Biology of FUNgi Lecture 4 The non-fungi A look back... What is a biotroph/saprotroph? What is an obligate/facultative biotroph? What is the 3 domain system? Where do fungi fit in this scheme? Where are the non-fungi? 1
Fungus of the day - Dictyostelium discoides Taxonomy: Phylum (subphylum) Dictyosteliomycota Order - Dictyosteliales Family - Dictyosteliaceae Common names: the slug What is it: Cellular slime mold. D. discoides has an amoeba phase which is phagotrophic on bacteria. An outstanding example of healthy family dynamics: the zygote forms a macrocyst, which digests other loving members of the family. D. discoides is among those haploid organisms which have been chosen as model organisms for cell cycle and genome research. Life cycle is a kick as well. D. discoides amoeba and a sorocarp Fungus of the day - Dictyostelium discoides From Alexopoulos et al. 1996 Check out p. 15-20 in Carlile Life cycle The Slug Sorocarp = sorus-containing structure Sorus = mass of spores or sporangia + Meiotic division of the macrocyst; return to haploid phase Zygote feeds on the fellow amoeba cannibal Karyogamy = nuclei of the dikaryote fuse; diploid phase Plasmogamy = cytoplasms fuse; dikaryote phase The giant zygote = macrocyst Primary cell walls surround dikaryotic macrocyst and surrounding fellow amoeba 2
Fungus of the day - Dictyostelium discoides Life cycle From http://dictybase.org/ Fruiting body = sorocarp Pseudoplasmodium = slug Fungus of the day - Dictyostelium discoides For tid-bits and more trivia check following; D. discoides as a model for biomedical research: http://www.nih.gov/science/models/d_discoideum/ Movies aggregation stream and more: http://www-biology.ucsd.edu/~firtel/movies.html D. discoides genome project: http://genome.imb-jena.de/dictyostelium/ 3
A look ahead... Let s dive into the protistan tail from the deep end. In other words, let s look at the non-fungi. True and cellular slime molds. Biflagellates - the oomycetes Kingdom Fungi in three domains The true fungi would include four fungal phyla. The rest of the organisms previously considered as fungi would mainly be protistan. Let s look at those. This is also known as the approach of climbing to a tree from the base.?? Basidiomycota Ascomycota Zygomycota Chytridiomycota Animalia 4
The non-fungi These are the groups studied by mycologists, but not included in the modern kingdom Fungi. Animalia Fungi Plantae Protista Monera Currently, they seem to fall into phyla of their own - e.g. Dictyostelium, a cellular slime mold, Physarum - a true slime mold, Achyla - an oomycete. From Pace 1997 Science 276: 734-740. From Alexopoulos et al. 1996 The non-fungi - what are they? What are fungi? Heterotrophic, mainly aerobic and filamentous eukaryotes which obtained nutrients and energy by absorbing compounds from their substrate. They were characterized by septate or aseptate hyphae made of chitin. 5
From Alexopoulos et al. 1996 The non-fungi - what are they? What are the non-fungi? Three groups of organisms historically included in fungi. 1) The true fungi - Kingdom Fungi 2) Stramenopiles - fungus-like organisms with flagella. 3) The slime molds - protistan amoeboid groups. From Alexopoulos et al. 1996 The non-fungi - what are they? 1) The true fungi - Monophyletic, well-supported 2) Stramenopiles - Monophyletic, somewhat well-supported 3) The slime molds - evidently polyphyletic 6
The slime molds First group are the so-called slime moulds (protozoan). Not fungi because they are 1) Phagotrophic (amoeboid), not absorptive 2) Not hyphal, ever 3) Assimilative plasmodia usually have no cell wall (exception cellular slime moulds). Dictyostelium - Dictyoistelid cellular slime mold Note that these are clearly not monophyletic and a uniform group. Physarum - true slime mold The slime moulds From Alexopoulos et al. 1996 We will consider two of the four phyla. 1) Phylum Dictyostelimycota (Dictyostelida) - cellular slime moulds 2) Phylum Myxomycota (Myxostelida) - true slime moulds 3) Phylum Acrasiomycota (Dictyostelida) - cellular slime moulds 4) Plasmodiophoromycota (Plasmodiophorida) - endoparasitic slime moulds Note: there is a serious incongruence how your text treats these phyla 7
Phylum Dictyosteliomycota cellular slime moulds The fungus of the day was an excellent example of the cellular slime molds. Characterized by 1) Phagotrophic haploid amoeba 2) Pseudoplasmodium - multicellular somatic phase 3) reproductive stationary sorocarp From Alexopoulos et al. 1996 Myxoamoeba aggregate to form pseudoplasmodium Phagotrophic myxoamoeba Pseudoplasmodium which will form the sorocarp - Dictyostelium Phylum Dictyosteliomycota cellular slime moulds Main difference between Dictyosteliomycota and Myxomycota is the presence or absence of individual cells in the (pseudo-)plasmodium. Habitat and occurrence Common in soil, dung and decaying plant material. Remain unseen because sorocarps are minuscule. Phagotrophically feed on bacteria on the substrate Sorocarp - Dictyostelium discoideum 8
