Mucor mucedo genus species use asexual reproduction. When erect hyphal sporangiophores are formed. The tip of the sporangiophore swells to form a globose sporangium that contains uninucleate, haploid sporangiospores. Aseptate mycelium comprises of hyphae which are not divided by septa. This type of mycelium has no partitions between the nuclei. It is seen in Rhizopus and Mucor. Coenocytic mycelium comprises of hyphae which has many nuclei in the continuous cytoplasm.
Coenocytic cells are present in diverse and unrelated groups of algae, including Xanthophyceae e. They are called sac fungi because their sexual spores, called ascospores, are produced in a sac or ascus…. Classification of Fungi. Septate is a morphological term defined in biology in two different instances: In human biology, it is used to describe a divide.
For example, a septate uterus would be a divided uterus. In mycology, it is used to describe the condition of spores or hyphae that possess or lack a septa to divide cells. A septate uterus can be treated with a surgery called a metroplasty. The procedure is now carried out with a hysteroscopy. The hysteroscopic procedure allows for treatment to be done within the uterus without the need for an outer abdominal incision.
Xylem fibres are either divided along their length with some partitions. These partitions make them septate. You can observe the divisions in the central lumen of septate xylem fibre.
If the xylem fibre is not divided by any partitions projecting inside the lumen, it is termed to be aseptate. Asexual reproduction is via sporangiospores, which can be released from the sporangium and carried by air currents. When the spores reach an appropriate substrate, they germinate to produce new hyphae. Bread molds do not usually cause human disease. In fact, in some countries they are used in food production.
Rhizopus, however, is an opportunistic human pathogen; it is especially dangerous to people with diabetes mellitus that is not well controlled.
Ascomycota sac fungi : Members of the subdivision Ascomycota include molds that have septate hyphae and some yeasts. They are called sac fungi because their sexual spores, called ascospores, are produced in a sac or ascus. Asexual reproduction is via conidiospores. The Ascomycetes include fungi that cause chestnut blight and Dutch elm disease. The budding yeasts reproduce asexually by budding off a smaller daughter cell; the resulting cells may sometimes stick together as a short chain or pseudohypha Figure 1.
Candida albicans is a common yeast that forms pseudohyphae; it is associated with various infections in humans, including vaginal yeast infections, oral thrush, and candidiasis of the skin.
Some fungi are dimorphic, having more than one appearance during their life cycle. These dimorphic fungi may be able to appear as yeasts or molds, which can be important for infectivity. This ability helps dimorphic fungi to survive in diverse environments. Histoplasma capsulatum , the pathogen that causes histoplasmosis , a lung infection, is an example of a dimorphic fungus Figure 2. Figure 2. Histoplasma capsulatum is a dimorphic fungus that grows in soil exposed to bird feces or bat feces guano top left.
It can change forms to survive at different temperatures. There are notable unique features in fungal cell walls and membranes. Fungal cell walls contain chitin , as opposed to the cellulose found in the cell walls of plants and many protists. Additionally, whereas animals have cholesterol in their cell membranes, fungal cell membranes have different sterols called ergosterols. Ergosterols are often exploited as targets for antifungal drugs.
Fungal life cycles are unique and complex. Fungi reproduce sexually either through cross- or self-fertilization. Haploid fungi form hyphae that have gametes at the tips. Later, the nuclei fuse in an event called karyogamy to create a diploid zygote.
The zygote undergoes meiosis to form spores that germinate to start the haploid stage, which eventually creates more haploid mycelia Figure 3. Depending on the taxonomic group, these sexually produced spores are known as zygospores in Zygomycota , ascospores in Ascomycota , or basidiospores in Basidiomycota Figure 4.
Fungi may also exhibit asexual reproduction by mitosis, mitosis with budding, fragmentation of hyphae, and formation of asexual spores by mitosis. These spores are specialized cells that, depending on the organism, may have unique characteristics for survival, reproduction, and dispersal.
Fungi exhibit several types of asexual spores and these can be important in classification. Figure 3. Click for a larger image. Zygomycetes have sexual and asexual life cycles.
The fungi are very diverse, comprising seven major groups. Not all of the seven groups contain pathogens. Some of these groups are generally associated with plants and include plant pathogens. For example, Urediniomycetes and Ustilagomycetes include the plant rusts and smuts , respectively.
These form reddish or dark masses, respectively, on plants as rusts red or smuts dark. Some species have substantial economic impact because of their ability to reduce crop yields. Glomeromycota includes the mycorrhizal fungi , important symbionts with plant roots that can promote plant growth by acting like an extended root system.
The Glomeromycota are obligate symbionts, meaning that they can only survive when associated with plant roots; the fungi receive carbohydrates from the plant and the plant benefits from the increased ability to take up nutrients and minerals from the soil.
The Chytridiomycetes chytrids are small fungi, but are extremely ecologically important. Chytrids are generally aquatic and have flagellated, motile gametes; specific types are implicated in amphibian declines around the world. Because of their medical importance, we will focus on Zygomycota, Ascomycota, Basidiomycota, and Microsporidia. Figure 9 summarizes the characteristics of these medically important groups of fungi. The Zygomycota zygomycetes are mainly saprophytes with coenocytic hyphae and haploid nuclei.
They use sporangiospores for asexual reproduction. The group name comes from the zygospores that they use for sexual reproduction Figure 3 , which have hard walls formed from the fusion of reproductive cells from two individuals. Zygomycetes are important for food science and as crop pathogens. One example is Rhizopus stolonifer Figure 4 , an important bread mold that also causes rice seedling blight. Mucor is a genus of fungi that can potentially cause necrotizing infections in humans, although most species are intolerant of temperatures found in mammalian bodies Figure 4.
Figure 4. These images show asexually produced spores. The organism is a Mucor sp. The tips of bread mold are the dark, spore-containing sporangia.
The Ascomycota include fungi that are used as food edible mushrooms, morels, and truffles , others that are common causes of food spoilage bread molds and plant pathogens , and still others that are human pathogens.
Ascomycota may have septate hyphae and cup-shaped fruiting bodies called ascocarps. Some genera of Ascomycota use sexually produced ascospores as well as asexual spores called conidia , but sexual phases have not been discovered or described for others.
Some produce an ascus containing ascospores within an ascocarp Figure 5. Figure 5.
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