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Fantastic yeasts and where to find them

Copyright: BBSRC
Professor Roslyn Bill

Professor Roslyn Bill, a biotechnology specialist from Aston University, shares her top five fantastic yeasts and where to find them.

With its first noted use around 4,000 years ago (older than the Egyptian Sphinx but younger than Griffins), yeasts have been cultivated by humans. Over 1,500 yeast species are known, many of which are important to our daily lives. These fantastic single-celled fungi provide us with bread, beer, wine, cheese, fermented foods, and medicines; they are used to recycle waste products and clean-up the environment; in the laboratory, studying yeasts has been central to several Nobel Prize wins. Some yeasts live on our skin and in our guts, where they normally do us no harm. However, if our defences are down, they can infect us and cause disease. Below are five of my favourite yeasts and where to find them.

Fantastic yeasts and where to find them

Copyright free (Wikimedia Commons/Creative Commons CC 3.0) The Bread-Winner: Saccharomyces cerevisiae 

No top-five listing of fantastic yeasts would be complete without Saccharomyces cerevisiae. This yeast is found on the skins of grapes and other fruits. Bakers and brewers have used S. cerevisiae for thousands of years because of its ability to make carbon dioxide (which causes bread to rise) or its alcohol-producing properties (for the production of beer, wine, vinegar and, more recently, biofuel). Insulin is produced on an industrial scale using S. cerevisiae, as is the vaccine against the human papilloma virus. No fewer than five Nobel Prizes in Physiology or Medicine have been awarded for scientific studies using S. cerevisiae; all have had important implications for human health. These ground-breaking discoveries include understanding how cells repair their worn-out parts, how they divide and copy the genetic information stored in DNA and how they shuttle the components they need to different internal locations. Studies such as these are now providing the basis for discovering new drugs to treat Alzheimer's and Parkinson's diseases in humans.

Copyright free (Wikimedia Commons/Creative Commons CC 3.0).

Copyright free (Wikimedia Commons/Creative Commons CC 3.0) The Anti-Cancer Assistant: Schizosaccharomyces pombe 

Schizosaccharomyces pombe was first isolated at the turn of the last century from African millet beer, an alcoholic beverage made from malted millet; ‘pombe’ is the is the Swahili word for beer. S. pombe is found growing on fruits, in kombucha (a fermented tea) and in the molasses used to produce distilled spirits such as rum and tequila. It is also used by wine-makers to reduce undesirable acidity because it is able to degrade malic acid. S. pombe is distantly related to S. cerevisiae; we now know that these two yeasts separated from each other during their evolution 350 million years ago. While S. cerevisiae divides by budding off a smaller daughter cell, S. pombe maintains its rod shape by dividing in half to produce two daughter cells of equal size. This property led to its use, alongside S. cerevisiae, in the Nobel Prize-winning studies that described how human cells divide. This research has helped scientists understand how cancer occurs when such processes go wrong. More recently, S. pombe has been used to understand how to stop resistance to anti-cancer drugs.

Copyright free (Wikimedia Commons/Creative Commons CC 3.0).

Copyright: University of California, Riverside Bomb Disposal Specialist: Yarrowia lipolytica 

Yarrowia lipolytica is found in contaminated soil and water. On account of its ability to grow on fats and oils, Y. lipolytica naturally detoxifies oily pollutants in an environmentally-friendly manner. This has led to its use in the clean-up of crude oil spills or waste water steams from olive and palm oil mills. This rather unconventional yeast has also been used to degrade soil-based pollutants such as 2,4,6-trinitrotoluene (TNT) and organophosphate insecticides. Unlike S. cerevisiae and S. pombe, Y. lipolytica does not produce ethanol; instead, it can convert oily wastes into useful products such as biodiesel, edible oils, citric acid (which is used as an acidity regulator or flavour enhancer) or the building blocks for polymers. When it is not cleaning up the environment, working in bomb-disposal or up-cycling waste into useful chemicals, Y. lipolytica can also be found contributing towards the texture and flavour of the cheeses and hams in which it is also found.

Copyright: University of California, Riverside.

Copyright free (Wikimedia Commons/Creative Commons CC 4.0) The can-turn-nasty Opportunist: Candida albicans 

While yeasts typically grow below human body temperature, Candida albicans can grow at 37oC. This means it survives naturally on the skin and in the gut of around 50-70% of the UK population. C. albicans is generally harmless to healthy people, but may be problematic for individuals who are immunocompromised (such as those with HIV) or who have used antibiotics for an extended period and therefore lack the bacteria that normally keep this yeast in check. In these situations, C. albicans becomes an ‘opportunistic pathogen’ by developing outgrowths, called ‘hyphae’. These hyphae penetrate and irritate surrounding tissues causing them to become speckled white, resembling a thrush’s chest. Oral and vaginal thrush, athlete’s foot and nail fungus can all be caused by C. albicans, while C. albicans infection is a leading cause of hospital-acquired infections. Fortunately, C. albicans is a well-studied yeast, with active research ongoing about what turns the harmless form pathogenic.

Copyright free (Wikimedia Commons/Creative Commons CC 4.0).

Copyright: Leanor Haley, Centers for Disease Control and Prevention's Public Health Image Library The Secret Agent: Cryptococcus neoformans 

Cryptococcus neoformans is found on leaves, soil, decaying wood, in tree hollows and in dried bird droppings. Unlike most yeasts, C. neoformans cells are surrounded by a rigid capsule, which allows them to avoid detection by the human immune system. Humans become infected by inhaling dust containing C. neoformans; it has been suggested that this is most likely to occur in childhood. Most people who breathe in C. neoformans never become ill. However, in people who have weakened immune systems, a disease called cryptococcosis develops, which resembles a persistent pneumonia. If the infection spreads from the lung to the brain, cryptococcal meningitis results. C. neoformans infection is extremely rare in healthy people; most cases occur in people who are taking immunosuppressive drugs, but its incidence is on the increase, meaning this is one yeast to watch.

Copyright: Leanor Haley, Centers for Disease Control and Prevention's Public Health Image Library.


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