Phylum Myxomycota true slime moulds Carlile p. 20-25. From Alexopoulos et al. 1996 Haploid spores Haploid Swarm cells Meiosis Myxoamoeba Characterized by 1) Phagotrophy 2) Three types of uninucleate, haploid cells: spores, swarm cells, myxoamoeba 3) Multinucleate somatic phase; true plasmodium 4) reproductive stationary sporangium Sporangium Resting stage, sclerotium Plasmodium Zygote Karyogamy Stemonitis fusca sporangia Plasmodium - motile, chemostatic, not cellular Phagotrophic myxoamoeba Phylum Myxomycota true slime moulds Occurrence Cosmopolitan group, in moist temperate forests, lawns, flower beds. Usually, on wood, leaves or bark. Substratum, however, is more of a habitat - myxomycetes feed on bacteria and organic particles (phagotrophs). Physarum cinereum on tall fescue leaves in Kansas Stemonitis fusca - young and mature stalked sporangia Fuligo septica - troll butter - is another common myxomycete on lawns; stalkless sporangia 9
Phylum Myxomycota true slime moulds Myxomycete trivia - Fuligo septica is fondly called the blob - 1973 was exceptionally wet year; F. septica seemed to enjoy these favorable conditions A quote of a sheriff s report:, an unidentified Growing Object (big as platter, foamy and creamy and pale yellow) terrorized Mrs Harris s backyard for three weeks. Apparently, the blob died of a sunstroke and nicotine poisoning - rains ceased and Mrs. Harris was a heavy smoker. TheBlob - a horror movie from 1958 Fuligo septica - sporangia More non-fungi... Second group includes the Oomycota in stramenopiles a.k.a. biflagellates An odd number of other fungus-like organisms (e.g. hyphochytrids) and algae also belong to this group 10
Oomycetes - the water molds Stramenopiles were those organisms that are united by presence of two flagella (biflagellates) of unequal length, form or movement (heterokonts). Monophyly seems to be somewhat well supported. Oomycota (water moulds) - these are more similar to eufungi - absorptive nutrition Oomycetes - the water moulds Oomycetes are oomycetes because 1) Asexually reproduce with zoospores (heterokont, biflagellate) with a hairy tinsel flagellum and a smooth whiplash flagellum Saprolegnia sp. - oospores. Saprolegnia sp. - zoosporangia. 2) After fertilization, diploid thallus which forms gametangia 3) Sexually reproduce by gametes; plasmogamy and karyogamy result in resting structure known as oospores. 4) Cell wall usually not chitinous; glucans, cellulose. Some species may have chitin. A zoospore with tinsel (one with hairs on the flagellar membrane) and whiplash flagellum (One without the hair) 11
Oomycetes - the water molds Significance and occurrence... The zoospores need water for dispersal - hence the flagellum. Most of the aquatic oomycetes are saprobes decomposing the remains of dead plants and animals - a major component in nutrient cycling in rivers and lakes. The woolly patches on the hatchery fishes are often Saprolegnia. Many aquatic species are parasites of fish and their eggs. Oomycetes - the water molds Also terrestrial species. E.g. Phytophthora infestans, the causal agent of potato blight. P. infestans is also the cause of the great Irish famine, which resulted in the great Irish migration to North America. Phytophthora infestans. - zoosporangia. Foliar necrosis resulting from potato blight Taters infected with Phytophthora infestans (soft rot) A zoospore with tinsel and whiplash flagellum 12
Oomycetes - the water molds Significance and occurrence... Although many oomycetes are aquatic and saprotrophic, there is at least one example of terrestrial disease-causing oomycete Pythium insidiosum. Pythium insidiosum causes pythiosis in mammals. P. insidiosum can also infect humans. Life cycle. Phylum Oomycota oomycetes Mitotic zoospores Mitotic zoospores Key points to ponder: - diploid, mitotic zoospores, which may form resting cysts. Some species like Saprolegnia go through encystment more than once. Resting cysts Karyogamy Resting cysts - Meiosis occurs in oogonium and antheridium - plasmogamy and karyogamy give rise to a zygote, oospore Thallus with sporangia Plasmogamy Gametes Thallus with sporangia Gametangia 13
Oospore Phylum Oomycota oomycetes Oogonium and antheridium To sum up... Eufungi vs. slimemolds and biflagellate Oomycetes Lifecycles of slimemolds and Oomycetes The significance and occurrence of the nonfungi 14