What are the Keystone Species? The Most Fundamental Microbes for a Healthy Gut Microbiome

The human gut microbiome is a complex and dynamic ecosystem consisting of trillions of microorganisms that play essential roles in digestion, immune function, and overall health. Within this intricate community, certain species—known as keystone species—exert a disproportionate influence on the stability and functionality of the ecosystem. Identifying these keystone probiotic species is crucial for developing targeted therapies and dietary strategies to promote gut health.

What Are Keystone Species?

In ecological terms, keystone species are organisms that have a significant impact on their environment relative to their abundance. In the context of the gut microbiome, keystone probiotic species are those that help maintain microbial diversity, modulate immune responses, and prevent pathogen overgrowth. Their presence and activity are essential for the resilience and functionality of the gut ecosystem.

Among the myriad of probiotic strains, several have been identified as keystone species:

Lactobacillus spp.

Lactobacilli are among the most studied probiotics, known for their ability to produce lactic acid, which inhibits pathogenic bacteria, and for maintaining mucosal barrier integrity (Liu et al., 2021). They also modulate immune responses and support digestion.

Bifidobacterium spp.Bifidobacteria are dominant in the infant gut and are associated with anti-inflammatory effects, production of short-chain fatty acids (SCFAs), and strengthening of gut barrier function (Turroni et al., 2020). They are considered cornerstone species in maintaining microbial diversity.

Akkermansia muciniphila

Although not traditionally classified as a probiotic supplement, Akkermansia muciniphila is a mucin-degrading bacterium that plays a vital role in maintaining mucosal integrity and metabolic health (Ottman et al., 2020). Its presence correlates with reduced inflammation and obesity.

Faecalibacterium prausnitzii

A key butyrate-producing bacterium, F. prausnitzii is linked to anti-inflammatory effects and gut homeostasis. Its decline is associated with inflammatory bowel diseases (Sokol et al., 2021).

Roseburia spp.

Another genus of butyrate producers, Roseburia contributes to colonocyte health and anti-inflammatory pathways, making it a critical component of a resilient microbiome (Vital et al., 2020).

Why Are These Species Considered Keystone?

Research indicates that these species help sustain microbial diversity, inhibit pathogenic colonization, and modulate immune responses. Their presence fosters a balanced gut environment, which is vital for overall health, including mental well-being, metabolic regulation, and immune defense (He et al., 2022).

Implications for Probiotic Therapy

Understanding keystone species guides the development of targeted probiotic formulations. Supplementing with specific strains like Lactobacillus, Bifidobacterium, or Akkermansia may help restore or maintain gut homeostasis, especially in conditions like inflammatory bowel disease, obesity, and metabolic syndrome.

"There might be more than just dozens, but hundreds of species of keystone species...The list is still evolving..."

Key Summary

• Akkramansia - improves the connective barrier and is associated with lower inflammation, and preventing immune overreaction. 
• People with higher levels have healthier triglyceride levels and lower blood sugar the more Akkramansia species they have. 
• B. longum: The best are those that produce the most butyrate.
• L. Reuteri is a keystone species because it breaks down resistant starches into nutrients that feed many other beneficial microbes. 
• They are fundamental for regulating the microbiome entire system because many other beneficial microorganisms depend on them. 
• Resistant starch and high fiber food are their favorite: like apples, pears, green bananas, green papaya, avocados, asparagus, 

References

He, X., Li, D., Wu, J., & Zhang, Y. (2022). Keystone species in the human gut microbiome: Their roles and potential as therapeutic targets. Frontiers in Microbiology, 13, 837456. https://doi.org/10.3389/fmicb.2022.837456

Liu, Y., Wang, Y., & Chen, X. (2021). Lactobacillus spp. as probiotics: A review of their safety and efficacy. Microbial Biotechnology, 14(3), 865–878. https://doi.org/10.1111/1751-7915.13737

Ottman, N., Geerlings, S. Y., & Belzer, C. (2020). Role of Akkermansia muciniphila in human health. Microbial Biotechnology, 13(5), 1354–1364. https://doi.org/10.1111/1751-7915.13554

Sokol, H., Leduc, R., & Seksik, P. (2021). The role of Faecalibacterium prausnitzii in inflammatory bowel disease. Gut Microbes, 13(1), 1923997. https://doi.org/10.1080/19490976.2021.1923997

Turroni, F., Milani, C., & Duranti, S. (2020). Bifidobacteria and their role in the human gut microbiome. Frontiers in Microbiology, 11, 567089. https://doi.org/10.3389/fmicb.2020.567089