Microbes represent 95% of the biodiversity of the living world, but when the issue of biodiversity preservation is raised, these invisible organisms rarely get a mention. To mark the International Day for Biological Diversity, Philippe Sansonetti, Professor Emeritus at the Institut Pasteur and the Collège de France, spoke about the importance of protecting microbial biodiversity.
There is an urgent need to include monitoring of microbial ecosystems in the environmental narrative
Philippe SansonettiPhilippe Sansonetti, Professor Emeritus at the Institut Pasteur and the Collège de France
Why are microbes often neglected when we talk about biodiversity?
Philippe Sansonetti: The main reason is because we can't see them. To observe them and appreciate their diversity, we need the help of a microscope. The microbial world is both invisible and silent. How can something exist if you can't see or hear it? Macroscopic biodiversity, and the depletion of this biodiversity, is of course more obvious.
The microbial world is also generally seen as something complex and hard to grasp, and it often comes with negative connotations, even fears, because of the confusion between microbes and pathogens. But pathogens are just a tiny minority of microbes. This confusion has sparked "germophobia" that is often maintained and exploited for commercial purposes.
How much do we know about microbial diversity?
P. S.: The first thing to say is that microbial biodiversity represents approximately 95% of all biodiversity in the living world. That is a huge amount, and it represents a vast pool of genetic capital that guarantees the resilience of the living world on our planet. There are millions of microbial species, and exploration of the land and the oceans using state-of-the-art metagenomic analysis tools is constantly revealing previously unknown species. There is no place on the planet, even in volcanic fumaroles, in the ocean depths or in bubbling geysers – which are populated with "extremophile" microbes – that does not have its own adapted ecosystem. Microbes, in all their diversity, play a crucial role in the planet's main vital cycles (carbon, methane and nitrogen), produce a large part of our oxygen, clean up the land and the oceans, and are involved in vital symbioses for the animal and plant world.
Given the human impact on the environment and climate, is microbial biodiversity also under threat?
P. S.: Yes, but the impact of microbial biodiversity loss needs to be measured in terms of the immense diversity of the affected ecosystems. The spatio-temporal dynamics need to be determined and the effects need to be demonstrated scientifically. There is an urgent need to include monitoring of microbial ecosystems in the environmental narrative and to add it to the agenda of future COPs. It is worth pointing out that microbes represent 16% of Earth's biomass.
What factors are contributing to the depletion of microbial biodiversity? Why is it crucial to protect it, and what are the implications of a loss of microbial biodiversity for ecosystems?
P. S.: These are crucial questions. If we go back to what I said earlier, the loss of microbial biodiversity will have a negative impact on all the processes I mentioned: the planet's vital cycles, cleanup capabilities, plant health, agricultural production, and animal and human health. Let's take a simple example: if the microbial biodiversity in soil is affected – and this is happening because of climate change, especially warming –, it will have a negative impact on the microbial symbioses that fix nitrogen for plants and produce plant amino acids. A reduction in these vital symbioses could be compensated by the large-scale use of nitrate-based chemical fertilizers, but this is not an option given the ongoing environmental crisis.
What are the consequences for human health?
P. S.: From a specifically human perspective, it seems that the species diversity in the gut microbiota – our most diverse microbiota – has been halved since the emergence of the Anthropocene, especially in industrialized countries. This loss is largely a result of our modern lifestyles: water and food hygiene, antibiotics, some drugs with "hidden" antimicrobial effects, pollutants, stressors and food imbalances. The liberal use of antibiotics, particularly outside the field of human and veterinary medicine, has turned them into "environmental pollutants," with two major negative impacts on human microbial ecosystems: antibiotic resistance and diversity loss. We need to save both microbes and antibiotics, and that is a mammoth undertaking.
Diversity loss in the human microbiota is associated with the emergence of non-communicable "post-modern" diseases such as allergies, asthma, atopy1, obesity and diabetes, certain autoimmune diseases, inflammatory bowel disease, colorectal cancer, etc. Researchers are actively working to confirm the causal role of microbial diversity loss in the growing incidence of post-modern diseases.
Did the COVID crisis change our perspective on ecosystems, especially microbial ecosystems? If so, how?
P. S.: It's hard to say. We would need to carry out effective surveys among the general public to find out more. I would like to think that the pandemic will leave people with a clearer understanding of diversity and the extraordinary evolutionary and adaptive capabilities of viruses, what we need to do to guard against them, the barrier role of the bacterial microbiota in humans and animals in protecting against viral infections, and the concept of "One Health" that unites humans, animals and plants within a shared planetary ecosystem.
1 A genetic predisposition to the cumulative development of common allergies
For more information:
- Sansonetti P., Microbes sans frontières, Paris, éditions Odile Jacob, 2024
- Sansonetti P., Lecture at the Collège de France, Évolution des écosystèmes microbiens sous la pression du changement climatique (How the pressure of climate change is transforming microbial ecosystems).
- Sansonetti P., Inaugural lecture at the Collège de France, Des microbes et des hommes. Guerre et paix aux surfaces muqueuses (Of microbes and men. War and peace on the mucosal surfaces).