Man and his microbes: we are together!
About the friendship of bacteria and man
RIA NewsOne hundred trillion bacteria live in our body.
They not only help digest food, but also affect our behavior and health. Nikolai Kukushkin, an employee of the Harvard Medical School, biologist, tells about the friendship of man and bacteria, fecal transplantation and the benefits of yogurt.
2004, St. Petersburg State University Biofac, first year, lecture on introduction to biology. The lecturer of the Department of Genetics O. N. Tichodeev talks about the symbiosis of man and bacteria on the example of the "once popular" song of the group "Alice" "We are together" (the audience indignantly reacts: "She is popular now!" – biology students at that time were not distinguished by progressive tastes).
The title of this song, indeed, quite accurately describes the relationship of the species Homo sapiens with hundreds of species of microorganisms, the vast majority of which are represented by bacteria. As it has become clear in recent years, bacteria do not just hang around on the remains of undigested food, but fully participate in the work of our body, affecting even the most "sophisticated" systems: nervous, immune and endocrine. Konstantin Kinchev was right: we are really together.
In the body of an adult, on average, there are ten times more bacteria than our own cells. In fact, bacteria form a full-fledged organ in our body. Most of them inhabit the digestive tract, primarily the colon. The remaining bacteria live on the skin, mucous membranes and in the genital area. It is curious that in each microenvironment, bacteria form their own ecosystems, which differ both among themselves (for example, the microflora of the navel does not resemble the microflora of the heel) and from person to person.
Bacteria and humans: which of us is smarterIn popular consciousness, the bacterium lies somewhere on the border of inanimate and living matter, deeply stuck at the very base of the evolutionary tree.
At first, she swims uselessly in the ocean, then she has a nucleus, then flagella with cilia, then she divides and forms a kind of medusoid cake, which quickly transforms into a fish that climbs out with the help of muscular fins to the shore, where her tail falls off, lungs appear, then wool, then a stick in her hands, and here, finally, before us, straightening up before our eyes and throwing off the bonds of wild nature, stands a man – the pinnacle of evolution. He is separated from bacteria – primitive nuclear–free cytoplasm bubbles - by billions of years of hard work to improve his own body.
In fact, as you may have guessed, it's not quite like that. The idea of evolution as a gradual transformation of some currently existing living beings into others is a gross mistake, leading to questions in the spirit of "if evolution exists, then why don't monkeys in zoos turn into people". All modern forms of life appeared from a single ancestor, but this does not mean that bacteria evolved less than humans. Moreover, "evolutionary time" is measured not by years, but by generations. Considering that the human generation lasts about twenty years, and the bacterial one can last twenty minutes, we can figure out which of us is more skilled in the art of evolution. Indeed, from the standpoint of bacteria, everything that we consider a sign of evolutionary perfection is completely meaningless. We have grown a huge brain and powerful sensory organs to analyze the environment and not get into trouble. The bacterium is not afraid to get into trouble. It boldly develops new territories and habitats – for example, the navel or the heel – and if there is even the slightest chance of survival in these new environments within its variability, the bacterium (more precisely, its large, friendly and actively reproducing family) will find this chance. The story resembles an old joke about a capitalist colonizer. He was explaining to an aborigine sitting under a palm tree how to set up a coconut business in order to get rich and, after years of hard work, sit quietly under a palm tree. So we look down on the "primitive" forms of life, which need our frontal cortex or complement system literally like an umbrella for a fish.
There is something stunningly elegant in the fact that you and I are the product of these two opposing survival strategies: "to be perfect yourself" or "to multiply incredibly to become perfect as a whole" (in terms of ecology, they are called K- and r-strategies, respectively). It is "we" – because the more scientists know about human bacterial satellites, the clearer it becomes that separating "us" from "them" no longer makes sense. It may seem offensive to someone, but it's probably not worth giving up yogurt because of this.
Psychotropic kefirRemember the new buzzword: psychobiota.
The term is still far from unambiguous recognition by the scientific community, but visionary journalists are already juggling it with might and main. Anyway, it has been reliably established that the intestinal microflora affects the development and functioning of the nervous system, including pain sensitivity, irritability and emotionality.
