1. Zoosporic fungi Kingdom - Fungi

2. Zoospores Motile asexual spores = zoospores No cell wall, one or two flagella Flagella – long slender structures extending from cell and surrounded by cell membrane 9+2 microtubular structure characteristic of eukaryotes

3. Zoospore Flagellum anchored in cell with basal body

4. Zoosporic fungi Asexual reproduction by zoospores produced in zoosporangia Fungal zoospores have one posterior flagellum Vegetative thallus variable – range from globose, multinucleate to hyphal forms Growth may be determinate or indeterminate

5. Zoospores Produced in zoosporangium Swim away Zoospores encyst – withdraw or lose flagellum, rapidly form a cell wall Cyst then germinates to form rhizoids and enlarges

6. Zoosporic fungi Divided into 3 phyla Chytridiomycota (706 spp) Neocallimastigomycota (20 spp) Blastocladiomycota (179 spp)

7. Chytridiomycota Habitats – zoospores require free water in which to swim – many occur in aquatic habitats, also found in soil water Many species are saprotrophic – grow on a variety of substrates, most are aerobic, Some are parasitic on algae, other fungi, aquatic animals, some parasitic on higher plants (crops), one is parasitic on frogs

8. Chytridiomycota Includes 4 orders, distinguished on basis of habitat, zoospore ultrastructure, other characterisitics  Chytridiales – mainly aquatic Spizellomycetales – mainly in soils Rhizophydiales - Monoblepharidales – small no of species, all filamentous, unique sexual reproduction

9. Zoospore ultrastructure

10. Chytridiales – “chytrids” Primarily aquatic Saprotrophs grow on variety of substrates – “baiting” Parasites of algae, fungi, animals, higher plants – “black wart of potato” caused by Synchytrium endobioticum Olpidium brassicae is a cabbage parasite that is a vector for a plant virus

11. Sexual reproduction Great deal of variation, but nuclear events, e.g. meiosis, not clearly determined Fusions have been seen between zoospores, gametangia, rhizoids

12. Vegetative thallus Single multinucleate thallus with no appendages –If grows within host cell it is endobiotic –If entire thallus is converted to zoosporangium, it is holocarpic

13. Vegetative thallus Many species form rhizoids – tapering structures that anchor thallus and increase surface area for absorption of nutrients During differentiation, the entire thallus is not converted into a zoosporangium – eucarpic May be within host cell – endobiotic or outside - epibiotic

14. Vegetative thallus Some chytrids produce only one zoosporangia per thallus – monocentric Others produce multiple zoosporangia – polycentric Produce rhizomycelium

15. Vegetative thalli

16. Zoosporangia Thallus (or part) differentiates into zoosporangium Triggered by environmental conditions, thallus size, nutrient concentration Multinucleate cytoplasm is cleaved into a number of zoospores Golgi produce vesicles that are deposited around nuclei – form plasma membrane, flagella Once formed zoospores escape sporangium

17. Zoosporangium

18. Zoosporangium formation

19. Zoosporangium Zoospores are released from zoosporangia by Breakdown of sporangium wall Forming 1 or more discharge papillae Opening in papilla may be A lid = operculum By becoming thin and dissolving - inoperculate

20. Resting spores Chytrids may form resting spores – thick cell wall, may be ornamented with spines, knobs or may be smooth Typically undergo a period of dormancy

21. Batrachochytrium dendrobatidis Parasitic on amphibians – colonizes the epithelium of adult frogs –causes a fatal inflammatory disease responsible for decline of frog populations -

22. B. dendrobatidis The disease only discovered in 1998 Very low specificity for frog species The chytrid also infects tadpoles – in mouthparts but does not kill them

23. Monoblepharidales Small order of filamentous eucarpic thalli that produce zoosporangia on ends of hyphae Produce small motile male gametes and large non motile female gametes Thought that life cycle is haploid, i.e. germination of zygote includes meiosis

24. Neocallimasticomycota Occur in rumen and hindgut of mammalian herbivores, also in anaerobic aquatic environments Morphologically similar to chytrids Degrade lignocellulose, ferment glucose to acetate, lactate, ethanol & hydrogen Are obligately anaerobic – no mitochondria, have hydrogenosomes Monocentric or polycentric, zoospores uniflagellate or multiflagellate

25. Blastocladiomycota Relatively small order – mainly saprotrophs, great variation in vegetative thallus Characteristics –Produce brown, thick-walled pitted resting sporangia –Characteristic zoospore (nuclear cap containing cellular ribosomes) Representative genera

26. Coelomomyces Obligate parasite of aquatic animals – diploid phase on mosquito and midge larvae, haploid phase on copepods Forms a holocarpic, endobiotic thallus Forms isogametes that are motile for sexual reproduction Possible biological control agents for mosquitoes (importance in understanding life cycles)

27. Coelomomyces life cycle

28. Blastocladiella Monocentric thallus, eucarpic Asexual life cycle – can form two types of sporangia depending on environment –Thin walled zoosporangia –Thick walled resting sporangia when CO 2 concentrations are high Has been used to examine the biochemistry of differentiation along these two pathways

29. Blastocladia Forms polycentric thallus but exhibits determinate growth

30. Allomyces Great deal of research on development and genetics Some species reproduce both sexually and asexually, in others only asexual reproduction Some species exhibit a haploid – diploid life cycle –Haploid vegetative mycelium –Diploid vegetative mycelium

31. Allomyces Haploid and diploid mycelia are identical except for the reproductive structures they produce –Haploid mycelium produces gametangia –Diploid mycelium produces zoosporangia and resistant sporangia Hyphae branch dichotomously, produce septa with many perforations

32. Allomyces life cycle Haploid zoospore germinates to form 1n thallus Tips of hyphae produce male and female gametangia Male gametangia orange Female gametangia colorless

33. Allomyces life cycle Cytoplasm in gametangia cleaves to produce gametes Both gametes are motile, leave gametangia through discharge pores in papillae

34. Allomyces life cycle Gametes swim –Male gametes smaller, orange –Female gametes larger, colorless Female gametes produce substance, sirenin that attracts male gametes chemotactically Male and female gametes fuse (plasmogamy and karyogamy) to form zygote

35. Allomyces life cycle Zygote swims and encysts Germinates to produce diploid mycelium Produces zoosporangia – 2n zoospores that encyst and germinate to produce 2n thallus

36. Allomyces life cycle Zoosporangia

37. Allomyces life cycle 2n mycelium also produces resistant sporangia – thick walled, pitted, brown structures that can remain dormant When resistant sporangia germinate, they undergo meiosis to form haploid zoospores that start the cycle over

38. Allomyces life cycle