Classification of Fungi

1. Classification of Fungi

2. Kingdom Fungi • Has over 100,000 species • Classfied according to their structure and method of reproduction • Four main groups • Common molds (Zygomycota) • Sac fungi (Ascomycota) • Club fungi (Basidiomycota) • Imperfect fungi (Deuteromycota)

3. Zygomycetes • Have life cycles that include a zygospore • A resting spore that contains zygotes formed during the sexual phase of the mold’s life cycle • The hyphae of zygomycetes generally lack cross walls, although the cells of their reproductive structures do have cross walls

4. Zygomycetes • Ex. Bread mold • Black mold on bread known as Rhizopus stolonifer • Features two different types of hyphae: • Rhizoids • rootlike hyphae that penetrate the bread’s surface • anchor the fungus and absorb digested organic material • Stolons • Stemlike hyphae that run along the surface of the bread • Form sporangia at their tips • A single tip may contain up to 40,000 spores

5. Life cycle of black bread mold

6. It sexual phase begins when hyphae from different mating types fuse to produce gamete-forming structures known as gametangia • Haploid (N) gametes produced in the gametangia fuse with gametes of the opposite mating type to form diploid (2N) zygotes • When conditions are favorable the spores germinate

7. The Sac Fungi • Phlyum Ascomycota • Named for the ascus, a reproductive structure that contains spores • 30,000 sepcies • Some are very large while others are microscopic

8. Life cycle of Sac Fungi • Includes both asexual and sexual reproduction • In asexual reproduction, tiny spores called conidia are formed at the tips of specialized hyphae called conidophores • If spores lands in a hospitable environment it grows into a haploid mycelium

9. Life cycle of Sac Fungi • Sexual reproduction occurs when the haploid hypae of two mating types + and – grow close together • The N + N hyphae then produce a fruiting body in which sexual reproduction continues • Gametangia from the two mating types fuse • The haploid nuclei do not fuse • Results in producing a hyphae that contain haploid nuclei from each of the mating types N + N

10. The ascus forms within the fruiting body • Within the ascus, two nuclei of different mating types fuse to form a diploid zygote (2N) • The zygote soon divides by meiosis producing four haploid cells • Next most will undergo a round a mitosis and produce eight cells known as ascospores • In a favorable environment, an ascospre can germinate and grow into a haploid mycelium

11. Sac Fungi • Ex. Yeasts • Yeasts are unicellular fungi • The yeasts used by humans for baking and brewing are classified as ascomycetes • Classified this way because they form asci with ascospores during the sexual phase

12. Yeast in cooking appears to be a dry lifeless powder • It is actually ascospore, which become active in a moist environment • If water is added they will undergo asexual reproduction in what is known as budding • The yeast grows in anaerobic environment and undergoes alcoholic fermentation • As it grows it creates the by products carbon dioxide and alcohol • The carbon dioxide causes the bread to rise, while the alcohol evaporates during baking

13. The Club Fungi • Phylum Basidiomycota • Gets its name from a specialized reproductive structure that resembles a club • The spore-bearing structure is called the basidium

14. Life cycle of Club Fungi • Undergo elaborate life cycle • A basidiospore germinates to produce a haploid primary mycelium, which begins to grow • Next, mycelia of different mating types fuse to produce a secondary mycelium • The cells of the secondary mycelium contain haploid nuclei of each mating type • Secondary mycelia may grow in the soil for years, reaching an enormous size • A few have found to hundreds of meters long!

15. When, the right conditions moisture and nutrients occurs, spore-producing fruiting bodies push above the ground • These fruiting bodies are recognized by us as mushroom • Each mushroom begins as a mass of growing hyphae at the soil’s surface

16. Fruiting bodies expand with astonishing speed • Some fully develop overnight! • This remarkable grow is caused by cell enlargement not cell division (they simply take in water)

17. When the mushroom cap opens, it exposes hundreds of tiny gills on its underside • Each gill is lined with basidia • The two nuclei in each basidium fuse to form a diploid zygote cell • This then undergoes meiosis forming clusters of haploid basidiospores • Within hours the badiospores form at the edge of each basium, ready to be scattered

18. The Imperfect Fungi • The Deuteromycota are fungi that cannot be placed in other phyla because researchers have never been able to observe a sexual phase in their life cycles