Kingdom Fungi
Please read Chapter 31 in Campbell and Reece before reviewing the following online lecture material.

Fungi are....

• mainly multicellular, eukaryotic heterotrophs
   
• currently divided into 5 Phyla - all fungi can be traced back to a common ancestor, probably an aquatic, flagellated protist
   
• more closely related to animals than plants, based on recent molecular evidence
   
• historically grouped with the plants - probably because both have cell walls and are not mobile.
  (But plant cell walls are made of cellulose, fungal cell walls are made of chitin - a big difference!)

Nutrition

• Absorption - they excrete powerful enzymes and absorb organic molecules. 
    ("digest, then ingest vs. ingest, then digest")
   
• Large surface area and rapid growth is critical to this mode of nutrition.

Ecological Roles

• decomposers (saprobes) - absorb nutrients from dead organic material, including:
  • wood  (click for image)
  • non-living organic material (dead plants and animals, feces)
  • man-made products (paper, leather, cloth, food products)
    
    
    Decomposition is a critical ecological role! Fungi return staggering amounts of CO₂ to the atmosphere and return nutrients to the soil. Without fungi and bacteria, critical nutrients would be unavailable -  'locked up' in dead plant and animal matter.     Remember - mold is good!  (By the way, 'mold' is not a taxonomic term.  It merely refers to the rapid, asexual growth of many types of fungi).
    
    
• mutualistic symbionts - almost all plants depend on fungi to increase surface area for  water and mineral absorption from the soil.  These associations between plant roots and fungi are called mycorrhizae.  The fungus benefits by obtaining organic nutrients synthesized by the plant.  Mycorrhizae are critical to both natural and agricultural ecosystems and may have contributed to colonization of plants onto land by enabling them to thrive, even in nutrient-poor soils.
  
  
  
• parasites - absorb nutrients from other living cells. 
  
  • some are serious plant pathogens (Chestnut blight, ergotism)
    
  • some are animal pathogens (athlete's foot, jock itch, ringworm,  yeast infections)
    
    
    
• food source - many animals, including humans include fungi in their diet.  Many species of fungi are poisonous and may cause death if ingested.  Fungi should NEVER be ingested unless one is absolutely sure of identification.
  
  Overview of Edible and Poisonous Mushrooms (Conservation Commission of Missouri)
  Fly agaric - a poisonous and hallucinogenic mushroom

Additional Impacts on Human Society

• Used in baking, brewing and winemaking
• Production of some cheeses, soy sauce and tofu
• Production of antibiotics and other medicines (cyclosporins)

Vegetative (non-reproductive) Structure

Hyphae

threadlike tubes may be divided into cells by septa   may be coenocytic (cytoplasm is continuous with many nuclei)

• cell walls of chitin
  
  
• typical eukaryotic cytoplasm and organelles
  
  
• nuclei haploid

 

Mycelium

• mass of interwoven hyphae 
  
  
• enormous surface area/volume ratio
  
  
• often hidden - permeating the substrate on which it feeds

 

There are also single-celled fungi, called yeasts which do not form hyphae or mycelia.

Fungal Life Cycles  - (Also refer to Chapter 31 of textbook)

Important definitions

Spore

a reproductive cell capable of dividing to produce a multicellular individual without fusing with another cell.

Sporangium

a structure ('container') in which spores are produced

Gametangium

a structure ('container') in which gametes are produced

Plasmogamy

fusion ('marriage') of cytoplasm of two different cells

Karyogamy

fusion of nuclei of two different cells

Syngamy

fusion of two cells in sexual reproduction (fertilization)

Dikaryotic (n + n)

having two genetically different nuclei within one cell (this is different than either haploid or diploid!)
(This is a special case of the more general term 'heterokaryotic', which describes the condition of having genetically different nuclei within the same hyphae or mycelium)

Sexual Reproduction

The fungi you are probably most familiar with (mushrooms, puffballs, bracket fungi) are the fruiting bodies of various fungi.

Classification and Characteristics of Fungi

Note: Only 3 of the 5 recognized phyla will be described. The Chytridiomycota and Glomeromycota will not be included.

Division Zygomycota  - Zygote fungi  (Example in Lab:  Rhizopus stolonifer)

• Form mycorrhizae  - critical in mineral nutrition of vascular plants
• Parasitic on some insects -  potential for biological control
• White 'molds' - cause spoilage of various foods (View image)

Structure and Life Cycle

• Hyphae are coenocytic
• Asexual reproduction is common via sporangia
• Sexual reproduction forms the heterokaryotic zygosporangium - a protective structure very resistant to harsh environmental conditions - persists until conditions allow spore formation and dispersal   (View image)

Division Ascomycota - Sac fungi  (Examples in Lab:  Peziza sp.,  Variety of Lichens)
    View some images

• Blue-green, red and brown 'molds' cause food spoilage
• Powdery mildews on plant leaves- dutch elm disease and chestnut blight
• Morels and truffles - edible delicacies
• Many 'yeasts' (unicellular fungi) used in bread, beer and wine production
• Lichens (associations with green algae or cyanobacteria)

Structure and Life Cycle

• Sexual sporangia called asci (singular: ascus) form at the tips of dikaryotic hyphae.  These 'sacs' (the asci) give the division it's common name of 'sac fungi'.
• Asci line the surface of the ascocarp
• Karyogamy followed by meiosis followed by mitosis within each ascus results in 8 ascospores per ascus.

Division Basidiomycota - Mushrooms and relatives (Examples in Lab:  Agaricus bisporus, Coprinus sp.)

• Familiar as mushrooms, puffballs  and shelf fungi
• Rusts and smuts - serious plant pathogens
• Form mycorrhizae - especially with temperate trees and shrubs
• Especially important in plant litter decomposition

Structure and Life Cycle

• An extensive, dikaryotic mycelium forms which is very long-lived and gives rise to the fruiting body (basidiocarp) when environmental conditions are appropriate.
• Sexual sporangia (basidia) form on specific locations (lots of surface area!) on or inside the basidiocarp. 
• Karyogamy followed by meiosis produces basidiospores.   A single basidiocarp may produce billions of spores.