Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 31: Fungi - Mighty Mushrooms Fungi are diverse and widespread They are essential for the well-being of most terrestrial ecosystems because they break down organic material and recycle vital nutrients

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Outline for fungi: How do they obtain organic materials? Body structure Asexual vs. sexual life cycles Fungal diversity – we will see examples of fungi Relationships between fungi and other organisms Lichens – fungi living along with bacteria or algae Pathogenic fungi and uses of fungi

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fungi are heterotrophs that feed by absorption Despite their diversity, fungi share key traits, most importantly the way in which they derive nutrition Fungi are heterotrophs but do not ingest their food They secrete exoenzymes that break down complex molecules, and then they absorb the smaller compounds Fungi exhibit diverse lifestyles: – Decomposers – Parasites – Mutualistic symbionts

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Representation of a saprobe and its mode of action to get energy source from the environment. Extracellular digestion in a saprobe with a cell wall.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Body Structure The morphology of multicellular fungi enhances their ability to absorb nutrients Fungi consist of mycelia, networks of branched hyphae adapted for absorption Most fungi have cell walls made of chitin Some fungi have hyphae divided into cells by septa – called septate hyphae, with pores allowing cell-to-cell movement Coenocytic fungi are fungi whose hyphae lack septa

Reproductive structure Hyphae Spore-producing structures Mycelium 20 µm The body structure of fungi

Nuclei Septate hypha Septum Pore Cell wall Nuclei Coenocytic hypha The two types of hypha in a fungus Porous septa in septate hyphae functions similar to gap junctions in animal cells and plamodesmata in plant cells – they allow easy transfer of molecules. In this case, it is transfer of molecules throughout the hypha.

Hyphae adapted for trapping and killing prey Fungal hypha Haustorium Plant cell Haustoria Plant cell plasma membrane Plant cell wall Nematode Hyphae 25 µm Some unique fungi have specialized hyphae that allow them to penetrate the tissues of their host These hyphae then secrete exoenzymes in order to digest outside food sources to absorb the released nutrients Specialized hyphae

Haploid (n) Key Heterokaryotic (unfused nuclei from different parents) Diploid (2n) PLASMOGAMY (fusion of cytoplasm) Heterokaryotic stage KARYOGAMY (fusion of nuclei) Mycelium SEXUAL REPRODUCTION Zygote Spores GERMINATION MEIOSIS Spore-producing structures ASEXUAL REPRODUCTION Spores GERMINATION Spore-producing structures Fungi produce spores through sexual or asexual life cycles Fungi propagate themselves by producing vast numbers of spores, either sexually or asexually

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sexual Reproduction Plasmogamy is the union of two parent mycelia In many fungi, the haploid nuclei from each parent do not fuse right away; they coexist in the mycelium, called a heterokaryon In some fungi, the haploid nuclei pair off two to a cell; such a mycelium is said to be dikaryotic Hours, days, or even centuries may pass before the occurrence of karyogamy, which is nuclear fusion During karyogamy, the haploid nuclei fuse, producing diploid cells The diploid phase is short-lived and undergoes meiosis, producing haploid spores

Asexual Reproduction In addition to sexual reproduction, many fungi can reproduce asexually Many of these species grow as mold, sometimes on fruit, bread, and other foods

Parent cell Bud Other fungi that can reproduce asexually are yeasts, which inhabit moist environments Instead of producing spores, yeasts reproduce asexually by simple cell division Many molds and yeasts have no known sexual stage Mycologists have traditionally called these deuteromycetes, or imperfect fungi Asexual Reproduction

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fungi descended from an aquatic, single-celled, flagellated protist Systematists now recognize Fungi and Animalia as sister kingdoms In other words, fungi and animals are more closely related to each other than they are to plants or other eukaryotes Molecular evidence supports the hypothesis that fungi and animals diverged from a common unicellular, flagellated ancestor Fungi probably evolved before the colonization of land by multicellular organisms The oldest undisputed fossils of fungi are only about 460 million years old Fungi were among the earliest colonizers of land, probably as symbionts with early land plants

