Classification of Fungi

Classification of Fungi

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)

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

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

Life cycle of black bread mold

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

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

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

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

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

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

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

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

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!

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

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)

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

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

Classification of Fungi