Lecture 23 “The Hidden Kingdom” (Fungi)

Core traits of fungi

• Eukaryotic, heterotrophic organisms

• Reproduce via sexual and/or asexual life cycles

• **plants would not succeed in colonizing terrestrial environment without fungi

  • why?

  1. Early plants had no roots > can’t absorb minerals

  2. 2.Fungi could break down rock — plants could not > preapre land for plants

  3. Fungi helped plants access water in dry environments

• Large surface area–to–volume ratio for absorption

• Produce distinctive fruiting bodies (mushrooms, ascocarps, basidiocarps)

• Estimated 2.8–3.8 million species, only 150,000 described, ~300 human pathogens

six major phyla of fungi

Microsporidia, Chytridiomycota, Blastocladiomycota, Zygomycota, Glomeromycota, Dikarya (Ascomycota + Basidiomycota)

Microsporidia characterisitics

• Unicellular, 1–4 μm, no mitochondria

• asexual

• Obligate (=can only live) intracellular parasites of animals

• have coiled filaments to pentrate host cell and inject its DNA into another cell

• e.g. HIV / AIDS Epidemic > caused by microsporidia

Chytridiomycota

• unicellular

• Mostly aquatic (need water for zoospores to swim)

• Produce zoospores with flagella (motile spore > spore that can swim)

  • asexual / sexual

• have rhizoids (=root‑like anchoring structures) (not hyphae =long, thread‑like filaments that make up the body of most fungi.)

• Saprophytes

• some are obligate or facultative pathogens of animals and plants

  • facultative = can take adv of situation but can survive without

• symbionts of herbivorous vertebrates (digest cellulose in the gut)

  • symbionts = organsims that lives in a long-term, close relationship with another species

Blastocladiomycota

• unicellular / multicellular

• mainly Aquatic/moist habitats

• Alternation of generations (haploid + diploid)

• Produce zoospores > sexual / asexual

• Saprophytes (=feeds on dead and decaying matter) and parasites

Zygomycota

(transition from aquatic environment to terrestrial environment)

• multicellular

• First major terrestrial fungi

• Filamentous (=long,thin, hair-like) hyphe →lead to terrestrial environment

• molds, decomposers

• evolution from zoospore to hypha : sexual / asexual

• fast growing saprophytes > bread molds and insect pathogens

Glomeromycota

• Arbuscular mycorrhizal fungi

• Obligate mutualists of 80% of plants

• Only asexual

• Enabled plant colonisation of land 460 million years ago

• Multualism : fungi provide plants with phosphorus & plants provide fungi with carbohydrates

  • arbuscules: allow transfer of nutrient between plants and fungus

Ascomycota

• sexual / asexual

• 75% of described fungi (65,000 species)

• Produce spores in an ascus

• cellulose degraders, some plants and animal pathogens

Basidiomycota

• 30,000 species

• Mushrooms, puffballs, rusts, smuts

• some have complex life cycles

• Mostly sexual reproduction

• Includes Armillaria ostoyae, one of the largest organisms on Earth-8.8km2

Mutualisms

Mycorrhizae (Glomeromycota)

• Fungi provide phosphorus & minerals

• Plants provide carbohydrates

• Critical for plant survival in nutrient‑poor soils

Lichens

• Partnership: fungus + green alga/cyanobacterium

• Fungal partner provides nutrients & minerals & carbon dioxide

• Photosynthetic partner provides sugars and oxygen

• Morphologies: crustose (crusty), foliose (leafy), fruticose (bushy)

• mutualistic > allow present in extreme environments

Symbionts in animal guts

• Chytrids help herbivores digest cellulose

Pathogens

• Bd (chytrid fungus) → amphibian declines

• Rusts and smuts (Basidiomycota) → plant diseases

• Microsporidia → human and animal infections

Describe the role fungi have in the ecosystem

1. decomposers, nutrient cycling

2. therapeutic use

3. biological control agent

4. biotechnology or mycoremediataion