Chytrids Zygote fungi Arbuscular mycorrhizal fungi Sac fungi Club fungi Basidiomycota Ascomycota Glomeromycota Zygomycota Chytridiomycota Fungi have radiated into a diverse set of lineages Fungi phylogeny is the subject of much research Molecular analysis has helped clarify evolutionary relationships between fungal groups, although areas of uncertainty remain

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chytrids Chytrids (phylum Chytridiomycota) are found in freshwater and terrestrial habitats They can be saprobic or parasitic Molecular evidence supports the hypothesis that chytrids diverged earliest in fungal evolution Chytrids are unique among fungi in having flagellated spores, called zoospores Hyphae Flagellum

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Zygomycetes The zygomycetes (phylum Zygomycota) exhibit great diversity of life histories They include fast-growing molds, parasites, and commensal symbionts The zygomycetes are named for their sexually produced zygosporangia The life cycle of black bread mold (Rhizopus stolonifer) is fairly typical of the phylum Zygosporangia, which are resistant to freezing and drying, can survive unfavorable conditions Some zygomycetes, such as Pilobolus, can actually “aim” their sporangia toward conditions associated with good food sources

Rhizopus growing on bread Mating type (+) Mating type (–) Gametangia with haploid nuclei PLASMOGAMY Key Haploid (n) Heterokaryotic (n + n) Diploid (2n) 100 µm Young zygosporangium (heterokaryotic) SEXUAL REPRODUCTION KARYOGAMY Zygosporangium (heterokaryotic) Diploid nuclei MEIOSIS Sporangium Mycelium Dispersal and germination Dispersal and germination ASEXUAL REPRODUCTION Sporangia 50 µm Life cycle of black bread mold (Rhizopus stolonifer)

Pilobolus can “aim” their sporangia toward conditions associated with good food sources

10 µm Spore Developing microsporidian Host cell nucleus Microsporidia Microsporidia are unicellular parasites of animals and protists They are now classified as zygomycetes

Glomeromycetes The glomeromycetes (phylum Glomeromycota) were once considered zygomycetes, but are now classified in a different phyla Glomeromycetes form a distinct type of endomycorrhizae called arbuscular mycorrhizae

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ascomycetes Ascomycetes (phylum Ascomycota) live in marine, freshwater, and terrestrial habitats The phylum is defined by production of sexual spores in saclike asci, usually contained in fruiting bodies called ascocarps Ascomycetes vary in size and complexity, from unicellular yeasts to elaborate cup fungi Ascomycetes reproduce asexually by enormous numbers of asexual spores called conidia Conidia are not formed inside sporangia; they are produced asexually at the tips of specialized hyphae called conidiophores

The cup-shaped ascocarps (fruiting bodies) of Aleuria aurantia give this species its common name: orange peel fungus. The edible ascocarp of Morchella esculenta, the succulent morel is often found under trees in orchards. 10 µm Tuber melanosporum is a truffle, an ascocarp that grows underground and emits strong odors. These ascocarps have been dug up and the middle one sliced open. Neurospora crassa feeds as a mold on bread and other food (SEM). Ascomycetes

PLASMOGAMY Key Haploid (n) Dikaryotic (n + n) Diploid (2n) SEXUAL REPRODUCTION KARYOGAMY Four haploid nuclei MEIOSIS Dikaryotic hyphae extended from ascogonium ASEXUAL REPRODUCTION Diploid nucleus (zygote) Dispersal Germination Mycelium Mycelia Conidiophore Conidia; mating type (–) Mating type (+) Ascus (dikaryotic) Eight ascospores Asci Ascocarp Germination Dispersal Ascomycetes life cycle

