Yeast, the fungus that kneads human beings

Among organisms formed by a single cell there is a basic division, those that have a differentiated nucleus where the DNA is located and those that do not have a separate nucleus and therefore the DNA is not found within an internal membrane. Among the first, microorganisms with a nucleus, the most frequent on a global scale is the species Saccharomyces, which in Greek means sugar fungus. The most frequent is Saccharomyces cerevisiae, which has a long tradition of use by our species. It is what we use to make bread, beer or wine, but, if we think about it, perhaps it is the fungus that uses us.

One of the main characteristics of Saccharomyces is that it is capable of using sugar to produce alcohol. In principle this would be a disaster. Alcohol is a molecule without a biological function, extremely toxic and represents an incomplete oxidation of sugar, so producing alcohol is a waste of energy. However, the fungus uses this alcohol production as a chemical weapon to eliminate competition from other microorganisms, since it is resistant to alcohol and the rest of the microbes are not. This explains why it is the majority in many ecosystems. He is a relentless killer.

There is another obstacle to overcome. How can you survive winters in cold climates? It seems that this fungus is capable of colonizing part of the digestive system of some species of wasps, and in this way it spends the winter taking advantage of the warmth of wasp nests. When spring arrives, the wasps transport these yeasts from flower to flower, and there they once again display their evil tricks, but this time in a more sibylline way. The alcohol produced by yeast when digesting sugar has another use. It is capable of solubilizing some of the volatile molecules produced by the plant and thus making its chemical signals better transmitted, so that the plant colonized by Saccharomyces It will be more successful because it will be able to emit its signals at a greater distance and will prefer to be visited by wasps, so a three-way relationship is created that causes the yeasts to be beneficial for both the wasps and the plants. Machiavellianly he is cruel to his equals, but servile to superior organisms.

But there is another characteristic of yeast that has influenced the evolution of our species. It is found naturally in the skin of many wild fruits. This means that when they mature and are loaded with sugars, the yeast begins to ferment and convert part of that sugar into alcohol. Numerous cases have been documented of animals that have a preference for consuming these fermented fruits, precisely seeking to get drunk. At a biochemical level we have developed mechanisms to eliminate alcohol from the blood, mechanisms that we do not have for other toxic substances that are lethal to us. This is an unequivocal sign that throughout evolution we have been exposed to the presence of alcohol, which has allowed us to develop enzymes such as the so-called alcohol dehydrogenase, capable of oxidizing this alcohol to neutralize its toxicity. Therefore, yeast has been able to direct the evolution of our species for millions of years, so that we choose those fruits that had fermented and this has caused natural selection to provide us with mechanisms to detoxify alcohol.

After millions of years of evolution, the human species invented livestock and agriculture. The first evidence of a fermented (wild) grape juice is found in China, which would be the ancestor of wine. The Sumerians discovered a way to make beer, and the Egyptians discovered that if they added the dregs left in the beer vats to the flour dough, it became more spongy and appetizing, inventing soft bread. In fact, the Egyptians were the first to trade in yeast, although they did not know that it was a living organism. They thought they had domesticated it, when the reality is that it was the yeast that had been influencing our evolution and domesticating us for millions of years.

From nature to the pantry

— Saccharomyces cerevisiae It is the majority mushroom that we use for food, but it is not the only one. In hot countries there is a yeast Schyzosaccharomyces pombe which is found naturally in the skin of bananas and is used in some types of beer.

— In the preparation of Kumis (fermented mare's milk drink) in addition to Saccharomyces fungi of the genus usually participate Kluyveromyces and Candida.

— Coffee, tea and chocolate, as well as many cheeses and yogurt, are also foods that require microorganisms in their production.

_