- Identify the various classes of fungi and major features among them
- Identify key representatives of each class
Fungi are eukaryotic, heterotrophic, nonphotosynthetic organisms in a separate kingdom of the same name. The majority consists of microscopic filaments called hyphae, and the network of filaments is the mycelium. They live either as parasites or as saprophytes, absorbing organic material from their environment. Their cell walls contain chitina polymer of the sugar glucosamine. Fruiting structures arise from the mycelium, having names such as sporangium, ascus, and basidium, to name just a few. These fruiting structures can contain sexual spores or asexual spores. The hyphal filaments are haploid (1N).
The classes of fungi are based mainly on the type of sexual spore that is produced, i.e. zygospore, basidiospore, ascospore. The sexual spores are produced by meiosis, and are often contained within a structure. Even yeasts produce sexual spores, although they more commonly reproduce by asexual budding. On the other hand, asexual spores are the more common spores (conidiospores, sporangiospores),, their function being dispersal so that the fungus can disseminate itself throughout the environment. There are various reproductive modes for production of asexual spores---fragmentation, budding, fission, and so on.
There are quite a few classes of the kingdom Fungi---Chydridiomycota, Ascomycota, Basidiomycota, Zygomycota, and Deuteromycota. The Deuteromycota group contains the unclassified fungi that mycologists don't really know where to put,due to a lack of currently defined sexual spores. In addition, fungi make up part of the composite organisms called lichens. The lichens are actually mutualistic, symbiotic relationships between fungi and photosynthetic algae or photosynthetic cyanobacteria.
In this lab, you will identify representatives from 3 categories of fungi:
- Basidiomycetes (representative: mushrooms)
- Ascomycetes (representative: Penicillium, Saccharomyces, various dermatophytes)
- Zygomycetes (representatives: Rhizopus)
- culture of Saccharomyces cerevesiae
- prepared slides of Rhizopus, Penicillium, Aspergillus, and Candida albicans
- prepared slides or images of dermatophytes (Microsporum, Trichophyton, Epidermophyton)
- fresh cultures of fungi on agar plates (Rhizopus, Penicillium, Aspergillus)
- fresh Agaricus mushrooms
Yeast reproduce asexually by budding, small daughter cells arising from the mother cell. They will stay attached until disturbed, and then break off.
- Make a wet mount of the culture (SMALL inoculum) in a drop of lactophenol cotton blue (10X and 40X). Use phase-contrast or brightfield microscopy.
- Make a smear of the yeast and simple stain with crystal violet. Use brightfield microscopy.
- Look at prepared smears of mixed yeasts (Saccharomyces and Candida)
Rhizopus prepared slides
If 2 different strains (called + and – strains) are placed together on a culture medium (or in nature), the hypha will grow towards each other and conjugation will occur. This produces a sexual spore called a zygospore—a diploid sexual spore.
- On 10X and 40X, identify hyphae, sporangia, and sporangiospores.
- Differentiate between the sexual zygospores and the sporangiospores on the slides.
Penicillium and Aspergillus
- On 10X and 40X, identify hyphae, conidia fruiting structures, and the asexual conidiospores.
Dermatophyte genera: Microsporum, Trichophyton, Epdermophyton
- There should be demo slides set up for you.
- Look at the gills of Agaricus mushrooms.
- Add lactophenol cotton blue for a wet mount.
IMAGES OBSERVED UNDER THE MICROSCOPE
Candida albicans Saccharomyces cerevisiae, showing budding cells
Asexual spores of Rhizopus, along with sexual spores
Rhizopus sporangia with asexual sporangiospores within
- Record the shapes and features of the various fungi.
- The mushrooms are in what class of fungi?
- Is a zygospore a sexual spore OR an asexual spore? WHY?
- Name a couple of ways in which the molds and yeasts differ.
- By what major criterion are the fungi subcategorized into classes?
- Differentiate hypha and mycelium.
Contributors and Attributions
Jackie Reynolds, Professor of Biology (Richland College)