Fly agaric (Amanita muscoria), a common species in conifer forests in the northern hemisphere Maiden veil fungus (Dictyphora), a fungus with an odor like rotting meat Shelf fungi, important decomposers of wood Puffballs emitting spores Basidiomycetes Basidomycetes (phylum Basidiomycota) include mushrooms and shelf fungi The phylum is defined by a clublike structure called a basidium, a transient diploid stage in the life cycle The life cycle of a basidiomycete usually includes a long-lived dikaryotic mycelium In response to environmental stimuli, the mycelium reproduces sexually by producing elaborate fruiting bodies call basidiocarps

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mushrooms are examples of basidiocarps

PLASMOGAMY Key Haploid (n) Dikaryotic (n + n) Diploid (2n) SEXUAL REPRODUCTION KARYOGAMY MEIOSIS Dikaryotic mycelium Basidium containing four haploid nuclei Dispersal and germination Basidium 1 µm Mating type (+) Mating type (–) Haploid mycelia Gills lined with basidia Basidiocarp (dikaryotic) Basidia (dikaryotic) Diploid nuclei Basidiospore Basidium with four appendages Basidiospores The numerous basidia in a basidiocarp are sources of sexual spores called basidiospores Asexual reproduction is much less common in basidiomycetes than in ascomycetes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fungi have a powerful impact on ecosystems and human welfare Fungi are efficient decomposers - They perform essential recycling of chemical elements between the living and nonliving world Fungi form symbiotic relationships with plants, algae, and animals All of these relationships have profound ecological effects by helping each other survive Mycorrhizae are enormously important in natural ecosystems and agriculture They increase plant productivity

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecological associations of fungi – their lifestyles Influence fungi can have on other living organisms in the environment – Symbiotic relationship: Organisms that live in close nutritional relationship, required by one or both organisms – Types Mutualism – both organisms benefit (mutualistic symbionts) Commensalism – one organism benefits, other not harmed Parasitism – host/microbe relationship, microbe benefits, host is harmed – Non-symbiotic relationship: Organisms are free-living, and do not rely on each other for survival – Types Synergism – shared metabolism between members, not required Antagonism - competition between microorganisms where some organisms growth is inhibited or they are destroyed by others

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mycorrhizae are mutually beneficial relationships between fungi and plant roots Ectomycorrhizal fungi form sheaths of hyphae over a root and also grow into the extracellular spaces of the root cortex Endomycorrhizal fungi extend hyphae through the cell walls of root cells and into tubes formed by invagination of the root cell membrane The fungi aid the plant’s uptake of nutrients and increase the surface area for water uptake. (root hairs also increase the total surface area of a plant’s roots!) These relationships between the fungi and the plant roots allow vascular plants to grow tall. Without the fungi, the plants wouldn’t grow as tall as they would not take up nutrients as easily. Mycorrhizae

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fungi have a powerful impact on ecosystems and human welfare

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fungus-Animal Symbiosis Some fungi share their digestive services with animals These fungi help break down plant material in the guts of cows and other grazing mammals Many species of ants and termites use the digestive power of fungi by raising them in “farms”

A fruticose (shrub-like) lichen A foliose (leaf-like) lichenCrustose (crust-like) lichens Lichens Lichens are a symbiotic association of millions of photosynthetic microorganisms held in a mass of fungal hyphae

Fungal hyphae Algal cell Soredia Algal layer Fungal hyphae Ascocarp of fungus 10 µm The fungal component of a lichen is most often an ascomycete Algae or cyanobacteria occupy an inner layer below the lichen surface to complete the lichen formation with the fungus Lichens

Corn smut on cornTar spot fungus of sycamore leavesErgots on rye Pathogens About 30% of known fungal species are parasites, mostly on or in plants Animals are much less susceptible to parasitic fungi than are plants The general term for a fungal infection in animals is mycoses

Staphylococcus Penicillium Zone of inhibited growth Practical Uses of Fungi Humans eat many fungi and use others to make many different cheeses, alcoholic beverages, and bread. Genetic research on fungi is leading to applications in biotechnology Antibiotics produced by fungi treat bacterial infections