UNICELLULAR FUNGI: FUNCTIONS, USES, REPRODUCTION - BIOLOGY - 2025

The unicellular fungi are composed of a single cell and are yeasts, all other types of fungi are multicellular. Yeasts are single-celled members of fungi and are commonly found in baker's and brewer's yeast.

They are considered one of the first domesticated organisms known to man and can be found naturally in the skins of certain ripe fruits.

Yeast is too small to be seen individually with the naked eye, but can be seen in large clusters of fruit and on leaves as a white powdery substance. Some yeasts are mild to dangerous pathogens for humans and other animals, especially Candida albicans, Histoplasma, and Blastomyces.

As a single-celled organism, yeast cells rapidly develop into colonies, often doubling in population size in 75 minutes to 2 hours. Furthermore, they are eukaryotic organisms that cannot obtain their nutritional needs by photosynthesis and require a reduced form of carbon as a food source.

Yeasts play an important role in industry, particularly in the food and beer areas. Brewer's yeast gets its name from its use as a leavening agent in the brewing industry.

The carbon dioxide produced during the fermentation process of Saccharomyces cerevisiae (in Latin beer), is also a yeast agent frequently used in the manufacture of bread and other baked goods.

Function of single-celled fungi

Single-celled organisms have a variety of functions, although they generally need to synthesize all the nutrients necessary for the cell to survive, since the organism must carry out all the processes for the cell to function and reproduce.

They are generally resistant to extreme temperatures, this means that they are able to survive in extremely hot or cold temperatures.

Single-celled fungi, like yeast and mold, have a purpose. Besides being used to make baked goods such as bread and in the production of beer and wine, it also has the important function of breaking down dead matter.

Reproduction

As mentioned, yeasts are eukaryotic organisms. They are typically about 0.075mm (0.003 inch) in diameter. Most yeasts reproduce asexually in budding: a small bump protrudes from a stem cell, enlarges, matures, and falls off.

Some yeasts reproduce by fission, the stem cell dividing into two equal cells. Torula is a genus of wild yeasts that are imperfect, never forming sexual spores.

Natural habitats

Yeasts are widely dispersed in nature with a wide variety of habitats. They are commonly found on the leaves of plants, flowers, and fruits, as well as in the soil.

They are also found on the surface of the skin and in the intestinal tracts of warm-blooded animals, where they can live symbiotically or as parasites.

The so-called "yeast infection" is typically caused by Candida albicans. As well as being the causative agent of vaginal infections, Candida is also the cause of diaper rash and thrush of the mouth and throat.

Commercial use

In commercial production, selected yeast strains are fed a solution of mineral salts, molasses, and ammonia. When growth ceases, the yeast is separated from the nutrient solution, washed and packaged.

Baking yeast is sold in compressed cakes containing starch or dried in granular form mixed with cornmeal.

Brewer's yeast and nutritional yeast can be eaten as a vitamin supplement. Commercial yeast is 50 percent protein and is a rich source of vitamins B1, B2, niacin, and folic acid.

Scientific interest

Yeast is a focus of study for researchers around the world, and today there are thousands of scientific articles.

This interest is due to the fact that this single-celled fungus is a rapidly growing organism in a flask and whose DNA can be easily manipulated, while providing insight into basic human biological processes, including disease.

Furthermore, since they are unicellular organisms, they are easy to study and have a cellular organization similar to that found in higher and multicellular organisms such as humans, that is, they have a nucleus and therefore are eukaryotic.

This similarity in cellular organization between yeast and higher eukaryotes translates into similarities in their fundamental cellular processes, so discoveries made in yeast often provide direct or indirect clues as to how biological processes work in yeast. human beings.

On the other hand, single-celled fungi replicate rapidly and are easy to genetically manipulate. There are also well-defined genetic maps and methods for yeast that gave researchers their first insight into the genome and its organization, and were the culmination of genetic studies dating back to the first half of the 20th century.

In fact, because the yeast gene is similar in DNA sequence to a human gene, the information scientists have obtained in their studies has provided powerful clues about the role of these genes in humans.

Historical discoveries

Yeast is believed to have been used as an industrial microorganism for thousands of years and the ancient Egyptians used its fermentation to raise bread.

There are grinding stones, baking chambers and drawings of what are thought to be bakeries dating back thousands of years, and even archaeological excavations have uncovered suspected jars with remains of wine.

According to history, these single-celled fungi were first visualized in high-quality lenses around the year 1680 by Antoni van Leeuwenhoek.

However, he thought that these globules were starch particles from the grain used to make wort (the liquid extract used in brewing), rather than yeast cells for fermentation.

Later, in 1789, a French chemist named Antoine Lavoisier, contributed to the understanding of the basic chemical reactions necessary to produce alcohol from sugar cane.

This was achieved by estimating the ratio of starting materials and products (ethanol and carbon dioxide) after adding yeast paste. However, at the time it was thought that the yeast was simply there to initiate the reaction rather than being critical throughout the process.

In 1815, the also French chemist Joseph-Louis Gay-Lussac, developed methods to keep grape juice in an unfermented state and discovered that the introduction of ferment (containing yeast) was necessary to convert unfermented wort, demonstrating the importance of yeast for alcoholic fermentation.

Later, Charles Cagniard de la Tour in 1835, used a microscope with higher power to prove that yeasts were single-celled organisms and multiplied by sprouting.

By the 1850s Louis Pasteur discovered that fermented beverages resulted from the conversion of glucose to ethanol by yeast and defined fermentation as "airless respiration."

In order to detect zymase, Eduard Buchner in the late 1800s used cell-free extracts obtained by grinding yeast, the collection of enzymes that promote or catalyze fermentation. He was awarded the Nobel Prize in 1907 for this research.

Between 1933 and 1961, Ojvind Winge known as "the father of yeast genetics", together with his colleague Otto Laustsen devised techniques to micromanip yeast and thus be able to investigate it genetically.

Since then many other scientists have carried out groundbreaking research and some of them have been awarded the Nobel Prize for their significant discoveries, including: Dr. Leland Hartwell (2001); Dr. Roger Kornberg (2006); Doctors Elizabeth Blackburn, Carol Greider and Jack Szostak (2009), and more recently Doctors Randy Schekman, James Rothman and Thomas Südhof (2013) and Doctor Yoshinori Ohsumi (2016).

References

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