Antibiosis: what it is, characteristics and examples

Antibiosis helps to understand the behavior of bacteria and their usefulness in medicine.

Microorganisms are the basis of existence on Earth. In 2018, a team of researchers decided to quantify the amount of biomass in the form of carbon present on our planet, and their results were published in the journal Proceedings of the National Academy of Sciences.

After their calculations, they found that 15% of the organic matter on the Earth's surface (70 gigatons) was locked up in the least expected place: microscopic living beings, specifically bacteria.specifically, bacteria.

It is estimated that every 6.5 square centimeters of a smartphone screen contains 25,000 bacterial units, a value 10 times greater than the microbial load of, for example, a dog's food bowl.

With these data, it is clear that bacteria surround every habitable surface in the world, from our mouth and eyes to the surface with the maximum environmental inclemency where radioactivity is the only resource (as in the case of Desulforudis audaxviator). In order for many bacteria to delimit their terrain and specialize without competition, they carry out an interaction known as "antibiosis".. Today we tell you all about it.

Relationships in the bacterial world

Before talking about antibiosis, it is necessary to point out that there are many types of biological relationships in the world of bacteria. From a scientific point of view a biological interaction is defined as the effect that two taxa or species have on each other as they interact in the ecosystem in which they live together.. You may be familiar with the mutualism of the clownfish and the anemone: the tentacles of the invertebrate protect the fish and, in turn, the animal parasitizes the anemone and feeds on pathogens that may harm it.

In the bacterial world, phenomena such as parasitism, symbiosis, commensalism or amensalism become rather more diffuse, as we are moving on microscopic scales. A clear example of parasitism is that of the bacterium Helicobacter pylori in humans: this microorganism bores into the intestinal mucosa of carriers and secretes the enzyme urease, which promotes the conversion of the chemical urea into ammonia. Prolonged exposure to this compound causes, in 20% of cases, damage to the intestinal mucosa and ulcers.

On the other side of the coin, we find the symbiotic relationship of the bacterial flora in the environment of our gastrointestinal tract. Colonies of various genera (Firmicutes, Bacteroidetes, Actinobacteria and more) help us to degrade and metabolize plant compounds (up to 10% of the calories in our diet), activate our immune system during our early stages of life during our early stages of life and also prevent other microorganisms from proliferating in our tissues. It is this last concept that most attracts our attention right now, as we can effectively link it to the phenomenon of antibiosis. It's time to get into the nitty-gritty.

What is antibiosis?

From the broadest point of view, an antibiosis can be defined as any relationship between two organisms that is harmful to at least one of them. In the most literal meaning of the term, it is the opposite of symbiosis. the opposite concept of symbiosis, that interaction which brings some kind of benefit to those involved in the interaction..

For example, a predatory relationship could be an antibiosis: one of the two specimens dies so that the other can survive another day. Following this train of thought, all types of parasitism would be antibiosis in themselves.

Anyway, the real interest of this word lies in its microbiological meaning: in the world of bacteria and other microscopic organisms, we can define antibiosis as a relationship between two bacteria, in which one actively expels the other by secreting a particular metabolic compound, called an antibiotic.. Before continuing, it is necessary to mention the most important antibiosis phenomenon for mankind: that of Penicillum against other microorganisms.

Penicillium and antibiosis

When we talk about penicillin, we refer to a group of beta-lactam Antibiotics produced by various species of ascomycete fungi of the genus Penicillium. Of the more than 300 species included in this taxon, the most famous is Penicillium chrysogenumdiscovered by Alexander Fleming in 1928.

Although the mechanisms of action of penicillin are not fully understood, it is believed that this compound acts by inhibiting the transpeptidation process, which is essential for the production of peptidoglycan or murein.. Peptidoglycan is a protective layer that is responsible for protecting bacteria from osmotic breakdown in aquatic environments, so without it, it is easier for osmotic lysis of pathogens to occur during cell multiplication.

The antibiotic properties of penicillin have already been described a thousand and one times, but why does this fungus synthesize a compound of human utility? In fact, this beta-lactam antibiotic this beta-lactam antibiotic is useful to humans because we can take advantage of it, but its primary function is not to prevent us from disease.. The Penicillium fungus synthesizes this compound to destroy adjacent bacteria and thus have more room to grow, develop and reproduce.

When a living being is able to displace other members of the ecosystem, its ecological niche expands. If it has more access to food and space, it will be able to reproduce more and, therefore, it will have more offspring that synthesize bactericidal substances and will be able to continue growing throughout the generations. Humans have taken advantage of this quality, but clearly, the evolutionary mechanisms of living beings the evolutionary mechanisms of living beings are not aimed at benefiting us..

Antibiosis in the human body

At this point, it is essential to emphasize that the antibiotic is the chemical that destroys the bacteria, while antibiosis is the phenomenon that leads to their production.. Therefore, it is not entirely correct to designate the taking of an antibiotic as a phenomenon of antibiosis: in this case, a natural interaction between two living beings is not taking place.

If we want to look for examples of natural antibiosis, we can turn our attention to the female reproductive system (and almost any part of the human body). (and almost any part of the human body). For example, the vaginal flora is dominated by the microbial species Lactobacillus crispatus, L. jensenii and L. gasseri. These protect the female reproductive tract in the following way:

• By specifically adhering to the epithelium. It may sound simple, but if there is no room to settle, other bacteria cannot infect the mucosa.
• By producing antimicrobial compounds. This is a clear phenomenon of antibiosis.
• By coaggregating with pathogens, which enhances their microbicidal effect.

Bacteria of the genus Lactobacillus ferment the glucose secreted by the cells of the vaginal mucosa and convert it into lactic acid, which acidifies the pH of the vaginal mucosa.which acidifies the pH of the environment of the female genital tract. At a pH of 4, almost no microorganism can grow properly, so Lactobacillus can multiply at will as long as the immune system of the human host allows it to do so.

In addition, these bacteria also produce hydrogen peroxide (H202) during their metabolism, which prevents the establishment of many pathogens that cause sexually transmitted infections (STIs). Lactobacillus benefit from not sharing space with other microorganisms and, due to the antibiosis relationship they establish with pathogens in the environment, they protect the woman who hosts them in her genital tract.

Summary

As you may have observed, antibiosis is the result of coevolution between species, as some actively expel others in order to obtain more resources and space to develop.. Humans have learned to benefit from antibiosis, but of course, these mechanisms have never been directed towards us: the only interest of the bacteria is to reproduce and multiply, whether this is good or bad for the organism in which they live.

Therefore, if the host's immune system is depressed or shows some serious structural maladjustment, what was originally a symbiosis based on an antibiosis mechanism can become a deadly parasitism. There are cases of infections of the heart (endocarditis) by the lactobacilli described above, especially in patients with structural heart disease and anatomical deformities. If the bacterium has room to grow beyond its limits and immune barriers, it will surely do so, whatever the cost.