Bacteria That Live In The Intestine: Characteristics, Types And Functions
Bacteria have inhabited 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, as simple as they are essential for life.
In fact, according to the endosymbiotic theory, aerobic bacteria and cyanobacteria were phagocytosed by ancestral eukaryotic cells to give rise to mitochondria and chloroplasts, respectively. In other words, the most accepted postulations 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 mobile phone to thermal areas at 60 degrees Celsius that lack oxygen or light. In any case, you don’t have to go far to discover the functionality of bacteria: you just need to analyze the human digestive tract. If you want to know everything about the bacteria that live in the human intestine keep reading.
Curiously, the term intestinal flora does not make any sense on a biological level, since bacteria have little to do with the Kingdom Plantae and its closest relatives. The most 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, it is expected to find microscopic living beings in the skin, eyes, urogenital tract, sexual organs, upper respiratory tract, mouth, pharyngeal area and intestines, among other things.
We are open systems that constantly exchange substances with the environment, hence bacterial colonies settle without difficulty in our mucous membranes For this reason, it is conceivable that bacteria exist in the intestine or nasal passages (open systems), but not in the heart or brain (structures “closed” to the outside).
The microbiota can be autochthonous and allochthonous. The first is the one that lives throughout or almost the entire life of the individual with it, that is, for a long time, evolving together with the species in a positive symbiotic process for both parties. On the other hand, foreign microbiota is that which can grow in other media, but reaches the host through contact or other events. They are usually commensal organisms, that is, they do neither harm nor good.
Furthermore, these bacterial colonies can be latent (they remain practically throughout the host’s life cycle) or transient, which They fluctuate depending on environmental conditions, emotional state, diet, season and many other things As you can imagine, the symbiotic and most important microbiota is the latent one.
With all these bases explained, we can conclude that the intestinal flora, normal microbiota or intestinal 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 “native” and “dormant” alike. In other words, they are essential for our lives to develop correctly.
What bacterial species make up the intestinal environment?
Usually, The mistake is often made of believing that the intestinal microbiota colonizes the entire digestive system , from the stomach to the colon: nothing could be further from the truth. The pH of the stomach environment, due to secreted acids, ranges between 1.0 and 3.0. Only a bacteria is capable of lasting long-term in such a hostile environment: Helicobacter pylori. ⅔ of the world’s population are infected by this organism, but far from being a symbiont, 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 enzymes of gastric acids are deactivated and the values increase to a pH of 5.0 to 7.0, reaching 8.0 in the large intestine. According to Harvard Medical School, nearly 100 trillion bacteria have settled in our intestinal tract, organized by functionality and exploiting a specific ecological niche.
Anyway, Genetic analyzes 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 can be isolated and amplified, such as 16S ribosomal RNA, a component of the minor subunit of bacterial ribosomes. When analyzing a human deposition with these techniques, we are surprised that up to 76% of the genetic information corresponds to new, undescribed species of microbes.
With these exorbitant figures in mind, Since 2008, the Human Microbiome Project has been sequencing the microorganisms that live in our intestines Thanks to research and tireless work, it is estimated that these are the most common bacterial groups in our intestine:
Despite the variety of intestinal microbiota in individuals depending on age, diet, sex, ethnicity, origin, place of residence and many other things, a total of 127 bacterial genera have been recorded that are universal in all normal intestinal tracts. They stand out among them Coprococcus, Ruminococcus, Bacteroids, Faecalibacterium, Streptococcus, Blautia and Oscillospira. The variety of the microbiota between populations is measured with ecological parameters, as if it were a forest ecosystem (saving distances).
Functions of the intestinal microbiota
Digestion occurs in the digestive system, 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 it may seem like an anecdotal task, It is estimated that 10% of the energy obtained from the diet is due to these processes mediated by symbiotic bacteria
On the other hand, these microorganisms have an essential role in the specialization and implementation of the immune system. Bacteria that come into contact with the newborn promote the specialization of pro-inflammatory T lymphocytes In other words, these allow 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. Firstly, simply by occupation, colonies prevent pathogens from settling in their same niche. Besides, common representatives of the intestinal microbiota such as lactobacillus are capable of releasing bactericidal enzymes/peptides on their own that is, they attack potentially pathogenic microorganisms.
Summary
As you can see, the number of functions of the gastric microbiome go far beyond food digestion. It has been proven that these bacteria interact with the immune system, that they prevent infections actively and passively, and that they could 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 clear causalities.
In summary, The microbiota is essential for life in every sense Without it, we would not be able to properly digest many plant substances or prevent the entry of infectious pathogens. As they say in the microbiology community, “without our bacteria, we are nothing.”
