Do you remember that 1987 movie, “Innerspace“? In it, a pilot commands a miniaturized ship that, by mistake, travels through the body of a very hypochondriac man. Well, if we could, like that pilot, reduce ourselves to just a few millimeters, put on a safari hat, and travel equipped with an explorer’s kit to our intestine, we would discover that it is nothing like the gloomy place we might imagine, dark, where lonely, sad, and hungry bacteria huddle together. Far from it!
We would discover that our colon is a real jungle where, instead of trees, insects, and animals, we mainly harbor bacteria, of several hundred different types of species per individual, but also viruses, fungi, archaea, and yeasts. All these microorganisms make up our gut microbiota, are as numerous as human cells, and all act together, in unison. And for this, they continuously communicate with each other and with our cells.
And as happens in the jungle, where all the beings that live in it relate to each other, they not only talk to each other, but also compete, collaborate, and even devour each other or benefit from one another. “Moreover, they are very promiscuous and exchange genes among themselves very easily,” jokes Ignacio López-Goñi, a professor of microbiology at the University of Navarra and a member of the Spanish Society of Microbiology. “This is how antibiotic resistance is transmitted, for example,” adds this microbiologist.
Our health depends, in some way, on this communication. Because when something alters that “dialogue” and imbalances occur, health problems usually appear. To date, more than 300 diseases have been described that are linked to the gut microbiota, such as obesity, diabetes, or allergies, but also depression, cancer, or even Alzheimer’s.
Hence the importance of better understanding how bacteria communicate, their “social life.” One of the channels they use is ‘quorum sensing,’ which allows them to know if they are a sufficient number of bacteria to activate and deactivate genes and, therefore, to turn on or off certain functions. To do this, they produce chemical substances that let them know if they are many or not and whether it is worth it or not, for example, to secrete a toxin, which involves a high expenditure of energy.
Continuing with the simile of the tropical jungle, just as there are some species that are key to the balance and good health of that ecosystem, and if you remove that particular species the whole ecosystem collapses, something similar happens in the intestine, where a huge diversity of microorganisms lives, including key species, bacteria, that are essential to maintaining the balance of the entire ecosystem. “Those bacteria, if they change, change the whole ecosystem and that is because they communicate with each other and through the metabolites they produce, which other bacteria use,” says Goñi.
Bacteria, moreover, like us humans, weave networks and get along better with some than with others, and they need each other to survive. And that is something that scientists have learned recently. Take, for example, one of the most “famous” bacteria recently, Akkermansia muciniphila, associated with people of correct weight and that seems to have positive effects to combat obesity and type 2 diabetes. This bacterium can be isolated from the feces of infants and also from the elderly, which implies that it accompanies us throughout our life. However, cultivating it in the laboratory is very complicated, precisely because, as Goñi points out, Akkermansia needs other travel companions to grow, although we don’t know yet who they are and that is why, although it can be isolated and obtained in the laboratory, it is complicated to do so in a high concentration.”
“Those bacteria, if they change, change the whole ecosystem and that is because they communicate with each other and through the metabolites they produce, which other bacteria use“
This microbiologist, author of “Microbiota: los microbios de tu organismo” (Ed. Guadalmazán, 2018), emphasizes that, although we usually refer to good or bad bacteria, as we have just done with Akkermansia, the truth is that they are neither one thing nor the other. “What they want is to multiply, and live in peace. In that sense, all of them are good.” And, in fact, the vast majority of microorganisms are because they carry out a multitude of functions in nature, without them life on Earth would not be possible. However, “some of those microorganisms in their eagerness to multiply compete with other bacteria and other living beings and can produce diseases. For that reason, they are often labeled as ‘bad’ or pathogenic,” he explains.
Many of those considered “bad” bacteria live within us, so they are commensals; we share an ecosystem. If one ends up proliferating too much, it can cause a disease. Therefore, they are called opportunistic pathogenic bacteria. And it is the “good” bacteria that are in charge of keeping them at bay, helped by the immune system. “When we are with low defenses or the microbiota is altered, those opportunistic pathogenic bacteria take the opportunity, proliferate, grow and can end up causing an infection”. López Goñi highlights the case of Clostridium difficile as an example, a bacteria that many people carry that in healthy conditions is kept at bay and in other conditions can proliferate and cause a very potent intestinal infection.
In the end, it’s not about good or bad bacteria, but about an ecosystem in balance or out of balance, this microbiologist insists. “If you are in a tropical jungle, you do not want a particular species to grow too much and alter the whole ecosystem.” Finally, Goñi emphasizes, “knowing the social life of bacteria, how they communicate and relate to the organism is going to represent a paradigm shift in personalized medicine of the future.”
