What is the holobiont and why can it change our way of understanding the world?

In nature, competition reigns and the strongest survives.

Or at least that's what we've often heard.

However, the planet is much more complicated than that, because we earthlings relate to other species at levels that we often do not suspect.

As Lynn Margulis and Dorion Sagan once said, to understand the true complexity of life you must understand how organisms come together in new and fascinating ways.

That is exactly what the holobiont is about, a concept that refers to an entity formed by the association of different species that become an ecological unit.

In other words, when an animal or plant (host) lives in symbiosis with the microorganisms it hosts (symbionts), it is a holobiont.

Something like a group of fused beings or a multi-species complex.

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You are not an individual, you are a crowd

Scott F. Gilbert, developmental evolutionary biologist, Howard A. Schneiderman Professor Emeritus at Swarthmore College, and Distinguished Professor Emeritus at the University of Helsinki, explains it this way: “All organisms appear to be holobionts, and we are composed of not only from cells derived from the zygote, but also from symbiotic bacteria, fungi, and viruses.

Each animal is a biome, a set of interactive ecosystems.

Also, these symbiotic microbes don't just travel with us.

They help build our bodies, regulate our metabolic processes, and build our immune capabilities.

This has many implications for our way of viewing life.”

All organisms appear to be holobionts, and we are also composed of symbiotic bacteria, fungi, and viruses.

Each animal is a biome, a set of interactive ecosystems

Scott F. Gilbert, Evolutionary Developmental Biologist, Professor Emeritus at Swarthmore College

In fact, our bond with microorganisms is so deep that we become the ecosystem where they live, while they influence our development, health, and even behavior.

For the microbial ecologist and academic at the Universidad Antofagasta Cristina Dorador, “the holobiont invites us to think in different magnitudes.

It seems that the microscopic and the immense do not converse, but in reality they do”.

This has been revealed by technological advancement.

“The big step was in the 2010s with massive DNA sequencing techniques, because complete microbial groups were discovered that were invisible to classical techniques.

In addition, the Human Microbiome Project unveiled the microbial diversity in the human body, debunking some theories that were out there at the time,” she adds.

microbial human

Perhaps the best-known example is the intestinal microbiota, the community of microorganisms that allows us to break down food and is key to our immune system.

“From an anatomical point of view, approximately half of the cells in the human body are microbial.

In addition, each species of microbe is not associated with us randomly, but is found in specific places.

We receive these microbes as we pass through the birth canal.

They are parting gifts from our mother.

These microbes colonize our body, especially our intestine, and help

our development”, Gilbert details.

Unsurprisingly, microbes also play a role in diseases ranging from depression to cancer.

Indeed, tumors have an associated microbiome and the presence of these microorganisms would explain why some people are more sensitive to immunotherapy.

In another area, there are studies that show that the replacement of bacteria in the intestine would help reduce autistic-type behavior in rats.

Dorador, who participated in research on autism and microbiota, says that “it has been reported that around 40% of people on the autism spectrum have some gastrointestinal problem.

It has been determined that an enrichment of certain groups of bacteria occurs.

We wanted to find a model to explain whether this change at the microbial level, which we don't know how it occurs, is generating metabolites or

that alter neuronal function in some way."

Clearly, there is much to unravel yet.

For Scott Gilbert we are not so different from the fungi on the trees, which is why he has always said that "we are all lichens". Paula Díaz Levi

Team more than individual

The holobiont generates new morphological, physiological, and immunological characteristics, among others, that do not exist in the species separately.

Entomologist Constanza Schapheer's favorite example is nutrient-recycling insects, such as termites.

“These animals harbor microorganisms such as bacteria and protists in their digestive system that help the termite absorb nutrients that it could not otherwise.

The acquisition of intestinal symbionts was key in the evolution of these insects.

There are many similar examples in nature, among the most paradigmatic are lichens and corals”, says the also postdoctoral researcher at the Faculty of Agricultural Sciences of the University of Chile.

