Among organisms composed of a single cell, there is a basic division: those that have a differentiated nucleus in which the DNA is located, and those that do not have a separate nucleus and therefore the DNA is not located within an internal membrane located. Among the first nucleated microorganisms, the Saccharomyces species, which means sugar mushroom in Greek, is the most common in the world. The most common 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 benefits us.
One of the main characteristics of Saccharomyces is the ability to use sugar to produce alcohol. In principle, that would be a catastrophe. Alcohol is a molecule with no biological function, is 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 because it is resistant to alcohol and the other microbes are not. This explains why it represents the majority in many ecosystems. He is a relentless killer.
There is one more obstacle to overcome. How to survive winters in cold climates? It seems that this fungus is able to colonize part of the digestive system of some species of wasps and in this way spend the winter taking advantage of the warmth of the wasps' nests. When spring comes, the wasps transport these yeasts from flower to flower and show off their evil tricks again, but this time in a more sibylline way. The alcohol produced when sugar is digested by yeast has another use. It is able to dissolve some of the volatile molecules produced by the plant and thus improve the transmission of its chemical signals, so the plant colonized by Saccharomyces will be more successful since it can send its signals over greater distances and this is also preferred by wasps are visited, a three-way relationship is created that makes the yeasts beneficial for both the wasps and the plants. Machiavellian, he is cruel to his own kind but submissive to superior organisms.
But there is another property of yeast that has influenced the evolution of our species. It occurs naturally in the peel of many wild fruits. This means that as they mature and become loaded with sugar, the yeast begins to ferment and convert some of the sugar into alcohol. There have been numerous documented cases of animals preferring to consume these fermented fruits to get drunk. At the biochemical level, we have developed mechanisms to eliminate alcohol from the blood, mechanisms that we do not have for other toxic substances that are fatal to us. This is a clear sign that during 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, over millions of years, yeast has been able to control the evolution of our species so that we select the fruits that were fermented, and this has led to natural selection that provides us with mechanisms to detoxify alcohol.
After millions of years of evolution, the human species invented animal husbandry and agriculture. The first evidence of fermented (wild) grape juice is found in China, the ancestor of wine. The Sumerians discovered a way to make beer, and the Egyptians discovered that adding the dregs left in the beer barrels to the flour made the flour dough spongier and more appetizing, and invented soft bread. In fact, the Egyptians were the first to trade in yeast, even though they didn't know it was a living organism. They thought they had domesticated it, when in reality it was the yeast that influenced our evolution and domesticated us for millions of years.
From nature to the pantry
— Saccharomyces cerevisiae is the main fungus we use in food, but not the only one. In warm countries there is the yeast Schyzosaccharomyces pombe, which occurs naturally in the peel of bananas and is used in some types of beer.
— In addition to Saccharomyces, fungi from the genera Kluyveromices and Candida are usually involved in the preparation of kumis (fermented mare's milk drink).
— Coffee, tea and chocolate, as well as many cheeses and yogurt, are also foods that require microorganisms to produce.
JM Mulet He is a professor of biotechnology.
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