For example, an international team of scientists led by John Binenstock and John Cryan investigated the effect of intestinal bacteria on receptors for gamma-aminobutyric acid (GABA) – an inhibitory neurotransmitter, that is, a substance that reduces the activity of nerve cells. Lack or low sensitivity to GABA can lead, for example, to increased irritability and depression. After feeding mice grown in sterile conditions with the bacterium Lactobacillus rhamnosus (by the way, this is one of the main bacteria in kefir and other fermented milk products), scientists found that there are more GABA receptors in their brains. In other words, intestinal bacteria help the brain to calm down better. The "kefir" mice themselves react more calmly to stress and, in general, seem to have a philosophical attitude to intimidation by fiends-scientists. This effect is achieved due to signals coming to the brain via the vagus nerve – the main "neural highway" connecting the digestive tract with the brain. Similar "antidepressant" properties of other bacterial species have been shown in rats and even in human volunteers, although the specific mechanisms in these cases remain unclear. But not everything is so clear: a group of scientists from the Karolinska Institute in Stockholm, for example, on the contrary found that mice without intestinal bacteria are characterized by increased mobility and reduced anxiety. It is suggested that the intestinal microbiota can affect the brain not through nerve channels, as in the example described above with the vagus nerve, but directly by releasing psychoactive substances into the blood.
Bacteria take care of our healthIf the relationship between the intestinal microflora and the psyche is a fashionable topic, but today it is very little studied, then everyone who has ever watched TV knows about the influence of bacteria on digestion.
The advertising industry has even come up with special euphemisms to describe this low-aesthetic topic ("Yogurt X will help you stay light!"). But even here everything is much more complicated than it seems. Traditionally, the role of bacteria in the intestine has been reduced to recycling waste that we cannot digest ourselves. Here again, our painful anthropocentrism is evident: it is very difficult to admit that "primitive" bacteria are engaged in something other than sanitation on our territory. In fact, the joint evolution of mammals with bacteria has led to a close relationship of all aspects of our metabolism with the vital activity of the intestinal microflora.
Some "beneficial" bacteria (this is not some special group of bacteria, but any bacteria living in our body that, as far as we know, are not harmful), for example, secrete short-chain fatty acids. These substances cause a whole range of complex and seemingly beneficial effects in our body. They reduce lipogenesis (i.e. fat deposition), accelerate intestinal contractions and reduce appetite. They weaken inflammatory and oxidative processes in the liver and adipose tissue (these processes are often associated, for example, with the development of obesity and type II diabetes). In addition, they constantly stimulate the immune system.
From a practical point of view, all the described effects are both good and bad news at the same time. The good news is that by manipulating the composition of the microbiota in the intestine, we can potentially solve almost all modern problems of humanity: from obesity to allergies. The bad news is that we have no idea how to do this.
Our practical capabilities in the intestinal-bacterial area resemble the surgical skill of barbers in the Middle Ages, mainly reduced to bloodletting and cutting off excess body parts. That's about how we – albeit with great suspicion – are now using such a colorful method as fecal transplantation. In June 2013, the method was approved in the United States for the treatment of intestinal infection with the bacterium Clostridium dificile, which causes severe, prolonged diarrhea that does not respond well to antibiotics. The logic is simple: if a patient is injected with a stool extract from a donor with a "good" microflora, it will displace the "bad" microflora. A tube is inserted through the nose into the intestines of patients, through which half a liter of saline solution with a stool loosened in it from a healthy donor is pumped for half an hour. This method is much more effective than conventional antibiotics.
It is quite possible that a "stool transplant" can help with other diseases in which there is a disorder of the intestinal microflora. Thomas Borodi, an enthusiast of fecal therapy from the University of Sydney, generally seems to suggest treating all diseases with feces: from allergies to obesity. In light of the latter, the following study is interesting. In it, feces were transplanted not from person to person, but from human to mice, but pairs of twins were chosen as donors (in order to minimize the influence of congenital factors), sharply differing in the degree of obesity. The results were phenomenal: mice injected with feces from fat twins got fatter significantly!
On yogurt and sleepGerminal development has long been considered one of the few areas of human activity "untouched by bacteria".
Up to the moment of birth, the embryo develops in sterile conditions – what kind of influence of bacteria can we talk about? But recently, even pregnancy has been the object of study by microbiologists. The fact is that although the fetus does not really have its own microflora, maternal bacteria can seriously affect embryonic development, both directly by releasing bioactive substances passing through the placenta into the blood, and indirectly by affecting the mother's metabolism. For example, an international group of scientists led by Ruth Ley from Cornell University in the USA managed to show clear stages of changes in the composition of the microbiota in the intestines of pregnant women. In the later stages of pregnancy, these changes lead to increased fat accumulation and reduced insulin sensitivity. Although under normal conditions such effects are considered unfavorable, during pregnancy they are beneficial for the mother and fetus. Well, during and after birth, maternal bacteria actively "infect" the newborn, providing, if you want, the continuity of the microflora.
Given the role of intestinal bacteria in almost every aspect of the development and functioning of our body, it is possible that in a few years we will start talking about "bacterial heredity". To paraphrase another song – and now a popular one – "Mom is anarchy, Dad is a glass of kefir."
Portal "Eternal youth" http://vechnayamolodost.ru06.12.2013