseased plants. • M. orale and M. salivarium are found almost in every healthy adult. • M. hominis is present in a large proportion in sexually active adults. • Diseases like primary atypical pneumonia (PAP) in the mouth, pharynx and genito-urinary tract and tonsillitis in humans are caused by mycoplasma. Structure of Mycoplasma Cell Structure of Mycoplasma: • In mycoplasma, the cells are small varying from 300 nm to 800 nm in diameter. • Rigid cell wall is absent. • Cells are surrounded by a triple layered lipo- proteinaceous unit membrane. • It is about 10 nm thick. Unit membrane encloses the cytoplasm. • Within the cytoplasm RNA (ribosomes) and DNA are present. • The ribosomes are 14 nm in diameter and 72 S type. • DNA is double stranded helix. • It can be distinguished from bacterial DNA by its low guanine and cytosine content. • The DNA is up to four percent and RNA is about eight percent and it is less than half that usually occurs in other protoplasm’s. • The guanine and cytosine (G and C).Contents in DNA range from 23- 46 percent. • In some species e.g., M. gallisepticum some polar bodies protrude out from one or the other end of the cell. • These are called bleb and are considered to be the site of enzymatic activities and attachment during infection. • Possess a replicating disc at one end which assist replication process and also the separation of the genetic materials. • Most mycoplasma require a rich nutrient medium containing sterols and serum protein for growth. On solid (Agar) medium mycoplasmas form minute, transparent colonies that typically have a characteristic “fried egg” appearance. Reproduction in mycoplasma • Mycoplasmas are highly pleomorphic, reproduce by budding and/or by fission and by producing small bodies. Schematic presentation of the mode of mycoplasma reproduction. Cells may either divide by binary fission or first elongate to multinucleate filaments, which subsequently breakup to coccoid bodies. General Characters of Mycoplasma: • They are unicellular, smallest, non-motile and prokaryotic organisms forming fried egg shaped colonies • pleomorphic i.e., able to change about 10 nm thick. their shape depending upon • Within the cytoplasm ribosomes culture media- rod like, ring like, are found scattered in the globoid or filamentous. peripheral zone. These are 14 nm • The filaments are of uniform in diameter and resemble with diameter (100-300 nm) and vary in bacteria in sedimentation length from 3 nm to 150 nm. characteristic of both the • Some mycoplasma predominantly nucleoprotein and nucleic acid. assume spherical shape (300-800 • The ribosomes are 72S type. nm in diameter). • Within the cytoplasm fine fibrillar • They are ultra-filterable i.e., they DNA is present. It is double can pass through bacteria-proof stranded helix. filters. • They do not possess rigid cell wall. • The cells are delimited by soft tripple layered lipo-proteinaceous membrane. It is unit membrane • Mycoplasma generally grow more slowly than bacteria. • They are also killed by temperature of 40-55°C in fifteen minutes. • They do not produce spores. • Like other prokaryotes, they usually divide by binary fission. • They have Heterotrophic nutrition. Some live as saprophytes but the majority are parasites of plants and animals. • The parasitic nature is due to the inability of mycoplasmal bacteria to synthesise the required growth factor. • The Fungi • Protista – The Protozoa • They are eukaryotic, spore bearing, achlorophyllous microorganism. • Study of Fungi is Mycology. • Fungi is a eukaryotic organism that includes microorganisms such as yeasts, moulds, and mushrooms. These organisms are classified under kingdom fungi also called as Myceteae • The organisms found in Kingdom fungi contain a cell wall and are omnipresent. • They are classified as heterotrophs among the living organisms and live as saprophytes, parasites, Symbionts. • Almost all the fungi have a filamentous structure except yeast the cells. • They can be either single-celled or multicellular organism. • Fungi consist of long thread-like structures known as hyphae. These hyphae together form a mesh-like structure called mycelium. • Fungi possess a cell wall which is made up of chitin and polysaccharides. • The cell wall comprises of protoplast which is differentiated into other cell parts such as cell membrane, cytoplasm, cell organelles and nuclei. • The nucleus is dense, clear, with chromatin threads. The nucleus is surrounded by a nuclear membrane. • Fungi are eukaryotic, non-vascular, non-motile and heterotrophic organisms. • They may be unicellular or filamentous. • They reproduce by means of spores. • Fungi exhibit the phenomenon of alternation of generation. • Fungi lack chlorophyll and hence cannot perform photosynthesis. • Fungi store their food in the form of starch. • Biosynthesis of chitin occurs in fungi. • The nuclei of the fungi are very small. • During mitosis, the nuclear envelope is not dissolved. • The fungi have no embryonic stage. They develop from the spores. • The mode of reproduction is sexual or asexual. • Some fungi are parasitic and can infect the host. • Fungi produce a chemical called pheromone which leads to sexual reproduction in fungi. For eg., mushrooms, moulds, yeast. • Kingdom Fungi is classified based on different modes. • The different classification of fungi are as follows: • On the basis of nutrition, kingdom fungi can be classified into following groups. • Saprophytic – The fungi obtain their nutrition by feeding on dead organic substances. Examples: Rhizopus, Penicillium, and Aspergillus. • Parasitic – The fungi obtain their nutrition by living on other living organisms (plants or animals) and absorb nutrients from their host. Examples: Taphrina, and Puccinia. • Symbiotic – These fungi live by having an interdependent relationship association with other species in which both are mutually benefited. Examples: Lichens and mycorrhiza. Lichens are the symbiotic association between algae and fungi. Here both algae and fungi are mutually benefited as fungi provide shelter for algae and in reverse algae synthesis carbohydrates for fungi. • Phycomycetes: They are fungi with an decomposers, parasitic or saprophytic. unicellular, non-septate mycelium (500 The sexual spores are called ascospores. species). The spores (endospores) are Asexual reproduction occurs by enclosed in special sporangia. conidiospores. Example – Reproduction is sexual and asexual. Saccharomyces Atypical representative of Mucor (bread • Basidiomycetes – Mushrooms are the mould) is Mucor mucedo. Pathogenic most commonly found basidiomycetes species of this Mucor (mould) may and mostly live as parasites. Sexual cause infection of lungs, middle ear and reproduction occurs by basidiospores. general severe infectious process in Asexual reproduction occurs by conidia, man. budding or fragmentation. Example- • Zygomycetes – These are formed by the Agaricus fusion of two different cells. The sexual • Deuteromycetes – They are otherwise spores are known as zygospores while called imperfect fungi as they do not the asexual spores are known as follow the regular reproduction cycle as sporangiospores. The hyphae are the other fungi. They do not reproduce without the septa. sexually. Asexual reproduction occurs by • Ascomycetes – They are also called as conidia. Example – Trichoderma. sac fungi. They can be coprophilous, : male and female reproductive structures are present in the same plant or fungal mycelium : an organ or cell in which gametes are produced that is found in many multicellular protists, algae, fungi, and the gametophytes of plants : a reproductive particle, usually a single cell, released by a fungus, alga, or plant that may germinate into another : a case, capsule, or container in which spores are produced by an organism : the fusion of two nuclei within a cell : stage of sexual reproduction joining the cytoplasm of two parent mycelia without the fusion of nuclei • Reproduction in fungi is both by sexual and asexual means. The sexual mode of reproduction is referred to as and the asexual mode of reproduction is referred to as . – By budding, fission, and fragmentation – This takes place with the help of spores called conidia or zoospores or sporangiospores – ascospores, basidiospores, and oospores – The conventional mode of sexual reproduction is not always observed in the kingdom Fungi. In
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