Kingdom Fungi

Kingdom Fungi contains more than 81,000 known species (most terrestrial) All fungi are eukaryotes Cells contain Membrane-enclosed nuclei Mitochondria Other membranous organelles

Fungi are heterotrophs Most are decomposers Some are parasites Found universally wherever organic material is available

Optimum pH for most species is ca. 5.6 Some can tolerate pH ranges from 2 to 9 Many can grow in Concentrated salt solutions Sugar solutions, e.g. jelly Fungi tolerate wide temperature range

Characteristics of fungi Enclosed by cell walls at some stage in life cycle Most fungi have cell walls consisting of complex carbohydrates including chitin

Two main types: molds and yeasts Vegetative body plan of molds consists of hyphae Hyphae form mycelium Some hyphae are coenocytic Some are divided by septa into individual cells containing one or more nuclei Yeasts are unicellular

Fungus body plan

Most fungi reproduce by spores, either nonmotile or motile Spores usually produced on Specialized aerial hyphae Aerial hyphae of some fungi form fruiting bodies Fruiting structures

Germination of a spore to form a mycelium

Germination of a fungal spore Hypha emerges Mycelium infiltrates growth medium Mycelium degrades complex organic compounds to small organic molecules

Fungi that do not fit these phyla classified as Deuteromycota Four main phyla Chytridiomycota Zygomycota Ascomycota Basidiomycota Fungi that do not fit these phyla classified as Deuteromycota

Chytridiomycetes are the most primitive fungi alive today Produce flagellate cells at some stage in their life cycle No other fungal phyla are flagellate

Fungal evolution

Distinguishing characteristics of chytridiomycetes Motile cells have a single, posterior flagellum Reproduce sexually and asexually Are parasites or decomposers

Life cycle of Allomyces Has an alternation of generations: spends part of its life as a haploid thallus and part as a diploid Haploid thallus bears male and female gametangia When a flagellate male gamete fuses with a flagellate female gamete, result is a diploid thallus

Life cycle of Allomyces arbuscula

Distinguishing characteristics of zygomycetes All produce zygospores Hyphae are coenocytic Septa form to separate the hyphae from reproductive structures

Life cycle of Rhizopus stolonifer Hyphae meet to form gametangia Gametangia unite, the nuclei fuse A single zygospore develops Meiosis occurs, zygospore germinates Emerging hypha develops a sporangium Spores are released

Life cycle of Rhizopus stolonifer

Distinguishing characteristics of ascomycetes Sexual spores are produced in asci Hyphae usually have septa, but cytoplasm is continuous

Life cycle of a typical ascomycete Gametangia fuse, forming dikaryotic hyphae Asci develop from dikaryotic hyphae Asci are incorporated into an ascocarp

Life cycle of a typical ascomycete, cont. In each ascus, the nuclei fuse to form the zygote Meiosis occurs, forming four haploid nuclei Mitosis occurs, producing eight haploid nuclei

Life cycle of a typical ascomycete, cont. Each haptoid nuclei becomes incorporated into an ascospore When ascospores are released, they germinate and form new mycelia Asexual reproduction involves the formation of haploid conidia

Life cycle of a typical ascomycete

Distinguishing characteristics of basidiomycetes Develop basidia Each basidium is an enlarged hyphal cell Four basidiospores develop on the tip of the basidium

Basidia line the gills of Omphalotus olearius

SEM of a basidium

Life cycle of basidiomycetes When a hypha of a primary mycelium encounters another monokaryotic hypha of a different mating type, the two hyphae fuse The two haploid nuclei remain separate

Life cycle of basidiomycetes, cont. A secondary mycelium is produced The n +n hyphae of the secondary mycelium grow The hyphae form buttons along the mycelium Button develops into a basidiocarp

Life cycle of basidiomycetes, cont. In the young basidia, haploid nuclei fuse, forming diploid zygotes Meiosis takes place, forming four haploid nuclei Extensions of the basidium develop

Life cycle of basidiomycetes, cont. The nuclei and some cytoplasm move into the basidium Each extension of the basidum becomes a basidiospore A septum forms, separating basidiospore from the rest of the basidium

Life cycle of a typical basidiomycete

Distinguishing characteristics of deuteromycetes Are all similar, but are probably polyphyletic Do not have a common ancestor

Most deuteromycetes have no sexual stage during their life cycle Some have lost the ability to reproduce sexually Others reproduce sexually only rarely Most reproduce only by means of conicidia

Lichen Dual organism: symbiotic association between a phototroph and a fungus Phototrophic component is either a green alga, a cyanobacterium, or both Fungus is an ascomycete or a basidiomycete

Cross section of a typical lichen

Typically, lichens exhibit one of three different growth forms Crustose Foliose Fruticose Lichens reproduce mainly asexually

Crustose, foliose, and fruticose growth forms Crustose Lichens (Bacidia, Lecanora) Foliose lichen (Parmelia)

Ecological significance of fungi as decomposers Absorb nutrients from organic wastes Release water, CO2, and mineral components of organic compounds These elements are recycled

The ecological role of mycorrhizae Mycorrhizal fungus decomposes organic material in soil Benefit plants by increasing their absorptive surface area

The ecological role of mycorrhizae, cont. Roots supply fungus with sugars, amino acids, and other organic substances Scientists have measured movement of organic materials from one tree species to another

Western red cedar grown without mycorrhizae

Western red cedar grown with mycorrhizae

Economic and medical importance of fungi Beverages Food Medicine Chemicals

Fungal diseases of plants Dutch elm disease Chestnut blight fungus Smuts and rusts Verticillium wilt

Fungal diseases of humans Ringworm and athlete’s foot Histoplasmosis Aspergillosis Cancer (contributory factor) Sick building syndrome (contrib- utory factor)