Several trillion microorganisms live on and inside a person, without which immunity would break down, digestion would stop, and brain activity significantly decreased. Weight, smell and mental health of a person depend on them. How microbes control people and why one cannot survive without them - in the material of RIA Novosti.
There are 21 thousand genes in the human genome - about the same as in the roundworm Caernorhabditis elegans (20.5 thousand genes), and significantly less than in the “water flea” Daphnia Daphnia (31 thousand genes). But, unlike homo sapiens, none of the representatives of the animal world can speak and think hard.
The unique abilities of a person are determined, among other things, by his microbiota - a set of microorganisms that inhabit all tissues of the body, notes in the book “10% Human. How microbes control people”biologist Alanna Collen. One and a half kilograms of bacteria, viruses, fungi and archaea add about four and a half million genes to homo sapiens, and they, together with a person's own genes, control his complex organism.
Ten to one
Scientists have not yet come to a consensus on how many microbes live in humans. When the first results of the international Human Microbiome Project were presented in 2012, they talked about one hundred trillion microorganisms and more than ten thousand species. But it was clarified that the "microbial population" may differ from person to person. Sometimes there are as many microorganisms as their own cells, and sometimes there are up to ten microbes per cell.
Today, they are inclined to more cautious estimates: from 30 to 40 trillion microorganisms live in a person, and bacteria predominate (about 90 percent). Plus yeast, viruses, and archaea.
There is no single set of microbes. Very few strains of bacteria are found in all humans. Each person's microbiota is as unique as a fingerprint and changes throughout life.
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Microbial metropolis
One of the most densely populated areas of the body is the intestines. It is home to about a thousand species of microorganisms. They break down dietary fiber molecules, inactivate enzymes and toxins, and help the synthesis of vitamins in the body. It was also established that intestinal bacteria can affect the central nervous system, contribute to the development of anxiety disorders, depression, autism, and strengthen the immune system.
Bacteria of two types predominate among the inhabitants of the intestine: Firmicutes and Bacteroidetes. The weight of a person depends on their balance. With obesity, the first species multiplies rapidly (for example, Clostridium coccoides), and the second (Bacteroides, Prevotella) shrinks. Scientists argue that knowing only the composition of the microbiota can determine whether a person is obese.
A variety of microbes living in the human body / Illustration by RIA Novosti. Depositphotos / andegraund548.
But microorganisms are wary of the stomach. Its extremely acidic environment is too tough for few. One of them is the Helicobacter pylori bacteria. It is she who is to blame for stomach and duodenal ulcers, gastritis and even stomach cancer.
However, 80 percent of carriers of Helicobacter pylori do not have any stomach diseases. Those who do not have this bacteria in their bodies are at risk. Scientists have identified a link between the disappearance of Helicobacter pylori from the gastrointestinal tract and the development of asthma.
One microbiota for two
Approximately 800 species of microorganisms have taken root in the human mouth. The most numerous there are streptococci. Although these microbes are notorious (cause tooth decay, severe sore throats - from strep throat to necrotizing fasciitis), some of them are beneficial by driving away hostile pathogenic bacteria and viruses.
Other microbes, by secreting nitric oxide and thereby relaxing the arteries, help regulate blood pressure. But they, as it turned out, cause migraines. But if the bacteria Klebsiella pneumoniae gets from the mouth into the intestines, ulcerative colitis or Crohn's disease is guaranteed.
The community of microorganisms in the mouth is the most volatile. Its composition can change several times a day. Still, the oral microbiota overlaps in different individuals by 40-50 percent. And the longer people live together (for example, married), the more similar the microbial communities in their mouths.
Additional microbial skin
Microorganisms that live on human skin are an additional sanitary cordon for internal organs. Most are commensals protecting against pathogens. However, they can cause skin conditions - from acne to dandruff - and are responsible for the unpleasant smell of sweat.
The settlement of microorganisms on the skin depends on the living conditions. So, propionic acid bacteria (Propionibacterium), feeding on the oil of the sebaceous glands, select the skin of the face and back. Corinebacteria (Corynebacterium) and staphylococci (Staphylococcus), which like high humidity and feed on nitrogenous compounds from sweat fluid, prefer the navel, armpits and popliteal fossa.
Skin lodgers are the most variegated and varied. Even in one person, the microbes on the right hand are significantly different from the inhabitants of the left. The composition of skin microorganisms in different people differs on average by 85 percent and is unique for each of us.
By the way, biologists from the University of Chicago (USA) drew attention to this feature, who suggested looking for criminals using the microbiota imprint. As part of the study, burglaries of ten houses were staged. Scientists on the composition of microorganisms left by the "criminals" calculated them with an accuracy of 70 percent.
Alfiya Enikeeva