Zygomycota Kingdom Fungi Zygomycota Vegetative stage well developed

“Zygomycota” Kingdom Fungi

“Zygomycota” • Vegetative stage – well developed aseptate hyphae • Asexual reproduction by nonmotile sporangiospores • Sexual reproduction – Zygospore produced in a zygosporangium from fusion of two similar gametangia • Ca. 800 spp.

“Zygomycota” • Is polyphyletic has been divided into four subphyla • Will discuss major orders – Mucorales – saprobic (420 spp) – Entomophthorales – parasites of arthropods (240 spp) – Harpellales & Asellariales (Trichomycetes) – smaller (135 spp), less well understood, are commensals on surface and in guts of arthropods

Mucorales • Zygospore production is generally similar among species, therefore classification is based on characteristics of asexual reproductive structures • Asexual reproduction is typically by production of sporangiospores, but we will see lines of evolution in which the number of spores/sporangium is reduced until there is only 1 spore/sporangium conidium

Mucorales • Grow saprotrophically on decaying plant and animal remains in soils, dung, etc. • Produce large numbers of asexual spores that are dispersed in the air • Common contaminants in laboratory • Some are important in spoiling food – common bread mold, storage diseases of fruits and vegetables • Some infect humans and animals – opportunistic pathogens

Mucorales • Typically form aseptate hyphae, septa formed to delimit reproductive structures • Some species form rhizoids

Multispored sporangium • Morphology of sporangia varies, basis for classification • Typical multispored sporangium contains • Sporangium wall • Columella • sporangiophore

Development of sporangium • Tip of sporangiophore swells • Swelling increases, contains multinucleate cytoplasm • Cytoplasm is cleaved to form all spores at one time – cell membrane and cell walls laid down around nuclei

Development of sporangia • After formation, sporangial wall may break and release spores into the air or • A drop of fluid may envelop the sporangium with spores being dispersed by small animals that touch the sporangium

Reduction of sporangium • Several lines of evolution in the reduction of number of spores/sporangium • Examples of modifications of sporangia • Thamnidium – both multispored sporangium and smaller sporangia = sporangiola

Reduction of sporangia • Blakeslea – sporangiola with 3 spores/sporangiolum • Cunninghamella – one spore/sporangiolum, spore wall and sporangiolum wall indisdistinguishable except with EM

Reduction of sporangia • One group in the Mucorales produce cylindrical sporangia = merosporangia • Also see a reduction in the number of spores/sporangium in this line • Syncephalastrum

Other sporangial modifications • Pilobolus – fungal shotgun • Grows on herbivore dung • Sporangiophore contains carotenoids, acts as a lens to focus light and direct the growth of the sporangiophore to point the sporangium at light source

Pilobolus • As the sporangium and sporangiophore mature, the sporangiophore builds up a very high turgor pressure • Sporangium as a whole is shot off suddenly, directly at the light – up to 3 m • A drop of fluid on the sporangium causes it to stick to whatever it hits • Phototrophic ability allows sporangium to be shot out of a pile of dung, land on grass, be eaten by herbivores

• Passage through gut of herbivore activates spore germination • Sporangium is dark in color to prevent damage from UV when attached to grass Pilobolus

Sexual reproduction • Involves fusion of two multinucleate gametangia that are similar in structure, may differ in size • Gametangia are produced as terminal swellings of hyphal branches • After plasmogamy – a thick walled zygospore is produced with a zygosporangium • Both homothallic and heterothallic species

Life cycle • Vegetative mycelium is haploid, reproduces asexually by producing sporangiospores in sporangia • In a heterothallic species, when two compatible strains come together, hyphal branches form, enlarge to form progametangia

Life cycle • Septa form, producing multinucleate gametangia and suspensors

Life cycle • Plasmogamy occurs, end walls of gametangia dissolve and cytoplasm of gametangia mixes

Formation of zygospore

Life cycle • Zygospore forms inside zygosporangium • Zygospore develops thick wall, warty appearance, dark in color • Karyogamy occurs at different times in zygospore formation in different species, so zygospore is diploid at some point

Life cycle • When zygospore germinates, meiosis occurs to start the haploid portion of the life cycle over again

Life cycle

Variation in zygospores • Some variation is seen in zygospore formation

Entomophthorales • Arthropod parasites, 240 spp. • Asexual reproduction by one spored sporangiola (conidia) • Mycelium exhibits limited growth in the body of the host, forms septa and fragments • Entomophthora is a parasite of flies – seen when fly is stuck to window, white halo around it

Entomophthora • Mycelium fills up body of fly, forms sporangiophores that extend out of segments of abdomen

Entomophthora • Sporangiophore builds up pressure, shoots off sporangiolum when there is air movement (another fly) • If misses, can form another structure that shoots it off, up to 3 times • Sexual reproduction not well understood, form resting spores that are similar to zygospores

Entomophthorales

Glomeromycota • Obligate biotrophs • Biotrophic in the roots of higher plants, form arbuscular mycorrhizae • Ca. 169 spp.

Glomerales • Form tree-like structures = arbuscules in cells of plant – exchange of nutrients between fungus and plant • Form large spores in soil –azygospores, and chlamydospores depending on species

Glomales • Azygospores • Chlamydospores

Phylogenetic relationships

Trichomycetes • All but a few species are obligate commensals in guts or on exoskeleton of arthropods • Found in freshwater (mayfly, stonefly, midges) and terrestrial (millipedes)

Trichomycetes • Thallus is relatively simple – produce a holdfast that anchors them to lining of gut

Trichomycetes • Thallus may be unbranched and aseptate or branched and septate • Variety of asexual spores produced (generally 1 spore/sporangium)

Trichomycetes • Sexual reproduction involves formation of zygospores (in one order) • Fusion of cells in thallus • Formation of zygosporophore and then zygospore

“Lower fungi” • Major groups of lower fungi – Chytridiomycota, Blastocladiomycota, Neocallimastigomycota, “Zygomycota”, Glomeromycota (Oomycota) • Exhibit diversity in vegetative thallus, asexual and sexual reproduction • Mycelium when present is typically aseptate • Used to be placed in one class = “Phycomycetes” – now clear that they do not share a common phylogeny

“Lower fungi” • Asexual reproduction – spores produced inside a sporangium – sporangiospores • In Chytridiomycota, Blastocladiomycota, Neocallimastigomycota, and Oomycota, zoospores produced • Transition from multispored sporangia to conidia in both the Oomycota and “Zygomycota”

Reproduction • Asexual - Sporangia – produce sporangiospores, in some zoospores • Sexual Life cycles • Haploid life cycles – Zygomycota produce zygospore, isogametangia • Diploid life cycles – Oomycota produce oospore, oogonia and antheridia • Haploid – Diploid life cycles – Allomyces,