“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

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

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,