The Human Mycobiome ;)

MYCOBIOME

Fungal diversity in the human skin microbiome

A discussion of the importance of fungi in microbial community composition and stability.

by Doğa Tekin

We used to associate bacteria with disease and disease only. In recent years, we’ve been becoming more comfortable with the idea of commensal bacterial presence in different microbial communities throughout our bodies. However, in this effort to accept friendly bacteria, we’ve completely ignored the same role played by fungi. Most of us still think of fungal interactions with humans to be solely pathogenic. Recent research within the up and coming field of the human microbiome has revealed that fungi play just as significant a role in microbial community composition and stability as bacteria do. 

Although most studies on the human microbiome have focused solely on bacteria, a new study performed by Findley et al. showed that our skin microbiome exhibits a vast amount of fungal diversity as well (1). The term ‘microbiota,’ which we are quite familiar with, is primarily used to describe bacterial communities, whereas ‘mycobiota’ can be used to describe the fungal component of our microbiome (2).  

Mycobiota on our skin consist of much more than toenail infections and athlete’s foot. Findley et al. demonstrated that the diversity and composition of microbial communities on our skin depends highly on the topography of the inhabited region. They analyzed 14 regions of the skin in 10 healthy adults to determine the genera and species composition of the mycobiota. Their results indicated the highest level of fungal diversity in the plantar heel, toenail and toe web. All other regions were primarily dominated by the genus Malassezia, which also displayed a higher level of species diversity in the three foot regions (see Fig. 1). This genus contains yeasts that have been known to be part of the natural human flora for over a century. Malassezia yeasts depend on lipids for survival, which is why they are commonly found in skin microbiomes. (3)

To test temporal stability, Findley et al. sampled six of the healthy volunteers one to three months later. Their results showed consistency in topography-based diversity, which indicates structural and temporal stability of the mycobiota. (1)

Furthermore, they investigated the bacterial profile of the same region using genomic sequencing. Their results indicated lower bacterial diversity compared to fungal diversity in foot regions, and higher bacterial diversity compared to fungal diversity in arm regions. This entails a high level of complexity in the composition of the skin microbiome, and suggests that the microbiota and mycobiota form based on different characteristics (1).

While Findley et al. focus on the skin, other studies reveal similar fungal diversity mycobiotic composition in different parts of the human body. For example, in a study of the oral mycobiota, Ghannoum et al. identified a total of 101 species in the oral cavities of 20 healthy individuals (4). This was the first study that identified the oral mycobiota. Although they did not include bacterial communities, the level of fungal diversity alone is sufficient to indicate a highly delicate ecosystem.

 The human microbiome is just like all ecosystems; organisms are linked through multiple layers and networks of interactions. In this sense, to understand changes in our microbiotic ecosystem – especially those with the potential of causing us harm – we must familiarize ourselves with all of the organisms that partake in it. Exploring the diversity of our fungal inhabitants is key to understanding our microbiome, and has potential applications to treat microbial infections. Research in this field has indicated a high level of complexity in fungal and bacterial interactions. The two communities influence each other directly and indirectly (5). Therefore, future implications of these studies are huge. Understanding the commensal inhabitants of our microbiomes and their interactions with each other and the environment can enable us to develop new and more successful therapies for fungal and bacterial pathogenicity. (6) 

REFERENCES

1. K. Findley et al., Nature 498, 367 (2013).

2. D. M. Underhill, I. D. Iliev, Nature Reviews Immunology 14, 405 (2014)

3. A. J. Kindo, J. Kalyani, S. Anandan, Indian Journal of Medical Microbiology, 22, 179 (2004)

4. M. A. Ghannoum et al., PLoS Pathog. 6.1, (2010)

5. A. Y. Peleg, D. A. Hogan, E. Mylonakis, Nature Reviews Microbiology 8, 340 (2010)

6. E. A. Grice et al., Genome Res. 18, 1043 (2008)