Cows, meanwhile, eat grass, but their genome does not produce enzymes capable of digesting cellulose or other compounds in their feed.

The good news (for them) is that their symbiotic microbes, located in their rumen, are responsible for processing what these mammals cannot.

What we consider an 'organism' is actually a set of integrated organisms.

For this reason, scientists and philosophers question the existence of the 'individual' as we usually understand it.

In addition, some change when they acquire new microorganisms.

The American biologist exemplifies the red turpentine beetle: “It is a minor pest in the United States, where its symbiotic fungi dig holes in damaged trees.

However, when it was accidentally exported to China, the beetle gained a new set of fungal symbiotes that allowed it to bore holes in healthy trees, killing them."

In other words, what we consider an "organism" would actually be a set of integrated organisms.

For this reason, scientists and philosophers, such as Gilbert and his colleagues, have questioned the very existence of the "individual" as we usually understand it.

“We have evolved to expect these symbiotic microbes and their signals.

So each of us functions as a community or a team.

We are only individuals to the extent that one community differs from another community or one team differs from another team.

I am

'”, points out the scientist, who has also participated in the book

Its importance in nature

Understanding ourselves as holobionts not only has implications for our health, but also for the environment.

Human beings tend to conserve species or ecosystems separately, without worrying about maintaining the relationships and cycles that sustain organisms as a whole.

A forest or desert cannot survive without the links that its macro and micro inhabitants weave.

This inspired Schapheer and other colleagues to propose the concept of "ecosystem holobiont" which refers to a holobiont that carries out key ecological processes for the conservation of nature.

We call this phenomenon an emergent property, it occurs thanks to a holobiont and is part of a key ecosystem process.

Our planet has its conditions thanks to these processes, it is vital to maintain them

Constanza Schapheer, entomologist, Agronomic Sciences of the University of Chile

Let's go back to the creatures that decompose organic matter, a fundamental task to have healthy soils that support, for example, agriculture.

If the degradation of said matter were

only by microorganisms, it would be very slow (due to their tiny size), but if they have a larger partner —such as an insect— they will carry out the process together more quickly and easily.

This is because the animal, which houses them in its digestive tract, has a greater ability to move and has mouthparts to break up the material.

Schapheer explains that “we call this phenomenon an emergent property, when this property occurs thanks to a holobiont and is part of a key ecosystem process, we are talking about an ecosystem holobiont.

Among the reasons why our planet has the conditions it has is thanks to these processes, for which it is vital to maintain them”.

Climate change can also trigger the breakdown of symbiotic relationships, as happens with coral bleaching that occurs when these animals lose their symbiont microalgae.Picasa

we are diversity

Health crises, biodiversity loss and climate change are some of the big problems we are currently facing.

Among the multiple consequences is the breakdown of symbiotic relationships, such as soil degradation that deprives plants of their symbiont fungi and bacteria, or the increase in sea temperature that stresses corals, which in response expel their microalgae, triggering the bleaching.

Likewise, the excessive use of biocides (such as antibiotics or disinfectants) kills microbes with which we have evolved.

Gilbert stresses that “being a holobiont means we are products of our environment in ways we never imagined before.

A healthy environment is necessary for healthy individuals.

This means that the environment must be healthy for the microbes we need for our bodies to function, as well as the microbes that help make the plants we eat."

For this reason, thinking in a “holobiont way” could contribute both to the understanding of the phenomena and to possible solutions.

“For the conservation of species, rather than conserving the

, we should focus on conserving

, that is, the set of beings that make up the holobiont.

In this way, organisms and ecosystem processes would be considered so that the planet continues to function”, Schapheer asserts.

But for Dorador there is also a lesson in humility: “We are an ecosystem, where it is also important to share and cooperate.

The massive symbiosis that exists on the planet and the holobionts open ways to understand complex problems and help us to position ourselves from diversity”.

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