Fungi - Yeast

 

 

Fungi

Yeast

 


Yeast are single cell microorganisms classified as members of the Kingdom Fungi. Over 1500 species have been identified and they are estimated to make up around 1% of all fungi.  Sizes vary, depending on environment and species, but they usually measure 0.003-0.004mm (although some grow to 0.04mm in diameter). Most yeast reproduce asexually by budding; a bump swells on a mother cell, grows, matures, and a daughter detaches.  Yeast occurs widely in nature on leaves, flowers and fruits, in soil, on the surface of the skin and in the intestines of warm blooded animals. 

 

Yeast has been used as an industrial microorganism for millennia. Ancient Egyptians used it to leaven bread and evidence, including grinding stones, baking chambers and 4000 year old drawings of bakeries, has been found. Archaeologists have uncovered jars containing traces of 7000 years old wine!


Wine is produced by fermenting sugars from grape must into ethanol. Wine fermentation can be activated by yeast naturally present in vineyards, but many wine makers add pure yeast culture to better control the process. One yeast cell can ferment approximately its own weight in glucose per hour! Carbon dioxide is usually released as a by-product, but bubbles in sparkling wines, including champagne, are produced by secondary fermentation in the bottle which traps released CO2.  Yeast also ferments wheat, rice, barley and corn sugars to produce alcoholic drinks. S. carlsbergensis is a variety used to make lager!

 

Baker’s yeast ferments the sugars in dough, again producing CO2 and ethanol. CO2 becomes trapped in small bubbles in the dough making it rise. Sourdough bread is an exception - it is made with a combination of wild yeast and bacteria.

 

Yeast extract is the contents of yeast cells without the cell walls.  Yeast extract is high in protein and B vitamins and can be consumed by vegans as a protein substitute.  It is used in food colouring and flavouring, and as nutrients for bacterial culture media.

 

Yeast has numerous commercial applications including in the petrochemical industry to produce biofuels such as ethanol, in the production of industrial chemicals and enzymes, and in the production of detergents and lubricants. Strains of yeast have even been used in environmental bioremediation to remove metal from mining waste.  I wonder if it could be used in the removal of micro-plastics from drinking water treatment plants?

 

Yeast is widely used in pharmaceuticals including the production of anti-parasitics, anti-cancer compounds and biopharmaceuticals (eg vaccines and insulin).  It is a ‘go-to’ organism in studies identifying drug targets and potential novel drugs.   Yeast is popular in the study of human disease because of the level of similarity between yeast and human genes.  Yeast replicates quickly (doubling time is about 90 minutes) and is easy to genetically manipulate. Studies using yeast have helped identify genes involved in cancer and neuro-degenerative diseases like Parkinson’s and Alzheimer’s. In 2006 Roger Kornberg was awarded the Nobel Prize for his work on gene expression, using yeast as his model.

 
Not everything about yeast is positive.   Yeast infections are typically caused by Candida albicans. In addition to being the agent in vaginal yeast infections, Candida causes nappy rash, thrush in the mouth and throat and athlete's foot.   Candida causes serious infections if it grows out of control or enters the bloodstream or internal organs. Some Candida yeasts are resistant to antifungals – for example Candida auris is an emerging multidrug-resistant yeast that poses a serious global health risk.  It spreads easily and can cause severe infections.

 

Overall yeast is great though – because wine!

 


 

 

 

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