Fungi Lecture Notes PDF

What are Fungi? / What is a Fungus? They represent a unique group of organisms which are extremely diverse with respect to their activities, shape and form. Unicellular yeasts Humongous fungi; Amillaria (microns; 1/1000 of a (>100 tons; 15,000 years old) mm) Smith et al. (1992) Nature 356, 428 De...

What are Fungi? / What is a Fungus? They represent a unique group of organisms which are extremely diverse with respect to their activities, shape and form. Unicellular yeasts Humongous fungi; Amillaria (microns; 1/1000 of a (>100 tons; 15,000 years old) mm) Smith et al. (1992) Nature 356, 428 Defining Characteristics of Fungi ➢Eukaryotes ➢Cell Wall (chitin and polysaccharides) ➢Reproduction Sexually and Asexually Nuclei are usually haploid; i.e. one set of chromosomes (n) ➢Heterotrophs (“obtaining energy by degrading complex organic molecules”) Contain no chlorophyll Can not utilise CO2 as a single carbon source Can not fix N2 Defining Characteristics of Fungi (2) ➢Heterotrophs Absorb nutrients from their environment and live as either; SAPROPHYTES – derive nutrients from dead remains } NECROPHYTES – derive nutrients from organisms they have killed BIOTROPHS – derive nutrients from living host Parasites ➢Astonishingly successful heterotrophs! Ability to use diverse range of C sources Provided with suitable C and N sources – impressive array of bio-synthetic powers Occupy a diverse array of ecological niches Fungi are not plants! A-level text book – 1984! Key differences between Plants and Fungi: Plants are photo-autotrophs (photosynthesizers) Fungi secrete enzymes and digest/absorb organic material Fungi are usually ‘filamentous’ in form Plants are made up of ‘box-like’ cells Fundamental differences in cell wall composition Nuclear mitosis: fungi – takes place within the nucleus Other eukaryotes – nuclear envelope breaks down Classification of fungi Historical Perspective 1950s: Cellular organisation of bacteria recognised as distinct to other organisms 1969 (Whittaker, R.H. Science 163, 150 -160) The five kingdom classification Modern tree of life 1990s modern molecular approaches ? Note: Fungi and animals are each others closest relatives! How do fungi propagate? Growth and Reproduction Range of fungal growth forms Yeasts e.g. Saccharomyces cerevisiae; Schizosaccharomyces pombe - Single cell/single nucleus - Oval or spherical - Reproduces asexually by producing an identical but separate daughter cell - Can aggregate to form a colony or ‘pseudohyphae’ - 3 – 5 µm diameter S. cerevisiae Sch. pombe Range of fungal growth forms (2) Filamentous fungi (molds) Vast majority of fungi Multicellular Long ‘thread-like’ filaments – hyphae Polarised tip growth Mycelium – colony or mass of hyphae Large complex bodies – interwoven mass of hyphae Reproduce via spores (see later) tip growth Playback movie mycelium Range of fungal growth forms (3) Dimorphic yeasts/fungi Environmental cues (e.g. temperature, CO2) trigger transition between yeast and filamentous forms. Medically important Reproduction in fungi (3) Yeasts - typically bud a daughter cell Asexual Filamentous fungi - generate light weight spores for effective dispersion - colonise food supply rapidly - haploid - formed from specialised aerial extensions from mycelia - produced in many different species-specific ways Sexual - union of compatible nuclei to form diploid (2n) state - usually when nutrients are in poor supply - sexual spores are usually more hardy structures allowing survival in adverse conditions - heterothallism: results in exchange of genetic material and requires two different mating types (+, -) - homothallism: some fungi are able to self-fertilize and produce sexual spores – (what is the advantage in this?) Examples of asexual spore formation Generalised overview of sexual reproduction in fungi Three major divisions (phyla) of fungi Division Chytridiomycota (Chytrids) Zygomycota (Zygomycetes) Ascomycota (Ascomycetes) Basidomycota (Basidiomycetes) Deuteromycota (Deuteromycetes) Number of species 1000 1000 65,000 30,000 Zygomycetes – Life cycle of Rhizopus stolonifer asexual reproduction Zygomycetes – Life cycle of Rhizopus stolonifer sexual reproduction Zygomycetes ➢Aseptate hyphae (haploid) ➢Smallest phyla ➢Asexual features - haploid sporangiospores from sporangia ➢Sexual features - diploid zygospore ➢Most are saprophytes (e.g. Rhizopus stolonifer) ➢Contains Glomus spp. - important mycorrhizal fungi. Modern molecular techniques place them in their own clade (glomeromycetes - ~160 species). Ascomycetes – asexual reproduction Ascomycetes – sexual reproduction Ascomycetes ➢Septate hyphae (haploid) ➢Asexual features - haploid conidospores from conidiophores ➢Sexual features - haploid ascospores (meiosis followed by mitosis) ➢Most are saprophytes ➢Model organisms (e.g. S. cerevisiae; Aspergillus nidulans; Neurospora crassa) ➢Many important plant pathogens (e.g. Claviceps; Erysiphie) Basidiomycetes Sexual reproduction Basidiomycetes Sexual reproduction (2) Basidiomycetes ➢Septate hyphae (dikaryons) ➢Asexual cycle is uncommon ➢Sexual features – haploid basidiospores (meiosis) ➢Various types of fruiting body (basidiocarps) Basidiomycetes (2) ➢Most are saprophytes (lignin decomposers; Serpula lacrymans) ➢Food (Agaricus bisporus fruiting bodies – edible mushrooms) ➢Many important plant pathogens (e.g. rusts; Puccinia spp.) Deuteromycetes ➢Sexual reproduction cycle absent ➢Asexual spores formed in various ways (e.g. conidiospores & arthroconidia) ➢Fungi imperfecti ➢Most were ascomycetes and did include the important food spoiler, Aspergillus flavus, and the industrial workhorse Aspergillus niger.