Biology 3B Laboratory Fungi Page 1 of 5 Biology 3B Laboratory Fungal Diversity Objectives • To describe the general characteristics of the phyla in the kingdom Fungi • To learn the anatomy, life cycle and identification of representative fungal organisms • To discuss the ecological role and economic importance of fungi Introduction The kingdom Fungi is one of four kingdoms in the domain Eukarya. This kingdom consists of over 70,000 identified species with estimates over 1.5 million fungal species. This kingdom consists of a diverse group of organisms that range from unicellular (yeasts) to multicellular (most) organisms. Fungi are economically and ecologically important. Economically fungi are beneficial in that they are used to produce various food items (leaven bread, cheeses etc.), medicines, beverages, etc. Some fungi are parasitic on plants and animals. Numerous fungi have even cause widespread famine or diseases as a result of infestations (potato famine, ergotism). All members are heterotrophic, where many obtain their nutrients by releasing exoenzymes into their surrounding environment to breakdown “food items” outside the body and then absorbing the nutrients into their cells. Fungi that feed on dead organic material are referred to as saprobes and comprise one of the principal decomposers one Earth. Parasitic fungi that found on other living organisms have specialized structures called haustoria (haustorium – singular) to penetrate the host organism for nutrient absorption. There are still other fungi that form a mutualistic relationship with another organism while a few are even predators of nematode worms. Although fungi were once classified with plants, fungi have several major differences from plants. As mentioned before, fungi are heterotrophic. Like plants, all fungi have cells walls, however fungal cell walls are composed of chitin instead of cellulose. Fungal bodies (vegetative) are composed of long slender filaments called hypha (hyphae – plural) which form more complex structure when compacted together. In most fungi, the hyphae form a tangled mass called a mycelium (mycelia – plural). These hyphae can be completely separated by septa (septum – singular), or incompletely separated thus allowing for communication between adjacent filaments. As a result of this incomplete separation, this is why most fungi grow very rapidly when there is ample water and nutrients present. Some fungi have no separations at all (aseptate) and thus are multinucleated (coenocytic). Fungi can reproduce both sexually and asexually (Figure 1). In either case, haploid spores are produce. When these spores land on a suitable substrate, they germinate (divide via mitosis) into a mature haploid organism. During asexual reproduction, reproductive structures such as sporangia and conidia produce spores via mitosis. Two other forms of asexual reproduction include budding, as seen in the imperfect fungi (i.e. yeasts) and by fragmentation of the hyphae. There are three distinct phase in sexual Figure 1: Generalized fungal lifecycleBiology 3B Laboratory Fungi Page 2 of 5 reproduction: haploid, diploid and the heterokaryotic (dikaryotic) phase. Gamete producing cells (gametatangium/gametatangia) in the haploid organism produces haploid gametes via mitosis. Gametes from different organisms then fuse forming a diploid zygote that undergoes meiosis to form haploid spores. When these spores land on a suitable substrate, they germinate forming the mature haploid organism, beginning the process again. Scientists that study fungi are called mycologists. They have separated the kingdom Fungi into four distinct phyla and one non-taxonomic group. These are: Part A: Phylum Chytridiomycota – chytrids This phylum includes about 790 aquatic species that are commonly called chytrids. Many chytrids are either saprobes or parasites. Members in this phylum were once excluded from being classified as fungi because of flagellated zoospores. However more recent molecular data supports classifying chytrids as a primitive fungus instead of with fungus-like protists. Chytrids have cell walls composed of chitin like other fungi. They also utilize similar enzymes and metabolic pathways as other fungal groups. It has even been hypothesized that chytrids may be the link between protists and fungi ¾ Examine chytrids if available Part B: Phylum Zygomycota – Zygote fungi (zygomycetes) There are approximately 600 species of zygote fungi categorized in this group due to the resting sexual spores called zygospores. Most zygomycetes are terrestrial, found living in the soil or are saprobic on decaying plant/animal matter. Zygomycetes that have mutualistic relationships with plant roots are often referred to as mycorrhizae. Rhizopus stolonifer is the black bread mold that most are familiar with. Their hyphae have modifications called rhizoids that penetrate the substrate. Hyphae are connected via structures called stolons. Hyphae filaments that become upright are called sporangiophores (asexual) that terminates at the columella. Surrounding the columella is the sporangium (sporangia – plural) that produces the asexual haploid spores. R. stolonifer is heterothallic, possessing opposite strains (+ or –), and can reproduce sexually when conditions become less ideal. This requires that (+) and (–) hyphae fuse (see Figure 31.7 in Campbell and Reece). Then hormones cause these hyphae to develop gametatangia which will become separated from the fungal body. The nuclei fuse, forming a diploid zygote that develops into the zygospore. The zygospore is protected by the thick-walled zygosporanganium that is resistant to harsh conditions (desiccation, temperature, etc.). When the zygosporangium matures, a sporangium germinates from the zygospore. It is during this time when spores are produced via meiosis and released into the surrounding environment. ¾ Be able to identify and the know the functions of the following on live and prepared slides: o Rhizoids, stolons, hyphae, columella, sporangiophore, sporangium, gametatangia, zygospore, zygosporangium o Know the portion of the lifecycle (n, 2n) the particular structure is fromBiology 3B Laboratory Fungi Page 3 of 5 Part C: Phylum Ascomycota – Sac fungi (ascomycetes) There are