The educational content in this post, elaborated in collaboration with Lesaffre, was independently developed and approved by the GMFH publishing team and editorial board.
Why gut fungi are essential for a healthy gut
The gut microbiota is mainly composed by bacteria, but also includes archaea, viruses, fungi, protists, and helminths. While bacteria are the most abundant microorganisms, gut fungi also play an important role to help keep your gut microbiota healthy. The whole community of fungi residing in the gut and their genome is known as the gut mycobiome.
Recent research has revealed that they are at least partly acquired from the mother but are also found in the environment and food and are important for having digestive and immune systems in good shape.
Saccharomyces cerevisiae and Candida albicans are the most abundant fungi in healthy human adults’ gastrointestinal tract and are involved in:
- Training of the immune system
- Nutrient absorption and metabolism
- Protection against harmful microorganisms
- Keeping the gut healthy by working in tandem with bacteria
One way by which resident fungi in the gut contribute to maintain health and protect against digestive (e.g., inflammatory bowel diseases) and extra-digestive disease (e.g., cystic fibrosis) is through interacting with the gut-brain axis.
How fungal communities in the gut keep a good health by interacting with the gut-brain axis
Gut fungi interact with bacteria and the gut-brain axis through involving three main ways:
- Immune system cells in the gut:
S. cerevisiae and C. albicans allow a proper development of host immune homeostasis. Yet, over activation of anti-fungal immune components can occur (e.g., some patients with Crohn’s disease have higher levels of antibodies against the commensal S. cerevisiae).
Interactions occurring between the gut mycobiome and the host immune system also affect organs that apparently are not connected with the gut. For example, an altered gut mycobiome composition is related with the severity of allergic airway disease.
- Neurotransmitters and other fungi-derived metabolites:
Some preliminary reports suggest that fungi can synthesize neurotransmitters that can shape brain function (e.g., norepinephrine) and even appetite and sleep-wake cycles (e.g., histamine). Fermenting yeast can also produce short-chain fatty acids that may reach the brain via the bloodstream.
The other way can also occur. Some neurotransmitters produced by the host impact gut fungi balance.
- Interactions between fungi and bacteria:
Gut fungi are important in keeping bacteria in good balance, thus affecting the composition and functions of the microbiome. Findings in mice showed that when gut bacteria are altered after a course of antibiotics, this imbalance can be mitigated in part with the administration of exogenous fungi such as Candida albicans or S. cerevisiae.
Implications of an altered gut mycobiome for health and disease
Studies published in the past 10 years have also found that alterations of gut fungi communities are associated with metabolic (e.g., obesity and diabetes) and neurological disorders (e.g., Parkinson’s disease).
In the context of disorders of gut-brain interaction (formerly known as functional bowel disorders), an increased relative abundance of the yeast Candida albicans, considered a gut commensal, has been found in patients with IBS.
A potential mechanism suggested to explain the role of gut mycobiome in IBS includes mast cell activation under stress leading to histamine and tryptase release that finally drives barrier dysfunction and visceral hypersensitivity, which leads to abdominal pain.
Overall, these findings suggest that some specific fungi can have a far-reaching effect on the gut at the systemic level and on the gut-brain axis. While it is too early to know if an altered gut mycobiome is the cause or the consequence, these findings highlight a link between the dysbiosis of the gut mycobiome and the development of diseases.
Concluding remarks
Beyond bacteria, gut fungi also play a role in maintaining a microbiome-gut-brain axis in good shape. The most studied ways by which the gut microbiome communicates with the brain includes neurotransmitters, the gut immune system and microbial-derived metabolites.
While most research has focused on gut bacteria, emerging findings highlight that gut fungi are also relevant in the maturation and proper functioning of the gut-brain axis and can have a far-reaching effect of the gut at the systemic level.
While it is too early to know if an altered gut mycobiome is the cause or the consequence of diseases, fungi emerge as a potential target in prevention and management of digestive and even neurological diseases.
References:
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Soret P, Vandenborght LE, Francis F, et al. Respiratory mycobiome and suggestion of inter-kingdom network during acute pulmonary exacerbation in cystic fibrosis. Sci Rep. 2020; 10(1):3589. doi: 10.1038/s41598-020-60015-4.
Enaud R, Vandenborght LE, Coron N, et al. The mycobiome: a neglected component in the microbiota-gut-brain axis. Microorganisms. 2018; 6(1):22. doi: 10.3390/microorganisms6010022.
Jiang TT, Shao TY, Gladys Ang WX, et al. Commensal fungi recapitulate the protective benefits of intestinal bacteria. Cell Host Microbe. 2017; 22(6):809-816.e4. doi: 10.1016/j.chom.2017.10.013.
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Neto DPA, Sant’Ana AS. The mycobiota-gut-brain axis in Parkinson’s disease: A review on what we know and what paths we can still to advance this field of study. Fung Biol Rev. 2023; 46:100327. doi: 10.1016/j.fbr.2023.100327.
van Thiel I, de Jonge Wj, den Wijngaard Rm. Fungal feelings in the irritable bowel syndrome: the intestinal mycobiome and abdominal pain. Gut Microbes. 2023; 15(1):2168992. doi: 10.1080/19490976.2023.2168992.
