Bacteria living in the intestine: characteristics, types and functions.

An overview of the bacteria that live in the human gut, and their Biological characteristics.

Bacteria have inhabited the Earth for more than 3.5 billion years, making them the oldest life forms on Earth.

It is not surprising, therefore, that 15% of the organic matter in the Earth's crust (70 gigatons of carbon) is stored in these prokaryotic beings, which are as simple as they are essential for life.

In fact, according to the endosymbiotic theory, aerobic bacteria and cyanobacteria were phagocytosed by the ancestral eukaryotic cells to give rise to mitochondria and chloroplasts, respectively. In other words, the most widely accepted postulates indicate that bacteria have been part of the development of our own cell bodies..

Beyond evolutionary theories, these microorganisms inhabit all terrestrial environments, from the screen of your cell phone to thermal zones at 60 degrees Celsius that lack oxygen or light. In any case, you don't have to go very far to discover the functionality of bacteria: all you have to do is analyze the human digestive tract. If you want to know all about the bacteria that live in the human gut, read on.continue reading.

What is the intestinal flora?

Curiously, the term intestinal flora does not make any sense at the biological level, because bacteria have little to do with the Plantae Kingdom and its closest relatives. The more correct term is microbiome or normal microbiota, which refers to the set of microorganisms that inhabit various parts of the human body environment.

In general, microscopic living organisms can be expected to be found in the skin, eyes, urogenital tract, sexual organs, upper respiratory tract, mouth, pharyngeal area and intestines, among other things.

We are open systems that are constantly exchanging substances with the environment, which is why bacterial colonies can easily settle on our mucous membranes.. It is therefore conceivable that bacteria exist in the intestine or nasal cavities (open systems), but not in the heart or brain (structures that are "closed" to the outside world).

Microbiota can be autochthonous and allochthonous. The former is that which lives for all or almost all the life of the individual together with it, i.e. for a long time, evolving together with the species in a symbiotic process that is positive for both parties. On the other hand, allochthonous microbiota are those that can grow in other environments, but reach the host by contact or other events. They are usually commensal organisms, i.e., they do neither harm nor good.

In addition, these bacterial colonies can be latent (they remain practically throughout the host's life cycle) or transient, fluctuating according to environmental conditions. fluctuate according to environmental conditions, emotional state, diet, season and many other things.. As you can imagine, the most important symbiotic microbiota is the latent one.

With all these bases explained, we can conclude that the intestinal flora, normal microbiota or gut microbiome refers to the set of bacteria that live in the intestine, in a symbiotic way, both commensal and mutualistic. Because many of these bacteria have been with us for thousands of years and have evolved along with us, they fall into the category of "indigenous" and "dormant" alike. In other words, they are essential for our life to develop properly.

What bacterial species make up the intestinal environment?

Normally, the mistake is often made of believing that the intestinal microbiota colonizes the entire digestive system, from the stomach to the colon: from the stomach to the colon.from the stomach to the colon: nothing could be further from the truth. The pH of the stomach environment, due to secreted acids, ranges from 1.0 to 3.0. Only one bacterium is capable of enduring long term in such a hostile environment: Helicobacter pylori. ⅔ of the world's population is infected by this organism, but far from being symbiotic, it can cause peptic ulcers and even gastric cancers.

On the other hand, the pH of the small intestine is much more "friendly", because the gastric acid enzymes are deactivated and the values increase to a pH of 5.0 to 7.0, reaching 8.0 in the large intestine. According to the Harvard Medical School, about 100 trillion bacteria, organized by functionality and exploiting a specific ecological niche, have settled in our intestinal complex.

In any case, genetic analyses have opened a door to the analysis of the intestinal microbiota in a very different way.. Using polymerase chain reactions (PCR), genetic regions of great interest, such as 16S ribosomal RNA, a component of the minor subunit of bacterial ribosomes, can be isolated and amplified. When analyzing a human stool with these techniques, we are surprised to find that up to 76% of the genetic information corresponds to new, undescribed microbial species.

With these exorbitant figures in mind, the Human Microbiome Project has been sequencing the microorganisms that inhabit our intestine since 2008.. Thanks to research and tireless work, it is estimated that these are the most common bacterial groups in our gut:

• Firmicutes (with a relative abundance of 65%): here we find the famous Bacillus. Microorganisms of the genus Lactobacillus are the most represented in this phylum.
• Bacteroidetes (relative abundance 23%): gram-negative bacteria, very abundant in the feces of warm-blooded animals, including humans.
• Actinobacteria (with an abundance of 5%): in general, they are found in soils and are part of the decomposition cycles of organic matter.

Despite the variety of intestinal microbiota in individuals according to age, diet, sex, ethnicity, origin, place of residence and much more, a total of 127 bacterial genera have been recorded that are universal in all normal intestinal tracts. Among them, the following stand out Coprocococcus, Ruminococcus, Bacteroides, Faecalibacterium, Streptococcus, Blautia y Oscillospira. The variety of the microbiota among populations is measured with ecological parameters, as if it were a forest ecosystem (saving distances). (saving distances).

Functions of the intestinal microbiota

Digestion takes place in the digestive tract, so it is natural to think that the most important function of these microbial communities will be, in all cases, the assimilation of food. This is partly true, but the symbiont bacteria in our body have functions far beyond obtaining energy.

Many of these microbes are capable of digesting complex carbohydrates of plant origin (such as cellulose) and converting them into short-chain fatty acids, which can be metabolized by the human body. Although this may seem anecdotal, it is estimated that 10% of the energy obtained from the diet is due to these processes mediated by symbiont bacteria..

On the other hand, these microorganisms play an essential role in the specialization and implementation of the immune system. Bacteria that come into contact with the newborn promote the specialization of proinflammatory T lymphocytes.. In other words, they enable the immune system to begin to recognize what is harmful and what is positive.

Beyond this, intestinal bacteria actively participate in the defense of the digestive tract. First of all, simply by occupation, colonies prevent pathogens from settling in their own niche. In addition, common representatives of the intestinal microbiota such as lactobacillus are capable of releasing bactericidal enzymes/peptides themselves, i.e. they attack microorganisms in their own niche.i.e. they attack potentially pathogenic microorganisms.

Summary

As you can see, the number of functions of the gastric microbiome go far beyond food digestion. These bacteria have been shown to interact with the immune system, to actively and passively prevent infections, and may even help the functioning and development of neurological systems. Studies postulate that imbalances in the microbiota could play essential roles in the development of conditions such as autism, although it is very risky to establish such categorical causalities.

In summary, the microbiota is essential for life in every sense of the word.. Without it, we would not be able to properly digest many plant substances or prevent the entry of infectious pathogens. As is often said in the microbiological community, "without our bacteria, we are nothing".