Fungi and McDonald's

    Fungi might be more closely related to everyone's favorite fast food chain than most people know.  No, there isn't mysterious fungi in McDonald's food (that I know of). So before you freak out and call the USDA, know that their similarity lies in their hours of operation.  Since fungi lack chlorophyll, they aren’t dependent on light.  This allows them to grow in the dark, in any direction, through things like dead logs, and even inside other organisms. 
    Fungi are heterotrophic, meaning they don’t make their own food.  Fungi are known for being decomposers of dead organic material.  They use thread-like structures called hyphae (right) to take in nutrients.  The hyphae are a network of fibers that forms the mycelium, a structure similar to the root system of a plant.  This system, like a good McDonald's, is active 24 hours a day! 

    When a fungus gets nutrition from a dead organism, it is classified as a saprophyte.  These types of fungi are important in recycling carbon, nitrogen, and minerals in the environment.  False morels are classified as saprophytes.  This type of fungi is known for decomposing, but just what does it decompose?
    Gyromitra esculenta grows on dead trees, wood chips, or fallen leaves, like in the picture on the right from blogspot.com.  They get their nutrition from the plant's cell wall components, the soil, and from animal waste. 

    Saprophytes take polymers like cellulose, lignin, and hemicellulose found in cell walls and break them down into simple sugars and amino acids.  They return some of these products to the soil, where plants and microorganisms can use them.  Hence, they are often designated as nature's recyclers. 
    Once the mushroom gets the glucose, they do much the same thing we do to get nutrition from it.  ATP is made by oxidative phosphorolation, which is the process mitochondria go through to make energy.  It includes glycolysis, the Krebs cycle, and the electron transport chain.     
    Dead plant material provides a good source of carbon and amino acids, but what about other nutrients?  Inorganic compounds in the soil can be converted to forms of nitrogen, phosphorous, and sulfur mushrooms and plants can use.  The false morel can also get nitrogen from amino acids.  In fact, they can use proteins as efficiently as glucose because they get nitrogen, carbon, and sulfur from them.  Another place they get components necessary for growth is herbivore waste.  It might seem gross to you, but dung full of vitamins, minerals, and growth factors is like a smorgasbord to fungi.    
   
    Unlike saprophytes, parasitic fungi feed on a living organism.  An example of a fungal parasite is Candida albicans, which causes yeast infections (below, right).  Mutualistic fungi have a symbiotic relationship with another organism that is beneficial to both.  A lichen (below, left) is a mutualistic relationship between a fungus and an algae or cyannobacteria.  More information about lichens can be found here. 
    Lastly, there are commensalist fungi in a symbiotic relationship that is only beneficial to one of the species involved.  Fungi from the class trychomycetes often undergo commensalism with insects by living in their gut.                                                                            
  

        Unlike humans and other heterotrophs that ingest their food then digest it, fungi digest their food then ingest it.  Saprophytes use exoenzymes to break down the substrate like a dead log.  First, the tip of a hypha releases the exoenzymes into whatever is being broken down.  The enzymes digest the substrate, and the hypha extends further into it and ingests the broken down food particles.  In this way, the mycelium continues to grow.

    Water availability is extremely important to the fungal lifestyle.  This is because fungi don't have transport tissues like plants.  If they did, we would probably see mushrooms as tall as trees!  Fungi absorb water directly through the walls of every individual cell.  That is why fungi are often found underground, and usually only occur in temperate climates with plenty of water in the air and soil.  

    To find out how the mycelium fits into the rest of the morel life cycle, see the reproduction page. 

Pictures on this page were taken from Wikipedia.com

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