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Fungi: Harmful and Helpful Fungi

Images of Fungi

Penicillium variabile, a mold most associated with asthma.  Photo: Wellcome Images.

Tempeh is a fermented product made from beans and grains.

Stem rust-infected wheat plant.  Photo: USDA

Yeast cells of the species Saccharomyces cerevisiae.  Photo: Jef D. Boeke and Sarah Richardson, JHU

Closeup view of onion smut sori on the cultivar ‘Red Label’.  Photo: Washington State University

Harmful Fungi

About 200 species of fungi are toxic to humans. Ingestion or exposure can have mild effects, like rashes or nausea; or more extreme complications, causing organ failure and even death.

  • Some types of fungi produce spores that cause a form of meningitis, an inflammation of tissue surrounding the brain or spinal cord.
  • Five species of molds - aspergillus, fusarium, lomentospora, scedosporium and mucormycetes - have been identified as “killers of humans”. 
  • Oral thrush and diaper rash are caused by the yeast Candida albicans

Animals are also susceptible to fungal infections. Species of candida were found in cows suffering from mastitis; pythium insidiosum causes skin lesions in both horses and dogs.

Fungal infestations also lead to billions of dollars in damage to plants and food crops every year.

  • Smuts belong mostly to class ustilaginomycetes, which causes diseases in plants. They are among the most destructive to wheat, oats and related grain crops. The name comes from the dark dusty masses the infection produces. 
  • Plants infected with rusts (of the class pucciniomycetes) display colored spots on the leaves and stems, which range from yellow-orange to reddish-brown or black.  Rust epidemics have been mentioned in writings back to the times of Aristotle.

Related reading:

*= in LHL print collection

Selected Books: Harmful

Helpful Fungi

Fungi have important roles in the food industry:

  • Certain types of molds enhance the flavor of cheeses (e.g. Stilton and brie cheeses).
  • Corn smut is pathogenic to plants; however, it's considered a delicacy in Mexican cooking (called cuitlacoche or huitlacoche)
  • Baking, brewing, and wine production are a result of the yeast Saccharomyces cerevisiae converting sugars into carbon dioxide and ethyl alcohol. It's also the main ingredient in nutritional yeast.
  • Tempeh, a meat-alternative, is produced using species of the Rhizopus fungi.
  • Mushrooms can grow above or below ground. About 100 species are edible to some degree, and contain more protein than most non-animal foods. Morel, portabella, white button, and oyster are some well-known varieties. Technically, mushrooms are the fruiting body of a  fungus.
  • In 1929, microbiologist Alexander Fleming discovered that the mold Penicillium inhibited the growth of bacteria, leading to the development of penicillin as the first world's antibiotic. 

Fungi are also used in the development of pharmaceuticals such as cephalosporins (antimicrobials) and statins (cholesterol-lowering drugs). 

Related reading:

*= in LHL print collection